EEVBlog #862 - BK Precision 8601 DC Electronic Load

[Dubbie]

Nor my request....

I'm interested to know if the new model injects noise like the old one.


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[max-bit]

"Mayuno" is the original OEM manufacturer All brands ITECH, BP Prec etc .... this customer OEM products. (But there may be others subcontractors)
This company BKPrecision:
no designs
does not have any factories

It is not that to evaluate this or that brand.
Only to realize the reality of origin.

It is the same with other companies, cheaper products are manufactured generally in China.

[jitter]

Nor my request....

I'm interested to know if the new model injects noise like the old one.


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Wait for the review, this was just a teardown.

[mcinque]

Industrial espionage? My ass! IMO, they're all affiliated and we're being told porkies by someone who's overpricing... 
Come to think of it, this may also be the real reason for them not sueing one another...

Yes, could be.

Reminds me some BK precision PSUs (like the one that Dave has, the black 40A version) or Peaktech PSUs. They rebrand Manson PSUs, requesting some different color part, then overprice them about 30-40% more. Same CrapXcon inside. Same circuitry.

With BKP, someone think that on their product there is some "added value" someway, but I'd like someone show me what that "added value" is.

Warranty? Hmm...

Better support? Well, having "BOIS" instead "BIOS" tells me everything about their product design quality control.

For a "cheap" product could be considered ok. For the same product ovepriced by 30-40%, is taking the piss out.

Look at the products images below, the "original" Manson versions costs even 40% less than the rebranded BK.

This company BKPrecision:
no designs
does not have any factories
It is not that to evaluate this or that brand.
Only to realize the reality of origin.

[jitter]

Look familiar?



Apparently Tonghui is well known for their LCR-meters, including the rebranded ones. Now this image got me wondering who's making what in China...
At least this front panel with the rounded buttons looks the same as the current Itech/BKP models, but that may just mean that this is what I would call a rip-off.... or is it an OEM? I don't see the forest for the trees anymore... 

link

And talking about looking familiar, how about this Keithley?




I'd love to see a teardown of this one. The rear panel looks conspicuously like a BKP 8600...

Edit: removed last post and added to this one.

[Macbeth]

I received my Maynuo M9710 "China market only" yesterday and will post some internal photo's soon.



I attach the factory calibration "certificate" below. I notice how all the Min and Max specifications are exactly the same as for the M9711/M9712. How can this be when the M9710 has inferior specifications, being made with junk from the Shenzen market and all that?

I'm comparing my document with Martin Lorton's M9712 which he shows here

[Towger]

Why does the certificate look like a photo copy? Does the serial number match your unit.?
I am tempted. About USD280 on Allieexpress.

[jitter]

That's probably because it's a scan to a pdf.
I'll attach the document from my M9812 so you can see, and to compare with the newer model. The original looks laser printed, the pdf has a bit of a photo copy quality to it, although not as pronounced as Macbeth's.

The only difference in specs I see is in the 150 V range, 3 V. The remote voltage testing has to be within +/- 250 mV on the M9710 whereas on the M9712 and M9812 it must be within +/- 30.9 V. All other tolerances seem to be the same.

[Macbeth]

@Jitter - How odd with that 150V 3A range? However my Certificate has a chinese red star stamp on it, so I think it Donald Trumps yours! 

@Towger - Yes, the serial numbers are correct. The "Cert" is actually a pretty crap laser print - no doubt Maynuo are running low on that cheap ebay bulk toner. It's quite hilarious that the red star stamp is actually under the laser print, like a blank sheet has been pre-stamped! 

As for total cost including DHL customs handling (yet to pay - they keep texting me for it, but I want a proper invoice delivered for the £10 fee they do to work out USD/GBP * china_declared_value * 20% VAT). Let's just say I got it for £209 all in from Aliexpress in 7 days.  Taobao will no doubt be cheaper.

I think I will resurrect the old M9710/M9711 thread with the photos. I will say now that I suspect the rather strange published specs of these loads are probably based on the cruddy PC software that Maynuo supply, rather than the actual hardware. The only hardware difference I can tell is the faceplate print has been changed from M9711 to M9710. 

[nowlan]

Are all these electronic loads just for stressing power supplies?
I have a feeling a lot of us would be more interested in measuring performance for battery operated devices, using lipo or supercap.
Looking at standby power, sleep modes, etc.

Im suprised that the keithley looks to be rebadged, is that true? Is similar firmware, with new face plate?

Other wise what options are available for monitoring low power devices as I mentioned above?
The other extreme seems to be the ebay load kits etc. But I suspect the software would be more important to recording performance etc.

[jitter]

Are all these electronic loads just for stressing power supplies?

That's their main function, but it's not the only one.

