### Author Topic: Staggered 50uH and 250uH inductor design for LISN  (Read 45126 times)

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#### CopperCone

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##### Staggered 50uH and 250uH inductor design for LISN
« on: March 12, 2018, 04:44:54 pm »
So i am going to make a LISN for mains power. I looked at the tekbox design and it seems strait folward.

My only design constraint right now is 2.65mm wire, which i have alot of.

I see that the tekbox design splits a 250uH inductor into four sections each in parallel with what looks to be 68 ohm resistors.

I can try to emulate their design from pictures but i am wondering why they have the resistors in parallel with the inductors.

Also to extend the highfrequency performance isaw that tesla suggested the inductors be staggered to imitate a conical torroid. I am interested in these performance gains.

I know how to calculate an inductor but i am not sure what geometry to go for, like the ratio of lenght to width, and i am not sure how to stagger the four sections.

Can someone suggest some initial dimensions and step ratiobetween these inductors and some general rational for these designs?

Or i would be for making a conical inductor that fufils the design requirement.

#### BNElecEng

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #1 on: March 12, 2018, 05:05:14 pm »
I don't have the answer to your question but I did come across an interesting read on a DIY LISN.

http://www.feng.pucrs.br/~fdosreis/ftp/publicacoes/Conferencias/IECON/IECON2003/lepuc6elio.PDF

#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #2 on: March 12, 2018, 05:18:01 pm »
I think you'll find it's the other way around, the 250uH are on the spools (more layers = more inductance in a smaller package), while the 50uH is sectioned, in single layers.

The spool winding has deeper resonances, and at lower frequencies, making it unsuitable for the inductor facing the EUT; but where it is, it doesn't need much impedance (compare to the 5 ohm resistor it's effectively in parallel with), so it's a fine way to save space.

Estimate the dimensions and enter them here:
http://hamwaves.com/antennas/inductance.html
This is the best calculator I know of anywhere, for single layer solenoids.  It is more accurate than anything you can physically measure, and includes frequency dependent effects.

The inductance of the chain will be slightly higher than the sum of each section in series, due to mutual inductance.  There's probably k ~ 0.1 between sections, giving a similar (~10%) increase above that figure.

Dimensions?  L/D ~ 1-4 is good.  Longer means higher impedance peaks, but less efficient (inductance per wire length, which peaks around 1:1).

Play with dimensions, see what fits.  Also see the self resonant frequency, or the estimate at least.  (If you're getting warnings and no output, try increasing pitch or decreasing wire size a bit.  That's usually what does it.  The lower Q won't affect the calculation much.

As for winding form, they probably used phenolic tube or something like that.  Easily found at McMaster Carr or the like (...if you don't mind paying for it).  Cardboard (say, paper towel tube) can be used, but it's not dimensionally stable and your winding will come loose.  The tube or winding can be coated in glue or varnish to help with this.

Tim
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#### CopperCone

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #3 on: March 15, 2018, 04:54:25 pm »
Does anyone know about dampening the coil sections? I made 4 12uH sections on a single core. I can adjust their distance to tune the overall inductance via mutual inductance.

I see in the commercial one they have 68ohm resistors in parallel with the coils.

Wont these resistors significantly degrade the highfrequency responce? Don't you need parallel inductors that block high frequencies? Does anyone know what the standard says about this?

#### David Hess

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #4 on: March 17, 2018, 05:01:09 am »
The parallel resistors lower the Q of the inductors to prevent resonance peaks.  This is commonly done in decoupling networks.

#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #5 on: March 17, 2018, 05:53:08 am »
I have only these pics of 50uH chokes for a 277VAC 15A LISN. They are quite big inductors 3" dia and have 4 damping resistors 100R every 10 turns or so, same as prev. post mentioned:
Building a Low Cost Line Impedance Stabilization Network for EMI Tests

There's a thread on eevblog where ferrite core inductors are used, makes me cringe. Ferrite core is proven usable to 30MHz by JDiddy
« Last Edit: June 11, 2018, 05:10:32 pm by floobydust »

#### CopperCone

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #6 on: March 17, 2018, 04:06:28 pm »
You don't happen to have a schematic do you?

Unfortunately I wound my inductors in 4 sections on a PVC pipe, I was hoping to be able to tune the two to have equal inductance by moving the sections around slightly. I have more like 20 windings per section with a smaller core to make 12.5uH measured of course.

I am interested in the undocumented things these guys have, like what appears to be RF feedthroughs and small inductors, etc. Why the diodes? Limiters?

Also, what exactly happens if you use ferrite cores? It only is for 30MHz (don't worry, I wound giant air coil inductors on PVC pipe ,and it took me way too long )

Could you possibly make a schematic for us with your equipment?
I found this one in addition to the tek box one (it explains more)
http://www.ets-lindgren.com/sites/etsauthor/ProductsManuals/LISNs/3816-2%20LISN%20399198%20C.pdf

I believe the principle difference is the first stage, where they went for a parallel RC dampener, rather then a serial one. I am not sure what the trade off is, I believe one requires larger cap values, and the other one has a poorer high frequency response.
« Last Edit: March 17, 2018, 04:33:19 pm by CopperCone »

#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #7 on: March 17, 2018, 08:05:42 pm »
Not to highjack your inductor design question, I drew a rough schematic, it has a some unknowns and I never did figure out small inductor color codes.
Notice the distributed resistor/capacitor arrays, staggered inductor damping resistors - I believe it's all to lower parasitics. The 10dB attenuator seems to have a BPF.

It's good you went with air-core inductors, I can't see typical SMPS ferrite cores having the bandwidth and self-resonant frequency out of the way. How many amps?

I'm surprised the ETS Lindgren unit is so basic compared to this Com Power unit which has clamp diodes to protect your spectrum analyzer's front-end. Who would leave those out!?

For coil forms, threaded ABS plastic pipe nipples would work, the wire just lays in the groove.

I find I really need CM/DM capability in a mains LISN, something you might consider adding.

edit: updated schematic
edit2: corrected R8 value in Compower schematic
« Last Edit: May 12, 2018, 04:55:10 pm by floobydust »

#### CopperCone

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #8 on: March 18, 2018, 11:15:58 pm »
How many watts should those 5Ohm resistors be? Non inductive type?

The 30K is exposed to line voltage directly, so thats easy enough, but whats reasonable for the ones in series with the cap?

say, 330 volts, so its like 3.4 watts, so 5W resistors here.
« Last Edit: March 18, 2018, 11:25:23 pm by CopperCone »

#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #9 on: March 19, 2018, 03:49:10 am »
It's too bad we don't have a 'home brew' design out there, for all us poor people.

Nearly all power resistors are spiral-wound, have steel end-caps so parasitic inductance is a problem at 30MHz.
I'm not sure what resistors are suitable, you'd have to model to see the effects of their inductance here.
This resistor should be made up of several in parallel, like 5 of 25R 1W as a guess.
Sees large inrush currents if switched in at peak line. Carbon comp are probably ideal but hard to find.
Ohmite WH/WN non-inductive.pdf WW rated 1nH at 1MHz.

5R resistor in series with 8uF:
120VAC is 1.1Wpk and average 0.55W
240VAC is 4.4Wpk and average 2.25W (5Vpk)

This older design had huge wirewound parts: https://www.eevblog.com/forum/testgear/lisn-50uh-solar-electronics-9252-50-teardown/

I would check the frequency response of the LISN when you are finished.
I still don't like the Lindgren 0.47uF cap from mains direct to the LISN output, that would kill a spectrum analyzer input IMHO.

#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #10 on: March 19, 2018, 05:28:36 am »
Note that the 5 ohm resistor's inductance appears in series with the 50uH choke, so if its inductance is a suitably small fraction of the total, it doesn't matter.  Namely, under 0.5uH would be more than fine.

Another way to put it: a resistor with an F = R / (2*pi*L) cutoff frequency over 1.6MHz.

I think I'd be shocked to see a 5 ohm with even that much.  Typical wirewound vitreous resistors are in that range, and smaller parts are much better.

A similar argument applies to higher value resistors.  Besides the 30k resistors not being in the signal path (I think they're intended only to discharge the capacitors when off), they're much more likely to have an overall capacitive characteristic.

The general rule is this: resistors over 200 ohms are capacitive, while resistors under 50 ohms are inductive.  The exact crossover point varies with construction (a wirewound of several kohms may still be inductive at a few MHz, before capacitance takes over), but the trend remains.

Tim
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#### CopperCone

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #11 on: March 19, 2018, 03:00:13 pm »
Floobydust in your last picture there are capacitors in a circular configuaration.

Do you know if this is one of the higher values in the schematic or is it the ? Value one?

I assume they are lower capacitance caps meant to make some kind of rf feedthrough?

#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #12 on: March 23, 2018, 09:48:04 am »
The Compower LISN ring structure of capacitors and resistors I believe mainly is to lessen parasitics, such as the capacitor's inductance.
Using a single 0.1uF cap vs 10 of 0.01uF cap in parallel, the self-resonant frequency of the resulting capacitor array is moved above our 30MHz top.

But that ETS-Lindgren LISN uses (single?) 0.47uF caps, so the SRF is not a problem... or one manufacturer here is a better design.

TDK/Epcos EMI supression X, Y caps

#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #13 on: March 23, 2018, 11:32:59 pm »
Note that series resonance isn't very important, as it causes high transmittance -- in contrast, the lack of resonance causes insertion loss!

The impedance is also very low, a small fraction of the system impedance (50 ohm).

An even more subtle point to make: the high frequency asymptote is not inductance, but the low frequency equivalent of a transmission line, consisting of the component leads and body.  The characteristic impedance depends on how close these parts are to ground, and their relative sizes; it seems unlikely that you'd be able to arrange a ground so that the impedances are all 50 ohms.  In a typical ground plane situation, you would expect the leads to have a modestly high impedance (roundabouts 100 ohms) and the body, probably something a lot lower, so you get a lowpass filter effect.  There can also be a mode with the body resonant on top of the leads, which would transmit a lot of energy into space (if not shielded), resulting in a notch in the stop band.

In the pursuit of that, though, it might pay to remove the ground plane beneath the body, to compensate for its size.  The advantage would be extending the pass band flatness, by maybe up to an octave?

Tim
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#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #14 on: March 24, 2018, 12:50:38 am »
Hi,
I am the designer of the LISN that was described in this message:

https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/msg404662/#msg404662

This LISN uses 5 pieces of a Wurth 744314110 inductor.

This was chosen for its high self resonant frequency.

The LTspice model reveals the equivalent circuit of the inductor:

These inductors can be placed in a simple 5uH LISN:

The simulation shows that input impedance matches the requirement of the CISPR specification. There is no impact on the performance from using this inductors.

The transmission is also 'textbook':

There is nothing wrong with using cored inductors in a LISN.

The important feature is that the impedance of the inductor is high, compared to 50 Ohms over the frequency band of interest.

Here is the inductor in a test circuit to measure its impedance:

And the results from that simulation:

You can see that even above the self-resonant frequency the inductor still has high impedance.

I also designed the Line voltage LISN shown in this message:

https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/msg641108/#msg641108

It was designed using similar ideas to those described above.

Regards,
Jay_Diddy_B

« Last Edit: March 24, 2018, 12:52:53 am by Jay_Diddy_B »

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #15 on: March 24, 2018, 01:01:25 am »
Hi,

The reason of the ring of capacitors in this picture:

Is probably the result of somebody copying somebody work without understanding it.
This is the main coupling capacitor in the LISN. One end is connected the line voltage, the other end is connected to a Spectrum analyzer.

This capacitor should have a very high safety rating, a Y class capacitor. It is not easy to get high values of Y capacitors so several Y capacitors may need to be connected in parallel.

The requirement is that this capacitor is low impedance, compared to 50 Ohms across the frequency range of interest.

SPICE is a very tool for engineering LISNs.

Regards,
Jay_Diddy_B

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #16 on: March 24, 2018, 03:28:49 am »
Hi,
I have looked at the schematic for the Com Power LISN 115A contributed by floobydust in reply 7.

This is my interpretation of the 10dB limiting circuit.

This is the frequency response of the schematic shown above.

I didn't make any attempt to use the same component designations.

I have attached the LTspice model.

