Author Topic: Why is BK Precision still in business? BK8500 programmable load OEM found  (Read 57661 times)

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Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #75 on: October 10, 2012, 07:18:40 pm »
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]
« Last Edit: October 10, 2012, 07:28:48 pm by saturation »
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Offline robrenz

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #76 on: October 10, 2012, 07:27:57 pm »
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.

Offline LaurenceW

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #77 on: October 10, 2012, 07:30:01 pm »
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!

:)
If you don't measure, you don't get.
 

Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #78 on: October 10, 2012, 07:39:34 pm »
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.
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 Saturation
 

Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #79 on: October 10, 2012, 07:44:23 pm »
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!

:)
Best Wishes,

 Saturation
 

Offline T4P

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #80 on: October 12, 2012, 11:47:14 am »
Hmm ... how about using the mains to test fuses  :P
 

Offline tom66

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #81 on: October 12, 2012, 12:35:18 pm »
Hmm ... how about using the mains to test fuses  :P

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.)
 

Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #82 on: October 12, 2012, 02:25:23 pm »
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  :P

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.)
« Last Edit: October 12, 2012, 02:37:25 pm by saturation »
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Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #83 on: October 12, 2012, 03:19:00 pm »
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.




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 Saturation
 

Offline poorchava

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #84 on: October 15, 2012, 10:57:55 am »
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.
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Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #85 on: October 15, 2012, 04:44:24 pm »
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.   
« Last Edit: October 15, 2012, 04:46:41 pm by saturation »
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Offline poorchava

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #86 on: October 16, 2012, 11:02:20 am »
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 :)
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Offline videobruce

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #87 on: December 19, 2012, 02:04:53 pm »
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.  :-DD

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

Offline saturation

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #88 on: December 19, 2012, 03:10:26 pm »
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.  :-DD

I will never buy a B&K product again and I'm not very impressed with Sencore either. Actually never was.
« Last Edit: December 19, 2012, 06:33:41 pm by saturation »
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darciop76

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Re: Why is BK Precision still in business? BK8500 programmable load OEM found
« Reply #89 on: February 18, 2013, 02:50:30 pm »
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?
 

Offline metalphreak

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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.

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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!
 

Offline metalphreak

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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 :D


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).
« Last Edit: April 12, 2013, 01:07:29 pm by metalphreak »
 

darciop76

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...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!
 

Offline robrenz

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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.

Offline metalphreak

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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.

Offline saturation

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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. 
« Last Edit: April 12, 2013, 09:06:48 pm by saturation »
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Offline robrenz

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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.

Offline saturation

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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.
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Offline metalphreak

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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  :scared: 


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 :)
« Last Edit: April 13, 2013, 08:43:18 am by metalphreak »
 


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