Author Topic: EEZ Bench Box 3 (BB3)  (Read 76776 times)

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Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #575 on: May 14, 2021, 04:50:54 am »
Good morning Prasimix, another great project, the BB3 seems the answer to everything ;)
I notice that, I believe, the Q is not correct but I assume this is just a software fix as the others look reasonable enough, is this so?
With all these new features and modules coming on stream a big extension box may be needed :-+
Do you have any production time line for various modules yet?
Regards Mike
 

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #576 on: May 14, 2021, 05:15:32 pm »
It is the other 2 input where the spacing is too close for mains, especially around Q1 and R13. 

OK, but we have OK2 to disconnect path to Q1 when AIN3 input is in voltage mode. Do we still need some correction in that area?




The board picture also shows the weak point at the link from R35 to R32.  Ideally R35 should have separate contacts for current and voltage and R32 connected to the voltage reading contacts.  With more solder for this link the drift in the current may be reduced.

Fixed:



Another point I just notices is that the lowest current range (33 Ohms shunt R30) may have problems with 48 mA, as the diodes would start conducting. So the maximum usefull current would likely be lower, more like 30 mA.
For a different reason the mid range is likely also not really useful to 1.2 A as was noted in the schematics - likely more around 0.5 A. With more current the FETs may get quite warm and help heat up the resistors. One may have to consider a smaller fuse (e.g. 630 mA).

Fixed, R30 changed to 20R (22R was on the border).

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #577 on: May 14, 2021, 05:19:39 pm »
Good morning Prasimix, another great project, the BB3 seems the answer to everything ;)
I notice that, I believe, the Q is not correct but I assume this is just a software fix as the others look reasonable enough, is this so?
With all these new features and modules coming on stream a big extension box may be needed :-+
Do you have any production time line for various modules yet?
Regards Mike

Yes, it's possible that Q is not calculated correctly, that is work in progress.

We initiated a test production batch of new modules, i.e. PREL6, SMX46, MUX14D and MIO168 + AFE3. They should be ready next month somehow in line with the opening of our web store where it will be possible to buy them (as well as assembled BB3).

Online Kleinstein

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Re: EEZ Bench Box 3 (BB3)
« Reply #578 on: May 14, 2021, 07:45:42 pm »
With a maximum range to 240 V peak, the input 3 is not really suited for leasuring mains and not meant for this. It would still be good if it would normally survive an accidential connection to mains (230 V AC). For this the photomos relay does not offer much protection, as the porblem may happen with current measurement, so the clearance should also be behind Ok2. It is only past Q2, that there should be no higher voltage. One may still want clamping diodes (e.g. BAV199) parallel to R15.
Anyway the input 3 would still not get a CAT2 rating.
In addition the main part of the MIO168 board is also not that much protected. So it would need some special care to use mains with the 2 isolated inputs.

I see that there is not really much space left on the AFE3 board, so one may have to compromise in some areas, possibly even dropping current measurement for the input 3 alltogether.

For the current shunts with input 4, the middle shunt is a little tricky: The diodes used for the protection limit the voltage to some 1.5 V ( one could lower this a little by using Schottkey diode for D8 + D9, not that practical for D6,D7) or so. So worst case there can be quite some power / current, at least until the fuse blows. This may requite a relatively high power rating for the shunt. So it would help if the second current range would be smaller. A lower value shunt makes things only more difficult.
The other point is that the current would also need to flow through the FET switches and these are also limited. The FETs would also add to the heat near the shunts and there current rating is only valid with adequate cooling. In some respect the resistance from the FETs also helps in limiting the power, but they still contribute to the burden and overall heat. With some 1.5 A max for the FETs this would requite at least some 1 Ohms total resistance and thus more like at least 0.8 Ohms for R32. So with the given MOSFETs the maximum would be at around 500 mA for the range.

Finally there are 3 shunts to covver the whole current range. With coarser spacing one could get more sensitivity to low currents. The ADC has quite high resolution and could thus get away with the shunts well more than a factor 10 appart.  So I would more consider  ranges of 10 A  (maybe less for good accuracy),  300 mA and 10 mA or even 10A , 100 mA and 1 mA.
 