I believe the switch bypass the filter/attenuator/limiter. This arrangement gives the 10dB attenuation.

Regards,
Jay_Diddy_B

#### charliedelta

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #17 on: March 24, 2018, 08:50:01 am »
Just follow the CISPR design which includes the  470 ohm carbon resistor across every few turns. Download CISPR 16 standard and it has all the design and construction details in the appendix.

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #18 on: March 24, 2018, 03:31:49 pm »
Hi,
I am going to continue my analysis of the Com Power LISN 115A by looking at the ring-o-caps:

r

Humor Old Technology

Humor\

The believe is that is a countermeasure for parasitic resonances in the coupling capacitor. The impedance curves for typical capacitors is like this:

A model can be built which includes parasitic elements:

And this produces the results that match the capacitor datasheet. I have included the model for 6x 0.01uF capacitors in parallel. This assumes that the capacitors can be connected in parallel without any additional inductance (most unlikely).

The capacitor models can now be inserted into a LISN model. All other components in the LISN model are ideal. The first model looks at input impedance:

When you look at the results, there is very little difference between the three models.

Voltage Source - Zero Impedance

In this test the transmission of the three LISN is measured with a zero impedance. This low impedance is similar to the actual use case. In most case the emissions from the unit under test are low impedance.

The results are:

Apart from the obvious difference caused by 0.1uF versus 0.06uF at low frequencies, there is no significant advantage to using the 6 capacitors in parallel approach, to reduce the effect of the self-resonance.

There may be a benefit form a safety view point. You can get better grade of capacitors in low values (X versus Y)

Test with 50 Source

The test can be repeated with 50 source. This represent the test condition, for testing the LISN with a signal generator or VNA.

This analysis suggests that there is very little or no benefit to the ring-o-caps.

Regards,
Jay_Diddy_B

« Last Edit: March 24, 2018, 03:38:41 pm by Jay_Diddy_B »

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#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #19 on: March 25, 2018, 05:25:54 pm »
Jay_Diddy_B thank you for all your work, especially your analysis of the ComPower LISN.

I've only seen ring-arrays in high power RF transmitters, so the designer might have carried that experience over.

We disagree on one point- the use of power ferrite-core vs air-core inductors. It would be great to know SMT inductors that could instead be used for pre-compliance work, in a mains LISN.

The inductor core material is important and something I don't see covered.
Spice simple inductor models assume air-core, with some winding capacitance to model self-resonance, so I take simulation results as all rosy. Rising ESR due to core losses I think should be taken into account. I don't have a network analyzer to measure these parts, so I rely first on datasheet information.

If we need 50uH (and I have not seen the 250uH parts, assuming they are not critical and a line filter would suffice) then 5-10uH parts under consideration.
Your EEVBlog mains LISN with 5 of Wurth 7443331000 10uH 9A SRF 35MHz, not sure of the core material.

Wurth parts do not have frequency response curves but WE-HCC ferrite, Wurth says suitable to 5MHz.
WE-WCC iron powder, Wurth says suitable to 5-100MHz (but I'd say 40MHz), 4.7uH is max. offered.
Wurth "superflux" material alloy powder Wurth training module for the WE flatwire series states "switching frequency range: up to 10MHz".
Coilcraft SMT flatwound example SER805x datasheet has flat frequency response curves ending at 10MHz but look promising.
Fair-Rite 61 Material have to do math for gapped/rod.

I keep looking at complex permeability vs frequency. Can we ignore?
« Last Edit: March 25, 2018, 05:27:41 pm by floobydust »

#### CopperCone

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #20 on: March 25, 2018, 07:34:08 pm »
Well, just to review, the air coils I made came out to the following dimensions:

250uH coil = 2.65mm wire, 33 turns (2x), approximately 6 inches wide and 5 inches tall (made on a bobbin of wood and pvc pipe).

50uH coils - 13 inches long, 2 inches wide

Its going to be rather large.

using magnetic core materials would be nice yea
« Last Edit: March 25, 2018, 07:43:19 pm by CopperCone »

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #21 on: March 25, 2018, 08:49:44 pm »
Jay_Diddy_B thank you for all your work, especially your analysis of the ComPower LISN.

I've only seen ring-arrays in high power RF transmitters, so the designer might have carried that experience over.

We disagree on one point- the use of power ferrite-core vs air-core inductors. It would be great to know SMT inductors that could instead be used for pre-compliance work, in a mains LISN.

The inductor core material is important and something I don't see covered.
Spice simple inductor models assume air-core, with some winding capacitance to model self-resonance, so I take simulation results as all rosy. Rising ESR due to core losses I think should be taken into account. I don't have a network analyzer to measure these parts, so I rely first on datasheet information.

If we need 50uH (and I have not seen the 250uH parts, assuming they are not critical and a line filter would suffice) then 5-10uH parts under consideration.
Your EEVBlog mains LISN with 5 of Wurth 7443331000 10uH 9A SRF 35MHz, not sure of the core material.

Wurth parts do not have frequency response curves but WE-HCC ferrite, Wurth says suitable to 5MHz.
WE-WCC iron powder, Wurth says suitable to 5-100MHz (but I'd say 40MHz), 4.7uH is max. offered.
Wurth "superflux" material alloy powder Wurth training module for the WE flatwire series states "switching frequency range: up to 10MHz".
Coilcraft SMT flatwound example SER805x datasheet has flat frequency response curves ending at 10MHz but look promising.
Fair-Rite 61 Material have to do math for gapped/rod.

I keep looking at complex permeability vs frequency. Can we ignore?

O.K.

First thank you for kind comments regarding the Com Power LISN.

I was planning on doing some more analysis on LISN today.

There are 5uH LISNs and 50 uH LISNs. We can talk about the 250uH part later.

The inductors in my Line voltage LISN are Wurth HCC (Ferrite). I don't know how to model the change in permeability with frequency in LTspice. I can model different values of inductance.

The requirement is that the impedance of inductance is large, say 300 (for a 20% error in input impedance) at all the frequencies that you are interested in.

At 1 MHz need 50uH

At 10 MHz need 5uH

At 50 MHz need 1uH

so the permeability of the material could change and you still meet the minimum impedance requirements.

Similar if the inductance changes with current, it is not a big deal.

This set of model show the effect on impedance of changing the inductance.

And the results

Remember, the emissions are low Impedance, if they were high impedance, they would very easy to deal with. So an error in input impedance doesn't mean a (large) error when measuring emissions.

The 250uH inductor has very little impact on the LISN performance. you can model this inductor. If you look at input impedance, transmission with a 0 source and transmission with a 50 source you will see it has very little impact.

The place were it does impact is the transmission from the mains port to the output. The 250uH acts like an input filter. In my LISN I replaced the 250uH with a commercial line filter.

The air cored inductors have some issues. The self-resonant frequencies aren't very high. The other issue is coupling. I have seen reports were the inductor measures 58uH in free space, but 50uH when installed in the box. This means the flux from the inductor is coupling the metalwork or other things. Single layer solenoids with space between the turns will be better than multi-layer coils made with magnet wire.

Regards,

Jay_Diddy_B

« Last Edit: March 25, 2018, 08:51:17 pm by Jay_Diddy_B »

#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #22 on: March 25, 2018, 09:42:15 pm »
We disagree on one point- the use of power ferrite-core vs air-core inductors. It would be great to know SMT inductors that could instead be used for pre-compliance work, in a mains LISN.

The inductor core material is important and something I don't see covered.
Spice simple inductor models assume air-core, with some winding capacitance to model self-resonance, so I take simulation results as all rosy. Rising ESR due to core losses I think should be taken into account. I don't have a network analyzer to measure these parts, so I rely first on datasheet information.

Whose simple models? -- Well, if it's a 2nd order approximation, it would be an inductor, with some DCR and EPC, and no saturation.  (I don't know of anyone who's published saturable models, FYI.)

The best models I know of are from Coilcraft, and can be run in SPICE with little or no modification.  Of course, they're specific to what parts they have data on, but the model can be adjusted pretty easily to fit other Z(F) data.

And you can generate such data for an air core solenoid using: hamwaves.com/antennas/inductance.html

Higher order AC data isn't important here (ACR, Q, behavior above resonance), so we don't need to be any more precise than 2nd order, anyway.  Not a big deal.

The biggest problem is saturation: if you're testing a 1kW SMPS without PFC, peak currents will easily be 2-4 times the PF=1 (sine wave) peak current.  You don't want to miss EMI during those peaks, which are likely the most important, after all, because the FWB diodes are conducting the EMI straight into the LISN during that part of the mains waveform.  Reduction in inductance raises the LF cutoff, so you could potentially miss the switching fundamental ripple by some dB.

Well, a few dB still isn't very important for precompliance purposes, so YMMV.

Quote
Fair-Rite 61 Material have to do math for gapped/rod.

I keep looking at complex permeability vs frequency. Can we ignore?

Careful!  The effective permeability of a rod is much lower than for the material itself; and mu'' of air is zero.  Result: even if the material itself is lossy (#61 only at VHF+!), the resulting inductor has better Q than you expect from the plot.

Tim
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Bringing a project to life?  Send me a message!

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #23 on: March 26, 2018, 12:57:07 am »
Hi,

Time to break out the network analyzer. These measurements were made with an HP 8714C VNA. The same circuit was modelled in LTspice so that modelling and the actual components can be compared.

Test Circuit

The model shows the test circuit. I did not have the 10uH inductor in stock so I used the 6.8uH from the same series. The inductor is Wurth 744 332 0680. Here is a picture of the packaging, from Digikey:

Construction

A small piece of copper clad circuit board was used. A BNC connector was attached to one end and two 100 resistors were connected in parallel to make 50 .

There is a very small amount of inductance in the ground connection.

Resistive Test

The VNA shows that this is a resistor

The inductor was soldered in parallel with the resistor.

And the impedance was measured again:

This looks very much like the result from the LTspice model:

I zoom in to the 10MHz, the VNA gave me:

And the LTspice model gives me:

Remember, I am testing just one 6.8uH from the same family as the five 10uH parts used in my LISN.

The VNA test shows very little deviation from the ideal results from the LTspice modelling.

Regards,

Jay_Diddy_B

« Last Edit: March 26, 2018, 01:06:21 am by Jay_Diddy_B »

#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #24 on: March 26, 2018, 01:22:14 am »
Hi,

The previous LTspice model used an ideal inductor. If I use the model which includes the parasitic components:

I get the following result:

Which is even closer to the measured result:

.

The model is accurate.

Regards,

Jay_Diddy_B

#### floobydust

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #25 on: March 26, 2018, 06:40:56 pm »
Again, thanks for real measurements.

I had real trouble finding/seeing a power ferrite past 10MHz so I thought only air-core would be suitable.
Looked at SMT ferrite power inductors from several manufacturers; TDK/Epcos, Murata, AVX, Vishay, Coilcraft, Wurth etc.
Most have no specs for frequency/SRF, the better ones start rolling off L at 10MHz and SRF 30MHz or less.
This is for 4.7uH-10uH and >10A. I'm used to permeability/saturation being prioritized over operating frequency, you want minimum copper (losses).

