EEVBlog #862 - BK Precision 8601 DC Electronic Load

[EEVblog]

Dave takes a look at the BK Precision 8601 DC Electronic Load and compares with his older 8500 model.
A teardown and some playing around with the software

[Stonent]

I was up in the electronics lab at work and they had a BK Precision 2500W programmable load on their bench.
Probably was a full 4U rack mountable device, but it was just sitting on their bench.

[EEVblog]

I was up in the electronics lab at work and they had a BK Precision 2500W programmable load on their bench.
Probably was a full 4U rack mountable device, but it was just sitting on their bench.

Not uncommon to find rack mount gear on the bench.
Racks are great for production test systems etc, but a PITA for general use. So yeah, just whack'em on the bench.

[n3vti]

Aww, this looks awesome! I can't afford the $1100 so I have to put this on my Wish List. It does make for some good drooling, though.

[Gareth Lock]

I couldn't help but notice that you weren't actually using MS Excel at all, but LibreOffice. If the software is expecting to drop the data straight into Excel, then, could it be that the option is disabled as it has detected that Excel isn't actually installed on the computer.

[Bud]

The company is Maynuo. They have an interesting history and I am privy to it. Not what you might think if you listen to BK Precision.

http://dc-electronic-load.com/
The sales contact is Kate Zhou

I visited the link and was immediately chased by two annoying nag screens in a typical Chinee-ish look and feel. Was enough for me to close the browser and never go back. Thank you very much Kate you just lost a customer because of agressive manner the web site is built in.

[EEVblog]

 

[n3vti]

FAIL lol   

[jancumps]

The company is Maynuo. They have an interesting history and I am privy to it. Not what you might think if you listen to BK Precision.

http://dc-electronic-load.com/
The sales contact is Kate Zhou

I visited the link and was immediately chased by two annoying nag screens in a typical Chinee-ish look and feel. Was enough for me to close the browser and never go back. Thank you very much Kate you just lost a customer because of agressive manner the web site is built in.

Very surpised to hear that. Last time I dealt with Maynuo, the website was different. i sent an email to kate with a few questions and got a pleasant, fast response. They offered to ship to me direct and that was it....quick and simple. I then did again for one of their supplies. The transactions were smooth. Apparently, they are not doing their business any good by chasing away customers like you with annoying tactics.

It's not that bad. Just visited the website and those widgets aren't aggressive at all.

[EEVblog]

Sorry Dave, Maynuo is NOT fake.

Well the story as I hear it (and it may be one side of the story), is that the Maynuo founder worked at Itech who did these designs (BK Precision take the Itech designs and tweak them) and then illegally ran off with all the IP.
If that is incorrect then he's welcome to come here and tell his side of the story.

[RobertoLG]

The company is Maynuo. They have an interesting history and I am privy to it. Not what you might think if you listen to BK Precision.

http://dc-electronic-load.com/
The sales contact is Kate Zhou

I visited the link and was immediately chased by two annoying nag screens in a typical Chinee-ish look and feel. Was enough for me to close the browser and never go back. Thank you very much Kate you just lost a customer because of agressive manner the web site is built in.

maybe you should "improve" your browser, or use another one, like firefox

[Brumby]

Basic Output/Input System

Still means the same thing.   


(but I did LOL)

[EEVblog]

Sorry Dave, Maynuo is NOT fake.

Well the story as I hear it (and it may be one side of the story), is that the Maynuo founder worked at Itech who did these designs (BK Precision take the Itech designs and tweak them) and then illegally ran off with all the IP.
If that is incorrect then he's welcome to come here and tell his side of the story.

I heard that as well, from the principal dude at Manyou.

So he readily admitted to stealing the designs from Itech?

[Stonent]

I was up in the electronics lab at work and they had a BK Precision 2500W programmable load on their bench.
Probably was a full 4U rack mountable device, but it was just sitting on their bench.

Not uncommon to find rack mount gear on the bench.
Racks are great for production test systems etc, but a PITA for general use. So yeah, just whack'em on the bench.

Yeah, all their stuff is on their benches. I've lost count how many 3GHz Spectrum Analyzers they have.  We don't even do any RF stuff that I know of but I'm sure the range is handy for other reasons.

Here it is:



The interface is the same as the 300W version. Makes sense to me.

[Barny]

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

[motocoder]

Looks like they have a 120V 30A model (8600) that is a few hundred dollars (USD) less. Half the power, but otherwise same features.

May be time to unload that Array Solutions model that I am unable to update the firmware on.

[nowlan]

Im sure Maynuo is good value, but weren't they playing games with domestic vs export quality and prices?
Not sure who designed the BK listed above. Planning to watch later.

[EEVblog]

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.

[EEVblog]

Not sure who designed the BK listed above. Planning to watch later.

The BK ones are essentially designed by Itech. But BK does make their own mods to the designs I'm lead to believe.

[mcinque]

Despite the true details of the Maynuo/BK precision engineering will be never revealed (every company says what they want), AFAIK Maynuo DC loads had that kind of specs (quad display, resolution etc.) much before than BK Precision came on market with the new model.

So, since this and considering the influence of your videos, I would reconsider that "Maynuo are rip-off" on the video. Just my thought.

EDIT: I heard from Maynuo that the engineer took the designs BECAUSE he wasn't paid by BK for the original project. BK say the he took the design after being paid.

