Why is BK Precision still in business? BK8500 programmable load OEM found

[Wartex]

Hi everyone, talked to a large test gear distributor in Canada today, found the real OEM for BK's bench multimeters and programmable loads as well as other stuff. It's not "itech", it's maynuo. I played with the DC sourcemeter and it's awesome. They are coming out with an AC sourcemeter.


Looks familiar? http://maynuo.com/english/pro.asp?tid=26

[EEVblog]

I was told by BK Precision directly that the 8500 electronic load was designed and manufactured by iTech, a subsidiarity company of the BK Precision group.
So I'm not sure what's going on here?

Dave.

[EEVblog]

I notice that the display is different to the BK precision/Itech unit. Dual line instead of single.

Dave.

[T4P]

I notice that the display is different to the BK precision/Itech unit. Dual line instead of single.

Dave.

That might require just a minor OEM change, but yeah who am i to argue ...

[Wartex]

I was told by BK Precision directly that the 8500 electronic load was designed and manufactured by iTech, a subsidiarity company of the BK Precision group.
So I'm not sure what's going on here?

Dave.

I was told by BK directly that BK879 LCR was made from the scratch. It's a blatant lie as it's a stripped down Tonghui. Also whenever they say "subsidiary" it's usually an independent company that makes gear for 20 other companies. I have lost all respect for BK, they are nothing but a badgeneering shop. I'll shit bricks the day they grow a pair and respond to criticism and admit they design ZERO products.

[FenderBender]

Yeah I used to think "BK Precision. Good stuff right? Like a cheaper Tek/Fluke, right?" Wrong. There's nothing special about their products. They're not bad, just not unique...and how can you be when some overseas company is doing the engineering and production?

Only thing they might provide is customer service if you need it..

[olsenn]

Nah, this isn't the same as the BK/Itech ones; the specs are different, the displays are different, and I tried out their software with my IT8511 and it doesn't communicate with it, meaning the PC interface is different as well. They just look similar... in fact it was probably the Maynuo that copied BK, as BK is the most popular/famous company of the bunch.

[T4P]

Nah, this isn't the same as the BK/Itech ones; the specs are different, the displays are different, and I tried out their software with my IT8511 and it doesn't communicate with it, meaning the PC interface is different as well. They just look similar... in fact it was probably the Maynuo that copied BK, as BK is the most popular/famous company of the bunch.

And also a high probability "Itech" copied Maynuo and changed many things

Yeah I used to think "BK Precision. Good stuff right? Like a cheaper Tek/Fluke, right?" Wrong. There's nothing special about their products. They're not bad, just not unique...and how can you be when some overseas company is doing the engineering and production?

Only thing they might provide is customer service if you need it..

That's what they did with their scopes also ...

[Christe4nM]

Since I'm wondering what is going on here I took a moment to compare the specs of BK Precision's 8500 vs Maynuo's M9711. At first glance the Maynuo actually seems to have a bit better specs; at least greater accuracy than the BK.

Now I have no idea how to know whether to trust the specs stated by a manufacturer, nor how to now whether a Chinese manufacturer is only 'Chinese' (the common way we know their products...) or actually a high quality manufacturer. Yet since Manyuo's DC load is marketed as new, I don't think it to be odd that their specs are better; BK's one is around for quite a while now. I just wish we could see a teardown of the Maynuo to see the build & component quality.

There's very little information on the web about Maynuo, and so far I haven't been able to connect BK and Maynuo. Maybe the OP can shed a bit more light on this?

As far as look go I like Maynuo's load better, the light blue touch is kinda fresh ;-)

Maynuo M9700 specs
BK Precision 8500 Datasheet

Edit: Maynuo actually has a valid CE certificate. I know CE marking doesn't say anything, but at least we know it's not China Export. (This is of yet only for their PSU range though)

[Christe4nM]

To add to the confusion:
This is the Maynuo with Atten brand added. Zooming in on the upperleft corner shows Maynuo's name next to the Atten brand logo.

Does this mean Atten just rebranded this instrument, or that it's Atten quality :-(

[EEVblog]

Guys, I have asked BK Precision and they have responded and cleared this up.

To quote them:

To answer your question: Maynou was found by a former Itech engineer who left the company and took with him the technical documentation of the Itech line, which made it easy for him to copy many products in a very short time. As you may know this is a common practice in China. For the skeptics amongst your readers: Itech has been around since 2004 and this DC loads series was one of their first products. We started selling the 8500 shortly thereafter. Evidence of this can be found here : http://wayback.archive.org/web/*/http://itech.sh
Plug in the Maynuo URL and you can see that they have been around for only 2 years.

And there is more on how they add value to the Itech products, but I'll leave it up to BK to fill you in directly here. Just wanted to clear up the OEM confusion quickly.

Dave.

[FenderBender]

So much incest in this test equipment industry!

[Wartex]

Guys, I have asked BK Precision and they have responded and cleared this up.

To quote them:

To answer your question: Maynou was found by a former Itech engineer who left the company and took with him the technical documentation of the Itech line, which made it easy for him to copy many products in a very short time. As you may know this is a common practice in China. For the skeptics amongst your readers: Itech has been around since 2004 and this DC loads series was one of their first products. We started selling the 8500 shortly thereafter. Evidence of this can be found here : http://wayback.archive.org/web/*/http://itech.sh
Plug in the Maynuo URL and you can see that they have been around for only 2 years.

And there is more on how they add value to the Itech products, but I'll leave it up to BK to fill you in directly here. Just wanted to clear up the OEM confusion quickly.

Dave.

"Joy at MCS" messaged me today, he sells the BK stuff and they told him the same thing. So the ODM is iTech, and BK is a rebrand and Maynuo is a redesign of the original iTech product.

PS: Any chance you can ask them where they copied the BK879 LCR from (honest answer this time hopefully)?

[Bored@Work]

So the ODM is iTech, and BK is a rebrand

BK owns iTech (both BK and iTech say so). So I guess we can forgive them for putting a BK label on an iTech device.

As for the Maynuo story, I don't know if I should laugh or cry. Laugh, because an Asian company stealing technical documentation from another Asian company instead of a Western company. Cry, because yet another Asian company stealing ...

[LaurenceW]

This is an interesting thread for me, as i am in the market for an electronic load. it is for home/hobby use, so my budget is limited, and i cannot stretch to a "genuine" Itech or BK load. The Maynuo range had caught my eye, and they can be had on ebay (for the spec I want - >300V DC rated M9712B) for about GBP£470, landed.

The two products are indeed so incredibly similar, that I am prepared to believe (as BK appear to have confirmed) that the Maynuo is a pretty direct and simple-ish copy, albeit with a more detailed display. Maynuo must have had access to the original microcontroller source code, and recompiled it for a different display. The specs are very similar, so I am now left wondering whether the Maynuo does perform to the quoted spec, or they just copied the spec sheet, too!?

VERY little info about on Maynuo, but I did find this . It seems to exist, and work (not an in-depth test, but prrof the device is out there)

I have looked at cheaper Beich and Array "brands" of electronic loads but I suspect these may be "slower" to react to load changes. Also, markedly poorer (if still not actually poor) accuracy quoted for these.

And yes, Maynuo loads appear in ATTEN variants, too. No doubt about that.

If I do land one (in final negotiations with the Financial Controller at the moment!), I will of course "do a Dave"  - Dahnt turnit on, taykit apairt! (sorry, Dave )

Oh, and I think Joy at MCS would like me to confirm her gender. Definitely a lady of the female persuasion.

[saturation]

Atten makes a look a like too.  Since even the knobs and face are identical, it looks like B&K, if they were the designers, whomever they OEM it too made copies ad lib:

[mianchen]

This is an interesting thread for me, as i am in the market for an electronic load. it is for home/hobby use, so my budget is limited, and i cannot stretch to a "genuine" Itech or BK load. The Maynuo range had caught my eye, and they can be had on ebay (for the spec I want - >300V DC rated M9712B) for about GBP£470, landed.

The two products are indeed so incredibly similar, that I am prepared to believe (as BK appear to have confirmed) that the Maynuo is a pretty direct and simple-ish copy, albeit with a more detailed display. Maynuo must have had access to the original microcontroller source code, and recompiled it for a different display. The specs are very similar, so I am now left wondering whether the Maynuo does perform to the quoted spec, or they just copied the spec sheet, too!?

VERY little info about on Maynuo, but I did find this . It seems to exist, and work (not an in-depth test, but prrof the device is out there)

I have looked at cheaper Beich and Array "brands" of electronic loads but I suspect these may be "slower" to react to load changes. Also, markedly poorer (if still not actually poor) accuracy quoted for these.

And yes, Maynuo loads appear in ATTEN variants, too. No doubt about that.

If I do land one (in final negotiations with the Financial Controller at the moment!), I will of course "do a Dave"  - Dahnt turnit on, taykit apairt! (sorry, Dave )

Oh, and I think Joy at MCS would like me to confirm her gender. Definitely a lady of the female persuasion.

This gentleman has quite a lot of interesting videos...thanks good find

[kmel]

So I'm not sure what's going on here?

After I saw your EEVblog #281 it was clear to me: I need an Electronic Load.
So I did some digging as BK is too pricey for me.
Found Gossen Metrawatt K851A, as pricey as BK, but "Made in Germany"  PAH! Looks like a cheap ATTEN on aliexpress.

So here is what I know so far, datasheets and features are not yet evaluated:

BK Precision
- BK850x: 1 line VFD, carrying handle, front rubber
- owns ITECH

ITECH:
- IT851x: 1 line VFD, carrying handle
- started in year 2005
- ex chief designer: Xiao Tony

ARRAY:
- 371x: 4 button knob, 2 line LCD
- ex chief designer: Xiao Tony

MAYNUO:
- M971x: 2 line VFD, carrying handle, front rubber
- started in year 2009
- owner: Xiao Tony

Gossen Metrawatt:
- K851x: 4 button knob, 2 line LCD
- are from ARRAY, OEM

ATTEN:
- ATZ3710A: 4 button knob, 2 line LCD, is from ARRAY, OEM
- ATZ971x: 2 line VFD, carrying handle, front rubber
- ATZ9712 is from MAYNUO, OEM

REK:
- RK851x: 2 line VFD

BEICH:
- CH871x: 2 line LCD, carrying handle

EASY:
- EEL-660x: 2 line LCD, carrying handle, front rubber

Applent:
- AT851x: 3 line VFD, carrying handle

MCH:
- EL363x: 2 line LCD, carrying handle


I think I will go with MAYNUO, because there is the chief designer now, after ARRAY and ITECH.

--
kmel

[T4P]

So pretty much every 150W/300W 360V common rectangle shape loads were traced to Xiao Tony

Go figure! ... 

[saturation]

Very interesting information kmel.  How do you know Xiao Tony is/was the designer from these companies?  Do you have a reference or a source?   If true, he is a righteous dude, he knows his stuff.

It would makes sense why the Array 8510a and 8511 are decent product yet Amazon reviews for their PSUs, are not as reputable as the e-loads: its not the same person in charge.  The Array 3701a I'm testing is true to its spec sheet and the cheapest available that does basic e-load tests.  Luckily, the quality control hasn't suffered.

Some side issues, Atten also sells Array OEM, ATTEN ATZ3710A.  The Gossen is easier to find if you use the product number, SSL150 and SSL300 for their Array models. 