LTSpice sim with Wurth parts 744333, 332 and their RLC models;
It looks like qty. 7 of 6.8uH WE-HCC 7443320680 Isat 13A SRF=42MHz ferrite is good, as your the analyzer confirms. About $50 for qty. 14. Some Wurth HCC parts had losses at 20-30MHz, attenuation seems limited by the damping resistors. An air-core part is the size of a can of beer and ugly with no coilforms to keep the windings from springing around. The commercial LISN has a machined-nylon former. I could only see 1-1/2" or 3" ABS plumbing pipe as low cost but 10-14AWG windings would still move. So mechanically, the air-core is PITA- unless others have suggestions for OP. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #26 on: March 26, 2018, 07:19:50 pm » you can use super glue (sprinkle with baking soda to make it solidify fast), then every 8-12 turns add another dash of glue on the windings to keep it taught. This is what I did. Not perfect but it sorts works. I used wood clamps to hold it tight (with the rubber bits) when the glue is drying, and sometimes I had to beat it with a wooden dowel and a hammer (gently) to compress the windings (I am reusing 2.65mm magnet wire from other large inductors I have no use for) « Last Edit: March 26, 2018, 07:22:38 pm by CopperCone » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #27 on: March 26, 2018, 07:22:26 pm » Hi, I only measured 6.8uH because I didn't have any 10uH parts. Nothing particularly bad happens at the self-resonant frequency and beyond, except the impedance starts to drop. I will do some analysis later to show this. Regards, Jay_Diddy_B #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #28 on: March 26, 2018, 10:49:39 pm » Floobydust and the group, I looked at the model that you created and there are a few errors. This is the corrected version: The DUT under test is connected to the left side of the LISN, represented by the source V1. The line voltage input is normally connected on the right side. This can be open or short for the evaluation, because the 1uF capacitor on the right side is an effective RF short. There are two major parameters: 1) input impedance This is obtained by measuring the voltage applied to the LISN and dividing by the current. 2) Transmission You can measure the transmission from the source V1 to the output. The spectrum analyzer is represented by the 50 Ohm resistor connected to ground. I have attached my modified model. There is insignificant difference between all 4 models. Any of them are practical circuits. Regards, Jay_Diddy_B « Last Edit: March 26, 2018, 10:52:00 pm by Jay_Diddy_B » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #29 on: March 26, 2018, 11:21:26 pm » Hi, I promised early that I would analyze a LISN with a relative low SRF inductor. This is the model: Really there are three models. The top model is used to confirm the model of the inductor. The current source is 1A so the impedance is in Ohms. The impedance peaks at the self-resonant frequency and then decreases with increasing frequency. The second model is a LISN built with the 50uH inductor with a 7MHz SRF. The third model uses an ideal inductor for comparison. Results Even with a self-resonant frequency of 7 MHz this results in a LISN which is 10% low (45 ) at 150 MHz. I have attached the LTspice model. Regards, Jay_Diddy_B #### G0HZU • Super Contributor • Posts: 3137 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #30 on: March 27, 2018, 08:46:49 pm » Those lumped models look to be very basic... Using a model like this for a large 50uH inductor that has a SRF of 7MHz is not going to be adequate if you try and use that model out to something like 150MHz. I'm assuming here that the 50uH inductor in this case is a physically large solenoid wound with thick wire? An inductor like that will need to be modelled as a complex transmission line structure or (better still) usea VNA to obtain a two port s parameter model as this type of inductor will have multiple resonances by 150MHz and your basic lumped model can't capture this. « Last Edit: March 27, 2018, 08:55:32 pm by G0HZU » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #31 on: March 27, 2018, 09:04:24 pm » Those lumped models look to be very basic... Using a model like this for a large 50uH inductor that has a SRF of 7MHz is not going to be adequate if you try and use that model out to something like 150MHz. I'm assuming here that the 50uH inductor in this case is a physically large solenoid wound with thick wire? An inductor like that will need to be modelled as a complex transmission line structure or (better still) usea VNA to obtain a two port s parameter model as this type of inductor will have multiple resonances by 150MHz and your basic lumped model can't capture this. G0HZU, The model is very basic. Most of the discussion has been about whether it is o.k. to use a cored inductor in a LISN and what is the impact of the various parasitic elements on the LISN performance. The 50uH LISN is (normally) used in the frequency range from 150kHz to 30MHz. So it is the performance in this frequency range that is important. The modelling is been done to higher frequencies, because this is where the parasitic effects show up. I tested a 6.8uH Wurth HCC ferrite cored inductor on a VNA (HP8714C) and it behaved like the lumped model. I haven't tested one of the single-layer solenoids normally found in commercial on LISNs on a VNA. I don't expect it will perform all that well. If I was winding a single layer solenoid, I would space the winding from the coil former and I would ensure that there was some space between the turns to lower the turn-turn capacitance. Regards, Jay_Diddy_B #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #32 on: March 27, 2018, 10:36:16 pm » Hi group, I decided to wind a solenoid inductor using PVC coated wire. The coil is about the same size as a 12oz (355ml) pop can: I used 2" ABS pipe which 2.37 inches in diameter. And PVC coated 16Awg wire which is about 0.1 inches diameter. 35 turns, 4 inches long. I used the calculator found here: http://electronbunker.ca/eb/InductanceCalc.html I was aiming for 40 turns which would have resulted in the 50uH inductor. I only wound 35 turns at I got a measured inductance of 37uH. I put my dimensions back into the calculator I get the same answer: I then connected the inductor in parallel with a 50 resistor to a HP 8714C VNA and measured the impedance. I can see dips in impedance at 29, 43, 58 and 73 MHz. These are probably caused by some transmission line effects. These are the effects that G0HZU mentioned. Regards, Jay_Diddy_B #### G0HZU • Super Contributor • Posts: 3137 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #33 on: March 27, 2018, 10:38:29 pm » Thanks. I've not done anything with LISNs apart from seeing them get used many times for formal EMC testing at work etc. But some of the LISNs in the links use huge solenoids for the 50uH inductor and in the absence of the damping resistors I'd expect them to have resonances starting at maybe 7MHz but I'd also expect to see a significant series resonance by maybe 20-25MHz. Then more series resonances every 15-20MHz or so. Presumably the damping resistors are there to try and take this out. The Tekbox model looks a bit strange. Does it really use 68R damping resistors? This value seems really low. Their 4 section 50uH inductor also looks to be symmetrical which seems odd. I would have expected to see some deliberate asymmetry that aims to break up the various resonance modes. But then I've never tried to make a 50uH LISN like that. At work I do a lot of ultra wideband RF design work so I have to model inductors very carefully up to frequencies way beyond the first few resonances. Usually I do this with a 2 port VNA model but it can also be done (with limited success) with complex transmission line models. #### G0HZU • Super Contributor • Posts: 3137 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #34 on: March 27, 2018, 10:49:20 pm » Looks like we double posted... Yes, those are the series resonances in the solenoid. The first one crudely corresponds to the solenoid acting as a half wave transmission line. Energy enters one end and there is 180degrees phase shift by the far end. Then it hits the 1uF shorting cap at the far end and there will be a 180degree phase shift in the reflected wave (because it sees a short circuit here). Then there is another 180degrees on the return trip back through the solenoid. So it returns with 180+180+180 which means it returns in anti phase so it looks like a (lossy) short circuit where you want it to look like 50R. I expect that this will typically happen within the 30MHz bandwidth for a huge 50uH solenoid structure like this? The resistors (between turns) can damp this out but I'd also expect to see undamped sections between the resistors. Also I'd expect to see some deliberate asymmetry in the way the resistors are fitted along the structure. The (symmetrical?) Tekbox solenoids therefore look a bit strange to me but then again I've never tried to make a 50uH solenoid like that. Try tacking a few resistors along the windings to see how the dips get damped out? « Last Edit: March 27, 2018, 10:58:44 pm by G0HZU » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #35 on: March 27, 2018, 11:32:36 pm » Hi, The Tekbox LISN that can be found here: https://www.tekbox.net/test-equipment/tboh01-5uh-line-impedance-stabilisation-network-lisn-cispr25 is a 5uH LISN. According to the Tekbox documentation they use four 1.25uH air cored inductors connected in series. It is a little suspicious, because if you mount the inductors as close together as they seem to they will couple. Source: https://www.mikrocontroller.net/topic/323322 The manual shows the schematic: This is different than a 50uH LISN. Transmission line effects are less of problem in a 5uH LISN because the wire is shorter. Regards, Jay_Diddy_B « Last Edit: March 27, 2018, 11:38:30 pm by Jay_Diddy_B » #### G0HZU • Super Contributor • Posts: 3137 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #36 on: March 28, 2018, 01:03:23 am » I did a quick youtube video showing an old inductor model I developed at work many years ago. Sorry, there's no sound I don't have a microphone. It is created using the physical dimensions of the inductor (turns, diameter, length etc) and translated into a distributed model. The red trace data is s2p data taken of a real 400nH inductor. It works quite well to about three times the frequency of the first 1/4wave resonance at 250MHz. This resonance is the one that the crude/classic lumped model tries to capture. It shows how well the resonances and impedance agree up to about 1GHz. This old model worked really well if a VNA wasn't handy and it could also be used for transient analysis. It works for solenoids big or small and any L/d ratio (within reason). So it should be able to model the big inductors used in LISNs. But the best way to model an inductor is usually to use a 2 port VNA to extract a 2 port model. But this old inductor model of mine is still very powerful https://youtu.be/4HSWW672vtc « Last Edit: March 28, 2018, 01:14:26 am by G0HZU » #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #37 on: March 28, 2018, 03:45:37 am » Hi I'd be interested in building a LISN as well. I'd also be interested in any group buy of a PCB if that happened. That is likely to be the most expensive part. Dazz Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #38 on: March 28, 2018, 04:40:43 am » Hi I'd be interested in building a LISN as well. I'd also be interested in any group buy of a PCB if that happened. That is likely to be the most expensive part. Dazz PCBs are stupid cheap, most of the cost will be in the copper (and cores, if used)! The circuit is so simple, it's hardly worth making a PCB IMHO. Point-to-point is more than adequate here. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #39 on: March 28, 2018, 05:05:03 am » I think there's reluctance to make a PCB available, due to safety and liability concerns for a mains-powered design. Although, an air-core inductor ungluing or going sproing and shorting to something would be the worst. Or a point-to-point design not staying together, during an earthquake Commercial LISN's have no agency approvals, no fuse. Just an aluminum box to contain things. These things are used in a gray area, the lab. #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #40 on: March 28, 2018, 05:39:27 am » PCBs are stupid cheap, ... Not where I live. I am designing 2 boards at present that will be the most expensive component for each project. The circuit is so simple, it's hardly worth making a PCB IMHO. Point-to-point is more than adequate here. Are you including the protection circuitry for the port in your statement? Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #41 on: March 28, 2018, 06:24:50 am » Not where I live. I am designing 2 boards at present that will be the most expensive component for each project. PCB Shopper shows five mfg's that will do a typical board for this sort of project (100 x 150mm, 2 layers, 2 oz, nothing else special), <= 10 AUD/ea at qty 10? Is that not cheap enough? Quote Are you including the protection circuitry for the port in your statement? Yes, and filtering -- it's just a ladder network, easily done with SMTs on copper clad. Would only take me a few hours to scratch one out; or a few bucks first, if I didn't have the utility knife and copper clad on hand. Now, the enclosure, that's the real expensive item, if you don't have one handy. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #42 on: March 28, 2018, 06:43:43 am » PCB Shopper shows five mfg's that will do a typical board for this sort of project (100 x 150mm, 2 layers, 2 oz, nothing else special), <= 10 AUD/ea at qty 10? Is that not cheap enough? Which is exactly my first point. A PCB is a good idea and if 10 or more people want boards, the cost per board is very reasonable. So if there is enough interest to do a group buy on a LISN PCB, I'd be interested in joining. Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #43 on: March 28, 2018, 02:03:13 pm » How should i setup my 4 section 50uH inductor for tuning on the vna? Do i connect em all, put it in parallel with 50 ohms, measure, add the dampening resistors and hf coils then measure again? I am a vna noob #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #44 on: March 28, 2018, 02:23:41 pm » I think there's reluctance to make a PCB available, due to safety and liability concerns for a mains-powered design. Although, an air-core inductor ungluing or going sproing and shorting to something would be the worst. Or a point-to-point design not staying together, during an earthquake Commercial LISN's have no agency approvals, no fuse. Just an aluminum box to contain things. These things are used in a gray area, the lab. Floobydust nailed it. I am happy to share the 5uH LISN because it is normally used for low voltages. I am a little reluctant to share the 50uH PCB because of liability. I have sent the Gerber files to a few individuals on a case by case basis. The board is currently 4.5 x 4.5 inches. This didn't matter when I made the prototype for my own use using my LPKF Protomat c60. If I shrink the board to 100 x 100mm it opens up the possibility of using the very low cost manufacturers. It doesn't make sense to do a group buy if the board is 100 x 100mm. The distribution cost and effort is higher than ordering them direct. If you believe a LISN can built with cored inductors, build it as I did. If you are a non-believer and want to do air cored, use the same PCB and wire in the air cored inductors. Doing this you will benefit from the transient limiters and filters located on the board. If you are the fence, you can build both and compare them. You can also build the 5uH LISN on the 50uH PCBs. Does this make sense? Regards, Jay_Diddy_B #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #45 on: March 28, 2018, 02:25:47 pm » How should i setup my 4 section 50uH inductor for tuning on the vna? Do i connect em all, put it in parallel with 50 ohms, measure, add the dampening resistors and hf coils then measure again? I am a vna noob Which VNA do you have? I have been measuring the inductor in parallel with a 50 Ohm resistor. But if you tell me which VNA I might be able to help more. Regards, Jay_Diddy_B #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #46 on: March 28, 2018, 03:55:45 pm » :-//I have a 300MHz version of the E5100A Btw, I read (and suspected) that the parallel resistors may add a kind of HF shunt, and i read that filter designers recommend adding inductors in series with the dampening resistors if degraded hf responce is noted. https://www.google.com/url?sa=t&source=web&rct=j&url=http://ecee.colorado.edu/~rwe/papers/APEC99.pdf&ved=2ahUKEwj_yOjGsY_aAhUDTd8KHe8EAooQFjAMegQIBhAB&usg=AOvVaw22rdcGWHhoqkIZ98eQiuaw « Last Edit: March 28, 2018, 04:01:08 pm by CopperCone » #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #47 on: March 28, 2018, 04:47:21 pm » Damping resistors every 4 turns, then one oddball at the end on the CISPR air-core inductor. #### G0HZU • Super Contributor • Posts: 3137 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #48 on: March 28, 2018, 08:44:43 pm » That looks to be along the lines of what I'd expect to see. There are undamped sections between the resistors and some deliberate asymmetry in the structure #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #49 on: March 28, 2018, 10:25:37 pm » :-//I have a 300MHz version of the E5100A I am not familiar with the