[Zbig]

Despite the true details of the Maynuo/BK precision engineering will be never revealed (every company says what they want), AFAIK Maynuo DC loads had that kind of specs (quad display, resolution etc.) much before than BK Precision came on market with the new model.

So, since this and considering the influence of your videos, I would reconsider that "Maynuo are rip-off" on the video. Just my thought.

EDIT: I heard from Maynuo that the engineer took the designs BECAUSE he wasn't paid by BK for the original project. BK say the he took the design after being paid.

Exactly, two-line VFD Maynuo series 98xx is available since ages now.

[Switching Power]

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

The 8601 has the IO isolated internally so it uses a normal 1:1 serial cable (it even says so in the manual)

[nctnico]

Sorry Dave, Maynuo is NOT fake.

Well the story as I hear it (and it may be one side of the story), is that the Maynuo founder worked at Itech who did these designs (BK Precision take the Itech designs and tweak them) and then illegally ran off with all the IP.
If that is incorrect then he's welcome to come here and tell his side of the story.

I heard that as well, from the principal dude at Manyou.

So he readily admitted to stealing the designs from Itech?

Unless the PCB's and firmware are 100% the same the design isn't stolen. If you have created designs based on a certain microcontroller and switch employers (or start your own busines) it isn't stealing to use the knowledge you have gained for new designs.

[rizzy]

There had been a discussion on this forum about the BK Precision vs. Maynuo thing before:
https://www.eevblog.com/forum/testgear/why-is-bk-precision-still-in-business-bk8500-programmable-load-oem-found/

If it is true that the lead engineer of the 8500 founded Maynuo then I would not call that "stealing the designs" because it were somewhat his designs, although I agree that the Maynuos are blatant copies. I'm tending to believe that the post from kmel (from the above mentioned thread) is substantially right because all the listed test gear definitely has a very similar design. We will probably never find out the truth because either side will tell something different.

Anyway, I'm not a lawyer and also don't want to become one and as such I will leave all the stuff about "stealing IP" up to those who (or at least want to) earn their living with it. I'm really more interested about the the technical aspects of the electronic load, especially the specs and the precision.

At about 33:20 in the video, the software reads 1.4 mA before Dave turns on the load and it reads 9.1mA afterwards. At first I thought that's not within spec but after doing the math I realized that it was. In the "low" current settings of 0-3A you have an error in the accuracy of at least 3A*0.025% = 0.75mA but then for the readback of the current you have an additional 3A*0.05% = 1.5mA. So after all you get a spec of 22.5% of error if you want to draw 10mA. That does not sound like a suited device for measuring battery current in the low mA range.

[EEVblog]

If it is true that the lead engineer of the 8500 founded Maynuo then I would not call that "stealing the designs" because it were somewhat his designs

If you are employed as a designer for a company, then (unless you have special prior agreements) the designs and IP you come up with belong to the company.
Taking any technical information and design files etc.al with you when you leave is theft. And that's what happened according to BK Precision.
Of course you are free use whatever information is in your head and rebuild the product from scratch (subject to the usual copyright  and trademark and patent laws), but in this case, actual design files were supposedly taken.

[AF6LJ]

FAIL lol   

Almost lost my coffee....
Dave should have issued a spray warning with that picture.

[zal42]

the designs currently produced in China are different enough from the itech stuff that Maynuo is no longer worried about a lawsuit from Itech/BK based on Chinese law.

Altering the designs enough to technically pass the scrutiny of Chinese law means nothing in terms of whether or not the designs were stolen. This is an ethical, not legal or technical, issue.

[rizzy]

This is an ethical, not legal or technical, issue.

Totally agree on that one and in that sense what difference does it make if you copy the schematics to a USB drive and take them with you (i.e. steal them) or if you just "reverse engineer" your own work?
If it was you who figuered out every detail of the thing in the first place then you also know all the critical parts of the schematic and the layout and you can easily make a copy of the device. The critical part of the 8500 is really just a bunch of opamps, resistors and mosfets. It's not a space shuttle or the marse rover but just a quite simple electronic load that turns out to do it's job perfectly fine. Everyone from China could copy that if he knew enough about control circuits and power electronics and because the founder of Maynuo worked in this field for quite some time you can be sure he does know enough about it.

[Zbig]

The critical part of the 8500 is really just a bunch of opamps, resistors and mosfets. It's not a space shuttle or the marse rover but just a quite simple electronic load that turns out to do it's job perfectly fine. Everyone from China could copy that if he knew enough about control circuits and power electronics and because the founder of Maynuo worked in this field for quite some time you can be sure he does know enough about it.

Right, but why make it also physically identical, down to the color scheme, controls, etc.? Have you actually looked at both? I'm not taking sides here, don't know who copied who. But whoever it was, it's quite obvious he used the same enclosure design, perhaps ordered from the same contract manufacturer based on the same design files? Now, that is just lazy. <conspiracy theory> Unless it's really just an elaborate scheme plotted to cater to different market segments and it's really the same guys behind those two (three?) companies laughing at us at this very moment? </conspiracy theory>

[MobileWill]

Why do new devices still use VFD displays? I thought they were long gone. No LCD or OLED or something? Cost? Visibility?

[apis]

LCDs have limited viewing angle and worse contrast ratio. Might be nostalgia or aesthetic reasons as well. (There are many very good LCDs but not all LCDs are equal.)

[MobileWill]

LCDs have limited viewing angle and worse contrast ratio. Might be nostalgia or aesthetic reasons as well. (There are many very good LCDs but not all LCDs are equal.)