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Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #579 on: May 15, 2021, 06:56:55 am »
With a maximum range to 240 V peak, the input 3 is not really suited for measuring mains and not meant for this. It would still be good if it would normally survive an accidental connection to mains (230 V AC). For this the photomos relay does not offer much protection, as the problem may happen with current measurement, so the clearance should also be behind Ok2. It is only past Q2, that there should be no higher voltage. One may still want clamping diodes (e.g. BAV199) parallel to R15.

No, input 3 with only 240 V peak cannot measure 230 Vac, whose peak is 325 V. That is clear. Maybe it’s not clear my listing of ranges, and maybe I should write Vpp everywhere or specify an RMS value so it would be 170 Vrms or Vac if I may say so.

Anyway the input 3 would still not get a CAT2 rating.
In addition the main part of the MIO168 board is also not that much protected. So it would need some special care to use mains with the 2 isolated inputs.

I see that there is not really much space left on the AFE3 board, so one may have to compromise in some areas, possibly even dropping current measurement for the input 3 altogether.

Since the Cat II is the minimum that should be met to directly measure mains voltage, I’ll probably need to rearrange the PCB a little better. For the purposes of certification, I see that it needs to survive a test of 1390 Vac for 5 seconds and a pulse of 2500 V.

My question here is should some extra protection be placed on the input to survive 2500 V surges? I don't know how DG212 switches will survive this. Maybe to protect them with TVS?

Your idea to take out the current measurement on AIN3 now makes a lot of sense. This will provide space on the PCB for the components to be arranged differently. By the same logic I think I will throw out the voltage measurements on AIN4 so it will be just a current input.

The MIO168 module itself does not have any special protection other than being entirely floated. The mains voltage insulation relies on the quality of the 8-pin connector (WE 691322310008) on the AFE and it is rated 300 Vac. What else could there be done?

For the current shunts with input 4, the middle shunt is a little tricky: The diodes used for the protection limit the voltage to some 1.5 V ( one could lower this a little by using Schottky diode for D8 + D9, not that practical for D6,D7) or so. So worst case there can be quite some power / current, at least until the fuse blows. This may requite a relatively high power rating for the shunt. So it would help if the second current range would be smaller. A lower value shunt makes things only more difficult.
The other point is that the current would also need to flow through the FET switches and these are also limited. The FETs would also add to the heat near the shunts and there current rating is only valid with adequate cooling. In some respect the resistance from the FETs also helps in limiting the power, but they still contribute to the burden and overall heat. With some 1.5 A max for the FETs this would requite at least some 1 Ohms total resistance and thus more like at least 0.8 Ohms for R32. So with the given MOSFETs the maximum would be at around 500 mA for the range.

Finally there are 3 shunts to cover the whole current range. With coarser spacing one could get more sensitivity to low currents. The ADC has quite high resolution and could thus get away with the shunts well more than a factor 10 apart.  So I would more consider  ranges of 10 A  (maybe less for good accuracy),  300 mA and 10 mA or even 10A , 100 mA and 1 mA.

High range with a current shunt of only R010 makes no difference whether 10 or less amps will be measured because even with a maximum PGA = 12 it is still only 50% FS of the ADC. Maybe that shunt can double but we’ll have a higher burden voltage.

The real problem is Q3, Q4 heating for higher currents (e.g 900 mA). I could either put bigger MOSFETs there or maybe better shorten the mid range to say 500 mA. With the currently selected 0R22 and PGA = 2 we would have pretty well covered that range.

Online Kleinstein

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Re: EEZ Bench Box 3 (BB3)
« Reply #580 on: May 15, 2021, 09:51:32 am »
The DG212 switches would not survive 2500 V directly, but they can take quite some current surges to the internal parasitic diodes. So if the resistors in front would limit the current they should stand a 25 mA surge. This may cause a upset in the function and maybe a latchup, shorting the supply, but the supply is relatively weak, which is a good thing. It may need some diodes / TVS to prevent the supply to rise too much.