E5100A analyzer. I had a quick look at the manual and could not see how to get into the mode required. On the HP 8714C I set the desired frequency range I do a one port calibration with OSL standards. I set the VNA for reflection. The format to impedance and adjust the scaling. And you can see the display that I get. Regards, Jay_Diddy_B « Last Edit: March 28, 2018, 10:28:13 pm by Jay_Diddy_B » #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #50 on: March 29, 2018, 12:04:33 am » But I just still put in in parallel with a 50ohm resistor? #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #51 on: March 30, 2018, 08:04:17 pm » Sims show large inrush currents, if powered-up at Vpk line. 120VAC mains over 2.5Apk for very short time ~100nsec to charge the 0.1uF cap. The transient-limiter 1206 resistors+ LPF cap can get walloped pretty hard. The Tekbox protection scheme seems wrong, 5V TVS in parallel with GDT- which will never light up until the TVS pops... GDT appears ineffective, needs over 100usec to ionize and too slow to help. I'm not sure of options to ensure the input resistors don't get damaged. Spike average power is 0.5W and 120Wpk. ESD9L5.0 < 1pF #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #52 on: April 01, 2018, 04:29:50 am » Floobydust and group, The Tekbox 5uH LISN is a low voltage LISN, typically used for 12V Vehicles, 28V avionics etc. So it unlikely that the gas discharge tube will ever fire. The transient limiter in my line voltage LISN is styled after the HP11947A transient limiter. The manual can be found here: https://www.keysight.com/upload/cmc_upload/All/11947-90006.pdf The schematic is: The (partial) BOM: The HP 11947A is obsolete. Similar products are available: http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=275 Leo is a member of the forum and famous for his fast pulse generator: https://www.eevblog.com/forum/projects/yet-another-fast-edge-pulse-generator/msg1251589/#msg1251589 Regards, Jay_Diddy_B #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #53 on: April 01, 2018, 10:09:05 pm » Using a GDT gives impressive specs, who keyed up into this... "Maximum Input Level: Continuous: 2.5 W (+34 dBm), Pulse: 10 kW for 10 µS, DC:±12 V" For the mains inrush, the HP11947A transient-limiter through-hole 1/2W RN65 resistors can take some abuse. I'd prefer something stronger than 1206 chip resistor like MELF MMB0207 1W, 225W impulse and good past ~400MHz. Or maybe several clamp-diodes like LL4150 adds a pF. I think max. input 50mW is 2.24Vpk so two series strings of four maybe. The A-band (10-150kHz) LISN has bigger 0.25uF caps that would have very large inrush. For the 250uH inductor, I could not find much >10A off-the-shelf with ferrite cores. Abracom ATCA-08-251 10A DC toroid. Bourns 1140-270K-RC 270uH 12.4A DC. Instead, looking at using mains line filters, power entry modules, they have a CM choke which is easy to find at 250uH and 15A. But very little for DM attenuation. #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #54 on: April 03, 2018, 08:25:32 am » ... I am a little reluctant to share the 50uH PCB because of liability.... I am not a lawyer but I struggle to see how you could be held liable for supplying a PCB. A PCB is a component that can do no harm or damage. Someone else has to add a collection of components to it before they might be capable of damage or harm. Has a PCB designer/supplier been sued somewhere? Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #55 on: April 03, 2018, 09:00:44 pm » Ok, I assembled the coils and capacitors on a PCB. If anyone is curious, my shitty 50uH coils wound in 4 identical sections were an approximately 1.5% match at 100KHz. The spacing between the coil sections were about 1 inch. You can trim via mutual inductance, by moving them apart or seperate from each other. By squishing the live connected coil a bit (I wound the coils on wax paper over a PVC pipe, which I then bound with a line of super glue, then removed from the forming pipe to place on the actual inductor structure), I was able to tune it to about 0.5% match. Already alot better then my capacitors, which only had a 2% match, so I left it at that. I suppose I can tune it up a bit better, it would be nice for common mode response I guess. I would need to get some low value high voltage capacitors to fix that spec up... I think someone said the spec for a LISN is about 10% match between the sections though? #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #56 on: April 04, 2018, 01:36:56 am » What value of power would you use for the resistors that break up the circuit in parallel with the coil? If you use 270V, and the value is 460 ohm each, you get the following: Simulated with a 80mOhm resistance in the 250uH coil, and 80mOhm resistance in the secondary coil (higher because of all the solder joints despite being much shorter), and 5 ohms of series resistance with the 7.5uF capacitor. The parameters of the primary capacitor (2uF) can be ignored I think. 0.01Ohm Load - Short Circuit - 60mA, 470 Ohm 4x - so approx 2k parallel. Peak Power - 1.6kA for the load, which is approximatly 7 watts, across 4 resistors, so 1.8 watts per resistor, meaning you should use 3watt resistors. This means something shorted out real good. Possible even? 3 ohm load - 80Amps flowing through coil, 3.4mA going through the resistors, 18mW per resistor, so 1/4 watts is more then acceptable 7.5 ohm load - 35 amps flowing through coil.. 1/4 watt parallel resistor more then acceptable. The 2.65mm wire inside can handle it, if hooked into a 40 amp 2 phase outlet. Would need a special connector on it though. Now, I assume this beast should be fused.... so slow blow fuses? I don't know what the dynamic resistance of these guys is. As you can see the theoretical spread is pretty large. What would be a good practical value of wattage to use? What is the expected peak current from a reasonable outlet? How should a resistor be rated (I don't really see transient power specs on resistors). Do I need to go with 3Watt resistors to account for the possibility of the load shoring out? Or is this completely insane? How do you derate average resistance for a pulse that lasts in the microseconds? I assume its pretty nonlinear with respect to the gauge of wire used to manufacture the resistor. What kinda average current that the resistor cares about will a shorted outlet put out before the circuit breaker/fuse kicks in? I think the resistors can be damaged by hot spots.. but the time scales of these overloads ellude me, and the overload duration of the resistors cannot be easily found. Getting a kiloamp from a 20amp home outlet seems kinda unlikely, no matter how short the pulse is, but then again its a spark gap so . My hunch says I should just put like 0.75 watts of dissipation per resistor to tolerate stuff. « Last Edit: April 04, 2018, 01:48:34 am by CopperCone » #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #57 on: April 06, 2018, 09:30:42 am » The inductor is Wurth 744 332 0680. Here is a picture of the packaging, from Digikey: Jay_Diddy_B I have just read my way through this thread. I like all this modeled and measured data. My old Professor used to say it ain't true if it ain't measured. I note from the inductor data sheet that although the inductors are rated to 13A, the inductance starts to fall away at about 8A. I don't see this as a problem at all. I would just rate the LISN at a max current that is within the defined performance curves defined in the standard. It is relevant to me because I intend to test equipment rated to 10A. Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #58 on: April 06, 2018, 12:31:31 pm » Hi, You can choose inductors for the current rating that you desire. We can consider the impact of inductance changing with current. This is the curve for the Wurth 744 332 1000 Inductor: It is 10uH with zero current and 7uH with 10A. We can then build two models, and two additional models to create the CISPR 16-1-2 +/-20% limits: If you look at the results the LISN meets the CISPR 16-1-2 specifications, with 10A, except at a very small area between 150 and 180kHz where there is a minor discrepancy. Remember that I am plotting LISN impedance, in use you are measuring transmission from the DUT port to the Output with a low impedance source. The LISN impedance will have very little effect on the accuracy of the EMC measurements. You have to decide the current rating of the LISN you want and choose inductors accordingly. May aim was to make a small portable LISN rated at 5A which 600W at 120 VAC and 1.2kW with 240 VAC. Regards, Jay_Diddy_B « Last Edit: April 06, 2018, 12:37:09 pm by Jay_Diddy_B » #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #59 on: April 06, 2018, 03:35:05 pm » Remember that rectifier-input devices draw more peak current. Peak to RMS ratio may be 4 or more! This is especially troublesome for the LISN, because those peaks are also where you get the strongest signal: the diodes are conducting, carrying EMI from the EUT to the LISN. Result is, you could be missing some dB's at the low end, missing the switching fundamental by as much. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! The following users thanked this post: dazz1 #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #60 on: April 06, 2018, 04:16:04 pm » Has anyone had a look at the ground isolating inducotor in the tekbox schematic? Its specified at 1.8 milihenry. Atb60hz its reactance is 600 ohm. Should multiple inductors be used in a cascade here? You are pretty much forced to use ferrite. Should this guy be a torroid? I am getting very confused by the field interactions with this ground inductor. Do you need the heavy wire gauge here? Lets say your load has hv dc output earth ground referenced. If there is a short you might blow up a thin gauge ground isolation inductor right, then have a malfunctioning chassis at hgih potential. Also, since the reactance is 600ohm at 60hz, a hot ground would be potentially still pretty dangerous unless you have a gfic. You cant really rely on it to blow a fuse. I am worried that the gfic is pretty noisey and its kinda an off requirement to use one if its not built into the equipment. Especially dangerous since the gear being tested is experimental and is more likely to have wiring problems. Ideas? I thought maybe a mov or low voltage gdt across the 1.8mh inductor that could pass enough energy to blow the input fuse? Mov is a nonlinear junction and may mess with mixing emissions. What if like high voltage high frequency energy gets on your 1.8mh isolated gnd? Can a mov or gdt even shunt that reliably? If its the waveform output of dcdc converter before filtering, so say a 300v or more pwm signal thats passing through a live potential heatsink at frequency between 1khz to 20MHz or more.. Idk where the limits of switchin frequency are when it comes to high voltage dcdc converters or where it goes from heart attack hazard to slightly lessdangerous flesh cooking hazard In a lab setting at home you might be adjusting the equipment tosee output waveform at different operating conditions could be hazardous « Last Edit: April 06, 2018, 04:38:14 pm by CopperCone » #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #61 on: April 07, 2018, 02:12:07 am » I find that ground inductor uncommon and would not implement it. There are other means to look at CM noise only. Some reference to it being a holdover from old German VDE 0871 standard. It should be a 16A inductor. ETS-Lindgren: EARTH LINE CHOKE SWITCH The safety ground isolation choke selector switch switches the 1.6mH earth line choke IN and OUT of the safety ground circuit. The ground choke is designed and manufactured with sufficient capacity to conduct the maximum current rating of the Model 3816/2 and at no time is the safety ground of the unit compromised. The earth line choke avoids a double RF ground connection (safety ground and measurement ground) in the conducted emissions test setup." This is another ref. to it, I think: "Whenever the EUT dimensions are such that the protective earth conductor is long enough to show a significant impedance, or be close to ¼ of a possible wavelength, or the enclosure has poor conductivity, the test will be performed using the non-fused, built-in artificial protective earth." #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #62 on: April 07, 2018, 01:55:53 pm » But what about its high reactance and the fact that it will compromise safety? Will a 90V or less GDT in parallel with it work? I want it to blow the mains fuse if there is high voltage on any thing with a metal enclosure due to a short that can fry you in short order. I know it wont help much with a current limited short to chassis, but it would still make me feel alot better. MAYBE a partial short could be covered by the ground from a spectrum analyzer... but a BNC cable is no saftey ground for 16A!!!!!! (more like 40 for what I built). I am worried that the measurement ground, may not be connected at the time (i.e. powered up before the SA/EMI reciever is connected. And I don't really want a high current going through my spectrum analyzers ground. Or you might wanna hook up a battery powered instrument to it, like a hand held SA or hand held MM (for true rms) or hand held oscope, so you don't even have the option for a shitty saftey ground through a BNC/SMA cable (horror to ground 20A with a thin rg-whatever spagetti cable). It could explode and give you thermal burns! I don't feel comfortable with that level of saftey and I would like to find some kind of better solution. I don't even know how to setup a GFIC to measure current difference between the oscilloscope/SA ground either, accounting for the split ground impedance through the 1.8mH inductor. It sounds like this is not really a existing solution. « Last Edit: April 07, 2018, 02:03:14 pm by CopperCone » #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #63 on: April 07, 2018, 02:41:33 pm » But what about its high reactance and the fact that it will compromise safety? Will a 90V or less GDT in parallel with it work? I want it to blow the mains fuse if there is high voltage on any thing with a metal enclosure due to a short that can fry you in short order. You might want to recalculate the reactance of that part. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #64 on: April 07, 2018, 03:05:14 pm » rofl how did i fuck up an order of magnitude there But you still can get some kind of a short occurring at high frequency. The calculation I made is for 60KHz. Still think it needs some protection. For clarity/sanity I am interested in IGBT based induction heaters that run off mains. Kinda like this guy: http://www.instructables.com/id/30-kVA-Induction-Heater/ Especially since I am interested in things like water cooling. I know getting hot RF on the chassis is kinda unlikely but it bothers me. « Last Edit: April 07, 2018, 03:10:27 pm by CopperCone » #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #65 on: April 07, 2018, 03:19:05 pm » #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #66 on: April 07, 2018, 03:19:21 pm » Eugh, that instructable is a mess, no protection, no feedback, one slip and you're out a whole set of transistors. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #67 on: April 07, 2018, 03:20:26 pm » I don't plan to build that, I wanted phase shift control of power and optical driver and maybe some kind of circuit to track resonance as it works but thats just an example that circuit is bootleg in more ways then 1 and it has no interlocks on the chassis or anything normal for something so high powered, leak detector, etc. « Last Edit: April 07, 2018, 03:23:44 pm by CopperCone » #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #68 on: April 07, 2018, 04:45:42 pm » The mains LISN leakage currents due to the 8+uF caps are a huge danger. Just mentioning for the noobs. Lifting (RF) PE on the EUT I wouldn't do, lovely tank circuit with Y-caps. Warning labels on LISNs are also strongly recommended for: Their lethally high earth-leakage current The need to maintain two independent protective earth connections at all times Their use only by authorized and trained personnel Taken from In Compliance Magazine, Guide to Testing Conducted Emissions #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #69 on: April 07, 2018, 06:02:42 pm » Yea but its clearly designed in. I wish I had a higher power RF source to test with MOVs and GDT to see. My best RF source is 50Vpp Hmm maybe a step up transformer. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #70 on: April 07, 2018, 06:58:29 pm » Now that I thought about it, I swear I saw a teardown video with a MOV put across an isolation transformer for a HV power supply or something like that, so the unit would ground itself if the chassis voltage became high. I can't remember where though. May have been a capacitor that looks like a MOV, can't find any record of either though. « Last Edit: April 07, 2018, 07:43:09 pm by CopperCone » #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #71 on: April 07, 2018, 08:57:06 pm » Remember that rectifier-input devices draw more peak current. Peak to RMS ratio may be 4 or more! This is especially troublesome for the LISN, because those peaks are also where you get the strongest signal: the diodes are conducting, carrying EMI from the EUT to the LISN. Result is, you could be missing some dB's at the low end, missing the switching fundamental by as much. Tim I don't think this is necessarily a deal breaker. It should be possible to apply corrections to the measured values. This may require recording the current. As Jay said earlier: I haven't tested one of the single-layer solenoids normally found in commercial on LISNs on a VNA. I don't expect it will perform all that well. If I was winding a single layer solenoid, I would space the winding from the coil former and I would ensure that there was some space between the turns to lower the turn-turn capacitance. Regards, Jay_Diddy_B So I think the next step would be to measure the performance of a real air-cored inductor to see what effect all of the actual parasitics have on performance. The hypothesis to test being that ferrite with current induced inductance roll off will provide better performance that a large air-core with parasitics. I'd do it if I could but I don't have the test equipment. Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### fcb • Super Contributor • Posts: 2126 • Country: • Test instrument designer/G1YWC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #72 on: April 08, 2018, 10:31:08 am » The one thing I haven't seen so far on this thread, and in my view (& experience) something that is essential - a discharge mechanism on the power input. I built a LISN a few years back for my own lab, when I finished using it I switched it off at the wall socket and pulled the plug. Whilst handling it to put it away I touched the plug pins and got a real belt off it from the internal capacitors (obviously switched it off at peak cycle). Since then I fitted a mains relay inside that disconnects the L&N input and shorts the internal L&N to earth via a pair of 7W 4K7 resistors. https://electron.plus Power Analysers, VI Signature Testers, Voltage References, Picoammeters, Curve Tracers. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #73 on: April 08, 2018, 02:31:34 pm » The tekbox schematic has 30k going to ground on both L and N #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #74 on: April 08, 2018, 06:14:05 pm » With a mains LISN, the priority is RF signal integrity, not safety. There is no fuse, no on/off switch, no power on indicator lamp, and huge internal (10uF) capacitance. IEC 61010 requirement is that after disconnecting power, plug pins shall not be hazardous live after 5 seconds. Hazardous live is defined as 70VDC dry, 35VDC wet conditions. This sets the highest bleeder resistor value. 240VAC (339Vpk) down to 35VDC in 5 seconds, 10uF I calculate 220k ohms, and 0.26W steady state. 30k ohms is 0.7 seconds, and 1.9W steady state at 240VAC. A 5W wirewound resistor like venerable Yageo SQP rated 700V I would use. Lindgren is 39k ohm. An on/off light would be great, but neon generates some RFI and an LED would radiate switching hash from the rectifier diode(s), inside the LISN enclosure. If you could have a very RF quiet mains LED arrangement, I would definitely incorporate. #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #75 on: April 08, 2018, 08:00:29 pm » With a mains LISN, the priority is RF signal integrity, not safety. ... I am not a lawyer but I believe the health & safety legislation in every civilized country would take exception to that statement. If there was an accident involving equipment made/supplied by you, that statement would bite you very hard. The priority should always be safety first. Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #76 on: April 08, 2018, 08:48:43 pm » yea some kid might find it if you leave it laying around on the street #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #77 on: April 08, 2018, 09:17:23 pm » With a mains LISN, the priority is RF signal integrity, not safety. ... I am not a lawyer but I believe the health & safety legislation in every civilized country would take exception to that statement. If there was an accident involving equipment made/supplied by you, that statement would bite you very hard. The priority should always be safety first. How could you possibly ever get agency approval for a high voltage generator, a transient generator, an EMI generator, a... ? Test equipment is exempt from such restrictions for good reason. They must be used by qualified technicians, in suitable lab conditions, for the same reason! Example: the local Cooper/Eaton guys have a high voltage test lab, 20kV just sitting out in the air and all that. How is that acceptable? It is carefully caged behind a full height chain link fence, with several redundant interlocks. On top of that, they are very particular about their procedures: measuring voltage twice with a meter, to ensure a de-energized state; shorting anything that needs to be guaranteed safe while handling; wearing heavy rubber gloves; only allowing qualified personnel into the area (i.e., I watched from behind the fence), and so on. For the LISN, there isn't much you can do that fits within ordinary safety rules. You do want to address ground leakage and galvanic isolation, using an isolation transformer. This also allows you to plug it into a RCD/GFCI circuit. Fusing isn't needed on the network because the isolation transformer or mains circuit has it. The filtering somewhat addresses mains transients as well (which is where the 2.5kV hazard comes from), and if you provide any additional protection, that helps too. Tim « Last Edit: April 08, 2018, 09:27:12 pm by T3sl4co1l » Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #78 on: April 08, 2018, 10:24:48 pm » The one thing I haven't seen so far on this thread, and in my view (& experience) something that is essential - a discharge mechanism on the power input. I built a LISN a few years back for my own lab, when I finished using it I switched it off at the wall socket and pulled the plug. Whilst handling it to put it away I touched the plug pins and got a real belt off it from the internal capacitors (obviously switched it off at peak cycle). Since then I fitted a mains relay inside that disconnects the L&N input and shorts the internal L&N to earth via a pair of 7W 4K7 resistors. Hi, I have discharge resistor in the line voltage version of the LISN across the input capacitors, from Line to ground and neutral to ground. Regards, Jay_Diddy_B #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #79 on: April 08, 2018, 11:13:46 pm » Example: the local Cooper/Eaton guys have a high voltage test lab, 20kV just sitting out in the air and all that. How is that acceptable? It is carefully caged behind a full height chain link fence, with several redundant interlocks. On top of that, they are very particular about their procedures: measuring voltage twice with a meter, to ensure a de-energized state; shorting anything that needs to be guaranteed safe while handling; wearing heavy rubber gloves; only allowing qualified personnel into the area (i.e., I watched from behind the fence), and so on. And I am reasonably confident that they will have those procedures documented, site inductions, safety audits and all the other documentation that goes with modern H&S requirements in high risk work environments. I can guarantee their documentation does not include the statement "safety is not a priority" For the LISN, there isn't much you can do that fits within ordinary safety rules. You do want to address ground leakage and galvanic isolation, using an isolation transformer. This also allows you to plug it into a RCD/GFCI circuit. Fusing isn't needed on the network because the isolation transformer or mains circuit has it. The filtering somewhat addresses mains transients as well (which is where the 2.5kV hazard comes from), and if you provide any additional protection, that helps too. Tim You and others have described quite a few things that fit within ordinary safety rules. Typically H&S legislation has a "all practical steps" or similar approach to managing risk. That is not the same as eliminating risk. Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #80 on: April 09, 2018, 03:49:51 am » Found pics of Comtest TTi1600 LISN. 250uH inductor is large EE ferrite, and the four stacked (to 50uH) air-core parts which remind me of loudspeaker cross-over network inductors, like Solen. It was a repair, open 2R2 fusible resistor to the GDT. The unit uses lithium batteries to energize signal relays for limiter diode bias. edit: fixed battery purpose « Last Edit: April 09, 2018, 10:13:16 am by floobydust » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #81 on: April 09, 2018, 08:00:16 am » Found pics of Comtest TTi1600 LISN. 250uH inductor is large EC ferrite, and the four stacked (to 50uH) air-core parts which remind me of loudspeaker cross-over network inductors, like Solen. It was a repair, open 2R2 resistor to the GDT. The unit uses lithium batteries to energize signal relays. The manual, including the schematics, for this LISN can be found here: http://resources.aimtti.com/manuals/LISN1600_Instruction_Manual.pdf From the schematic in the manual, the lithium batteries are used to bias the clamping diodes. Biasing the clamp diodes will reduce the capacitance, and therefore the impact on high frequency response. I believe that the main inductors are single layer solenoids. L2 and L3 don't look right on the schematic, the value is too low. Regards, Jay_Diddy_B #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #82 on: April 09, 2018, 10:47:18 am » Yes they are low value- L2, L3 limiter inductors possibly 1mH not 1uH each? Seem to be Toku 8RBSH series, no datasheets but 8RBS range is 0.1mH-15mH and here I am again seeing ferrite-core parts run past SRF of 2.1MHz (#262LY-102K) to 30MHz. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #83 on: April 12, 2018, 10:13:10 pm » how would you guys position the 1.8mH inductor? I'm not sure what to do. I got ready made 1mH inductors, I could put two of em in series. But, should I put them up right, or in parallel with the 50uH long air inductors? If I place them upright, then they will be in parallel with the 250uH inductors, but physically kinda far away. Or I can put them up on an odd angle, but this seems stupid. And with the 1.8mH inductor, is there any reason to combine two of them? I figure this would be counterproductive to the self resonant frequency, and its better to just use two separate ferrite cores (vs removing the cap of the inductor with heat, and re-winding it with a single winding.. this would have a lower SRF... so other then it looking nice, I don't see a benefit, right?). Should I maybe shield them? They are the bobbin type. « Last Edit: April 12, 2018, 10:16:53 pm by CopperCone » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #84 on: April 12, 2018, 10:51:30 pm » how would you guys position the 1.8mH inductor? snip... Should I maybe shield them? They are the bobbin type. Can you share your schematic? Where is the 1.8mH inductor in the LISN schematic? The 50uH inductor is the main inductor that helps define the low frequency impedance, the 250uH inductor is essentially a line filter. Regards, Jay_Diddy_B #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #85 on: April 12, 2018, 11:41:21 pm » look at the tekbox schematic earlier in this thread. It is a optional switched in inductor for ground isolation between the tests so you don't have a group loop between the equipment and the ground connection of the LISN. It is directly between the ground output of the LISN and the DUT. I think it might be a useful sanity check, especially since I don't have a test lab with a very good earth ground, well throught out mains wiring, shielded room, etc.. neighbors can always buy some kinda jamming device (by this I mean some shitty PSU) on alibaba so it might be nice just to switch it in to see if there is some kinda problem going on. https://www.eevblog.com/forum/rf-microwave/50uh-and-250uh-inductor-design-for-lisn/?action=dlattach;attach=404645;image I am adding it but with a low voltage GDT in parallel with it so it can hopefully trigger the breaker if the chassis on the DUT becomes electrified with HF due to some kind of failure mode (at 60KHz it is already 2000 ohm impedance so it wont blow a breaker or significantly discharge its self. The main danger is a switching converter heatsink or some shit touching the DUT box (like we all know ATX supplies have live heatsinks.... ) . I don't want some 20 amp device going through the BNC/SMA cable into my expensive spectrum analyzer! or to be zapped during hookup if I accidentally have the inductor switched in, though it should be shorted when something is being plugged in for safteys sake, but mistakes happen).. of course this is less of a concern in a test lab where there is dedicated equipment probobly always plugged into the LISN at its own station, but I can't really justify that kind of shit and it will be used sparsely and probobly put away on a shelf after every use due to space concerns so there is alot of room for error). « Last Edit: April 12, 2018, 11:49:08 pm by CopperCone » #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #86 on: April 13, 2018, 03:02:23 am » Lifting the EUT (RF) ground, I wouldn't implement that. Many reasons, but the EUT will then seek capacitive coupling to anything like your bench, field wiring etc. and readings would be flaky, if a 3-prong (grounded) power cord to EUT vs. double -insulated device. Instead I would incorporate a splitter to look at CM verses DM. This is what I use for designing/evaluating SMPS input filters where I need weigh X and Y cap, CM choke values. #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #87 on: April 13, 2018, 07:47:11 am » Measurements are, of course, meant to be done in a reliable and consistent manner, so that capacitive coupling doesn't matter, it's just part of the test (or not). Given that CISPR 14 isn't very specific or consistent on how certain things are handled, like power cables... Usually, a nonconductive table is used, so that there is relatively little capacitance to ground, except through the cable. And what capacitance there is, is (relatively) strongly coupled to the antenna, so will show up on the vertical polarization measurement at low frequencies (~30MHz), while higher frequencies are just whatever because of random antenna elements formed from cables and such. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #88 on: April 13, 2018, 01:42:54 pm » Your not really lifting rf ground with most instruments though. Most oscilloscopes and spectrum analyzers and emi recivers will have chassis grounded coaxial connectors. So if you dont isolate the ground, you have a ground loop. The test does not measure 60hz, so the ground loop here is ok, but the blocming impedance begins to become significant where the test begins. I think thats the rational for it. There is no real point to running something with a lisn without instrumentation connected, so i think it will be ok. As for cm measurement i saw plans online how to make a network that would plug into the neutral and live sampling ports and combine them to give you a common mode response. I think the 1.8mH inductor is more of a sanity check for mains grounding issues? « Last Edit: April 13, 2018, 01:46:50 pm by CopperCone » #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #89 on: April 13, 2018, 02:01:24 pm » Also, as for using magnetic cores for the inductors, wont they act like nonlinearmixers, particulalry when current draw is heavy? When they are near saturation there might be significnant imd. So things like power up transients might have garbled frequency information, that is if you care. #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #90 on: April 13, 2018, 03:52:41 pm » Also, as for using magnetic cores for the inductors, wont they act like nonlinearmixers, particulalry when current draw is heavy? When they are near saturation there might be significnant imd. So things like power up transients might have garbled frequency information, that is if you care. This picture will partially answer the question. Two pairs of LISNs are being used to measure the same power supply. The power supply has spread spectrum modulation. One of the measurements is using a pair of Com-Power LI-550A LISNs and the other measurement is using a pair of Jay_Diddy_B 5uH LISNs: The peak measurements are particularly close. The cored inductors include an air gap or a distributed air gap, so they are fairly linear, and therefore there is little IMD. Since the emissions are normally 'rich' in harmonics, the small contribution from the inductor non-linearity is tiny. Remember the purpose of the inductor is to isolate the DUT from the power source. So long as the impedance of the inductor is 'large' compared to the impedance of the emissions the inductor will have little or no effect on the measurement. I would do a comparison of my line voltage LISN, 50uH, but I don't have a commercial LISN to compare against. I could measure a standard load, say an Agilent DSOX 3k scope and other people with access to a commercial LISN post a comparison? Regards, Jay_Diddy_B #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #91 on: April 13, 2018, 04:08:18 pm » Maybe a stupid request, but can you hook up two non synchronized spread spectrum power converters to thkse lisn? Reason i ask is because i am curious if two higher power signals will show evidence of mixing. I would expect this problem to be worse if something is going on during something like a load switch, i.e. dcdc converter 1 is operating normally and a heavy capacitive load is switched in where there is a capacitor being switched in by a load switch or relay. I dont know anything about magnetic mixing though, maybe its more present in frequencies over 