To quote Dave: "Hi!"
I've been working on a DIY DC Load for m'lab. It started as most DIY DC Loads start I imagine: because you need a frickin adjustable load to test something! In my case, a silly mod to 15V power supply.
The goal was to first and foremost use stuff I have on hand or could have for cheap/free. So I ended up up-cycling a couple heatsinks and using a small 2U server PC case I have. It has been sitting unused for at least 3 years so I figured why not. I also happened to have an old ATX power supply that was hacked up and used briefly as my bench 5V and 12V supply. [Light bulbs coming on everywhere]
Originally I wanted to put it in a spiffy extruded case like one of those automotive inverters, but couldn't find a free one fast enough. But the PC case is pretty cool I think, albeit big. With all the space, it might eventually morph into a horribly hacked semblance of an SMU one day....
The performance goal was to be able to sink at least 50W at up to 24V. The 2nd proto (probably temporary final version) is able to do that pretty easily.
I went through an early proto stage with some random IRF FETs I had access to just to prove out the control board. Then I weighed my options between buying a few cheapish power FETs, without SOA for DC, maybe designing a PCB, or just doing it right by starting with an IXYS Linear FET. So I paid a little under 9 American Dollarbucks for a IXTH80N075L2, just so I could go full overkill and feel safe about not blowing this thing up (easily).
So here's the rundown of the design, and I'd love any input on what I should add, such as protections, improvements etc.
DCin --> Power Resistor (2 or 4 ohms) --> IXYS Linear Fet --> 100mR Sense Res -- GND
Quad op amp to buffer control input from 10-turn Pot, scale it down by 10, drive powerFEt, provide scaled Vout to panel meter
Up-cycled PC heatsinks for the FET and power resistors
Amazonian banana binding posts and power resistors. Have 5x 4R 100W resistors. Considering 2S-2P configuration if I can find the right heatsink
You can see all the pictures here:
https://imgur.com/a/dc-load-linear-power-mod-xqmjoMdHaving trouble attaching more than one pic due to file size? Gotta get to bed but will direct upload more pics later.
Cheers!