I think oled would be great for this. I use them a lot for my designs. But in my case they are a lot smaller. 128x64.

Sent from my SAMSUNG-SM-N920A using Tapatalk

[Zbig]

Not sure whether that's still valid but OLEDs used to have fairly limited lifetime and benchtop T&M equipment often gets left powered on for months. My current model Yamaha AV receiver still uses VFD as well. But probably the real reason is they have already put an effort to integrate VFDs into their devices, secure the supply chain, etc.  The job is done, they work and there's little incentive to change that just for the sake of it.

[bktemp]

Not sure whether that's still valid but OLEDs used to have fairly limited lifetime

There are good ones and bad ones. It also depends on the colour and the exact type of organic material used. And of course build quality, because OLEDs get damaged by moisture. Yellow ones can be great (>10k hours), but blue and white typically have a rather short lifetime. I have seen displays with signs of burn in after less than 100 hours.
The lifetime of VFDs should be superior.

[jitter]

If it is true that the lead engineer of the 8500 founded Maynuo then I would not call that "stealing the designs" because it were somewhat his designs

If you are employed as a designer for a company, then (unless you have special prior agreements) the designs and IP you come up with belong to the company.
Taking any technical information and design files etc.al with you when you leave is theft. And that's what happened according to BK Precision.
Of course you are free use whatever information is in your head and rebuild the product from scratch (subject to the usual copyright  and trademark and patent laws), but in this case, actual design files were supposedly taken.

Thank you for your perspective on this Dave. For the most part, I completely agree with you. I respectfully point out that even though, from our western perspective, this is a pure and clear case of copying and flagrant theft of intellectual property, no matter how we slice it, we need to consider another point. You and I and others on this forum see this as a product that has copycat, fraud, fake, theft,  associated with it. Not so in China. There are copyright laws over there but they are flawed, much to the dismay of our lawmakers and the chinese lawmakers. There are simply not enought resources to enforce violations and there are plenty, believe me. The Chinese are coming around to seeing things our way and respecting our IP traditions. Maynuo's founder indulged himself and so far he has not been sued. These kinds of crimes  occur over there every single day. This why I chose  in the 1990s to not manufacture my own product there: Theft. Ask anyone  from China and they will tell you that unless you have a patent in China, all bets are off in terms of protection. BK Precision did not have good agreements in place and thus their official position ( for those who believe it) that they got ripped off by their partner Itek and Maynuo.

Nuff said. I can decent from my soapbox now.

@grouchbyte

Well, as an owner of a Maynuo M9812, and with access to a 150 W BK Precision, I can only say that to all intents and puropses, these devices look so similar that I had not suspected anything other than rebranding.
Even Maynuo's control software and BKP's had the same layout with only another colour scheme and fonts (no BKP's software didn't support the Maynuo).

Granted, the Maynuo has some differences with the BK Precision 8500, but I had put that down to nothing more than revision changes/small redesigns. And my unit looked a bit grubby on the inside with lots of flux residue, it also didn't have the plethora of QC stickers on the inside like the BKP.

If this was indeed "borrowing" an original design, then the Chinese take on IP is definitely quite different from our's... Here BKP would have sued the hell out of Maynuo first and then gone to work on them next...

[xygor]

If it is true that the lead engineer of the 8500 founded Maynuo then I would not call that "stealing the designs" because it were somewhat his designs

If you are employed as a designer for a company, then (unless you have special prior agreements) the designs and IP you come up with belong to the company.
Taking any technical information and design files etc.al with you when you leave is theft. And that's what happened according to BK Precision.
Of course you are free use whatever information is in your head and rebuild the product from scratch (subject to the usual copyright  and trademark and patent laws), but in this case, actual design files were supposedly taken.

In the US, it seems to me that it is the opposite of defaulting to company ownership.  Software and hardware designs are not a "work for hire" and therefore belong to the original author even if the author is an employee or a contractor, unless some other explicit agreement is in place.

http://www.metrocorpcounsel.com/articles/9954/work-hire-doctrine-almost-never-works-software-development-contracts

Patents, too, are default owned by the inventor and must be assigned to the employer if that is the desired end result.

I don't know if there is a distinction between owning a copyright and owning a design though.

Edit: the link provided does not actually back up what I said about employees.  In fact it contradicts it.

[MobileWill]

Not sure whether that's still valid but OLEDs used to have fairly limited lifetime

There are good ones and bad ones. It also depends on the colour and the exact type of organic material used. And of course build quality, because OLEDs get damaged by moisture. Yellow ones can be great (>10k hours), but blue and white typically have a rather short lifetime. I have seen displays with signs of burn in after less than 100 hours.
The lifetime of VFDs should be superior.

Some good points. I have use many but so far only 1 I have seen burn in. These are mostly white. I only have a few blue.

[EEVblog]

Thank you for your perspective on this Dave. For the most part, I completely agree with you. I respectfully point out that even though, from our western perspective, this is a pure and clear case of copying and flagrant theft of intellectual property, no matter how we slice it, we need to consider another point. You and I and others on this forum see this as a product that has copycat, fraud, fake, theft,  associated with it. Not so in China.

BK Precision (and presumably Itech) don't seem to think so. An employee stole the documents and went and copied the product. Just because they haven't been successful in stopping him doesn't magically make it some valid point.
Just because this is rife in China does not make it right. BK Precision and iTech have every right to call this guy out.