So here is what I know so far, datasheets and features are not yet evaluated:

BK Precision
- BK850x: 1 line VFD, carrying handle, front rubber
- owns ITECH

ITECH:
- IT851x: 1 line VFD, carrying handle
- started in year 2005
- ex chief designer: Xiao Tony

ARRAY:
- 371x: 4 button knob, 2 line LCD
- ex chief designer: Xiao Tony

MAYNUO:
- M971x: 2 line VFD, carrying handle, front rubber
- started in year 2009
- owner: Xiao Tony

Gossen Metrawatt:
- K851x: 4 button knob, 2 line LCD
- are from ARRAY, OEM

ATTEN:
- ATZ3710A: 4 button knob, 2 line LCD
- ATZ971x: 2 line VFD, carrying handle, front rubber
- ATZ9712 is from MAYNUO, OEM

REK:
- RK851x: 2 line VFD

BEICH:
- CH871x: 2 line LCD, carrying handle

EASY:
- EEL-660x: 2 line LCD, carrying handle, front rubber

Applent:
- AT851x: 3 line VFD, carrying handle

MCH:
- EL363x: 2 line LCD, carrying handle


I think I will go with MAYNUO, because there is the chief designer now, after ARRAY and ITECH.
--
kmel

[kmel]

Very interesting information kmel.  How do you know Xiao Tony is/was the designer from these companies?  Do you have a reference or a source?   If true, he is a righteous dude, he knows his stuff.

I asked info@maynuo.com who the OEM of the M9710 is.
 

Some side issues, Atten also sells Array OEM, ATTEN ATZ3710A.

Thanks, fixed my listing.

BTW the MAYNUO M9710 often sold on ebay/aliexpress isn't for international market, only CHI. I didn't find a distributor who sells it.

--
kmel

[Smoking]

Hi all,

This Jonas from ATTEN.EU and yes I can confirm the Maynuo loads are the same as the ATTEN.
We at ATTEN.EU also sell the ATM8811 power supply's / multimeter's ( end higher models if you like ) these are really nice products.
http://www.atten.eu/index.php/power-supply/atten-atm8811-programmable-power-supply.html

Personally I think you can not get a better a product for that price!

If any one needs some info please contact us : info@atten.eu

[T4P]

Thanks Jonas. Who makes the ATM8811 PSU? OK it's a maynuo

[Smoking]

Thanks Jonas. Who makes the ATM8811 PSU? OK it's a maynuo

Yes it is. ( We are working hard to get the www.maynuo.eu webshop on-line )

But what we also like about these units is there software interface!
I will put some more pictures on the shop later.
If you like more info please email us

[saturation]

This is good news, it suggests to me if you buy Array 3710 or 3711 you are buying one of his earlier works.  I don't know about the most recent 372x series, since he had left by then.

Also, since Itech or BKPrecision are all children of his skills, they should all be good so long as the current management maintain QC as he devised.

From what I see on eBay, the Maynuo or clones cost about the same as BKPrecision in the USA.  As BK is ~ 40 years old, it would make better sense to buy a BK model to get support or warranty, if priced the same and all features being equal.

The big names, Agilent, Chroma, and others, focus far more on modular units but few or no option for small bench units.  It leaves room for Maynuo and others to carve the market for themselves, Xiao is smart to focus here.

The other models listed: RK, Bost, Easy, appears to be Maynuos or copies of it.  Applent & MCH appear different, but the pictures suggest for the same money one can do better even with a Maynuo clone.

I asked info@maynuo.com who the OEM of the M9710 is.
 
BTW the MAYNUO M9710 often sold on ebay/aliexpress isn't for international market, only CHI. I didn't find a distributor who sells it.
--
kmel

[T4P]

To think somebody said the previously unknown engineer who designed the Itech's then "stole" the documents and gone to maynuo
It's just the same designer, it's his right to do whatever he wants

Going on taobao i see the maynuo only costs 400SGD for the 300W model and 256SGD for the 150W model

So BK's 8510 is TRIPLE the maynuo. Go figure
http://www.digikey.com/product-detail/en/8500/BK8500-ND/1135014

[saturation]

That's great T4P, what's the shipping cost to you from China?  Can you post the full taobao link here?

To think somebody said the previously unknown engineer who designed the Itech's then "stole" the documents and gone to maynuo
It's just the same designer, it's his right to do whatever he wants

Going on taobao i see the maynuo only costs 400SGD for the 300W model and 256SGD for the 150W model

So BK's 8510 is TRIPLE the maynuo. Go figure
http://www.digikey.com/product-detail/en/8500/BK8500-ND/1135014

[T4P]

By EMS it's going to cost not much at all.
http://item.taobao.com/item.htm?id=14577117671

Well what i mean by not much is that it only weighs 3.5Kg so my agent charges 7$ for the first 500g and 4$ for the subsequent 500g
So it's 31 dollars. Cheap! Plus it's EMS ...

Anyway ITECH has one these mini loads
http://item.taobao.com/item.htm?spm=2013.1.0.113.55ffca&scm=1007.77.0.0&id=14764899428

[saturation]

You're right T4P, I stand corrected.

As I wrote I checked with a taobao agent, and to the US worst case $100, still makes it cheaper. 

Taobao to me is closer to craigslist than ebay, so there is more risk, but its worth noting on this thread if one is interested in a low price.  I also checked the Array 3710 and 3711 prices versus local US sellers like Tekpowers or CSI, and the savings is between $100-200, but is not as great as getting Maynuo vs BKPrecision depending on shipping.

Have you purchased from taobao before, have you had any problems for delivery to SG?

By EMS it's going to cost not much at all.
http://item.taobao.com/item.htm?id=14577117671

Well what i mean by not much is that it only weighs 3.5Kg so my agent charges 7$ for the first 500g and 4$ for the subsequent 500g
So it's 31 dollars. Cheap! Plus it's EMS ...

Anyway ITECH has one these mini loads
http://item.taobao.com/item.htm?spm=2013.1.0.113.55ffca&scm=1007.77.0.0&id=14764899428

[kmel]

By EMS it's going to cost not much at all.
http://item.taobao.com/item.htm?id=14577117671

Well what i mean by not much is that it only weighs 3.5Kg so my agent charges 7$ for the first 500g and 4$ for the subsequent 500g
So it's 31 dollars. Cheap! Plus it's EMS ...

If you are in an European country you can count on import duties: 20-25% and carrier custom handling charges.

If you like it real cheap: MAYNUO sells them to you if you buy 20.

--
kmel

[T4P]

You're right T4P, I stand corrected.

As I wrote I checked with a taobao agent, and to the US worst case $100, still makes it cheaper. 

Taobao to me is closer to craigslist than ebay, so there is more risk, but its worth noting on this thread if one is interested in a low price.  I also checked the Array 3710 and 3711 prices versus local US sellers like Tekpowers or CSI, and the savings is between $100-200, but is not as great as getting Maynuo vs BKPrecision depending on shipping.

Have you purchased from taobao before, have you had any problems for delivery to SG?

No issues at all, bought a 2kilo item and it came nicely and the second one was a mouse from a not so good dealer (95% rating) and it came with a razer mousepad!

If you are in an European country you can count on import duties: 20-25% and carrier custom handling charges.

Use tbcart. 20-25% won't jack it all the way to 1300$ anyway

Pick one
http://tbcart.com/Product/14577117671/%3CSpan+class%3DH%3Emaynuo+%3C+span%3E+Meier+nuo+M9712+programmable+electronic+loads+300W+0-30A+0-150V+package+postal+discounts/
http://tbcart.com/Product/15094663354/Meier+nuo+%3Cspan+class%3DH%3EMaynuo+%3C+span%3E+M8831+programmable+DC+power+%2830W+0-1A+0-30V%29/
http://tbcart.com/Product/14015175967/Meier+nuo+%3Cspan+class%3DH%3EMaynuo+%3C+span%3E+level+agent+LED+load+M9812+authentic+last/

[kmel]

If you are in an European country you can count on import duties: 20-25% and carrier custom handling charges.

Use tbcart. 20-25% won't jack it all the way to 1300$ anyway

Pick one
http://tbcart.com/Product/14577117671/%3CSpan+class%3DH%3Emaynuo+%3C+span%3E+Meier+nuo+M9712+programmable+electronic+loads+300W+0-30A+0-150V+package+postal+discounts/

Ok... I pick the first one. $437.42 for the item, shipping to their warehouse and their handling fee.

If I pick the same item and seller via taobao.com: CNY 2000 = $322.58 for the item.
Agents handling fee should be about 10% or lower. I don't know the shipping fee to the agents warehouse, but I don't think it is the difference to $437.42. Or am I wrong? Can someone read taobao.com?

--
kmel

[T4P]

Agent fee.

[LaurenceW]

Guys, I got me a Maynuo M9712B 500V 300W electronic load, here in Blighty! Bought off fleabay, got nabbed for some customs fees, but still a good price.

Looking good so far. Some interesting features, some weak points easily fixed, one or two rough edges.  It works. I will do a teardown and review in a week or two.

Currently i have a calibration problem, so this will be a test of customer service, too!

[saturation]

Great to hear.  Looking forward to your review.  I've just about completed a hardware teardown on the Array 3710a, so it would be great to compare the two.

When you add the review, please let us all know how much custom duties added to your cost too.

Curious to see what the differences you found compared to the BK Dave reviewed.

Guys, I got me a Maynuo M9712B 500V 300W electronic load, here in Blighty! Bought off fleabay, got nabbed for some customs fees, but still a good price.

Looking good so far. Some interesting features, some weak points easily fixed, one or two rough edges.  It works. I will do a teardown and review in a week or two.

Currently i have a calibration problem, so this will be a test of customer service, too!

[kmel]

Guys, I got me a Maynuo M9712B 500V 300W electronic load, here in Blighty! Bought off fleabay, got nabbed for some customs fees, but still a good price.

Nice...  didn't you tell me that you didn't pay customs or taxes?

What did you get for the money besides the current load:
manual (engl./chin.), calibration certificate, CD with software,
galvanically insulated USB/RS232 interface cable,  power cord (UK/EU/US/CHI)?

Ordered a M9711 within the EU three days ago. Eagerly waitiing for a tracking ID... No tracking ID arrived, but the M9711 :-)

Currently i have a calibration problem, so this will be a test of customer service, too!

Can you elaborate the problem? I like to be prepared when my unit arrives.
And who is your customer service? Stantronic = MAYNUO distributor UK?

[LaurenceW]

My general experience of customs duties is VERY HIT AND MISS. It depends on where the goods came FROM, who they were carried BY, and what the sender might have DECLARED on the CN22 customs form. And that's just the UK! Other countries no doubt differ. Your mileage WILL vary.

I thought I'd "got away" without alerting the customs' interest, KMEL, but a couple of days after my Maynuo load landed with me, and invoice for GBP£25 followed - that's £15 VAT , and £10 to the carrier for the charge to levy the VAT charge! Charges on charges - great. That's the key, of course, make a deal whereby there is something in it for the carrier, and for sure they will collect your country's taxes from you!

OK - a few words on my Maynuo 300W 500V electronic load so far.

