Electronic load - heatsinking / managing thermals

[ifonlyeverything]

I found a partnumber for a good powerful heatsink, which works fine with a powerful noisy 70 mm fan. Here it is: IBM HEATSINK (40K7438) IBM X3400 / X3500 / X3650 (FRU 40K7438).
I have two of them. Tested one - it works fine with 200 Watts and 4500 rev/min 70mm powerful fan (and TO-247 FETs). A man who sold me them, said it may dissipate up to 600 W with a TO-264 FETs (?).

Those look pretty nice. How did you mount your FETs? Clamping, or drill & tap a hole in the heatsink base?

[Vovk_Z]

drill & tap. It is made of something like pure copper (or copper-like alloy). It is pretty soft and drills very easily.

[MathWizard]

I've been wanting to make a DCEL to test some computer PSU's. I have a couple of real schematics that are similar to a lot of the low power ones you'll see. And I would probably combine that with something like Scullom Hobby Electronics DCEL, that and the 2 sch's are both digital.


Last year I tried some big iron sheets as heatsinks, and they can't even dissipate the heat fast enough for 1 fet at 20W. Maybe I was doing something bad to those modfets, or they were knockoff's. But I haven't tried anything since.

Now I have some nice op-amps, but for the cost of all the other parts, like a giant heatsink, I'm back to looking at brand-name ones.

I have a +10yo 1,200W PSU. I should just give up on testing that, I'd need a multi-rail tester built for 2,000W.

But then there's those low voltage, high power heating elements, like 12V 400W, and cheap. IDK if they are really suitable, since I don't see anyone else using heater elements. But for a resistive load, with pass mosfets trying to control it, is that a good or bad idea ? Like if I wanted to test a 750W PSU, may I'd only use 600W of heaters, and the rest could goto just power mosfets on a heatsink.

[barshatriplee]

Using server CPU heatsinks can be a good option for cooling the MOSFETs in your electronic load. The Delta Electronics heatsink you mentioned (DHS-B9292-04A) with dimensions of 80x80mm and a thermal resistance of ~0.24°C/W can provide adequate cooling. You can fit two MOSFETs per heatsink, as you suggested. Additionally, using powerful fans and clamping everything together with bolts will help enhance the cooling performance.

[Jwillis]

I run 8 FDL100N50F in the ELoad I built. It can sustain around 900W before the thermal shut down kicks in at around 100C. Eventually I would like to improve the cooling but it supports my needs for now.

[Jwillis]

I would be wary of buying them on aliexpress. It is quite possible you won't get a genuine device.

I bought several from Digikey , Ebay and Aliexpress and they all work the same. Didn't see any difference between them. Aside from price.
Mind you I got them before the Covid thing so there was lots of them around then.

[MathWizard]

I run 8 FDL100N50F in the ELoad I built. It can sustain around 900W before the thermal shut down kicks in at around 100C. Eventually I would like to improve the cooling but it supports my needs for now.

That heatsink is not very big, but that can almost handle 900W ? Where do people get large heatsinks from anyways, what did it cost? I had a quick look around and I was seeing prices like $350 for anything big. Insane price markup I'm sure.

I know I'd need the fans to have the right spec's too.

[Jwillis]

I run 8 FDL100N50F in the ELoad I built. It can sustain around 900W before the thermal shut down kicks in at around 100C. Eventually I would like to improve the cooling but it supports my needs for now.

That heatsink is not very big, but that can almost handle 900W ? Where do people get large heatsinks from anyways, what did it cost? I had a quick look around and I was seeing prices like $350 for anything big. Insane price markup I'm sure.

I know I'd need the fans to have the right spec's too.

With forced air it will sustain 900W for the 5 minute without further temperature increase on the  test i did. I won't kid you , It gets hot . But most of the of the time I use it at around 400W to 600W.
I lucked out on these heat sinks. Found them for $40 a piece . I check junk stores, pawn shops and scrap yards. Sometimes I get lucky. Even metal shops have scraps they will sell you for peanuts. After all what is a heat sink but a chunk of metal.
I do have an advantage of having lots of petroleum companies around that have scrap yards. Sometimes they will just let you take it. Saves them from hauling it away.