As for the term "fake", I think it's a pretty valid term, but "copycat" is probably better. Have you seen the similarities in the design and look and feel?
If he truly just left and created a new product from scratch, it should not look and feel like the original model.
He deliberately created a knock-off product.

[Brumby]

If he truly just left and created a new product from scratch, it should not look and feel like the original model.
He deliberately created a knock-off product.

Every project that I've ever worked on has been implemented with something that I thought could have been done better.

If a design was taken as the basis of creating a similar product, then it would have those elements addressed - and it would be different.  For starters, external case design would be different to differentiate it from the competition.

By making it pretty well identical to the original, there is only one view you can take - It's a copycat, meant to ride on the coattails of the original.

[Dubbie]

Dave does this new DC load still suffer from the problem of injecting noise onto whatever you are measuring? I can't use mine for sensitive power supply noise measurements because it puts large spikes on the trace. Using a plain of resistive load makes the issue go away.

[steverino]

Thank you for your perspective on this Dave. For the most part, I completely agree with you. I respectfully point out that even though, from our western perspective, this is a pure and clear case of copying and flagrant theft of intellectual property, no matter how we slice it, we need to consider another point. You and I and others on this forum see this as a product that has copycat, fraud, fake, theft,  associated with it. Not so in China.

BK Precision (and presumably Itech) don't seem to think so. An employee stole the documents and went and copied the product. Just because they haven't been successful in stopping him doesn't magically make it some valid point.
Just because this is rife in China does not make it right. BK Precision and iTech have every right to call this guy out.

As for the term "fake", I think it's a pretty valid term, but "copycat" is probably better. Have you seen the similarities in the design and look and feel?
If he truly just left and created a new product from scratch, it should not look and feel like the original model.
He deliberately created a knock-off product.

It certainly is identical to the BK precision product. I have had them open side by side and it is clear to me that it was a ripoff just like we always knew to be true. So it is a fake. I can live with that label. I can also understand BK's position on this theft of IP. It certainly hurts their revenue stream as it now becomes a competitor in the world marketplace. As you may already know, there is little loyaly in China. Chinese customers really couldn't give a damm that some Yank company has a copycat product being distributed all around the world, including China. If its branded Maynuo or ITek, it makes no difference to the Chinese and it makes no difference to yours truly and possibly a vast number of eevblog viewers. Paying less than half for a quality product that gets the job done is far better in some cases than the alternative to paying full price for a legit product. I assume you received  two BK Precision electronic loads for free and after your teardowns and analysis certainly makes you deserving of them. I wonder how strongly you would feel about Maynou's theft of IP had they sent you a unit for free. No offense, Dave. I have viewed your videos for years and enjoy them immensely, but when you take a position that appears to defend the legitimacy of one of your benefactors without the salient facts from the other party, it indeed tweaks my sensibilities. I yield the moral high ground to you on this one.

Cheers
Respectfully

@grouchobyte

Lots of verbage which, bottom line, attempts to condon corporate ip theft.  I say Bullshit!

[grouchobyte]

Let me clarify and summariize my bloated post for those with ADD. There are no facts supporting the assertion that the founder of Maynuo stole or copied Itechs design. All we have  is the smoking gun vis a vis the fake product which is identical in most respects and some assertions from BK Precision. So much for the "facts"

Calling it stealing without putting Tony Xiao on trial is not how we exercise justice. Innocent until proven Guilty.

I am not an attorney and I dont play one on the tele. Amen.


@grouchobyte

[kmel]

There had been a discussion on this forum about the BK Precision vs. Maynuo thing before:
https://www.eevblog.com/forum/testgear/why-is-bk-precision-still-in-business-bk8500-programmable-load-oem-found/
...

There you also can find LaurenceW's investigation into his Maynuo M9712B electronic load and reverse engineering.
Here are his concluding comments:

Product: Very good! Pretty damn accurate, good resolution, excellent features, clear display. The cooling system, while good and adequate, might have some vulnerabilities in the event of a fan failure, but I know how to fix it for myself, and at this price point I don't expect perfection.
Company: Very good! They could have quietly ignored me, but they did not. <thumbs up>
Documentation: er, mostly OK. Which is a shame, really, because clearly it has not been produced by a native English speaker, and even if it was, it doesn't always tell you what you need to know. This is not hard to get right, and is how far eastern companies can easily differentiate themselves from one another. And to my mind, the documentation is as much a part of the product as the box itself.

That's two-and-a-half out of three, then. Pretty good.

So to answer the original OP's headline question - Why is BK Precision still in business? Search me.


The End.

OH - PS! A couple of other things that I didn't expect my Electronic Load to be -

- A half-decent standalone DC voltmeter or amp meter, with trend logging software
- A reasonable digital resistance up to a couple of K or so
- A background room heater for those chilly UK autumn days when it's not quite cold enough to turn the house heating on (toasty, here in my "lab"!)
- A crude PWM motor speed controller (you can set on and off periods in fractions of a mS, and connect this between your load and power supply as a switch)
- A topic of conversation!

[max-bit]

BK precision, the company itself did not produce, buy or orders from OEMs (Original Equipment Manufacturer) devices.
Multiplies the price twice and sells.
Maynuo M9812B price - 550 - 650 $
BK Prec - 1200 $

[max-bit]

Upss....