I have a feeling a lot of us would be more interested in measuring performance for battery operated devices, using lipo or supercap.

Notice that this is a load that will do such things too. Please look at some of Dave's videos regarding battery performance, and you'll see that it's very useful for just that.

Looking at standby power, sleep modes, etc.

No, that's the other way around. For this you would want to use a lab supply and/or multimeter with datalogging capabilities. 

Im suprised that the keithley looks to be rebadged, is that true? Is similar firmware, with new face plate?

I'm not, lower end stuff by Keysight, Tektronix, LeCroy, etc. are often rebrands nowadays.

Other wise what options are available for monitoring low power devices as I mentioned above?

An electronic device can be separated in the part that does what it's meant to do (the application) and its power source. The latter can be a battery, a solar cell, a PSU, to name a few.
A load is used to find out about the characteristcs of a power source. Looking at what the application circuit draws, etc. you're looking at voltmeters, currentmeters, power meters, oscilloscopes...

The other extreme seems to be the ebay load kits etc. But I suspect the software would be more important to recording performance etc.

A simple DC load is easy to make. Just a power resistor or a bulb can do that job, but only that job and only at a single load. A DC-load using active devices can be manipulated so that it can funtion over a wider range, but a DC load like this BKP 86xx is essentially microprocessor controlled. That way it's more versatile and you can e.g. simulate lots of different loads, e.g. a pulsed load to simulate an actual device switching in and out, and log the data in software.

[jitter]

@Jitter - How odd with that 150V 3A range? However my Certificate has a chinese red star stamp on it, so I think it Donald Trumps yours! 

Yeah, or perhaps I have one with invisible ink... 

Not 3 A, but 3 V, read in the 150 V range.
It's curious that that one range has such a wide spec. Perhaps there was some calibration issue with certain devices and they decided to sell these inside China only. If that's the case, I'd expect the exact same components inside, no "Shenzen market" stuff at all. Or maybe it's just a typo...

What strikes me about the cal values on your certificate is that they're all much closer (well, relative) to the target values than my unit. Given you have a nice Keithley meter, I'd be really interested to see if those cal values are the real values of your unit. The Chinese are known to be, let's say it mildly, creative with stuff like this  . Could you perhaps confirm/validate those? My unit appears to be bang on.

[Macbeth]

ah yes. The 2.750 is clearly a typo. For one the 150V range only goes to 10mV resolution. It should be 2.97 like the above.

I will get back to you with actual performance. But I've already noticed that the voltage readout is ~10mV even with the input shorted.

I've posted my pictures to the old M9710/M9711 differences thread

[manu]

Dave, did you use a Zero-Modem RS232 cable?
Perhaps that was the reason, no data got through.

I used the specific isolated one that came with my 8500.

Warning! the 8500 series has a misleading db-9 "RS232" connector despite it is a UART *TTL* interface (0/5V directly from the microcontroller in the unit I presume).
The 8600 series seems to a have a true RS232 interface (+/-5 to 12V probably) and you need a straight rs232 cable, according to the manual.

Code: [Select]

A straight pin-to-pin DB9 female to DB9 male serial cable is required for using the RS-232
interface. Do not use a null modem or crossover DB9 serial cable.

[KrystianJ]

Hello!
I'm looking for some more information about the MOSFET driver circuit used in this device.
Are those OP-AMPS only used as voltage followers to increase the current efficiency?
Should't all the MOSFETS be driven from one source and be connected in pararell?
How about those parallels sharing resistors, are they in series with the MOSFETS?

Thank You for any informations
Best Regards
Krystian

[motocoder]

Hello!
I'm looking for some more information about the MOSFET driver circuit used in this device.
Are those OP-AMPS only used as voltage followers to increase the current efficiency?
Should't all the MOSFETS be driven from one source and be connected in pararell?
How about those parallels sharing resistors, are they in series with the MOSFETS?

Thank You for any informations
Best Regards
Krystian

I'm sure others will weigh in with more info, but I an answer a couple of your questions. Yes, typically the MOSFETs would be connected in parallel to spread the current (and hence power dissipation) across multiple devices. A small resistor is often placed on the source of each MOSFET (or emitter of a BJT) to help make sure that the current across the paralleled devices stays even. The resistor provides a little negative feedback and counteracts a negative temperature coefficient in the active device that might otherwise lead to one device hogging the majority of the current and this situation escalating as the device heats up, eventually leading to failure.

[lukier]

Hello!
I'm looking for some more information about the MOSFET driver circuit used in this device.
Are those OP-AMPS only used as voltage followers to increase the current efficiency?
Should't all the MOSFETS be driven from one source and be connected in pararell?
How about those parallels sharing resistors, are they in series with the MOSFETS?