Getting a proper CAT2 rating is hard for such a modular system and especially for a crammed board with so many functions in a limited space.
At least this would requite incompatible connectors (e.g. larger spacing one for the high voltage part).
A mixture of protected and low voltage only parts is still a problem and may be difficult with the standards.

A possible option would be to have the card inside the BB3 low voltage only and have a connector that also provides power. So the input part with AMC33....  for channels 1 and 2 would be in an external box, that than can have proper mains isolation. So the channels 1 and 2 in the BB3 box would be only slightly protected voltage inputs with additional power for either the high voltage box or maybe an alterntive input like a small TIA and photodiode.

For tests like measuring a SMPS one would ideally use an isolation transformer and would thus not be directly mains connected. Still there is a chance for users cutting corners.

For the current ranges the shunt for the 10 A range has to be low value to limit the heat. Ideally one would a much larger form factor, but this needs quite some extra space and has higher costs. The current limit is not a hard limit: short peak may be higher and at 10 A the accuracy is likely allready reduced. Chanes are the best accuracy would be around 3 A or so, which is OK. I understand that 10 A would be nice, so that the combined current of 2 power modules could be measured without much risk for the fuse. So reducing the high current range is not really an option. Cutting the mid current range is less of an issue and makes things easier. So I don't understand the step in reducing the shunt from 0.33 to 0.22 ohms. The protection more wants a shunt in the 1 Ohms range and thus more like 200 mA for the 2nd range.
 
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Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #581 on: May 15, 2021, 10:08:33 am »
Cutting the mid current range is less of an issue and makes things easier. So I don't understand the step in reducing the shunt from 0.33 to 0.22 ohms. The protection more wants a shunt in the 1 Ohms range and thus more like 200 mA for the 2nd range.

The main reason for choosing the 0R22 shunt is that it is the highest value that exists in the ROHM GMR series (i.e. GMR100HTBFIR022) which has an excellent TCR, and 3 W dissipation in 2512 which I believe would survive a fuse break which we can reduce now from 1.25 to 0.63 A if the mid range is reduced to 500 mA.

Online Kleinstein

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Re: EEZ Bench Box 3 (BB3)
« Reply #582 on: May 15, 2021, 11:50:10 am »
The availability of good shunts is an argument I have not looked at before. Still it would likely need larger FETs. The current FETs (BSS214) would likely not survive the time until a 2 A surge blows a 600 mA fuse. Lower resistance FETs are an easy change.
With some 2 V, the peak current for the shunt may reach some 5 A before the diodes really kicks in.
 
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Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #583 on: May 27, 2021, 07:07:48 am »
Good morning Prasimix,  happy to say my DCM224 arrived from Mouser on Tuesday. All installed with no problems :-+
My question is that when calibrating voltage and current how many cal points would you suggest and at which values.  The reason I ask is that I added a few extra cal points but am now having issues with it reading way out below 100mA and voltage not really useable below 1.6v.  This sems the same on both channels so suspect it is to do with my calibration.  I followed the same method as for the DCP405s (as in the instruction manual), both of these are absolutely spot on accurate.  I realise the DCPs are a more capable supply than the DCM224 but would like an indication of the performance I should expect from the DCM224.
Thanks for any advice you can offer.
#Regards Mike
 
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Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #584 on: May 27, 2021, 07:11:07 am »
Sorry, one more question I forgot,  below 2.5 volts (approximately) the current limit operates correctly but the LED does not change to red, this is the same on both channels.  Not a complaint just would like to know if this is expected.
Thanks
 

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #585 on: May 27, 2021, 07:31:36 am »
DCM is not even closer to DCP, especially when comes to current limit accuracy, so think of it as auxiliary power for not sensitive loads. What you're experienced is not related to calibration, so calibration is two points should be enough.

Some of DCM could report about 100-150 mA even without any load connected, that is still a mystery to me. It is not offset value, but simply "idle" value, and it starts to display correct value as current increases (i.e. over 100-150 mA).