[max-bit]

Ultra stupid price
http://uk.farnell.com/b-k-precision/bk8601/dc-load-prog-60a-0-120v-250w/dp/2475140
1150 Pounds !!! (~1650 $ US) plus VAT !!!!
BK Precision +100%
Farnell +50%

....buyer gull let him paid

[EEVblog]

Let me clarify and summariize my bloated post for those with ADD.

Steverino already summarised it nicely.

There are no facts supporting the assertion that the founder of Maynuo stole or copied Itechs design. All we have  is the smoking gun vis a vis the fake product which is identical in most respects and some assertions from BK Precision. So much for the "facts"

You did more than that. You tried to argue that because copying and corporate theft like this is common in China, that makes it somehow OK.

The only "fact" we have is that BK Precision have stated their position that the founder of Maynuo left Itech and and took all the documentation and design files with him to start a new company and produce a duplicate product.
He's welcome to come here or elsewhere and explain his side of it.

Calling it stealing without putting Tony Xiao on trial is not how we exercise justice. Innocent until proven Guilty.

This is not about justice, it's about reputation in the court of world opinion.
People get to make up their own minds.
And if all the talking is one sided, then that's the fault of the parties involved. Mr Maynuo is more than welcome to come here and defend himself.

[tszaboo]

Dave, I'm not sure if you are right that those are ballast resistors. Ballast resistors are used, when the gates of the FETs are at the same voltage (+/- offset) and they are supposed to run almost the same current.
In this case I think they are low side shunts. Also, you have NE5532 per FET, which is a dual opamp, so one is probably amplifying the shunts feedback. This way you can use lower value resistor, which is good because all the reasons Im not gonna list.
Just a minor detail.
Also, I would have liked to see a proper current shunt on the output, probably bolted to the heatsink. You can get shunts for 50A, these coat hangers dont leave a lot of confidence in me. 0.1% max error is not a lot, when we are talking about 50+Amps. I wonder if they are in spec if you run if full load. 50ppm-100ppm/K from these shunts are not unusual, than you have self heating, ageing (can be huge for shunts under load), and issues with layout and terminals. I doubt if they are well within spec.

[grouchobyte]

BK precision, the company itself did not produce, buy or orders from OEMs (Original Equipment Manufacturer) devices.
Multiplies the price twice and sells.
Maynuo M9812B price - 550 - 650 $
BK Prec - 1200 $

Caveat Emptor!

[zal42]

There are no facts supporting the assertion that the founder of Maynuo stole or copied Itechs design. All we have  is the smoking gun vis a vis the fake product which is identical in most respects"

And how is that not a fact supporting the assertion?

Calling it stealing without putting Tony Xiao on trial is not how we exercise justice. Innocent until proven Guilty.

Would you feel better if people just stated that it looks an awful lot like stealing?

By the way, in the US, you are innocent until proven guilty in a court of law (theoretically, anyway). There is no ethical or legal stance that prevents people from deciding guilt or innocence in their own minds. That's a very good thing.

[djw]

With the 8600 series, are the RS-232 and USB ports isolated from the load?

[jitter]

I was wondering why BK Precision doesn't just sue Maynuo... and then it struck me, they can't.
If I'm not mistaken, BK precision is based in Taiwan and Maynuo in mainland China. Those two countries don't really have what you would call a love affair.

But perhaps BK Precision is copying some ideas from Maynuo in return. Maynuo was first with a dual line dot matrix display, and also the LED-mode seems to have been present on Maynuo's loads first.

[Macbeth]

I believe Maynuo are the more honourable company. BK are price gouging. The ITech stuff is cheaper than BK too.

I've not needed a load particularly as I have got by with an array of old toasters, incandescent bulbs, hairdryers, and high watt ceramic resistors

But the China Market Maynuo M9710 which is apparently the same as their export market M9711 which Gerry Sweeney gave a great review of is only ~£190 including DHL delivery on AliExpress - I couldn't resist.

Supposedly the M9710 uses "lower grade" components for the cheaper price. If I wasn't so cynical I would have paid the extra £50 or so for the M9711 label, but I prefer the gamble and will do a teardown and compare with Gerrys. 

As for the isolated RS232/USB. I intend to hardwire a cheap bluetooth serial board in there for the ultimate in isolation, so no need for that pricey M133 cable. 

[LyCannon]

I couldn't help but notice that you weren't actually using MS Excel at all, but LibreOffice. If the software is expecting to drop the data straight into Excel, then, could it be that the option is disabled as it has detected that Excel isn't actually installed on the computer.

LabView uses the Excel Interop Assemblies which require Excel to be installed. It would be nice if the software told you that though...

[jitter]

I believe Maynuo are the more honourable company. BK are price gouging. The ITech stuff is cheaper than BK too.

BK Precision aren't exactly strangers to rebranding and selling for a premium. I have a V&A VA520 LCR/ESR meter which cost me € 139 bought in a local store. At the time (about a year ago) it was also available as BKP in their colours for at least € 100 more. I didn't find it listed in BKP's product range anymore, now most look like Keysights in BKP's livery...
Edit: correction, I mixed up BK Precision and PeakTech here. It was the PeakTech 2170 that I had seen for a hefty premium, not a BK Precision.

But the China Market Maynuo M9710 which is apparently the same as their export market M9711 which Gerry Sweeney gave a great review of is only ~£190 including DHL delivery on AliExpress - I couldn't resist.