It came well packed and double boxed, with soft, "giving" packaging which will decelerate any delicate electronics to rest over a few mm of travel, so subjecting the items to lower "G" forces. Some firmer packaging (such as expanded polystyrene) I've seen in other instruments does not do this. GOOD
It came with the WRONG manual - FAIL
It came with the WRONG (wong?) Mains lead - FAIL! OK, I've got spares, but surely that is easy enough to get right?
It came with a propriety to USB interface which you need to hook the load up to anything else (GOOD - MAKE SURE you ask your supplier if that's included - it may not be as standard)
It DID NOT come with any PC software on CD - EVEN THOUGH that appeared in the eBay photo! FAIL But at least you can download it.
The PC software is pretty comprehensive, but the screen is probably designed  by a 12-year old who hasn't got a degree in man-machine interfaces - number display is CR@P - mimics 7-segment displays - WWHHAATT??? Should have stuck with a more readable Arial font, instead. NEAR FAIL
There are a number of mistakes in the printed specs - FAIL, but overall the accuracy is good within spec (which is pretty tight). Certainly, specs are 10X tighter than cheaper electronic loads. GOOD
The instrument did include a calibration sheet - Good
There are too many digits on the display! It's like measuring something with a ruler and declaring it to be 251.348mm long. It might be, or it might be 251.5mm long. You cannot tell with the measurement device in question, so the last digits are irrelevant.
The load's accuracy and performance are pretty good, but accuracy goes off at very low currents - below a few mA. You can manually compensate for this, though.
You can apparently adjust the electronic load's current setting, for example, in increments of 10uA, but the smallest incremental change that the load will actually resolve is 50uA. Another example of somewhat pointless resolution.
There are temperature sensitive fans, which vary continuously and smoothly according to the temperature demand - GOOD (not just on/off)
The display features four simultaneous measurements of Voltage, current, power and parameter under load control (voltage, current, power or resistance). Good
 The displayed character size is a little smaller than the ITECH/BK equivalents, as a result. You can get around this with the software app, if necessary.
The instrument is quite DEEP, but when you open it up, you'll see why - big, long heat sinks.
The case is of good quality overall. Standard tilt bail. Nice. Rubber bumper thingy at the front. I can take it or leave it (so can you - it comes off easy enough).
Most annoyingly, they have mounted the number pad buttons the wrong way up! Telephone style 1>9, rather than calculator style. You have to stop and think before keying a value in. Try rearranging your keyboard keys A>Z, and see what that does for your typing - FAIL
PROPER ON/OFF Switch - when it's off, it's off. GOOD
DO NOT RECALIBRATE THIS DEVICE (done through the front panel). I have £$%^&'d up the high current range as a result, and so far cannot get it back. FAIL (on the part of the user???) Waiting to hear from Maynuo...
Internal construction looks OK. It's no Agilent, but it will do. I don't get goosebumps plugging it into the mains... GOOD (enough)
There are no fewer that EIGHT paralleled MOSFETS sharing the load in my Maynuo. They don't look like they'll have a hard time doing their job.
Because the regulating elements are MOSFETS, the resistance of the load cannot go down to Zero. Mine goes down to about 0.25 Ohms
It is CEII marked (whatever that actually means), but the instrument does not carry any specs regarding isolation performance. The input is floating (not connected to earth), but how far away can I take it? 500V? Dunno
The computer interface NEEDS to use an external Propriety USB, 232 or 485 lead. (I've got the USB lead). These leads DO offer electronic isolation from the load - IMPORTANT
There is a rear-mounted BNC socket which carries a voltage proportional to the current flowing. Cheaper electronic loads skip this. This is useful for displaying current transients on a scope - GOOD. But again, Caution - this circuit is not isolated from the device under test.
Also rear-mounted wiring for separate load voltage sensing (to get around voltage drops of long cable at heavy currents) GOOD
Also Trigger inputs/outputs. Again, I've not seen these features on cheaper loads. GOOD
There are some great built-in battery test modes (cheaper electronic loads may skip these)
And the ability to program different currents or whatever at different times/durations, so that you can observe how your supply handles transient load changes. You can also set start up ramps (how quickly the load "comes on") - GOOD. Again, you may find these missing on cheaper loads.
YES, it's the same as the ATTEN, and YES, it is bl00dy similar to the ITECH/BK, but not the same. Probably a direct copy, from the country where the word "Copyright" means: "if you are going to copy something, copy it right"

Yeah - over all, quite happy with my purchase. But with just a little extra polish here and there, and more attention to detail and western standards, they could turn a good product into a GREAT product. C'mon, Maynuo...

[T4P]

"probably" a direct copy, NO!!! It's been said before! It's the same designer! How does a designer copy his own designs?

Anyway, i am placing a wish for the M9712 because of the battery test function, the other ones from Xiao Tony (except BK) do not have this
And ... the RS232 isolating cable is not standard, it's optional and it costs an extra 30USD if i buy it from china ... well

[kmel]

I thought I'd "got away" without alerting the customs' interest, KMEL, but a couple of days after my Maynuo load landed with me, and invoice for GBP£25 followed - that's £15 VAT , and £10 to the carrier for the charge to levy the VAT charge! Charges on charges - great.

That's a bummer! But you should be lucky for the "low" declaration value and no customs duties.

OK - a few words on my Maynuo 300W 500V electronic load so far.
...

Many thanks for you first mini review and for the warnings.

YES, it's the same as the ATTEN, and YES, it is bl00dy similar to the ITECH/BK, but not the same. Probably a direct copy, from the country where the word "Copyright" means: "if you are going to copy something, copy it right"

Check out the reply #17 of this thread, I did a not-point-by-point comparison between them.

[Wartex]

Very interesting information kmel.  How do you know Xiao Tony is/was the designer from these companies?  Do you have a reference or a source?   If true, he is a righteous dude, he knows his stuff.

I asked info@maynuo.com who the OEM of the M9710 is.
 

Some side issues, Atten also sells Array OEM, ATTEN ATZ3710A.

Thanks, fixed my listing.

BTW the MAYNUO M9710 often sold on ebay/aliexpress isn't for international market, only CHI. I didn't find a distributor who sells it.

--
kmel

http://www.select-test.com/ sell them, this is where I played with them

[kmel]

Anyway, i am placing a wish for the M9712 because of the battery test function, the other ones from Xiao Tony (except BK) do not have this

Today the M9711 arrived and the first thing I did was using the battery test function.

Grabbed an used LiPo battery, [I-set] constant current=100mA, [Shift-8] low voltage threshold: 3.3V, [On/Off].
Photo 1 is while the discharge is running.
Photo 2 is shortly after voltage arrived at 3.3V, display shows now the off-load voltage!

[saturation]

I've put a comparison of the 2 PCBs BK vs Maynuo, on kmel's photo post:

https://www.eevblog.com/forum/product-reviews-photos-and-discussion/maynuo-m9711-programmable-dc-electronic-load-photos/msg147455/#msg147455

regardless they are about ~95% identical.  There are some differences.  I'd be more cautious using the Maynuo on DC sources that may have superimposed AC.

Any eload that can plot a discharge curve on their PC software can be used to calculate AH.  While its convenient to have the test as push-button, the discharge curve gives you more information about the battery's overall health, in a simple quick view.  Most of China eloads have low-volt auto off and that can be set to the limit of a battery's working voltage, so the test terminates at that time.  If that function didn't exist, you'd have to manually discontinue the discharge or you'd over discharge the battery.

"probably" a direct copy, NO!!! It's been said before! It's the same designer! How does a designer copy his own designs?

Anyway, i am placing a wish for the M9712 because of the battery test function, the other ones from Xiao Tony (except BK) do not have this
And ... the RS232 isolating cable is not standard, it's optional and it costs an extra 30USD if i buy it from china ... well

[saturation]

That's a good link, a "local" option of Maynuo availability in North America.

http://www.select-test.com/ sell them, this is where I played with them

Overall this sound great in terms of functionality.  Why does it go off on low currents and how do you compensate for it?

Why did you try to calibrate it?  But this is an important test as in order to maintain your eload yourself, one should gauge its requirements to be user serviceable.

The parallel MOSFETS are a must, but its not easy to say if the loads are being distributed to each MOSFET equally.  Over time, if not so, and one or several MOSFETs take the brunt of the work, it will fail more likely that others.

For isolation, check the X-Y capacitors to ground, its roughly its rated max voltage to earth.  You can measure creepage distances of the load traces + and - on the PCB and then the clearance from the chassis, which you'll use to estimate the risk of arc over from the PCB and possibly to earth.

http://www.ce-mag.com/ce-mag.com/archive/01/03/ProductSafety.html

OK - a few words on my Maynuo 300W 500V electronic load so far.

..The load's accuracy and performance are pretty good, but accuracy goes off at very low currents - below a few mA. You can manually compensate for this, though.
DO NOT RECALIBRATE THIS DEVICE ..
Internal construction looks OK. It's no Agilent, but it will do. I don't get goosebumps plugging it into the mains... GOOD (enough)
There are no fewer that EIGHT paralleled MOSFETS sharing the load in my Maynuo. They don't look like they'll have a hard time doing their job.
..It is CEII marked (whatever that actually means), but the instrument does not carry any specs regarding isolation performance. The input is floating (not connected to earth), but how far away can I take it? 500V? Dunno
The computer interface NEEDS to use an external Propriety USB, 232 or 485 lead. (I've got the USB lead). These leads DO offer electronic isolation from the load - IMPORTANT

Yeah - over all, quite happy with my purchase. But with just a little extra polish here and there, and more attention to detail and western standards, they could turn a good product into a GREAT product. C'mon, Maynuo...

[LaurenceW]

It's probably just semantics, T4P, because clearly the heritage of the Maynuo and Itech devices is common. But what I meant was that if we assume that the design belongs to the company which commissioned it (and not the designer), and then said designer goes off to another company and starts building ostensibly the same thing, then I guess he has copied (stolen?) his own handiwork, yes.

The point I really wanted to make was that a B&K may very well be an ITECH,  and an ATTEN  just a Maynuo (same thing, different badge), but a Maynuo device does NOT come from the ITECH production line. it is a copy, rip-off, clone, call it what you will. Hey, welcome to a short lesson in Chinese business ethics and intellectual property rights.

It is interesting to see just how similar the two designs are. Aside from the display, when my own preference would be for the two-line (albeit smaller digit size) display of the Maynuo. Cant see the current output BNC on the back of the ITECH (which i guess was probably an easy add for Maynuo).

And I decided to calibrate it, Saturation, because I could! Or at least, because I thought I could. If it aint broke....   There is a "closed case" calibration routine that can be done from the outside, with a standard power supply and high accuracy volt/amp meters. But the instructions are suspect, and I think this is what has knocked the high current range out.
I'm now going to go away and read up on the ITECH manual, and see if I can learn more about my Maynuo!

[LaurenceW]

OK, a further update from me on my Maynuo M9712B Load.

Bare in mind that these loads come in a series of power, voltage and current ratings, so you need to choose the right one. Mine needs to cope with 500V, 300W and 15A (but not all at the same time!!). So the output devices (in my M9712B model) are 8 mosfets, , IRFPG50. These are good for 1000V and each easily capable of sinking 4Amps without breaking into a sweat. Each Mosfet is separately driven through a dedicated driver IC and Gate series resistor. The design ensures the eight mosfets power share equally and reliably, by each driving into their own 0.2R series resistor. Drawing no more than 2A a device, I am happy that the power side of the Maynuo is conservatively designed. I can't see one device running away with an unfair chunk of the load, and committing suicide in that way.