3MHz? I figure there has got to be a pretty good reason why people go through the trouble of winding these air core behemoths.. No one would wanna increase product size and stuff without good reason.. It seems that they at least make the 50uH bit air cored with more leway on the 250. Did you shift the measurements you took for clariyy or does your lisn have a different noise floor in the low frequency range? « Last Edit: April 13, 2018, 04:10:19 pm by CopperCone » #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #92 on: April 13, 2018, 04:33:42 pm » Snip... Did you shift the measurements you took for clariyy or does your lisn have a different noise floor in the low frequency range? The Jay_Diddy_B 5uH was just the PCB, not enclosed, this is probably why the noise floor is higher. It doesn't matter unless the noise floor is close to the limit. Regards, Jay_Diddy_B #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #93 on: April 13, 2018, 05:03:11 pm » Dynamic range is always nice. #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #94 on: April 14, 2018, 08:38:14 am » Hi I think the significant unknown here is how well the selected ferrite coils perform as the load current approaches or exceeds saturation, especially with peaky loads. When they saturate, do they significantly affect LISN readings. The key advantage of air cores is that they don't saturate. I presume CISPR circuit was designed taking into account the air coil parasitics. Dazz Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #95 on: April 14, 2018, 02:21:40 pm » Well the 250uH coil is not well defined. We have seen product examples going both ways, with big air coils and large EI core transformers. All commercial products do seem to use air coils for the 5 and 50uH. I also read some where that the 5uH coils are sometimes used for very heavy loads. I think this means that if you need to run something at ridiculous like ?200 amps, you use a 5uH lisn because the series resistance of the LISN is small vs the large voltage drop across 250/50uH... This was on some military website though. « Last Edit: April 14, 2018, 02:27:01 pm by CopperCone » #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #96 on: April 17, 2018, 01:26:31 am » What variation on impedances on the output coupling network did you guys see? The designs in this thread are 470nF, but I see the military standard is like 250nF. I figured smaller capacitor = better but this shit has gotten pretty complicated already. So long you calibrate it yourself, it does not really matter does it? #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #97 on: April 17, 2018, 02:11:45 am » Hi, For typical 5uH LISNs the coupling capacitor is 100nF. If you have a 50 source and a 50 load, 100 total. The -3dB point is 1/( 2 x Pi x RC) = 15.9kHz In practice you have a low impedance source, the emissions are low impedance, the -3dB point is 31.8kHz For a lot of 50uH LISNs the coupling capacitor is 250nF resulting: 1/ (2 x Pi x RC) = 1/( 2 x Pi x 100 x 25E-9) = 6.36kHz making it suitable for the military specification. If you are doing commercial equipment where the emission measurements start at 150 kHz you can use a smaller capacitor. This is NOT calibrated out . You build the LISN according to the relevant EMC specification and you use it. The only calibration is to make sure that impedance is correct and there is typically a +/- 20% window around the nominal. You can measure transmission if the LISN has a 10dB attenuator or filter. Regards, Jay_Diddy_B #### charliedelta • Regular Contributor • Posts: 73 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #98 on: April 28, 2018, 10:46:13 pm » Why guess about LISN construction? The are precisely defined and full details are given in the CISPR documents about their construction. Same goes for the MIL and IEEE standards. The most important detail that is often missed in the construction is the 430 ohm resistors across every other few turns on the 50uh inductor. These are clearly required in the CISPR designs. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #99 on: April 29, 2018, 12:55:22 am » I think its better to put inductors in series with the parallel resistors then to go to an undampened coil but I need to make sure #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #100 on: April 29, 2018, 01:20:40 am » Why guess about LISN construction? The are precisely defined and full details are given in the CISPR documents about their construction. Same goes for the MIL and IEEE standards. ... The discussion led to Jay Diddy B proving ferrite cores are suitable to 30MHz for high-current inductors, resulting in his LISN with physically smaller inductors than the CISPR standard-build with its massive air-core inductors. You don't need EMC lab certification-grade accuracy. A dB or two error is perfectly usable for pre-scans or design work, and even that could be corrected for with a little extra work. It's strange some commercial LISN's have corrected flat frequency response, and others are bumpy, just copying verbatim the CISPR schematic. #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #101 on: April 29, 2018, 03:01:14 pm » i think this is an interesting discussion in general and I don't see why someone is trying to shut us down making the LISN better in terms of linearity is always an option too. No reason to bow to a standard or compliance laboratory I am a fan of the mini LISN because the one I made is gigantic. « Last Edit: April 29, 2018, 03:07:10 pm by CopperCone » #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #102 on: April 29, 2018, 08:48:28 pm » Hi One of the benefits of standards is that they enable consistent results wherever you might be. One of the side effects of standards is that they stifle innovation. The standards should be written to account for the deficiencies of the standard design. If you make a LISN that is better than the standard, it may no longer comply with the standard. If you are testing for compliance, the better but non-compliant LISN isn't much use. Innovation and standards are both great. Both have limitations and side effects. Dazz Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #103 on: May 08, 2018, 12:55:26 pm » according to CISPR16-1 figure27 the L1 inductor is wound in one go but has 9 taps off it for some resistors to cancel some high frequency noise. when i recreate this coil in the air coil calculator i get 62.5uH. i'm assuming inside the metal box it must be ~50uH. https://ibb.co/mJFOR7 if you were building this inductor knowing your resistors were SMD you'd have to build this inductor in 9 separate coils similar to how the tekbox 5uH does it. the part that confuses me if i follow the number of turns in the picture and change the calculator to look at just 4 turns, but change the length to get the same pitch, i end up with 3uH for that 4 turn inductor. if i do the same thing for each separate coil, then sum them up i am no where near 62.5uH. https://ibb.co/jgYcm7 ps. sorry, i'll have to figure out how to link pictures properly later. gotta run! « Last Edit: May 08, 2018, 12:58:29 pm by slloyd » Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #104 on: May 08, 2018, 02:03:56 pm » Keep in mind the spacing between 5he coil section messes with inductance due to mutual inductance. I think i got within 5% measured on the calculator program you used with my finished inductor. I forgot about the god damn box messing with stuff. I might have made a 40uH LISN if the box reduces the inductance as much as you say #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #105 on: May 08, 2018, 05:16:43 pm » https://ibb.co/mJFOR7 Your wire diameter is huge at 6mm, check and try #12AWG, 2mm or something smaller « Last Edit: May 08, 2018, 05:19:11 pm by floobydust » #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #106 on: May 08, 2018, 07:01:26 pm » yea 6mm is kinda big thats like a truck suspension #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #107 on: May 08, 2018, 11:24:38 pm » i was just verifying the math using the 6mm with 8mm pitch that CISPR 16 uses in their example. in my own project i'll be using #12 or #14AWG. btw, if you want to read CISPR16 to see where all these circuits originated from, its here: https://law.resource.org/pub/in/bis/manifest.litd.9.html in the reference they show in fig23 that the circuit is good to 100A so perhaps that's why they used 6mm wire « Last Edit: May 08, 2018, 11:32:35 pm by slloyd » Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #108 on: May 09, 2018, 02:25:11 am » in CISPR16, figure 23, is this R5 a type-O? is it supposed to be R3? Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #109 on: May 09, 2018, 05:46:26 pm » Heh, looks like it. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #110 on: May 09, 2018, 07:11:16 pm » Yes, typo. Careful following those CISPR schematics verbatim, missing are safety-discharge resistors for C1, C2. #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #111 on: May 09, 2018, 07:51:52 pm » Alternately, run it from an isolation transformer, which discharges the caps ~instantly. Which is a good idea because of the large capacitance to ground, too! Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #112 on: May 10, 2018, 12:20:34 am » if i can find an isolation transformer that is 1.5kW rated and doesn't cost a fortune. otherwise, i'll just power it off a wall socket that is not GFI protected and use proper safety measures « Last Edit: May 10, 2018, 12:48:40 am by slloyd » Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! The following users thanked this post: Slh #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #113 on: May 10, 2018, 12:44:56 am » shown as X2 capacitors, probably should be Y2 ? Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #114 on: May 10, 2018, 12:48:00 am » Careful following those CISPR schematics verbatim, missing are safety-discharge resistors for C1, C2. Yes, i see that. Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### floobydust • Super Contributor • Posts: 7267 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #115 on: May 10, 2018, 02:49:37 am » shown as X2 capacitors, probably should be Y2 ? That's the as-built Compower 115A LISN, X2 was actually used if you look at the pictures (for the 1uF parts) and not sure about the big motor starting caps (?) and series resistor module. https://www.eevblog.com/forum/rf-microwave/50uh-and-250uh-inductor-design-for-lisn/msg1454320/#msg1454320 #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #116 on: May 10, 2018, 02:58:45 am » Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #117 on: May 10, 2018, 04:33:05 am » Quote That's the as-built Compower 115A LISN, X2 was actually used agreed, that's what they used. not sure why though, seems to me Y2 would be the appropriate choice. perhaps this is why 115A has been discontinued? any idea of the part number on those big yellow "motor start" capacitors? Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #118 on: May 10, 2018, 05:49:35 pm » X/Y ratings aren't very applicable here, partly because you can't get them in values large enough. Instead, use conventional parts, rated for the AC voltage, and protect against surges with MOVs. Another good reason for an isolation transformer, the added inductance (and potential for core saturation) helps attenuate surges, reducing peak current into MOVs and such. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #119 on: May 11, 2018, 11:31:28 am » the unmeasured line should be 50ohm terminated Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #120 on: May 11, 2018, 11:34:03 am » looks like some newer X2 on the market with high enough uF values now available. check out B32928A4825K by EPCOS. quantity 4, (i.e. not in parallel?) could be used here: Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #121 on: May 11, 2018, 11:39:21 am » based on CISPR and the info provided from the good members of eevblog.. i put together this schematic for a bench top LISN rated to 25A. the top half of the schematic will be free wired and the bottom half will be on a PCB. i still need to assign part numbers. schematic is posted as a DRAFT for comment and is not meant for construction. please feel free to comment next i'll be working on the inductor build Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #122 on: May 11, 2018, 11:51:29 am » speaking of building inductor. CISPR 16 has this to say about L2, 250uH inductor: Quote The inductance L2 should have a Q-factor not less than 10 over the 9 KHz to 150 kHz frequency range. In practice, it is advantageous to use inductors coupled in series opposition in the live and neutral lines (common-core choke). what exactly do you think they meant by that? when i read this it sounds like they wanted L2 to be wrapped on a gigantic torroiod. both L2 and L2*, in common mode configuration. but generally that's not what i see in the pictures posted of commercial LISNs. looks like two separate air core inductors each wound on a bobbin of any random size. Does your project need a high performance motor drive? Let's talk! www.powerdesigns.ca Do you like our work? Support Axiom to win the 2019 Hackaday Prize! #### CopperCone • Super Contributor • Posts: 1415 • Country: • *knock knock* ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #123 on: May 11, 2018, 06:43:45 pm » There was one LISN in this thread posted that has a CM EI core transformer for the 250uH bit. I assume you get some kind of reasonable cm effect through the chassis. T3slacoil I think the problem with MOV is that they are nonlinear. I think the error would be small though. And the same goes for using a cored transformer, it can saturate and distort on inrush and stuff. Most of my capacitors are X rated, a few are just film caps from a plasma television, they are 'protected' by the 5 ohm resistor at least. I think mine will just ride dirty with a input GDT lol. I never saw an air coil torroid before, its hard to imagine for some reason since its just air not a flux focuser. If you want to try: http://coil32.net/toroid-air-core-coil.html Too late for me. But,. that link is not really applicable, since for a decent CM response you want two half moon windings... « Last Edit: May 11, 2018, 06:52:02 pm by CopperCone » #### T3sl4co1l • Super Contributor • Posts: 22061 • Country: • Expert, Analog Electronics, PCB Layout, EMC ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #124 on: May 11, 2018, 08:31:43 pm » T3slacoil I think the problem with MOV is that they are nonlinear. I think the error would be small though. And the same goes for using a cored transformer, it can saturate and distort on inrush and stuff. You don't put the MOV on the EUT side. Measurements are not taken during inrush. Tim Seven Transistor Labs, LLC Electronic design, from concept to prototype. Bringing a project to life? Send me a message! #### dazz1 • Frequent Contributor • Posts: 737 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #125 on: May 11, 2018, 08:37:30 pm » based on CISPR and the info provided from the good members of eevblog.. i put together this schematic for a bench top LISN rated to 25A. the top half of the schematic will be free wired and the bottom half will be on a PCB. i still need to assign part numbers. schematic is posted as a DRAFT for comment and is not meant for construction. please feel free to comment next i'll be working on the inductor build Hi Just some questions. Why only 4 turns between damping resistors? Have you modeled 6 or 8 turns between resistors? It might save some work winding the coils. Why 2x 45MHz filters in series? Would one be enough? Without a buffer in between you may end up with an unexpected filter response. Have you modeled this? From a reliability (and safety) perspective having 20 caps in parallel reduces reliability by a factor 20. Reducing the number of caps to 10 will double the reliability and reduce the parts count. I think it would be prudent to consider adding a fusable link (2x) between the switch S1 and the parallel resistors/caps. In addition use a high enough power rating on R102-105 to prevent them vapourising before the link blows. This would also require wider PCB tracks. Have you modeled the fault current? Dazz Dazz Over Engineering: Why make something simple when you can make it really complicated AND get it to work? #### Jay_Diddy_B • Super Contributor • Posts: 2742 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #126 on: May 11, 2018, 09:41:11 pm » slloyd and the group, I have had a quick look at the schematic in an earlier message. I think the capacitors I marked S should have a good safety rating and the capacitors in the section marked N can be normal capacitors. Regards, Jay_Diddy_B « Last Edit: May 11, 2018, 09:42:52 pm by Jay_Diddy_B » #### slloyd • Contributor • Posts: 35 • Country: ##### Re: Staggered 50uH and 250uH inductor design for LISN « Reply #127 on: May 11, 2018, 10:22:49 pm » thanks for the comments dazz & Jay. the resistor damping on 4 windings (and 2 and 6) just comes from CISPR16. someone on this thread explained why there is value in making the two odd-ball winding choices of 2 & 6. i didn't design the filter so i can not explain the philosophy of the design choices like 2 filters. the 2nd filter is like$1 extra in parts so not a big deal.  two stage filter i guess for better filtering.  if they interact with each other that would be bad.  i haven't simulated it myself yet but i will.  jay already did in this thread and it shows flat response, so to a 2nd order approximation it was good.