Supposedly the M9710 uses "lower grade" components for the cheaper price. If I wasn't so cynical I would have paid the extra £50 or so for the M9711 label, but I prefer the gamble and will do a teardown and compare with Gerrys. 

That's very interesting. I believe he, or someone else on this forum, tried to get the "China only" model, and Maynuo declined to send it. My M9812 only has A-brand parts in it that also seem to be genuine. So I wonder if that China only model uses what the "Shenzen market" has to offer (knock offs, "recycled", etc.). I'm really looking forward to seeing your teardown.

[EEVblog]

I believe Maynuo are the more honourable company. BK are price gouging. The ITech stuff is cheaper than BK too.

If they did steal the IP as claimed, then no, they aren't honourable.
Doesn't matter how cheap they are or how much they innovate after the fact.

[nwvlab]

Nice vid

17.55: although the heatsink may be grounded as well, there is very little clearance between the screw of the power MOSFET and the chassis! Or maybe it's just the perspective?

[mcinque]

If the improvements of the BK version (quad display, resolution, transients, rise time, good software etc.) was available years ago from Maynuo, how can you state that Maynuo is copying BK?

What THEY (BK and Maynuo) tell to us is irrelevant: they can tell us a nice story to change our opinion about the competitor, so the only thing we can use to understand who is copying who are the product features.

IMO, Maynuo had the features of the new BK years ago. So it's quite strange that Maynuo is copying BK...

[Macbeth]

BK has their finger in every pie, and are known for rebadging equipment and adding their markup. Mayuno specialise in electronic loads and PSU's only. As they are cheaper by far I expect BK sources their stuff from them.

I wouldn't trust any gossip from biased salesmen.

[mcinque]

If they did steal the IP as claimed

it's claimed by BK. While Maynuo say a different story. We can't know the real details, that are only words said by marketing/sales people.
Both company could have adapted the story to make us believe they're the good and other the bad.
We can't judge without knowing the details.

So saying "Maynuo is a rip-off" it's wrong IMO.

[mcinque]

That's very interesting. I believe he, or someone else on this forum, tried to get the "China only" model, and Maynuo declined to send it

Because (hearing Maynuo) that model is for internal market because has lower quality and a "high repair rate" (at a low price): they can easily arrange a return and a repair within the chinese territory but certainly not overseas. So they don't sell that model overseas.

Don't know if it's true but it can have sense in China.

Some "smart" guy place that model on aliexpress shipping from china.

[jitter]

BK has their finger in every pie, and are known for rebadging equipment and adding their markup. Mayuno specialise in electronic loads and PSU's only. As they are cheaper by far I expect BK sources their stuff from them.

I wouldn't trust any gossip from biased salesmen.

Comparing several Itech/BKP/Maynuo items, I noticed that Itech/BKP use quite a few different display layouts whereas Maynuo seems to stick to a simple 4 quadrant dot matrix with all the same size letters and numbers. So when I stumbled across an Itech using a Maynuo style display, I first thought that maybe they were just using the same display and chose to put everything in exactly the same place as their "nemesis". And then I thought: yeah, right... maybe that Itech just is a Maynuo after all...  Of course I looked a bit more and wasn't surprised to find the same display being used by BKP as well.

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...

[dadler]

I posted info about the 8600 model back in April of 2015:

https://www.eevblog.com/forum/testgear/bk-precision-8600-electronic-load-teardown-photosreview/

Personally, I don't think the build quality is all that great. The software really sucks.

[motocoder]

I posted info about the 8600 model back in April of 2015:

https://www.eevblog.com/forum/testgear/bk-precision-8600-electronic-load-teardown-photosreview/

Personally, I don't think the build quality is all that great. The software really sucks.

I am so paranoid of buying brands with no English-speaking office. I have an Array 3720A. I am unable to calibrate it, and unable to update its firmware. The software just doesn't work. I have no idea what the issue is, because the only person that responds to their emails speaks just enough English to generate complete and total confusion. I went round and round and round with her, on two separate occasions, to no positive conclusion.

Now I see threads about people with Maynuo's not being able to calibrate them. They say that they hear it's possible, but were not able figure out how to get it to work. This sounds like *exactly* the same problem. So perhaps ITech and BK are the same hardware, and Maynuo is just as good a product, and the BK costs more than the other two. However, if buying from BK Precision means I get a manual written in English, software that works and which displays English error messages, and someone who can provide support to non-Chinese speakers if it's not working, than this is money well spent IMHO.

[EEVblog]

If they did steal the IP as claimed

it's claimed by BK. While Maynuo say a different story.

What is their story? I have not heard it.

So saying "Maynuo is a rip-off" it's wrong IMO.

Itech have been around a long time, and it's not disputed that Mr Maynuo (I don't now his real name) left Itech and started Maynuo, and then bam, products that look and feel almost identical emerge.
To deny that there is ripping-off being done is a ludicrous position to hold, it's demonstrably untrue.
The only question is whether or not Maynuo stole the IP as claimed. In either case the fact remains they are "rip-offs". They have been deliberately designed to look and work very similar to the original Itech's. This cannot be denied, it's an obvious fact.
Now it could very well be the case that the Maynuo "rip-off's" are actually better than the originals in some ways, and that's a different argument. But the fact is they are still rip-off's, so IMO it's certainly the right word to use.

From a design point of view, if you left a company and started your own to produce similar products, and you didn't take the IP, why would you go to the effort to engineer them again to look and feel almost identical?
Sorry, but the case does not look good for Maynuo being an innocent party here.