Found it! In tiny print, in the corner of the board, I read

MN9711-1.7
20110815

That suggests that this board was laid out some 4 years after the ITECH variant. Clearly, a lot is exactly the same, but the processor logic and D/A, A/D stuff has changed a fair bit.

Hmmm- although the load terminals are floating with respect to mains ground, the board Earth connection is indeed mighty close to the negative side of the load- maybe just 2mm of PCB track, and no attempts at isolation slots in the PCB

(Just like the ITECH/BK model) I am not too keen to see AC mains running down the PCB to the mains switch, either. But at least it's routed so that it is fairly hard to touch with a finger.

Other interesting chips - a precision 2.5V reference TI REF5025, putting out 2.5000V, says my high resolution Fluke

A Burr-Brown 16 bit precision DAC DAC8831i, but i can't see any ADCs (a couple of likely suspects, but markings unclear)

An interesting mix of SMD components (some, but not all, ICs some, but not all resistors, smaller caps), but also through hole components (especially close tolerance resistors, transistors, caps and even some DIL IC's!).

Three small relays on board, which appear to select front or rear voltage sensing, and high/low current range (although none of the relays are in the main current path - Good).

Apart from my model being fully populated with twin heat sinks, it is the same as the photos on another thread, so I wont duplicate those.

Regular linear power supply for the circuit - I see +/- 12V, 5V and also about 40V DC for the VFD display. All conventional stuff. No fuse on the PCBs (only a mains input fuse, in the mains socket on the back of the case.

I mentioned a loss of accuracy at very low currents, so I shall explain more.  Let's look at the load operating in its most common CC (Constant Current) mode.

As well as the "set" current (that which you define) there is an "actual" current (that which is really flowing). When the two are the same - in other words, your external supply is able to source the current you demand, then the Maynuo is defined as "regulating", and it displays "CC". If the external power supply cannot deliver the required current, then the two current reading will differ, and the display adds "Unreg" to warn you. All OK so far. However, these two current displays each go to five decimal places ("resolving" to 10uA - allegedly). The two current displays will always tend to differ just a little bit, which is slightly distracting/annoying, but you just have to learn to ignore it.

At currents below 10mA, there is a slight and consistent offset between the set current and that which flows. It is around 0.25mA.  The trick is to use an external meter to set the maximum current. After that, the Maynuo seems to at least stick to the current set in this way.

Maybe it is asking to much of a piece of equipment capable of measuring 300W to also resolve fractions of milliwatts, and certainly the specifications make no claims in this department. But it is as well to be aware of the limitations of any piece of equipment.

[LaurenceW]

A FURTHER UPDATE - and a bit of a GOTCHA - probably a general observation that applies to many electronic loads (Certainly it looks to apply to the Maynuo/ITECH/BK series).

In these types of electronic loads, the load control element is an array of high voltage and/or high current N-Channel MOSFETs all wired in parallel to some degree. This array acts like one giant MOSFET, present straight across the +/- load terminals.  There are no relays or other switches in the main current circuit.

Now, a reverse biassed N-Channel Mosfet is essentially a forward-biased PN semiconductor junction, and will conduct at or around 0.5V when reverse biassed. So even with the electronic load's own power supply switched off, the load terminals present a very low resistance short circuit path (I've measured well under 0.5 Ohm), if reverse biassed.

Here's the message. Don't go plugging a massive power supply across your electronic load the wrong way round - there is a chance you will blow something (either your test equipment or the tested equipment) up, before you've even powered up your electronic load!!

[saturation]

Thanks a ton for this, LaurenceW, its very helpful.  Can you tell us a bit more about the heatsinks?  Its mandatory to distribute load to each MOSFET equally but I think that may be limited by the single large heatsink with the fan only on one end, is this the case?

Cooling may not be even.  The only way to test this is to load the unit enough so the fans are engaged, and check the temperature of both ends of the heatsink, is it equal, how big a thermal gradient exists?

MOSFET internal resistance rise with temperature.  When the fans are engaged, the FET nearest the fan are cooled first, so it takes more share of the load, and the more distant FET will be hotter and will take less of the load.  Also, ambient air enters the front, but hotter air from the cooling front FETs are blown back, so the rear FETs aren't ever the same thermal conditions as the front.

I think the derating the current limits from 8x4=32A of those IRFPG50  [I think its even higher, about 6A per device, thus 8x6 = 48A] to 15A, because the load balancing could be offset by the uneven cooling, but this only becomes apparent when the units are used nearer their specified limits.

OK, a further update from me on my Maynuo M9712B Load.

Bare in mind that these loads come in a series of power, voltage and current ratings, so you need to choose the right one. Mine needs to cope with 500V, 300W and 15A (but not all at the same time!!). So the output devices (in my M9712B model) are 8 mosfets, , IRFPG50. These are good for 1000V and each easily capable of sinking 4Amps without breaking into a sweat. Each Mosfet is separately driven through a dedicated driver IC and Gate series resistor. The design ensures the eight mosfets power share equally and reliably, by each driving into their own 0.2R series resistor. Drawing no more than 2A a device, I am happy that the power side of the Maynuo is conservatively designed. I can't see one device running away with an unfair chunk of the load, and committing suicide in that way.

Found it! In tiny print, in the corner of the board, I read

MN9711-1.7
20110815

If the ground wire looks like the Maynuo photo of kmel, you can simply reroute it to increase the clearances.  As for creepages, if it looks too close one can either avoid using the load in humid climates or cut a track with a dremel. 

..Hmmm- although the load terminals are floating with respect to mains ground, the board Earth connection is indeed mighty close to the negative side of the load- maybe just 2mm of PCB track, and no attempts at isolation slots in the PCB

[saturation]

Good point.  This is a similar issue with the Array 3710a but only if powered on, input polarity reversed.  When powered off, it 500 ohms.  While the 3710a warns and beeps in case of reverse polarity, that its sinking the full load of the DUT should be made a warning sticker on the front of the unit.

A FURTHER UPDATE - and a bit of a GOTCHA - probably a general observation that applies to many electronic loads (Certainly it looks to apply to the Maynuo/ITECH/BK series).

In these types of electronic loads, the load control element is an array of high voltage and/or high current N-Channel MOSFETs all wired in parallel to some degree. This array acts like one giant MOSFET, present straight across the +/- load terminals.  There are no relays or other switches in the main current circuit.

Now, a reverse biassed N-Channel Mosfet is essentially a forward-biased PN semiconductor junction, and will conduct at or around 0.5V when reverse biassed. So even with the electronic load's own power supply switched off, the load terminals present a very low resistance short circuit path (I've measured well under 0.5 Ohm), if reverse biassed.

Here's the message. Don't go plugging a massive power supply across your electronic load the wrong way round - there is a chance you will blow something (either your test equipment or the tested equipment) up, before you've even powered up your electronic load!!

[nctnico]

MOSFET internal resistance rise with temperature.  When the fans are engaged, the FET nearest the fan are cooled first, so it takes more share of the load,

That is a common misconception. MOSFETs also suffer from thermal runaway (negative tempco) when operating in the linear region. Besides that there are large differences between MOSFETs. IOW it is absolutely necessary to balance the load between the MOSFETs.

[LaurenceW]

Well, the heatsink blocks are each comprised two fairly long (roughly 170mm) sections, that are interleaved with one another (take you hands flat, fingers extended, and interleave your fingers - that's the general idea, but with bigger air gaps between your fingers). These are then sealed into a square tube, with a fan bolted squarely to one end, and the other vented out the back of the case. All of the air that the fan draws in must pass down the heatsink tube, and out the back. There are two mosfets bolted onto each vertical side of the heatsink, making four per heatsink block, eight in the instrument (300W rated) overall.

All of the control electronics are both at the cooler (drafty!) end of all of this action, and also hardly putting out any heat themselves (less that 15W), so not under any threat.

I take your point about the devices running nearer the fan being to some degree cooler than the ones further down the heatsink, but to be honest my Mk1 temperature probe (Index finger) cannot detect a heat gradient. And anyway, it never gets uncomfortably hot. Even at 150W per bank, each fan is pushing a good deal of air out of the back, which eventually reaches around 30 degrees C above ambient.  And that's at the hottest end. Obviously, the Mosfet junction temps will be a little higher than this, but not greatly so. So the mosfets are still breezing it. The fans are on a bit of a mission by now, mind. Think: small hair dryer (which the Maynuo rather is, at this point...)

Blocking the air inlets while the Maynuo is at full chat causes the exhaust air temperature to spike! (I have not tested it to the claimed overtemp point). But opening the vents again very quickly causes the air temperature to revert to the previous value - around 53C. With all that air moving about, the rest of the outer case of the Electronic Load remains comfortably cool.

I cannot detect any significant variation or changing voltage drops in the series 0.2R resistors even over several minutes of full load operation. 100vDC at 3 Amps - OH YEAH!  Same results with 37V at around 7A. This suggests to me no shifting of duty between the mosfets, for any reason. I have no view on mosfets' temperature sensitivity, but I see no evidence of any such device behaviour impacting the instrument, overall.

OH! But I've just had a thought. There is a LOT of electronics between the two heatsinks, to do with the Mosfet gate drives. The gates could have all just been joined together, and then connected to the analogue drive voltage. But then, potentially one or more slightly lazier mosfets (with minutely different performance curves) might arguably have led to an uneven load distribution. But there are precision op amps , resistors and diodes scattered about, here, which now leads me to wonder whether this electronics isn't actively watching the individual mosfet current (as a voltage drop across each mosfet's 0.2R series resistor), and doing some load balancing that way. I am not about to do a further tear down and track out the mosfet gate drive electronics. but I could see that theory being the case.

(Electronic) Loads of fun!

[saturation]

Very nice report, LaurenceW it couldn't be more comprehensive.  It sounds like the unit is doing very well for its thermal management, and if you can't detect an imbalance in the drops across those sense resistors nor a temperature gradient then for practical purposes the temps and loads are ~ similar one end of the heatsink to the other.  This is very good news, so much rides on cooling when using eloads.

..I cannot detect any significant variation or changing voltage drops in the series 0.2R resistors even over several minutes of full load operation... electronics isn't actively watching the individual mosfet current (as a voltage drop across each mosfet's 0.2R series resistor), and doing some load balancing that way. I am not about to do a further tear down and track out the mosfet gate drive electronics. but I could see that theory being the case.

(Electronic) Loads of fun!

[saturation]

Hi LaurenceW, and follow up on the calibration issue?

[LaurenceW]

Hi Saturation, Still haven't cracked the calibration issue, no! I have at least had a reply from the Hong Kong retailer- a one line response to my (I thought my very detailed) explanation, and it makes no sense to me! I will try again, but I think I am on my own...

Here is the top and bottom of it.

Although the manual is slightly less than crystal on the subject (!), the Maynuo features two voltage ranges and two current ranges. These are not auto-ranging a-la multimeter. The lower ranges work over small voltages and currents, but give you more resolution. The ranges are

Voltage
LO: 0-20V with Four places of decimals displayed - and I think probably about believable. Given a stable voltage, these figures are stable; no noise or jitter
HI:  0-500V with Two places of decimals. Again, stable

Current
LO 0-3A with 5 decimal places shown, but the last one is iffy at best
HI 0-15A  with four believable decimal places

A relay can be heard to click when selecting between the two current ranges. This relay is not in the current path at all, but may be switching the point on the current shunt from when the voltage (representing the current) is taken - dunno for sure.

