SO I bought the version that doesn't come with a heatsink - you must add your own. 1000W, don't ya know.
https://www.aliexpress.com/item/1005001345772275.html1) The included 12v PSU is garbage. It cuts out intermittently, and you will waste an hour or 4. Roundbin it immediately.
2) The FET will promptly explode. The problem outlined by Syonyk (
https://syonyk.blogspot.com/2018/06/the-atorch-purple-fan-mosfet-destroyer.html) still exists. I think the problem is an opamp stage driving the fet: it is bode unstable, and the oscillations exceed the ±20v Vgs spec. My fet failed short circuit - which will cause big problems if connected straight to a Lipo battery (it's funny that the brand name is "ATORCH" -
this should be taken literally).
Replaced FET with FDH44N50. The specs to look for in this application: 1) lowest possible °C/Watt on Junction-to-case, and, 2) 175°C max junction temp (most big fets are 150).
I put a 16v Zener from gate to source to clamp the oscillations. There's probably an easier/better fix by changing something in the opamps' (there are multiple) feedback loop to improve stability, but I was too lazy.
3) Heatsink: my heatsink box yielded a nice copper sink with blower (not fan), 12v @ .8A, harvested from some old compaq P4. I drilled/tapped a 6-32 thread in the copper, and a screw holds it nice and hard against the fet.
4) Do not use the included white plastic standoffs - they interfere with your heatsink. Use rubber feet.
5) One other problem: there is a TO252 diode on the PCB, with a .7v forward drop. At the ATORCH's rated 20A... that's 14watts into the PCB, which may already be stinking hot from the fet. If you run high power at high amperage... I can foresee melted solder on the TO252.
Anyway, it works pretty good now. Reasonable accuracy (at higher voltages/currents at least; I didn't test a low current. You might have problems if you want to characterize an LR44 or somesuch).
I put 250W through it for a couple of hours, draining a 48V ebike battery, with no issues.
I put 500W through it for maybe 10 seconds, before dialing it back cuz I'm chicken. I wouldn't trust it more than maybe 300W.
Overall, not bad. For the money, it is alot of watts.