Author Topic: B&K Precision BK8514 electronic load 1200W 120V 240A teardown  (Read 8710 times)

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Offline TopLoserTopic starter

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This big heavy thing doesn't seem to want to be sold so i thought I'd open it up and see what's lurking inside. Good time to check that there is no obvious sign of magic smoke contamination!

It's 20Kg of mostly aluminium heatsinks. Inside there are 4 big heatsink modules that upon closer inspection turn out to be 8 cleverly interleaved modules. Each module has 4 big IRFP250N MOSFETS (214W, 200V 30A rating) plus some control stuff. It all seems to be nicely put together, very serviceable. They've scratched the part number off the micro but everything else seems easily available if you needed to repair it.

























« Last Edit: July 23, 2015, 08:06:08 am by TopLoser »
 

Offline bingo600

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #1 on: July 22, 2015, 05:13:14 pm »
That's some serious dimensioned electronics.

Thanx Ian for the insight.

/Bingo
 

Offline lukier

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #2 on: July 22, 2015, 06:35:21 pm »
Very interesting stuff. Rescaled BK/Maynuo/Itech load it seems :)

I'm thinking about building my own load, I got these nice big heatsinks (300x100mm) from Ian some time ago, I have a bunch of IRFP250N from eBay and I'm mostly inspired by Agilent 6060 schematics.

My question is: what is correct current sense topology. Agilent 6060 model has separate control loop and current sense resistor per MOSFET and these current sense signals from multiple MOSFETs go into a summing amplifier to produce +IMON signal. In BK/Maynuo/Itech loads they have these loops of chunky metal wire (nichrome?) at the input and that's where they seem to get their total current measurement. What are the advantages of this method?
 

Offline TopLoserTopic starter

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #3 on: July 22, 2015, 06:54:40 pm »
Yes but each of the 16 channels on this load have their own current sense resistor as well. Each channel must regulate its 1/16 share and then the big loops at the end measure total current.
 

Offline dom0

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #4 on: July 22, 2015, 11:23:32 pm »
Interesting. I would've expected more and more closely spaced, thinner fins on these fan/cooling aggregates. These seem rather few in number and relatively thick to me ... although they have these ... how do you call them? serrations?
,
 

Offline TopLoserTopic starter

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #5 on: July 22, 2015, 11:33:47 pm »
Lots of surface area on the heatsinks due to the serrated finish, makes the forced cooling a little easier..

Might hook up a car battery to it tomorrow and stress it a bit!
 

Offline Kjelt

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #6 on: July 23, 2015, 06:45:16 am »
Each module has 2 big IRFP250N MOSFETS (214W, 200V 30A rating) plus some control stuff.
But the PCB clearly states MOSTET  lol  :)
Thanks for the tear down, very nicely put together and modulair so they can use it for all different configurations.
For the DIY freak, replace the IRFP250 with the newer IRFP260 which can handle 49Amps and you have an extra safetymargin  8)
« Last Edit: July 23, 2015, 06:47:38 am by Kjelt »
 

Online nctnico

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #7 on: July 23, 2015, 07:11:50 am »
I don't like the copper(?) wire they soldered onto the board. Too much can go wrong in production with such a solution. A busbar would have been better.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline krish2487

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #8 on: July 23, 2015, 07:31:25 am »
Tinned copper wire it would seem..
I agree it serves little purpose other than to look impressive.


@toploser
I count 4 x IRFP250 + 1 x TO-220 (voltage regulator maybe) per pcb module
and 2 such pcb modules interleaved to form a heatsink wind tunnel.
and 4 such interleaved heatsink modules in total.


That would make it 32 devices in total wouldnt it??
I only ask because in another thread, theMG user has calculated 37.5 watts dissipation per device - which is consistent if it is 32 devices and not 16.
16 devices would make it 75 watts per device (which while on the higher side, would still be manageable)

If god made us in his image,
and we are this stupid
then....
 

Offline TopLoserTopic starter

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #9 on: July 23, 2015, 08:05:49 am »
Tinned copper wire it would seem..
I agree it serves little purpose other than to look impressive.