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #586 on: May 27, 2021, 07:37:40 am »
Sorry, one more question I forgot,  below 2.5 volts (approximately) the current limit operates correctly but the LED does not change to red, this is the same on both channels.  Not a complaint just would like to know if this is expected.
Thanks

The problem with CC is that the LT3763 does not have a built-in mode indication, so this is done on a trick with a single comparator and guessing the mode is not accurate in all cases.

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #587 on: May 27, 2021, 09:44:14 am »
Thank you for the information, much as I thought.
I have now recalibrated voltage and current on both channels with 2 cal points and it seems much more accurate.
As usual, impressed by the product and support :-+
Regards Mike
 
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Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #588 on: June 02, 2021, 04:22:06 pm »
The first preview of func. generator: BB3 as half- or full-wave power rectifier. It can generate both 100 and 120 Hz, up to 80 V, or 10 A (with two DCP405)

« Last Edit: June 03, 2021, 01:18:50 pm by prasimix »
 
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Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #589 on: June 13, 2021, 02:48:58 pm »
Hi, a simple question if you know the answer, hopefully someone can help.
When I try to assign my digital io to UART mode the option is not listed, what am I doing wrong?
I am running 1.6.1 firmware
Thanks in advance, Mike
 

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #590 on: June 13, 2021, 02:50:03 pm »
You're too fast :) UART is coming in v1.7, you can expect it in a week or two.

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #591 on: June 13, 2021, 02:55:25 pm »
Ooops, sorry about that, it is shown in the online instruction manual though |O
Thanks for the info, look forward to 1.7 coming Mega 25609 at the ready :-+
Regards Mike
 

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #592 on: June 13, 2021, 02:57:34 pm »
Sorry, for confusion. I'm usually try to keep in sync online manual with the latest firmware revision, but due to some "difficulties" with new website I published it prematurely.

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #593 on: June 13, 2021, 03:02:43 pm »
Not a problem, thanks for the instant support, loving my BB3 8)
Over the last 50 years I have used numerous different power supplies but this is way ahead of even most of the very latest. I had never even considered some of the features offered but now I am using them I wonder how I ever managed without them. In terms of bang per buck I don't think this can be bettered :-+
 
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Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #594 on: June 13, 2021, 03:10:20 pm »
Thanks for the kind words. Now we "only" have to find a way how to spread the word and generate some sales that we can continue materializing other ideas that popped up during development and what other backers already suggested here and on the discord server.

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #595 on: June 14, 2021, 01:38:54 pm »
Regarding the R4 failure issue I have had a look at mine with my thermal imager and the resistor is running at ambient, on a fluke 189 ac voltage is only 1 volt across it, on a scope it is showing very short duration pulses approx +-3v.  One thing I did notice though is that the Live and Neutral wires to the Meanwells are reversed compared with the schematic.  Under very close inspection R4 does look very slightly discoloured compared with R6, one other point is that I initially only had two modules installed and then a few weeks ago added a third so now running three Meanwells, could this be of any significance :-//
 

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #596 on: June 14, 2021, 02:02:30 pm »
Got a few pics of the waveform on R4, doesn't look as though it would bother a 2watt resistor, or am I falling into a trap for young players, as Dave would say?

EDIT-  this is the waveform ACROSS R4, just to be clear :palm:
« Last Edit: June 15, 2021, 04:10:02 am by Mike G »
 
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Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #597 on: June 14, 2021, 02:13:41 pm »
It is strange, perhaps you got Mean Well of premium quality :). Anyway, the best way to check if it is overheating is a thermal camera... you just need to have it. If you think that the problem is present, add a 4u7/X2 as stated on GitHub.

Offline Mike G

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Re: EEZ Bench Box 3 (BB3)
« Reply #598 on: June 14, 2021, 02:17:12 pm »
As I said in my post I have looked at it with my thermal camera and it is running at ambient now although it looks as though at some time in the past it may have been thermally stressed by the v ery slight discolouration.  Could the recent addition of a third Meanwell have made a difference I wonder |O
 

Offline prasimix

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Re: EEZ Bench Box 3 (BB3)
« Reply #599 on: June 14, 2021, 02:49:05 pm »
Huh, odd number of Meanwell's to cancel odd harmonics?  :-//


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