The Maynuo features NO adjustable pots inside - good. Instead, the instrument is calibrated from the outside, by a built in calibration routine, which simply requests that you feed the load certain defined voltages and currents.  You are invited to enter two pairs of voltages (which are used to set the hi and lo voltage calibration), and then two pairs of current, (allegedly) to set the hi and lo current calibration. I set all these against my Fluke 289 which I know to be pretty-well spot on, within it's own limits. Actually, the cal routine asks for certain value, like 2.0000V and 20.000, but you can just set your voltage source to something close like 2.0123V, and then key this actual value in. The software then interpolates this. That bit seems to work - nice.

So, I've got the voltage and low current calibration values spot on. But I cannot cal the hi current range. I notice that it is at least consistently wrong, so this evening i am about to do some deliberate "miss-calibration" tests and, like any good lab experiment, write the results down, and have a look.

I think I am looking at a BUG in the calibration routines, but I might be able to work out what current it is asking for, and work backwards...

**

GRR! I've also got a separate problem, in that I now cannot re-establish proper two-way comms with my PC. That's for another day...

[saturation]

Thanks for the update, LaurenceW,  this is the Maynuo's only true visible weakspot.  I took the liberty to research it and can't locate calibration protocols on BKPrecision or Itech either.  It seems to be left out of the manuals or other support literature.

Maybe you can get better luck writing BK?  The register storage format for all 3 items is =~ so maybe asking BK by email will be =~ solution as well?

While the adjustable pots are laborious, they are foolproof, low tech and easy to do with just about any volt or current reference, so I trust the Chinese can do it that well. 

My experience with close case calibration is its better if well done and if flexibility is allowed with calibrators used.   Its a boon if you have automated calibrators, but it can be more work if you're winging it with lab substitutes.

Its impossible to self-cal a Fluke 87V for example, unless you have access to all ranges required and in the proper sequence [ easiest using Fluke's $30,000 calibrator ] and completed.  Agilent 1272a's calibration routine is exactly as written but you can do any range any time and is a joy to self cal using any reference, but an earlier model 1252a doesn't respond as expected: enter 1.000 mA for example and it sets itself as 0.999 mA, that kind of glitch,  and one has to manually offset it by using the delta, e.g. 1.001 mA to get it to register 1.000mA.  Sounds like your problem too.  And yes, the voltage ranges are easier to set and respond as expected.  Even if the reference has some impedance issue, the meter reads the right current, yet, enters it with an offset.  Its a PITA.

However, old pot style Array 3710a, there are 6 pots to adjust, 2x for each range, hi and lo,  then another 2 for meters, and WYSIWYG with the Array.

... , <snip>
A relay can be heard to click ...

The Maynuo features NO adjustable pots inside - good. Instead, the instrument is calibrated from the outside, by a built in calibration routine, which simply requests that you feed the load certain defined voltages and currents.  You are invited to enter two pairs of voltages (which are used to set the hi and lo voltage calibration), and then two pairs of current, (allegedly) to set the hi and lo current calibration. I set all these against my Fluke 289 which I know to be pretty-well spot on, within it's own limits. Actually, the cal routine asks for certain value, like 2.0000V and 20.000, but you can just set your voltage source to something close like 2.0123V, and then key this actual value in. The software then interpolates this. That bit seems to work - nice.

So, I've got the voltage and low current calibration values spot on. But I cannot cal the hi current range. I notice that it is at least consistently wrong, so this evening i am about to do some deliberate "miss-calibration" tests and, like any good lab experiment, write the results down, and have a look.

I think I am looking at a BUG in the calibration routines, but I might be able to work out what current it is asking for, and work backwards...

**

GRR! I've also got a separate problem, in that I now cannot re-establish proper two-way comms with my PC. That's for another day...

[LaurenceW]

Saturation, Looks like just you and me having a private natter on this one... anyway, here is today's update.

The GOOD NEWS is that emails directly to Maynuo are eliciting a response! Not fulsome answers, but just requests to recalibrate this and that (getting quite good at that, now!)

Constant current, power and resistance all works, but setting a constant voltage causes the Maynuo to clamp to about (and a very consistent) 85% of the V-Set value.  Photo shows load with Vset to 10V on a 15V 0.5A max power supply, but the Maynuo clamping this to 8.447V (8.499V says Fluke, but I'll give it the 2mV...)

So much for the Maynuo's "unique feature" over the competition!

We press on...

[robrenz]

Saturation, Looks like just you and me having a private natter on this one... anyway, here is today's update.

Dont you believe it.  I am reading every word.  both of you please keep up the good work.

[saturation]

Thanks LaurenceW, always good to read your reports.  FWIW you have the only detailed review on the Maynuo on the net so once its archived, at least others can read it for posterity.  Often only a few folks ends contributing to a discussion, as eloads aren't a high interest item like DMM or DSOs.  Good to read robrenz here, we had the same issue with the Power Designs supplies, just maybe 2 or 3 discussants but it went a long way.

Great, you're testing their customer support!
Vset is annoying, but if its consistent you could work with it?  i.e., adjust the Vset up past 10 V until the proper voltage shows on the input?

On the side, I presume your test 15V 0.5A PSU is capable of providing the ~7.5W, some less well PSU end up dropping Vout when pulling the rated amps.  You could check out the test PSU first, set the eload to CC, start at 0.1A and adjust up and see if the test PSU voltage stays a stable 15V as you dial up to 0.5A.

Maynuo still plays like a good machine, like any V1.0 it probably has a few firmware issues here and there if the test PSU turns out good.

Saturation, Looks like just you and me having a private natter on this one... anyway, here is today's update.

The GOOD NEWS is that emails directly to Maynuo are eliciting a response! Not fulsome answers, but just requests to recalibrate this and that (getting quite good at that, now!)

Constant current, power and resistance all works, but setting a constant voltage causes the Maynuo to of the V-Set value.  Photo shows load with Vset to 10V on a 15V 0.5A max power supply, but the Maynuo clamping this to 8.447V (8.499V says Fluke, but I'll give it the 2mV...)

So much for the Maynuo's "unique feature" over the competition!

We press on...

[LaurenceW]

Hello Robenz, glad to know are following along! It gets kinda lonely otherwise...

Saturation, you raise a valid point about the "manliness" of my power supply - but rest assured, no concerns with this puppy! see pictures.

It's a TTI Triple programmable power supply PL330TP, good for 2 x 32V @ 3A each, plus 4-6V (i.e usually 5V) DC at 7A. All independently floating with 3200-count volt and amp meters on the main supplies (down to 10mV and 1mA resolution and[/i] good for that). So I can get combinations of up to 70V DC at 3A or 5V DC at 13A! The two main supplies don't automatically track one another (for symmetrical +/- 15V op amp supplies and the like), but I've no real need for that. The supply is remotely programmable via RS232 (I've verified that it works, but I have no pressing need to use it).

This supply is built like the proverbial brick sh!thouse!  I will give folks a tour of it, one day. I bought it as new, but end of line. TTI have moved on to a new range of power supplies now, but from what I have seen the changes are largely cosmetic. This generation of TTI supplies do crop up on FleaBay from time to time, and by and large are a SOUND buy, IMHO. I have no doubt that this piece of gear will outlast me. I couldn't say that for ANY of the other Chinese power supplies I've seen tear-downs of, on this and other sites. This TTI weighs a tonne - Four transformers! FOUR! All linear stuff, massively overspec'd output stages. No fans - no need. Very well behaved. No SMD components, fully documented with circuit diagrams and all.

So, I think it's good enough for the 7.5W, (or up to 96W per Ch), Saturation

(two pics, one of the load set to 2 x 32V and 3A current limit, plus 5V. Other with flash, but short camera exposure time shows misleading display)

ANYWAY - where were we? I set aforementioned power supply to 15V at 0.5A Max, so that I could prove (whether or not) the Maynuo M9712B would securely clamp the supply to a required 10V. Alas, it does not, seeming to think that 8.4V is "good enough". Yes, I can get the load to clamp at 10V by requesting a V-set of 11.91V, but clearly something ain't right...

[saturation]

Thanks LaurenceW, TTi is a righteous supply!  Silly question then too, the V range is calibrated on the Maynuo, I presume?

Otherwise, I can't think of any other issue other than a bug in firmware.

[LaurenceW]

So here is today's instalment of my investigation into my Maynuo M9712B electronic load, and a tiny bit of reverse engineering!

I've been impressed with the way the twin 60mm fans are driven - then only come on when they need to, and then only to the degree required. Being mid-mounted and some way from either the air intake (either side) and the exhaust (rear end) ports, they are reasonably muted, too.

A fellow poster uploaded some pictures of the M97xx series loads, so I refer you to those. Bolted to the centre of one of the heat sinks is a mystery device - an 8 Amp bridge rectifier. Now, this component alone isn't enough to manage the potential full 15 Amp load of the device, and is some way from the Maynuo's own power supply, to have been likely connected with that. What's more, I can find nothing connected to the two AC pins of the bridge rectifier, and the "+" lead is connected to ground - wtf... Very odd... Wait a minute!

Imagine a bridge rectifier symbol, but turn through 90 degrees, cathodes all pointing downwards. "-" at the top, two "AC" connections in the middle, "+" at the bottom (and connected to 0V). You now have two pairs of silicon diodes in series, all in a handy, insulated case, convenient for bolting onto a heat sink.  Now, as all electronic scholars will know (do they still teach this stuff?), a forward biased PN diode will conduct at about 0.6V, but that this drops at around 2.2mv per degree C. So two diodes in series will drop about 1.2V, reducing at about 4.4mV per degree rise in temperature.

And that's just what this rather over-rated component is doing! I can see 1.12V across it at 21C, dropping to 0.9V at 54C (which is as hot as it gets). That goes into a small circuit based on a couple of op-amps, and thence to a TIP41C TO220 NPN power transistor. This controls the current reaching the fan motors from about a 14V power supply.

And there you have it - a simple, analogue controller for the fans. They sit idle at room temperature, but just max out at full RPM after the Maynuo has been sinking 300W for six minutes. I imagine the same circuitry also sends the signal to the processor to disconnect the load, should it reach 80C, but I'm not about to try and force that...

Some more tests at FULL load, and to correct an earlier comment of mine about temperatures. Given the full 300W to sink, the MOSFETS nearest the hot end of the heat sink do get hotter than those nearest the fan, the former each reaching a case temperature of 70C after six minutes from cold, with the fans just at max rpm. Given that the MOSFET specs talk about a maximum temperature at their maximum (in this application) current of about 130C, I think they are well within thermal limits.  Indeed, the whole thermal management system seems to have no difficulty keeping pace with the dissipated heat.