i'm a little apprehensive about adding components such as a fuse (polyfuse?) in the signal path.  i'd have to simulate what the parasitic elements of this fuse would affect the measurement.  but as a take away from your comment i will add a note "do not operate switches under power".

Jay, i see your point.  the filter caps are not likely to be under extreme stress unlike C3 which is a little closer to the action and thus more likely to fail
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#### slloyd

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #128 on: May 11, 2018, 10:48:42 pm »
i was looking at some wire today from which to make the inductor.  in terms of skin effect, maybe the frequency is high enough to warrant using multistrand wire as compared to solid core.  but lots of LISNs made with solid magnet wire.

some #12 cable type THHN  the core is 2.05mm solid copper and it looks like 0.5mm of insulation.   such a winding using only the insulation itself to get the pitch (i.e. winding is tight with no spacers) would have to be wound on 3.5# PVC since it has a favourable outer diameter to get the ~62uH that the reference inductor had (presumably it is 50uH inside the box).  parameters like this:

« Last Edit: May 12, 2018, 12:57:30 am by slloyd »
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#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #129 on: May 11, 2018, 11:44:36 pm »
Q matters very little, this is not a power reactance application.  You can use whatever wire you like.

Tim
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#### dazz1

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #130 on: May 12, 2018, 12:05:14 am »

i'm a little apprehensive about adding components such as a fuse (polyfuse?) in the signal path.  i'd have to simulate what the parasitic elements of this fuse would affect the measurement.  but as a take away from your comment i will add a note "do not operate switches under power".

Jay, i see your point.  the filter caps are not likely to be under extreme stress unlike C3 which is a little closer to the action and thus more likely to fail

If one of those caps connected to line fails to a short, something is going to act as a fuse.   Adding a proper fuse will provide protection without adding significant parasitics.  You will get more parasitics through the switch etc.

I would use the same high voltage caps for all C3s to ensure symmetry though the signal paths, but I would reduce the number to a total of 10. If you model these then add one cap to see what difference is makes to the output. I think you will find that 10 is more than enough.

Dazz
Dazz

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#### slloyd

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #131 on: May 12, 2018, 12:56:01 am »
i'm totally OK with adding fuses up at the front end near the AC connector.  will act faster than my house breaker that probably won't trip before something burns.  maybe a panel mount reset able fuse
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#### dazz1

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #132 on: May 12, 2018, 02:57:11 am »
Hi
Do you have 25A breakers on the power circuits in your switchboard?  If not, they are likely to trip before a 25A fuse.  You will need to choose protection that won't trip on inrush but will still provide close protection.   You might end up with  a high current HRC fuse plus a circuit breaker.  Your aim should be to minimise the total energy input after a fault condition.

I think you need to model the currents with different faults to figure out the fault currents.  There is a risk that a fault to short on a C3 cap won't blow a 25A fuse on the mains input.  It is probable that a leaking C3 cap will cook the various downstream components (including the pcb) without ever tripping a 25A fuse.    The output is accessible to human touch so additional protection is justified.

I haven't done the calcs but I would expect a fuse rated to a few hundred mA would suitable to protect the switches and filter.

Dazz
Dazz

Over Engineering: Why make something simple when you can make it really complicated AND get it to work?

