Question: Controlling Atorch Electronic Load Expansion (DL24M-c) standalone...

[kexerth]

I'm looking for some input on controlling an Atorch Electronic Load Expansion (DL24M-c, aka purple/v3) from an Arduino without using the main Atorch unit (DL24MP); the expansions appear to be 4x MOSFETs controlled via 4x opamps, all in parallel. I've attached images of the unit without it's heatsinks (also removed the resistors so the traces beneath them are visible, as well as some detailed areas that are obscured under some silkscreen).

Product Link: https://www.aliexpress.us/item/3256804349891677.html

I found the following from probing the pins while one was in operation.
VCC = 12VDC
Fan = On = 3VDC (no PWM)
GND = Ground (Logic)
D = Load Positive (MOSFET Drain)
CV = "Control Voltage" (VDC Relative to GND) (feeding into LM321 opamps?)
S = Load Ground (MOSFET Source, via 6W 0.22Ω resistor in series)

The CV pin appeared to be just a small constant voltage (but was very noisy around that value, I didn't write down the noise envelope min/max), I used it's mean voltage over several points/settings to determine:
Load Current = (mV - 24.1) / 34.3
or
mV = 34.3 * Current + 24.1
(The other modes: Constant Voltage, Constant Resistance, Constant Power, appear to just be controller calculations that then vary the CV signal to maintain the desired setting)

As for the components:
IRFP264 = MOSFET
A63A = ?? LM321 Opamps?
431 = ?? LM431 Adjustable Zener Shunt Regulator?
Unlabeled IC to far bottom right of logic = ?? Transistor? (connects to fan header & connectors)
Black = resistors
Brown = capacitors

I started to create a schematic of the unit, but figured someone here might point out something I'm failing to notice in trying to control it first. The particular one in the images is defective (magic smoke was released from top/right when first powered on), so I can pull the ICs and take more pictures if desired (I have an assembled functional one as well for testing).


Anyways, I used a DAC to feed a desired CV voltage back into the expansion without the main unit present, but the MOSFETs didn't allow current to pass. (though letting CV float caused a large current flow)

Thoughts?

[kexerth]

Details attachments (due to attachment size limited)

[thm_w]

Yes A63A is LM321: https://www.ti.com/lit/ds/symlink/lm321.pdf?ts=1717105180210
and TL431 as you said.
Unlabeled SOT23 of that size is usually a high power FET.

Did you look through the previous threads?
https://www.eevblog.com/forum/testgear/cheezeball-dc-load-dl24p-pump-or-dump/msg3516952/#msg3516952

[kexerth]

I searched a bit, but I think I was being a bit too specific in what I was searching for. I'd run across the kirich blog link previously when I was trying to determine what would be needed to make my own load, then couldn't find the link again later... (thanks for pointing me back to it).


After looking at those schematics and reconsidering if CV might be PWM and I made a mistake, I determined that my assumed good DL24M-c is faulty as well:
I hooked the main controller and expansion together with only VCC, Fan, GND & CV, then hook up a battery to each unit's S & D; the expansion unit didn't pull any current while the main one did. I reached out to Atorch via AliExpress and yet again, they refuse to do anything about it. (so 2x bad expansions from separate orders 3 weeks apart).


I also just found this (coincidently while looking for pictures), which is pretty much exactly what I was seeking.
https://flaviutamas.com/2022/dl24m-electronics
https://flaviutamas.com/2022/dl24m-reversing

[kexerth]

I rechecked CV using my scope and setting the controller to CC 1A; despite looking like a signal, it's definitely a noisy DC voltage (the VCC pin passthrough from the included AC/DC adapter has an identically noisy signal, albeit at a different voltage).


I gave it a nice clean 12V feed and CV now produces a nice clean line, the expansion still doesn't work though...