Back to that TIP41C series pass element transistor which controls the fans, for a moment. The whole of the electronics are isolated from the grounded case, so in theory (and practice), neither "end" of the load + or - terminals needs to be referenced (i.e. connected) to earth. The negative lead could be at 100V with respect to earth, and the positive lead at 110V, for example. There must be a limit, here; at some point, something is going to spark over to earth. Earlier comments suggested that a true earth connection on the PCB was too close to the positive terminal (it is certainly more than close enough). But I do now also have minor concerns that the TIP41C transistor is electrically very close to the load's negative connection, but only separated from true earth (the heat sink) by a standard mica washer and nylon bush.  I have not been able to find any "official" figures for the insulation breakdown of standard T0220 insulators, but I don't think I'll be conducting any tests with the M9712B's negative lead more than 200V away from earth.

This isn't really a criticism of the Maynuo - any instrument is going to have limits to its isolation performance. But no claims either way are made for this, in the specifications - you are rather on your own.  Contrast this to my TTI power supply, which clearly states on the front panel "Outputs +/- 300V max to Gnd" So there you have it.


More on components - I notice that the capacitors in the power supply section are all G-Luxon brand. Now, I know that some readers will now be making the sign of the cross! These are not top-drawer, Panasonics or whatever. Does it matter?  But then, neither is anyone's life going to depend on this instrument running without fail for 30 years. The power supply section is linear and quite low-powered, so no nasty SMPS AC currents swishing about that might tax poorer quality caps.  At least they are 105C rated.  I am not going to lose sleep over it, and anyway they will be a piece of cake to replace, should the need ever arise.


One remaining calibration issue to sort, which is very easy to replicate and could well be a software bug. Well, this is Version 3.2, so there must have been 3.1 previous variants...  I don't think the software is going to be field-upgradable, alas I am in communication with Maynuo on this issue, however.

CALLING ANY MAYNUO M97xx series electronic load owners - can you get in touch? I would be interested to know if you can replicate my problem...

[T4P]

Yeah they still will always teach that stuff, but they always miss out the important details like negative temperature coefficiency.

[saturation]

Very nice further analysis LauwrenceW!  Glad to hear these updates.  For reference here's the other eevblog thread with photos:

https://www.eevblog.com/forum/product-reviews-photos-and-discussion/maynuo-m9711-programmable-dc-electronic-load-photos/msg147453/#msg147453


Maynuo's load module.

One concern is albeit the thermal management is adequate, I think it could have been better in order to reduce thermal induced accelerated aging of the load MOSFETs and increased operational reliability.  With a single fan, point A is cooled faster than B, making MOSFETs at C hotter than D; if load management was designed into the firmware or electronics, then MOSFETs at D will take up more of the work as MOSFETs at C are hotter, and have higher Rds.  Since the MOSFETs are over rated, its not a concern, but the load balance isn't equally distributed, particularly when run at its rated power.  In addition, the single thermostat at the center is a bit far from the heat sources, so the MOSFETs rely on thermal conductivity to get their heat to the sensor element, as the arrows show and there is a gap, this gap is even bigger for the MOSFETs on the other side of the heatsink.  Ideally, the fans should have been in the green circles to allow equal air flow, with added vents cut on the top or side of case.

Thermal management is better executed in the Array load modules, IMHO.  The 4 screws are the MOSFETs which are ~ equally spaced from the thermostat, and they put 2 of them instead of just one, maintaining physical equity in distances.  The module is also short, and the fan is literally in the center of rectangular frame formed by the 4 screws.  Then it has another 2 fans, one each in the rear of each module.  I've just finished a run at 130W x 4 hours, fans blowing continuously and like earlier tests, the temperature difference between the MOSFET is in 1-5^oC, that is the framed silvery opening of the heatsink.

Module B tends to run 5^oC warmer than A, as it picks up heat from control boards, F and G.

When the fans are on full continuously, the case interior temps are 10-15^oC warmer than ambient, so far max at 40^oC.  When the fans are off, the linear regulators at F & G peak at 50 and 70[ each, but when the fans kick in they drop to 40^oC and 55C.


Array's load module.

I have to reconfirm on my Array, but the load modules also being a chassis ground has points of concern; its great you pointed that out.

The caps used on Array are Jamicon, not the top rated, but not notorious either.

User kmel from Germany received one not far from yours, may be good to pm him and get an update.  I'm eager to see his opinion.

Bolted to the centre of one of the heat sinks is a mystery device - an 8 Amp bridge rectifier. Now, this component ..
..controls the current reaching the fan motors from about a 14V power supply. ..to disconnect the load, should it reach 80C, ..full 300W to sink, the MOSFETS nearest the hot end of the heat sink do get hotter than those nearest the fan, the former each reaching a case temperature of 70C after six minutes from cold, with the fans just at max rpm. Given that the MOSFET specs talk about a maximum temperature at their maximum (in this application) current of about 130C, I think they are well within thermal limits. 
Back to that TIP41C series pass element transistor which controls the fans, for a TIP41C transistor is electrically very close to the load's negative connection, but only separated from true earth (the heat sink) by a standard mica washer and nylon bush.  I have not been able to find any "official" figures for the insulation breakdown of standard T0220 insulators, but I don't think I'll be conducting any tests with the M9712B's negative lead more than 200V away from earth.any instrument is going to have limits to its isolation performance. But no claims either way are made for this, in the specifications - you are rather on your own.  Contrast this to my TTI power supply, which clearly states on the front panel "Outputs +/- 300V max to Gnd" So there you have it.

More on components - I notice that the capacitors in the power supply section are all G-Luxon brand. Now, I ..At least they are 105C rated.  I am not going to lose sleep over it, and anyway they will be a piece of cake to replace, should the need ever arise.

CALLING ANY MAYNUO M97xx series electronic load owners[/i] - can you get in touch? I would be interested to know if you can replicate my problem...

[LaurenceW]

Hello Saturation, I can't disagree with your comments - indeed we could further point out that, in the 300W model with two heat sinks, one complete set of 4 MOSFETS are not thermally monitored at all!  One possible failure mode, therefore - the failure of the right hand fan on the unmonitored heat sink (where populated).  There is nothing (that I can see) to catch that. A second bridge rectifier bolted to the second heat sink and electrically in parallel with the first bridge would answer that (in that either hot heat sink would then invoke the 80C trip-out of the load). I may add that, in time....

Clearly, the thermal control system assumes that the power is going to be dissipated (reasonably) equally across all devices within a fair degree of margin for any error. That does so far seem to be the case.  The thermal "speed" of the system seems pretty good. I cannot see any overshoot in the case temperature of the MOSFETS, while the rest of thermal detection circuit catches up (due to thermal inertia).

I guess every design is a compromise, somewhere. Maybe in a very hot lab, on a crowded equipment shelf, running flat out for days at a time, the Maynuo might show signs of stress. Maybe. But none of those events will occur in the life of my particular M9712B!

In the Array, are the fans individually controlled by those thermostatic switches, and either on or off? At full chat, can you get it to hover? 

Yes, I had seen KMEL's thread and picture posts, which is why I decided not to bother with any photos - I couldn't really better those.

[saturation]

Hello LaurenceW,

Wowouch, you're right.  That even carries on to the BKPrecision version, unless there is another thermostat elsewhere.

Yes, I think the end purpose matters. In my need for a design the eload should run on rated load indefinitely, ultimately protected by its overheat protection circuitry [ particularly if a fan or a MOSFET should fail while on duty].  Assuming the right load module is under the same thermal constraints as the left load module without monitoring is a bit of a gamble.

Yes, on the Array, each fan has one thermostat, and its on/off.  There are 2 speeds then, call it low and high.  Since the modules are beside each other, there is some cooling cause by the thermal conduction, so the 2 modules aren't mutually exclusive in terms of the fan effects, i.e, the fans are not just additive but synergistic as each is turned on.  You can tell its fully independent because the hotter load module A tends to turn on more than the load module B, and it set for the quieter intake bottom fans first.  Hover would be nice  but as bottom fans are intake, and the rear fans are exhaust, so maybe worse case the Array would fly off the desk towards me. 

Hello Saturation, I can't disagree with your comments - indeed we could further point out that, in the 300W model with two heat sinks, one complete set of 4 MOSFETS are not thermally monitored at all!  One possible failure mode, therefore - the failure of the right hand fan on the unmonitored heat sink (where populated).  There is nothing (that I can see) to catch that. A second bridge rectifier bolted to the second heat sink and electrically in parallel with the first bridge would answer that (in that either hot heat sink would then invoke the 80C trip-out of the load). I may add that, in time....

Clearly, the thermal control system assumes that the power is going to be dissipated (reasonably) equally across all devices within a fair degree of margin for any error. That does so far seem to be the case.  The thermal "speed" of the system seems pretty good. I cannot see any overshoot in the case temperature of the MOSFETS, while the rest of thermal detection circuit catches up (due to thermal inertia).

I guess every design is a compromise, somewhere. Maybe in a very hot lab, on a crowded equipment shelf, running flat out for days at a time, the Maynuo might show signs of stress. Maybe. But none of those events will occur in the life of my particular M9712B!

In the Array, are the by those thermostatic switches, and either on or off? At full chat, can you ? 

Yes, I had seen KMEL's thread and picture posts, which is why I decided not to bother with any photos - I couldn't really better those.

[ivan747]

So pretty much every 150W/300W 360V common rectangle shape loads were traced to Xiao Tony

Go figure! ... 

These are the untold stories behind this industry. I am getting a bit off topic here. I like The Amp Hour because they interview guests with stories as interesting as this.

[T4P]

I would go for the Array but it lacks v-set  And i'm not sure if the 372x would live up to the 371x

[LaurenceW]

Saturation, if the bottom fans on your Array are intakes, that's less of a HOVER and more of a HOOVER then

Buuuuuuuuut seriously, I wonder if we are over-analysing the issue, here? Check back with me in ten years, and I'll let you know if the thing ever blew up...

[robrenz]

All that so called over analysis is what educates all the EE wannabe's like myself.  Please keep it up. 

[saturation]

A hoover? A hidden benefit, it cleans my desk while doing load testing  !

IMHO, teardowns with commentary are the only reasonable methods to estimate a no-name device's quality: to live up to its spec sheet, perform safely, and guess at its working life.  Without a warranty or a reputation, we are on our own, so it would be good to know what we are up against.  Had it been a Kikusui, Agilent or Chroma eload it would be overkill, [ unless it was used and we had to do a bit of upkeep];  it would be more to admire brilliant engineering rather than looking for flaws.

There are more elegant tests available on the Maynuo that would not be easy to add to the Array, but added cooling is easier to implement.  Is the entire analysis overkill?  Not if it raises a concern in the reader to do something about it and if its all theoretical, it would still be more beneficial to an electronics forum than rants about religion and free speech going on on other topics.  If the heat discussion really has one skeptical, removing the top case and pointing a desk fan at it will substantially aid cooling to the Maynuo but its not that simple a fix to add constant voltage to the Arrays functionality.

Saturation, if the bottom fans on your Array are intakes, that's less of a HOVER and more of a HOOVER then
Buuuuuuuuut seriously, I wonder if we are over-analysing the issue, here? Check back with me in ten years, and I'll let you know if the thing ever blew up...

[kmel]

User kmel from Germany received one not far from yours, may be good to pm him and get an update.  I'm eager to see his opinion.

I did Laurences test routine on my MAYNUO M9711, 150W,  firmware v3.1 .
My report resulted to following comment from Laurence: "It sounds to me as though your Maynuo load is working exactly correctly!".