[Macbeth]

Dave, there are no actual facts here. Just rumour mongering, with lots of "chinese whispers". As far as I am concerned the Maynuo are very respectable and cheap loads. They only make DC loads and sources. Of course they probably don't make them at all, but rebadge something from deeper mainland china "DC Load City" purpose built for nothing but this stuff. They even have whole cities of thousands of workers geared up to producing nothing but bathroom taps, cutlery, and adult vibrating massagers for example. It's the communist mentality. The millionaires just stick a front company and sales office on top of all that cheap commie labour.

I'm sure BK get theirs from communist "DC Load City" too. They choose their options for their markets. Maynuo get theirs from the same source but have a different target market. Indeed, my M9710 I hope to tear down is meant to be a China only market model. The excuses like "China people don't worry and expect shit to be sent back and repaired all the time" doesn't wash with me. The simple change of a digit on the faceplate and trying to control markets is what I see here. 

Hopefully I get it soon as nobody in the free world appears to have one yet 

[EEVblog]

And BTW, for those wondering why I mentioned Maynuo being a "rip-off" in the BK Precision video is because, well, I'm reviewing a BK Precision unit. Maynuo have always sold very deceptively similar looking  loads, and many viewers might think they are the same thing just rebadged. They are most certainly not the same as the Itech or BK Precision units. I don't want viewers to be under any misapprehension.
BK Precision is Itech:
http://www.bkprecision.com/about-us.html

If Maynuo want to send me their load and tell me their side of the story, then they are most welcome to.
Until they do that I can only go on what I have been told, what the evidence implies, and what my spidey-sense tells me, that Maynuo's are "rip-off's".

[Macbeth]

If Maynuo want to send me their load and tell me their side of the story, then they are most welcome to.
Until they do that I can only go on what I have been told, what the evidence implies, and what my spidey-sense tells me, that Maynuo's are "rip-off's".

What if Maynuo are just another marketing division of the ultimate parent company, and it suits the parent company to boost the profile of the higher priced BK version? There is no reason to send the Maynuo to you as it defeats the purpose of the promo stunt. BK seem to me nothing but re-labellers, perhaps with a custom designed display panel, but the fundamental circuit and case are all the same. I would guess the IP involved is just the display panel.

Let's not forget the nonsense that IET have come up with rebadging the DER EE-5000 and more than doubling the price. (BTW, I think there are loads of EEV fans who would like to see a shootout and explanation of LCR meters, including pitching the IET vs the DER and all the others) but that's another topic.

ETA: Anyway, I have purchased the bottom of the range Maynuo china only load, and will provide a tear down (if I get it now that Maynuo are probably aware of this thread and will stop the AliExpress dropshipper in her tracks!)

[kmel]

Back in 2012 I asked Maynuo: "Who is the OEM, you or ITech Electronics? Or do you have both the same OEM?

Kate Zhou answered:
Our boss Mr Xiao Tony used to work for Array and ITECH as their cheif designer. He designed the Array 37xx and IT/BK85XX electronic loads. However, this does not means, among of the three manufacturers, Array is orginal and ITECH or MAYNUO is copies or OEM. Each has its own pattern. ITECH started in 2005 and Maynuo started in 2009.

[jitter]

And BTW, for those wondering why I mentioned Maynuo being a "rip-off" in the BK Precision video is because, well, I'm reviewing a BK Precision unit. Maynuo have always sold very deceptively similar looking  loads, and many viewers might think they are the same thing just rebadged.

Yes, that was my first impression too, and as you may have noticed, I'm not that sure it's a case of foul play. I mean, creating devices that look almost identical since 2009-2016, and still neither of the two (Maynuo vs BKP/Itech) chose to alter the appearance to set it apart from the other? Edit: maybe BKP/Itech have with the change to rounded buttons.

They are most certainly not the same as the Itech or BK Precision units. I don't want viewers to be under any misapprehension.

My Maynuo is definitely not identical to a BKP inside or out. But certainly by the same designer, the similarities are just too great to be a coincidence.
But now that BKP has a new DC load that's clearly a continued development of the old one, I'm curious to see what Maynuo comes up with. Although, that BKP in the vid isn't that new judging by the datecodes (including the PCB) being no older than early 2015.
If they don't match it exactly, then yeah, maybe Maynuo was a less than legal spin off. If so, the original design would be taken further by Maynuo and BKP independently, and the differences should become bigger as time progresses. If not, then maybe Maynuo might just be an OEM for Itech/BKP after all...

BK Precision is Itech:
http://www.bkprecision.com/about-us.html

If Maynuo want to send me their load and tell me their side of the story, then they are most welcome to.
Until they do that I can only go on what I have been told, what the evidence implies, and what my spidey-sense tells me, that Maynuo's are "rip-off's".

I hope Maynuo will!

[BloodyCactus]

I have an itech 8512+ and really like it. great little load that apart from one hiccup I posted on the forum has been really great.  doesnt have the BK's fancy outputs the 86xx models have tho. you can see there is some extra effort/design in the bk from the current it85xx range. I dont know if itech put out an 86xx range yet.

[jitter]

I have an itech 8512+ and really like it. {zip} I dont know if itech put out an 86xx range yet.

I think they do but call it the 8900 series (they already had an 8600 series, which is a bit of a different beast...)

