Could always hook a stepper motor up to the control arm and use a push up/push down button to control the resistance of the pot. That would be the DIY way would it not?
This is my active load 🙂 With fan cooling it works up to about 120W. The angle part is a bit thin and gets a bit hot, with better mounting it should be able to do a bit more. Each 2n3772 is driven by an IRF640 controlled by an opamp which measures voltage differentially over the shunt resistors.
An externally hosted image should be here but it was not working when we last tested it.
Something like this, I don't have a complete schematic. R3 = R4, R1 = R2. The ratio between them together with Rs sets transconductance. The buffer can be omitted if some nonlinearity over the pot travel can be tolerated. A capacitor is needed between negative in of opamp and the opamp output to stabilize it IIRC. The mosfet drives a 2N3772 in my circuit but IRFP250 or something similar can be used directly without driver (did one of those too). Both transistors in parallell have their own control circuit so they will share current equally.
Found a better schematic:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Found a better schematic:
An externally hosted image should be here but it was not working when we last tested it.
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