--
kmel

[saturation]

Good to know kmel, and thanks for the reply.  So you do not have the CV setting error and your current range are accurate?

User kmel from Germany received one not far from yours, may be good to pm him and get an update.  I'm eager to see his opinion.

I did Laurences test routine on my MAYNUO M9711, 150W,  firmware v3.1 .
My report resulted to following comment from Laurence: "It sounds to me as though your Maynuo load is working exactly correctly!".

--
kmel

[kmel]

So you do not have the CV setting error and your current range are accurate?

I fed the M9711 with 18V 1A and it ate 15W to regulate the voltage down to 15V if VSET=15V, even in voltage high mode when VMAX=150V. This is what Laurence asked me to do.

[LaurenceW]

Yes, just as Kmel says (though I think you meant "ate 15W").

With my PSU also set to 18V 1A Max, and the load set to a CV of 15V, it pulls the power supply down to the set 15V at 1A when I select the Low Voltage range (up to 20V), but fails to draw ANY current at all when on the High Voltage range. Indeed, on the high voltage setting, I have to lower the CV setting down to 8V, before the load will begin to draw any current at all !  It is still clamping the load (to, say, 12.9V actual when 6V is commanded), and it is a real "hard clamp" too - the actual voltage across the load sticks at a solid 12.9V, for a wide range of currents.

Yet all the while, it is the "commanded" voltage which is being ignored - the actual current through the load and any voltage across it are correctly displayed. So I don't think it's a calibration issue ...

[saturation]

Thanks, LaurenceW  & kmel, could help to email Maynuo this bug so they can get cracking at it.  With their marketing efforts fairly aggressive, my guess is they'll look into it more keenly if if 2 users complain, to suggest it can't be a one-off or user based fault.

http://www.maynuo.com/downloadfile/2012092532905455.pdf

Their latest catalog.

[LaurenceW]

OK, well a happy ending to report - for now.  Maynuo have been back in touch with me. Nowhere was it written in the (probably less than entirely clearly expressed) calibration instructions that it was necessary to calibrate the high voltage range with a >100V DC source, set to around 10mA limit current.  Bizarrely,  on Maynuo's instruction, when I recalibrated the M97 load using this source, it is now correct!  I may rewrite the calibration instructions and send them back to Maynuo.

There is still a question mark over the isolating serial>USB connector which is preventing the PC software from working correctly, so Maynuo are sending me a replacement one to see if that sorts the issue.

So my concluding comments are:
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!

[saturation]

This is great news,  the odds favored a response from Maynuo, given how aggressive they are in getting their name brand out to the world.

I'd rate Maynuo as the go-to eload so long as they are cheaper than Itech or BK.  Why pay more?  But, its issues wouldn't have arisen if it weren't for your diligent work, LauwrenceW.

I wish we could get taobao prices, in the US a Maynuo dealer want the same price as BK and Itech for the equivalent models

I double checked on the isolation issue on the thermal conductive pad for the MOSFETs, the cheapest variant have dielectric breakdowns of 1kV, so it will easily keep it isolated from the heatsink for the rated operating voltage.

You're list of unusual uses for eloads are great.  One could also emulate 'modified sine wave' output with a suitably high DCV then capacitive coupling to the output.


My current uses:
*For use with non-bench supplies such as battery or battery packs, or those missing these functions 
-Provide current limiting.  Likewise, you can test a circuits response with reduced currents, such as when supplied by an aging battery, (but a constant voltage mode would be better to provide voltage regulation instead)
-Testing power projects: put the eload in series, and set a current limit as an "electronic fuse"
*Characterizing salvaged supplies
*cycling NiMH battery packs
*Battery AH ratings
*Testing high power fuses [ I don't have a 20-30A lab source, but with a car battery I can provide up to 40A regulated by the eload]

[robrenz]

Thanks all for an excellent thread.  I learned a lot in the process and now know what eload I would buy plus what negatives to be aware of and other usefull things to do with it.

[LaurenceW]

I have another way of testing high power fuses -

POP! Yep, that one was good,
POP! Yep, that one was good,
POP! Yep, that one was good,
(silence) Nah! this one's duff!

[saturation]

You're very welcome, but a lot to LaurenceW for doing the heavy tests.  One thing I checked was, what about eBay second hand or old eloads?  Aren't they cheaper?  Unfortunately, the Chinese variant is actually akin to Rigol to low cost oscilloscopes, they created a new niche that didn't exists prior to the Arrays and Maynuo.

Many big name eloads for sale today are customized for power electronic markets or modules for racks.  Way out of the price range for small labs, IMHO.

Older eloads, e.g. 1980s style Transistor  Devices now TDI Power maker of Dynaload, are not as flexible or have crude progammability, not much better than a power resistor or a light bulb with built in voltmeters and ammeters.  Its one reason I never owned one until now.  Second hand 1990s era from Kikusui, Kenwood etc., are superb, but cost more than a new Chinese eload; there also maybe some unobtanium inside.  Also, power devices 'wear out', so although superbly made if they were heavily used by the prior owner, the main power MOSFETs could fail anytime.  New Kikusui begin at $2,000, so eBay units at $500 or so are a steal, but still higher than a new Chinese model.

Thanks all for an excellent thread.  I learned a lot in the process and now know what eload I would buy plus what negatives to be aware of and other usefull things to do with it.

[saturation]

Yes, I did the same for a long time, until I ran into counterfeit fuses.  These can be very very bad, they do not blow are the right amperes.  Its mostly for DC electronics: automotive and glass fuse types.  Unless its a recognized brand like in the US: Littelfuse or Bussman, I sacrificed a few in a box to cross check them.  If you buy in bulk it costs the same as buying just a box of 5, ~ $5, so bulk buying is cheaper.  But counterfeit is a bit out of hand in the USA. 

I have another way of testing high power fuses -

POP! Yep, that one was good,
POP! Yep, that one was good,
POP! Yep, that one was good,
(silence) Nah! this one's duff!

[T4P]

Hmm ... how about using the mains to test fuses 

[tom66]

Hmm ... how about using the mains to test fuses 

Or a small 5kV, 138uF capacitor.
Big Capacitor Safety
(I can't find the exact vid, but in one of them he showed the capacitor he had could discharge in excess of 80kA, as it shattered an 80kA (interrupt current) industrial HRC fuse.)

[saturation]

I cannot control mains current, I don't have an AC eload.  Recall, the voltage rating of a fuse is just the tested maximum arc potential between the severed pieces of the fuse conductor.  The amperage is purely current, regardless of voltage. 

What a test needs is a capacity to set current precisely, and monitor when fuse break occurs.  For current test, you need any current source, the voltage is not material.  For arc rating you'll need the rated voltage and current; most auto fuses I can do, but glass type fuses are often mains rated.

Before I got my eload, I simply used a bench power supply with adjustable current limiting.  Put a fuse between inputs; add a Fluke 87v in series on current with min-max mode enabled; the max mode would then record the break current as backup to the bench supply reading.  However, many bench supplies have short circuit protection and require some load, so then I add a power resistor in the loop.  I takes about 15 minutes to set up or longer, and I ran out of time to keep doing it.  With an eload its down to under 5 min.

A car battery can test all fuses up to 30A, the limit of my Array.  However, I just salvaged an old PC supply, and I think I can rig this up as a source of high current, low voltage.

Hmm ... how about using the mains to test fuses 

Or a small 5kV, 138uF capacitor.
Big Capacitor Safety
(I can't find the exact vid, but in one of them he showed the capacitor he had could discharge in excess of 80kA, as it shattered an 80kA (interrupt current) industrial HRC fuse.)

[saturation]

Fake fuses issues, here with fuse holder imbedded in socket subject to rated overload:




Counterfeit HRC fuse, also on observation the fusible wire gauge of the counterfeit one is a bit large and is improperly mounted, it should be set in apex of the fuse tip housing, not on the side:




Unlike fake electronic components, when it gets to DC power and main power electronics, counterfeit items can cause substantial havoc including personal injury.  I have circuit breakers mostly in AC mains, so fusing is not an issue, but in DC, most are fuses.

I found 2x improper fuses in auto accessories, either wrong value or improperly labeled break current ratings.  One caused a meltdown in the accessory socket saved only because of my car fuses.  Although you can buy name brand fuses from some reputable distributor like Amazon, PepBoys, Walmart, Radio Shack etc., you can't be sure who is legitimate in their supply chain.   As this has happened to me 2x, being able to test the fuses now became mandatory, but the time it was taking was more than I could spare.  The eload made it possible.

[poorchava]

Kikusui eloads cost a pile of dollars, but some of them have some serious flaws as well. We have one of them at work: it consists of central module and 3 power modules. And guess what: if you connect 3 of those in parallel (it's automotive, currents are high....) they cannot get along with each other and whole thing starts to oscillate as hell... Not the best way to spend like $8k.

[saturation]

Do they oscillate simply put together or under load?  For the money you spent you can get service under warranty as oscillation while quiescent means something is wrong, recall power products like eloads can fail from just usage so its best if a design never runs hot, and runs near room temperature under load always.  However, if under load, that is a phenomena associated with any good eload.  When instantaneous current is high enough, the cables will have inductive and resistive effects causing V and I to be out of phase, and when the eload attempts to compensate, it will oscillate.  The solution is to reduce the eload slew rate down until oscillations cease, and thus was born variable slew rate options in eloads, or for cheapies like the Array 3710a, put 1000uF capacitor [ rated for voltage], across the input of the eload.   

[poorchava]

Yeah, they oscillate under load. In that particular situation current wasn high at all (something like 1A IIRC) but we wanted to check something quickly and the parallel setup was already there

[videobruce]

Commenting on the posts on the 1st page;
I didn't see anyone add Sencore to the list of 'farming out' their products and claiming they were their design. 

I will never buy a B&K product again and I'm not very impressed with Sencore either. Actually never was.

[saturation]

I think it better to buy whomever provides a bang for buck, brands aren't  useless, but its not the best rubric to gauge their products by.

Things change: as of now, Rigol's star is rising, Teks is slowly falling, and LeCroy has taken a tailspin.  Agilent has, IMHO, maintained a stellar reputation, but its not the Bill and Dave's HP, but its better than no HP at all [The new HP by the way, is a fading star too].  Now, all that is not because of the brand name, but by weighing the quality of each product they produced as I or others who tell me, have encountered over the past decades and see how each fairs.

I like Sencore's PR57, its a model that's  fairly popular even today on eBay, never get's a price lower than $200, for something so low tech.  Today's Sencore is niched in the video industry, no longer in broad based cheapo T&M, and its one of the few companies that makes electronics in the USA.

http://en.wikipedia.org/wiki/Sencore

I admire both BK and Sencore for surviving for so long, they clearly exploit their niches; but I don't own any of their products as its niche, isn't mine; but it doesn't make them a dufus.
 
On the topic of this eload, you'll find its OEM is a company BK owns, so technically its not an OEM.  However, the device itself is a unique design, and what  clones exist so far are traceable to the OEM, Itech; its biggest clone maker is supposedly an ex-engineer who has struck out on his own,  Maynuo. 

Alas, one issue is the price of a Maynuo in the USA is the same price as the BK model, whereas if bought in China itself by taobao.com, and caveat emptor too, its far far  cheaper.