Itech lists only the IT8912E, a 300 W/500 V/15 A DC-load. I also found a 500 V version in BKP's lineup, but not yet in their 8600 series.
Funny... Maynuo has also added a 500 V version to their range: the M9812B.

I wonder what is needed to turn a 120-150 V model into a 500 V model...

Edit: hmm, I just came across this thread of an Applent AT8612. Now that one also has some striking similarities... is that a rip-off too? (oooh, I just love the looks of that sexy R-core transformer.)

[mcinque]

What is their story? I have not heard it.

Their story is that the engineer that designed the DC load wasn't paid by BK for his job, so he took his designs, left BK and founded Maynuo. But like BK's story, it's a story.

Until they do that I can only go on what I have been told, what the evidence implies, and what my spidey-sense tells me, that Maynuo's are "rip-off's".

It's your opinion and of course it's respectable.

But since your videos have a huge authority and influence (IMO), saying that opinion as a fact writing "Maynuo ARE rip-off" and not as a thought "in my opinion/for me Maynuo are Rip-Off" (toghether with "BK has some added value"), can inadvertently and unnecessarily improve the reputation of BK (other than make someone doubt that you're rooting for BK, while I bet it's not: you have always been honest and impartial in your reviews  ).

In two words, I think that with great authority and influence comes great responsibility: just with a couple of words you can influence a lot of viewers.

[grouchobyte]

Sorry to hijack the current discussion regarding the legitimacy of these brands but I would like to kindly request  some assistance of a techinal nature. Somewhere in this thread or another forum, there was talk of a mod to speedup the response of the shaft encoder using a pic or micro controller, specifically on the Maynuo. Would anyone here happen to know anything about that and if so would you mind posting some details or PMing me.

Thanks.

[motocoder]

Sorry to hijack the current discussion regarding the legitimacy of these brands but I would like to kindly request  some assistance of a techinal nature. Somewhere in this thread or another forum, there was talk of a mod to speedup the response of the shaft encoder using a pic or micro controller, specifically on the Maynuo. Would anyone here happen to know anything about that and if so would you mind posting some details or PMing me.

Thanks.

Might be worth starting another thread if you don't get a response here. I haven't got any responses to my query either. Seems this thread is all about the BK/Itech/Array/Maynuo butthurt.

[Dubbie]

Nor my request....

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


Sent from my phone using Tapatalk

[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.


Sent from my phone using Tapatalk

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.

[jitter]

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.

Nice!
120 A / 600 W in this form factor? Would you consider popping the cover and posting a few photos?

[deepskyridge]

Where does one find the big beefy binding posts used on these units. I have searched but cannot find them. ?

Thanks
Gary

[Fungus]

Where does one find the big beefy binding posts used on these units. I have searched but cannot find them. ?

I don't know about those but the audio loudspeaker world makes some big binding posts.

eg. http://www.ebay.com/itm/390857472929

[Macbeth]

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.

Nice!
120 A / 600 W in this form factor? Would you consider popping the cover and posting a few photos?

I would like to see the insides too. Looking at the rear I am guessing the same well known BK, Maynuo, ITech board of old we know well, but with dual fans on each heatsink extrusion, front and back. Maybe 

[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.

Nice!
120 A / 600 W in this form factor? Would you consider popping the cover and posting a few photos?

Thanks. But I'm afraid the opening of the cover will void the warranty, there is a sticker to protect the cover from removing.

Where does one find the big beefy binding posts used on these units. I have searched but cannot find them. ?

Thanks
Gary

I bought some of these and they seems better than those on the e-load, at least stronger and heavier. There is a hole for banana plug that Dave desperately needs.
http://www.aliexpress.com/item/3pc-lot-3-color-100A-Power-Amplifier-Binding-Post-Terminals-TO-BANANA-PLUGA-Test-Probes/1198898706.html

I would like to see the insides too. Looking at the rear I am guessing the same well known BK, Maynuo, ITech board of old we know well, but with dual fans on each heatsink extrusion, front and back. Maybe 

I found some inside photos from one of my friends.

[Thomas]

The 8513+ seems to be ~99mm deeper than the 150/300W versions, see 8500+ series datasheet: http://www.itechate.com/Upload/File/20150806091844.pdf
It also looks like it has more transistors on the heatsinks. That would explain the increased power handling capability.

[jitter]

I found some inside photos from one of my friends.

Thanks for the look inside.

Mostly it looks good, but I don't like the messy wires in the back.

Compared to Dave's BKP 8601, I'd say this comes from the same design, but has been modified for the higher load capability.
Some differences I see straight away are in the mains wiring and the transformer. On Dave's BKP the mains comes in the back and travels across wires to the front; the transformer is shielded. On this one, the mains travels through the PCB and the transformer is not shielded.

The 8513+ seems to be ~99mm deeper than the 150/300W versions, see 8500+ series datasheet: http://www.itechate.com/Upload/File/20150806091844.pdf
It also looks like it has more transistors on the heatsinks. That would explain the increased power handling capability.

Thanks, that would indeed account for the higher dissipation capabilities.

[the_mighty@420]

Can any body tell me is this resistor for balancing the MOSFET and if it is for balancing then the maximum current flowing through one MOSFET is 6 Amps and value of balancing resistor is 5.8 ohms so this resistor must be of 6*5.8 = ~35W. 

[Brumby]

If you are referring to the resistor outlined - I don't often work with such values, but that looks to me like a 0.05 ohm 5% wire wound.  If so, 6A through that gives 0.3W.