Programmable dummy load is great device for testing power supplies, batteries. It is up to you how you want to set load behave – like constant resistance or constant current or constant power. Wigman27 wrote extensive instructable on how he built his own version of dummy load. He used sandard technique that is used in most cases – MOSFET act as variable resistor controlled through op amp. Microcontroller takes care of reading and setting voltages to sustain selected level.
Current flow is controlled with BUK954R8 – 60E MOSFET. MOSFET gate is driven by LM324 Op-Amp which accepts DAC (MCP4922) control voltage. Microcontroller reads sense voltage from MCP3204 ADC. There is also a temperature sensor on heatsink which keeps an eye and turns fan if things get hot. Key parameters of load are:
max Voltage input – 24V;
max load current – 8A;
max dissipated power – 50W;
min load current – 15mA;
load current error – 3mA.
Project explanation is really great even for novice. If you are not going to built power load, then material may serve as refreshing course of basic electronics.