#### slloyd

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #133 on: May 12, 2018, 03:53:43 pm »
##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #177 on: September 02, 2019, 04:00:06 am »
is it a better choice? (i found metal to finish the project box so new capacitors are in budget)

I assume the self healing is a trade off for performance otherwise?

maybe I need to get a DC for the VNA to test, it has been on hold

maybe a amplifier across ground shunt can read ground current and brighten if the capacitors are passing too much without connection?

i feel like it needs a integrity test button that does not require too much equipment. i have some weird ideas for its use
« Last Edit: September 02, 2019, 04:07:19 am by coppercone2 »

#### Mangozac

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #178 on: September 24, 2019, 03:37:19 am »
I started building a LISN quite a while ago and have recently decided to get it finished off. I'm having issues characterising the impedance though, which seems to trace back to the 50uH inductor.

I custom wound an inductor based on the CISPR16 specifications, using 2.5mm cable so that we can test devices up to 20A.
Conductor Diameter:      2.5mm
Winding Pitch:      8.0mm
35 turns
Coil Length:      280mm
Corrected Inductance:      57.4654    µH    (supposed to be 50uH for CISPR16)
(From http://electronbunker.ca/eb/InductanceCalc.html)

The problem I have is that in practice it's simply not measuring correctly. The impedance at 150kHz should be ~47 . Using a signal generator with 50 output and measuring the voltage across the inductor I am getting an impedance of 50 at 86kHz and 110 at 150kHz. Using Xl = 2*pi*f*L these calculate to 92uH and 115uH, both way off the expected 50uH.

I've been racking my brain over this and the only potentially odd thing about my construction is the fact that I've used 7-strand copper wire, rather than single strand. I'm aware of phenomena such as skin effect but in the 150kHz to 30MHz range this is operating in I don't expect this to have an impact. The coil has the self resonance damping resistors soldered on in the photo but removing them makes no difference to the measurement.

Is there something obvious I'm missing?

#### amspire

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #179 on: September 24, 2019, 04:31:57 am »
Quote

The problem I have is that in practice it's simply not measuring correctly. The impedance at 150kHz should be ~47 . Using a signal generator with 50 output and measuring the voltage across the inductor I am getting an impedance of 50 at 86kHz and 110 at 150kHz. Using Xl = 2*pi*f*L these calculate to 92uH and 115uH, both way off the expected 50uH.

...

Is there something obvious I'm missing?
It looks like you are not doing your calculations right. If you inductance is correct, then you will get about half the voltage across the inductor to the generator output voltage at about 86kHz.

At 150Khz, you should get a voltage of 1/sqrt(2) of the generator output. If you generator is putting out 1V, you should get 0.707V across the inductor at 150KHz.

I think you are forgetting that the inductor is not behaving like a resistor.
« Last Edit: September 24, 2019, 05:17:53 am by amspire »

#### coppercone2

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#### coppercone2

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #184 on: September 25, 2019, 10:30:40 pm »
Sometimes I am very happy to make use of the scrap bin parts because it will keep growing and I get depressed thinking how everything is 'almost good'.. maybe its like playing tetris where I reduce the size of stockpiles...

I have seen too many threads where people threw out tons of shit that looks great. It's just something I noticed you can make with big old inductors, PVC scraps, etc. Usual horror story is 'i got tired of cleaning dust from this garbage over the last 20 years, fuck it'.

Motor salvage is the worst for this IMO. You need gearbox manufacturing ability/shaft fitting skills/spare pullies to make use of scrapped motors for useful purposes..

This thing eliminated spare PVC pipe, an old storm cover, many X/Y capacitors, unused outlets which do not look good, etc.. otherwise this will end up in a estate sale junk bin eventually.. normally these parts are too 'shady' to use in the things you like to do because of ware (i.e. old capacitors) but in the manner a LISN is used, it can be made 'safe enough'. (not left plugged in a corner for 10 years till it blows up when you are not home).. no one is going to leave a SA powered on hooked up to mains when they are not around...and usually those are the parts that look good to salvage (who does not want to remove a blue rectangle from a PCB that makes everything else seem like ants)?

I feel like when the LISN is deployed the atmosphere is tense and people are on guard (since its usually the conclusion to a big series of decisions that lead to something actually being put into a fucking BOX (holy shit its not a PCB on the ESD mat).. its kind of epic

but to play devils advocate, it is lame because you are not measuring against a mighty physical unit like the Volt or Hertz, but instead you are measuring something in regards to what goverment legislators came up with (i felt a bit better when I read about standards relating to the mono-pole E_field antenna but still, it came about because of a freaking war and radios interfering with each other within the limits of what people thought an attack bomber should look like within the limits of national resources and congressional decisions). I feel like mil-spec is a bit cooler but still it came down to what some bean counters thought was good rather then something fundamental.. .. 50 ohms.. why not 75 or 33 (whatever the other absolute point is).. there is nothing fundamental or theoretical about it, especially when you add the spread spectrum time-vs-absolute instantaneous RF power in the compliance spec.. 50 ohms kind of sucks.. then again you can get into how multimeters average PLC and it gets all ugly too.. is resistance the only noble measurement ?
« Last Edit: September 25, 2019, 10:50:57 pm by coppercone2 »

#### sixtimesseven

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #185 on: June 09, 2020, 03:17:10 pm »
Was any progress made on the designs?

#### wilhe_jo

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #186 on: June 09, 2020, 06:25:13 pm »
BTDT, don't overdo the design.

Design to 55-60µH and self resonance over 1MHz.

Some Resistors (around 500 ohms) on every other oder every 3 windings will do the rest - ie. bring up the series resonances.

I did a LISN for 500A. Quite interesting project...

73

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#### sixtimesseven

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #187 on: June 09, 2020, 07:55:25 pm »
Regarding the cored inductor discussion: Narda's 32A three phase LISN uses gapped ferrites in their design. According to their datasheet:

https://www.narda-sts.it/eng/products/lisn/l332/]https://www.narda-sts.it/eng/products/lisn/l332/]https://www.narda-sts.it/eng/products/lisn/l332/

It is a 250uH + 50uH design. However, I find it a bit unclear how they staggered the inductors. I guess the first two are part of the 250uH inductor and the third in the row are the 50uH inductor. However, optically the windings and the cores look identical. I did not have an LCR meter with me to confirm though. No inter-winding resistors either. Just Power resistors to the caps to ground and high value bleeder resistors.

Here are the teardown photos:
https://flic.kr/s/aHsmNJtRj4

Capacitors are simple motor film caps as far as I can see.

The lonly toroidal inductor on the input connects the mains earth to the chassis.

The RF coupling board is soldered to the plug directly and is interesting. Big X2 caps as expected, but then additional inductors, ceramic caps and, what looks like a three legged tantalum and another tiny inductor just before it goes inside the sma connector (hidden in the heatgunk).

The limiter and filter as well as switching are hidden in a soldered metal can. Can't open it since it is not mine.

Anyway, I thought it is quiet different from the other designs.

« Last Edit: June 09, 2020, 08:16:11 pm by sixtimesseven »

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#### T3sl4co1l

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #188 on: June 09, 2020, 09:21:14 pm »
Looks like a, maybe 3rd order, highpass to the RF port.  Not uncommon, keeps AC mains leakage away.

The 250uH choke likely doesn't need resistors as it's relevant at quite low frequency and impedance; the 50uH it can help.

the toroids are input side filtering; the bricks (stacks of EE33 ferrite, gapped) are the 50uH chokes.  8.2uF + 4.7R is used to dampen/terminate the input side.  Not shown here, I also put a highpass filter on, which I think cuts at 50kHz or something like that, since this is an FCC Part 15 150kHz-30MHz network.

I measured the chokes for insertion loss / reflectance; their impedance remains quite high over the bandwidth, no series resonance mucking things up.  Just 14AWG hookup wire looped back and forth, nothing at all fancy.  Maybe Narda didn't need anything, either.

The main downside with ferrite cores is, the inductance drops fairly quickly above saturation current.  I rated these for, I think 20A peak, which isn't really all that much RMS current if you're testing a power supply with poor power factor.

Powdered iron is fine too, with the saturation being more gradual, but also being pretty deep (say -30% or lower) if you don't want to use a huge heap of them.  That can still be fine, but be careful calibrating it, and understand that LF noise in phase with current peaks may be attenuated more than you think.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!

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#### Jay_Diddy_B

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #189 on: June 10, 2020, 01:44:13 am »
Hi,

There is no need to over-think the LISN. This model shows how it works:

There are two models here. In the bottom model the mains impedance is stepped from 1m to 10k and the impedance, green trace, seen by the device under test, DUT, is essentially the same. These two results are coincident on the graph below.
The blue trace is the impedance of the simplified LISN which illustrates that the capacitors are coupling capacitors.

The simplified model shows that the capacitors in the LISN are 'large' and only act as high frequency shorts and low frequency blocks.

The 50uH inductor defines how the impedance changes with frequency in the 100kH to 1 MHz range.
Since noise sources are typically low impedance, even variation in this has little effect on measured emc results

The requirement is that the impedance of the inductor is 'large' compared to 50 .

The second stage, the 250uH inductor is a line filter. It is to block interference from the mains side. It does not impact the impedance seen by the DUT.

It is traditional to build LISN with air cored inductors. There is absolutely no reason why cored inductors cannot be used, providing the inductors have sufficient inductance at the currents being tested.

Regards,
Jay_Diddy_B

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#### sixtimesseven

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #190 on: June 10, 2020, 03:41:09 pm »
Thank you Tim and all the others, this thread is great

##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #201 on: June 13, 2020, 04:52:41 pm »
i thought about this, but the fact that the LISN needs to be on a specific metal work bench with a ground strap thats not really suited for much else made me think its ok just to go with big air cores?

I am not sure if its worth the effort to design since its only saving some shelf space because the actual test setup is wasteful of space, you are not really supposed to have other stuff on the bench anyway I think

They draw it pretty specifically

It looks like it might be useful to reduce size if you make a few if you want to daisy chain devices and do multiple device test with multiple lisns but that test looks really expensive. I don't think a LISN embedded in a test equipment wall is very useful (main appeal of size for me). I don't think its even safe to put it on a rack, so mine ended up being a oddball geometry.
« Last Edit: June 13, 2020, 05:01:29 pm by coppercone2 »

#### sixtimesseven

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #202 on: June 13, 2020, 07:07:18 pm »
i thought about this, but the fact that the LISN needs to be on a specific metal work bench with a ground strap thats not really suited for much else made me think its ok just to go with big air cores?

Well the 50uH air cores are manageable, 60x70mm or so I think was calculated.  But the 250uH aircores would be big. Somwhere in the range of 300x70mm or so per coil.
And you probably want them either place orthogonal to each other or far apart to make sure they do not couple. See the design Dave opened.

The magnet cores are pretty cheap overall. You also save some copper and a lot of space. Also the field is contained in the fer-rite end you do not have to worry about the effects of the housing. Ok, air core is probably lighter.

If you want to test 1:1 like in a lab with the bench, size does not matter that much (You still have to store the thing unless you have a dedicated emc bench).
But I want mine mobile. I know of several cases where I had to troubleshoot devices and industrial machines which we suspected had massive em issues. There I want a portable SA and a portable 1-Phase and later 3-Phase 32A or even better 63A capable LISN whith a handle on them. It won't be ideal but to get the machines out you would need a crane and sometimes a hole in the building. Building single Phase is the test run for me.

#### sixtimesseven

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##### Re: Staggered 50uH and 250uH inductor design for LISN
« Reply #203 on: June 29, 2020, 03:35:31 pm »
Finally got everything.

I used the: B66329G0000X127 cores with 13 turns of 1.5mm wire, a resin printed bobbin and cardboard as spacer (0.5mm, toilet roll cardboard fits perfectly).
The windings are spaced apart as far as possible. But the second iteration will have spacers on the bobbin itself. So work in progress.
L: ~55uH @ 100khz, SRF: ~33MHz

As a side note, 405nm elgoo mars resin seems perfect for the job I found. It can produce very precise (and potentially small) bobbins. It is plenty strong even with 1mm wall thickness. In particular if used with a "plug" while winding for reinforcement. First I worried about temperature but it seems to withstand 450degC from the soldering iron without burn and is pretty hard to set on fire( 45-60s in a propane flame will result in sustained, slow burn with thick black smoke though).
« Last Edit: June 29, 2020, 04:15:15 pm by sixtimesseven »

Smf