@toploser
I count 4 x IRFP250 + 1 x TO-220 (voltage regulator maybe) per pcb module
and 2 such pcb modules interleaved to form a heatsink wind tunnel.
and 4 such interleaved heatsink modules in total.


That would make it 32 devices in total wouldnt it??
I only ask because in another thread, theMG user has calculated 37.5 watts dissipation per device - which is consistent if it is 32 devices and not 16.
16 devices would make it 75 watts per device (which while on the higher side, would still be manageable)

oops yes, 4 MOSFETS per module, total of 32. Original post amended now, thank you.
 

Online nctnico

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #10 on: July 23, 2015, 08:31:18 am »
This big heavy thing doesn't seem to want to be sold
Perhaps people know it's a rebranded Maynuo. This one looks exactly the same:
http://www.ebay.com/itm/Maynuo-M9714-USB-Programmable-DC-Electronic-Load-0-240A-0-150V-1200W-CC-CR-CV-CW-/111680125121
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline TopLoserTopic starter

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #11 on: July 23, 2015, 08:57:56 am »
This big heavy thing doesn't seem to want to be sold
Perhaps people know it's a rebranded Maynuo. This one looks exactly the same:
http://www.ebay.com/itm/Maynuo-M9714-USB-Programmable-DC-Electronic-Load-0-240A-0-150V-1200W-CC-CR-CV-CW-/111680125121

Good point, I reduced the price down to £850.
« Last Edit: July 23, 2015, 09:00:25 am by TopLoser »
 

Offline HighVoltage

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #12 on: July 23, 2015, 09:06:23 am »
Perhaps people know it's a rebranded Maynuo. This one looks exactly the same:
I come to the understanding, that all BKP DC loads are made by the same guy that started Maynuo, including the brand new and revised 8600 series. No surprise.
There are 3 kinds of people in this world, those who can count and those who can not.
 

Offline lukier

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #13 on: July 23, 2015, 12:47:15 pm »
For the DIY freak, replace the IRFP250 with the newer IRFP260 which can handle 49Amps and you have an extra safetymargin  8)

Well, even at TopLoser bargin prices 850 GBP is way too much for a PhD student, especially for pretty much a bunch of MOSFETs and heatsinks :) (even small 300W DC loads are around >300 GBP, you can buy a scope, a lot more complex instrument, with that kind of cash).
That's why I want to build my own and I have a lot of parts already (ADS1256 ADC, 16 bit DAC, big heatsinks, OP27s, AD8628s, everything either second hand or Aliexpress/eBay). Thanks for the tip with IRFP260, I've checked and they can be had cheaply at Aliexpress so I might consider using them instead.
 

Offline Pinkus

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #14 on: July 24, 2015, 09:03:08 am »
Quote
Thanks for the tip with IRFP260, I've checked and they can be had cheaply at Aliexpress so I might consider using them instead.
Caution: The genuine IRFP260 will allow this nice high current/voltage. You never know if cheap ones on Ebay or Aliexpress are fakes and if they will release lots of magic  smoke when stressed. I would always purchase critical parts (and these are the most critical parts in you application) at well known, reliable distributors.
 

Offline lukier

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #15 on: July 24, 2015, 09:22:19 am »
Caution: The genuine IRFP260 will allow this nice high current/voltage. You never know if cheap ones on Ebay or Aliexpress are fakes and if they will release lots of magic  smoke when stressed. I would always purchase critical parts (and these are the most critical parts in you application) at well known, reliable distributors.

Yeah, I know. That's always a gamble.

In this case there might be something really dodgy going on. IRFP260N costs 4.15 GBP at Farnell (including VAT) per piece, while from China (eBay/Aliexpress) it goes for 1 GBP / pcs or less. That is a lot cheaper and therefore more suspicious :)
 

Offline Pinkus

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Re: B&K Precision BK8514 electronic load 1200W 120V 240A teardown
« Reply #16 on: July 24, 2015, 09:59:00 am »
Check Digikey: http://www.digikey.com/product-search/en?keywords=IRFP260N%20
25 of them costs USD 2.43 each; if you purchase less it is USD 3.95 each.
 


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