Thank You for any informations
Best Regards
Krystian

I'm sure others will weigh in with more info, but I an answer a couple of your questions. Yes, typically the MOSFETs would be connected in parallel to spread the current (and hence power dissipation) across multiple devices. A small resistor is often placed on the source of each MOSFET (or emitter of a BJT) to help make sure that the current across the paralleled devices stays even. The resistor provides a little negative feedback and counteracts a negative temperature coefficient in the active device that might otherwise lead to one device hogging the majority of the current and this situation escalating as the device heats up, eventually leading to failure.

I don't know about BK/Maynuo/Itech architecture, but I bet it is pretty similar to Agilent 6060B and the like. In 6060B each MOSFET has its own sense resistor for its own control loop (one opamp for current sense amplifier, another closing the loop with DAC output as I_ref control). With such modular approach it is very easy to increase current handling capacity.

What I don't understand is the way the total current is measured. In 6060B the output of each current sense amplifier (8x) is fed into a summing amp and this is used for outer control loops for CV/CR/CP modes and goes to ADC for display. In BK/Maynuo/Itech however, they have these massive copper shunt right after the input binding posts and I assume that's the place current is measured. What are the advantages of this approach compared to summing amp used by Agilent? Each MOSFET load module already has current sense resistor, even in BK/Maynuo/Itech, so why add another global one?

[motocoder]

I don't know about BK/Maynuo/Itech architecture, but I bet it is pretty similar to Agilent 6060B and the like. In 6060B each MOSFET has its own sense resistor for its own control loop (one opamp for current sense amplifier, another closing the loop with DAC output as I_ref control). With such modular approach it is very easy to increase current handling capacity.

This surprises me. Why not just have one sense resistor for total current, one feedback loop, and the small source resistors to ensure relatively balanced load across the individual MOSFETs? Sensing current through and controlling the MOSFETs individually just seems like adding complexity for no benefit. I must be missing something.

[Thomas]

They have individual control loops because Vgs is different for each MOSFET, and this voltage is several volts.
So if you wanted to balance the currents in each MOSFET, each source resistor would have to drop a few volts. Not ideal in a load which you want to be operational at <1V.

Individual control loops fed with the same control voltage handles the MOSFET production spread effectively, even with a small sense resistor.

Current summing is probably a bit simpler with one common resistor, no need for precision low-voltage summing circuitry.

BJT transistors have Vbe of ~0.7V, so they are more suited for current sharing using simple emitter resistors. Just drop a few hundred mV at the desired current and you'll be fine.

[drago]

Isn't it that resistors in series with source are only required if MOSFET is operated in linear region where resistance decreases with increasing temperature?

[Thomas]

Isn't it that resistors in series with source are only required if MOSFET is operated in linear region where resistance decreases with increasing temperature?

If current regulation is wanted, a series resistor is required. It is usually placed in the source leg for convenience (works out nice for an opamp driving the gate).
Rds decreasing with increasing temperature will then be compensated by the feedback loop.

[motocoder]

They have individual control loops because Vgs is different for each MOSFET, and this voltage is several volts.
So if you wanted to balance the currents in each MOSFET, each source resistor would have to drop a few volts. Not ideal in a load which you want to be operational at <1V.

Individual control loops fed with the same control voltage handles the MOSFET production spread effectively, even with a small sense resistor.

Current summing is probably a bit simpler with one common resistor, no need for precision low-voltage summing circuitry.

BJT transistors have Vbe of ~0.7V, so they are more suited for current sharing using simple emitter resistors. Just drop a few hundred mV at the desired current and you'll be fine.

Ok, so the range of variation on the MOSFET Vth is such that the source resistor would have to be impractically large (i.e. would waste a lot of power) to compensate. Thanks, this makes sense.

[zlymex]

I've just bought IT8513C+, 120V, 120A, 600W, half width for 5600 RMB(equivalent to 867 USD) including p&p.
The functionality seems to be the same as BK Precision 8601. I installed two wooden feet at rear so that it stands on the floor.

[Zbig]

I've just bought IT8513C+, 120V, 120A, 600W, half width for 5600 RMB(equivalent to 867 USD) including p&p.
The functionality seems to be the same as BK Precision 8601. I installed two wooden feet at rear so that it stands on the floor.

Only it uses this horrible "starburst" alphanumeric VFD instead of the proper dot-matrix one. In my opinion, there's no excuse for using these in 2016.

EDIT:
I'm not so sure that your vertical stand mod is good from the thermal management standpoint (no pun intended). Unless it's only for storage and not for actual operation.

[zlymex]

I'm not so sure that your vertical stand mod is good from the thermal management standpoint (no pun intended). Unless it's only for storage and not for actual operation.

No worry. The hot air will be vented by fans and I leave enough room for it. I won't operate it in full power at this position.