Commenting on the posts on the 1st page;
I didn't see anyone add Sencore to the list of 'farming out' their products and claiming they were their design. 

I will never buy a B&K product again and I'm not very impressed with Sencore either. Actually never was.

[darciop76]

Hi folks!

   You guys have done a terrific job in characterizing and describing the Maynuo DC e-Loads. I've bought last week a Maynuo M9712C (300W, 150 V, 60 A) and it's doing fine, even though I haven't put it to hard work yet. I did notice that the software available at maynuo.com is only cosmetically different from the software available from BK Precision website (850x series). I think this suggests that both softwares are interchangeable between the two suppliers. I still have to check this because I don't have the comm adapter yet but what are your guesses?

Are the protocols and commands the same for both manufacturers allowing to use BK Precision software with a Maynuo unit for instance?

[metalphreak]

darciop76: I have a M9712C coming with the data cable soon. I will see if the BK software works with it as well. However, after installing both and having a look, they're basically the same anyway. Maynuo list all the commands and registers in their manual. It uses a serial modbus protocol which shouldn't be hard to interface with. I'm looking at using python and QT gui framework to see if I can come up with a better interface.

[darciop76]

Good, metalphreak! I got a bluetooth module that I'll use to interface the DC load to the PC. Lets see how they will perform!

[metalphreak]

Arrived today Check out the huge voltage drop on my crap cheap test leads. I have a bunch of silicone cable that just arrived from the UK to made up some proper leads.

Actually comes with a calibration sheet which is quite nice. Not the same as a calibration certificate, but for this level of kit it's quite good.



Will do some vids/pictures later and maybe a small teardown. For now, it's time to play


Edit: Got mine from workshopequipments on ebay: http://stores.ebay.com.au/workshopequipments

I sent him questions twice. In both cases, I got a response within 5 mins! Australia is in the same timezone but <5mins is impressive service by any means. Also, it did come with the USB to Serial cable which is quite important (that was the first question).

[darciop76]

...Check out the huge voltage drop on my crap cheap test leads.

I have a bunch of silicone cable that just arrived from the UK to made up some proper leads.

Good point, metalphreak! You must use good cables and connectors when operating a DC load or the drop along the lines will be considerable!

[robrenz]

Good place to use the remote sense leads of your powersupply if it has them. That will eliminate the voltage drop of the leads carrying the current.

[metalphreak]

Neither of my power supplies have remote sense. The Maynuo does though. Since it's operating as a load anyway, in most cases some loss in the cables is a moot point as long as you get the remote sense voltage from the source  Need to read the manual to see if there's an easier way to switch between local and remote sense. Going through the menu system is alright, but it's a quite a few button presses. PC software lets you switch it quickly.

By the way, the BK Precision software doesn't work with it. It comes up with "Model Error" so the app does some checking. The commands look the same though from a quick read through the manuals. The Maynuo software is *exactly* the same, but with a less fugly theme to it. The maynuo software also picks up that mine is the M9712C model. If I do end up writing some software, I will look into it more. Perhaps Dave could test it out with his BK then.

[saturation]

You could also simply double up on the connect cables and reduce the IR drop by half.  When doing PSU or battery testing it would help to make a custom cable of very large diameter wire, if you don't have remote sense. 

[robrenz]

Won't the load remote sense leads acomplish the same thing?  They would attach to the output jacks of the power supply preferably with fork or ring terminals directly on the binding post face not stacked bananas.

[saturation]

Yes, its best to have remote sensing on the e-load to insure the e-load calculations are based on the output of the DUT, it won't consider losses on the cables; but you'd still want to minimize cable losses.  Also, when using higher current, cable size, length and layout will begin to show inductance too, and could cause the e-load to oscillate; best to keep the AWG small [ i.e., large diameter wires], cables short and straight. 

Won't the load remote sense leads acomplish the same thing?  They would attach to the output jacks of the power supply preferably with fork or ring terminals directly on the binding post face not stacked bananas.

[metalphreak]

It all depends on what you are trying to achieve.

Without any remote sense - this gives you the total voltage, current, and thus power at the ends of the leads. Perfect if you are testing to see if a supply has adequate capacity to power a product.

With DC Load remote sense - this gives you the total load on the power source including cable losses. This would be DC Load + Cable Losses. Since this is testing the power source's output, the cable losses really do not matter as long as they are accounted for (which is where the DC Load remote sense comes in). Without remote sense, the DC load will tell you the supply is giving less watts than it actually is.

Power Supply Remote Sense - not sure how this helps at all. The power supply will compensate for the voltage drop, so the DC load will see the correct set voltage, but then the supply is putting out a higher voltage to cover the cable losses which the DC load still isn't taking into account for its measurements.


I was testing some old mobile phone chargers this morning. This LG one does 5.1V 700mAh output. Interestingly, despite increasing the current, the voltage remained very stable (there was no remote sensing done here). The wire is pretty thin so the charger must be designed to compensate (the engineer would know the cable type/length would remain constant). After abotu 830mAh the voltage and current drops completely. This would be the overcurrent protection kicking in. It restarts every second to check if the "fault" has cleared. The fun is going to begin once I get out the cheap chinese knock-off power sources   


The Maynuo DC Load also has a "short circuit" test mode which does exactly as it says. Let's just say the Overcurrent/Overtemp features of the AM1117 voltage regulator didn't stop it going pop

[eevblogfan]

hey

it's fairly easy to upgread the power supply to have remote sense , if you'd like please PM me and I'll show you

[metalphreak]

Testing a turnigy nano-tech 3S 1000mAh lipo @ 10A. Total capacity 990mAh. Usually ratings are done at 1C discharge as well not 10C like I did. Saving the image with the maynuo software doesn't show any of the values at the bottom of the graph which is annoying (just title and the line colour legend). The one above is a screenshot instead. You can export the dataset to Excel which works ok. Exporting to Word just spawned a winword.exe process that did not much besides chew some CPU time.

There is a capacitor test function shown in the battery test software page. Haven't had a look at that yet. I think it may be time to start my own thread and do a write up once I've tried out all the features


The best thing about these is the ability to remote control them. The commands are fairly basic 26byte serial packets. Imagine one of these combined with a programmable power supply. You could automate testing of Linear/Switchmode designs by doing a whole bunch of test measurements at different load levels, input voltage, output voltage etc.

[HKJ]

The best thing about these is the ability to remote control
them.

That is a very useful feature, I have using two of these load to mostly test batteries with, they have been running 24/7 for about a year with computer control. The computer does also  control a power supply and a relay box to control charging.

[gerrysweeney]

I all, I noticed this topic and have recently done a full video teardown of the Maynuo M9711 DC Electronic Load so you can see whats inside.

http://gerrysweeney.com/maynuo-m9711-dc-electronic-load-unboxing-teardown-and-quick-test/

Gerry

[darciop76]

Great review Gerry!

[saturation]

+1  Great way to contrast against Dave's BK 8500 review.

There is a review of the Maynuo elsewhere on eevblog with input from LawrenceW and myself.  One thing I'd like to see with your feedback later is not that it performs what it does which you showed, but that the unit doesn't fail after prolonged use at near or max load, ~ 150W.

[Salas]

I all, I noticed this topic and have recently done a full video teardown of the Maynuo M9711 DC Electronic Load so you can see whats inside.

http://gerrysweeney.com/maynuo-m9711-dc-electronic-load-unboxing-teardown-and-quick-test/

Gerry

Nice report. Sounding like a BBC pro presenter at times.

[Electro Fan]

I'm very late to this thread but two comments:  I think BK is an A-ok company.  They make good gear, they have lots of good distributors/resellers in their channels (customers can pick from a good variety of sellers), and they will definitely answer their phone and give you prompt, couterous, and knowledgable personal service.

Having said that, whether it's the 8500 or one of it's ancestors, recent predecessors, off-spring, other relatives or acquainteances somewhere in the world, or just a member of it's peer group from who knows where in the competitive landscape I'm of the opinion that the 8500 is a great electronic load and that electronic loads are one of the coolest and most useful pieces of test equipments you could have on your bench. 

We could start another thread on this (or just do it here), but if I were assembling a few key pieces of gear to help learn and develop basic electronics skills and headed toward the basic electricity/analog realm and the digital realm, I'd go with:

PC with access to the Internet
DMM
oscilloscope (preferrably mixed signal with Logic Analyzer)
power supply (prefferably programmable)
electronic load (preferrably programmable)
signal generator
soldering iron

Maybe in that order - although I'm sure it depends heavily on what you are trying to build, fix, learn, and I'm probably forgetting something(s).

Althlough I don't have one (yet), that 8500 sure looks like a very useful device for making sure you are on top of Ohm's Law and more.  And just because someone might have gotten a bee in their bonet about BK at some point, I don't think we want BK to disappear; I don't think that would do anyone any good.  Healthy choices for EE-land are better than limited choices.

PS, thanks to LaurenceW, saturation, and everyone else on this thread for all the good info!

[Mike Warren]

I received a REK RK8511 yesterday. First thing I did was test it at 150W. After about 5 minutes it shut off due to thermal overload. On inspection, I discovered that the fan was barely running.

I modified the fan control circuit by changing R31 from 10K to 4.7K. My guess is that the fan fitted to this unit draws slightly more current than the one the circuit is designed for. The drive for the fan is simply a TIP41 to ground, controlled by a LM324 and the bridge rectifier. A very simple idea, and effective as long as components aren't substituted, but not how I would do it. A different fan would change it's operating parameters significantly.

After running it for an hour at 150W it was still working fine and the heatsink temperature was stable.

This is obviously basically the same design as the BK Precision and Maynuo, but there have been some corners cut. The heatsink is just held off the case by a couple of spacers instead of being screwed down and the most serious thing is that there is no stand-off near the power switch. This causes the PCB to flex badly every time it's turned on or off.

Mine now has a stand off fitted.

[gerrysweeney]

I all, I noticed this topic and have recently done a full video teardown of the Maynuo M9711 DC Electronic Load so you can see whats inside.

http://gerrysweeney.com/maynuo-m9711-dc-electronic-load-unboxing-teardown-and-quick-test/

Gerry

Nice report. Sounding like a BBC pro presenter at times.

Thanks, thats nice of you to say...I need much more practice

[Electro Fan]

I'm thinking about acquiring a Maynuo M9712 - I have hunch it would be a very cool testing/teaching/learning tool.
 
I'm using a 30V 5A DC power supply with over voltage and over current protection.  I'm just doing simple Arduino stuff, teaching myself some basic electronics, etc. Seems like 300 watts, 150 volts, and 30 amps on the M9712 should keep me out of trouble but are there any "uses cases" or likely/typical combinations of settings that anyone can think of that would potentially cause a user (me) to exceed the specs of the M9712 and cause any damage or danger?

It isn't clear what the maximum resistance is that the M9712 will support; the spec sheet references 5K and 10K ohms, but I don't know if either of those are the max.  Anyone know?

Seems like watts are always something to keep an eye on if you don't want to cook a resistor, but at 300 watts it seems like there should be some head room.   

When one or more of the specs on the M9712 are exceeded does the unit gracefully protect itself and any attached devices?

I'm trying to create a safe test environment but I don't want to get too trusting, so anything you've learned to avoid given all the experience you EEVers bring would be appreciated.  Just trying to stay on the lookout for personal and equipment safety.  Thanks