Lop's Blog

Feb 14, 2017 - Design of a test load

For my 1000 watt power supply project, I need reliable and accurate way to test it. A test load basically converts power into heat in a precise way, but 1000 watts is a ton of waste heat to get rid of. This should be a fun side-project to figure out. Also, since I thought I had ordered an Arduino Due, but never did, I'm taking a short break from designing the power supply, and will work on this tool which I'll need later.

The circuit is fairly simple. R3 at the bottom right will be a set of 10 resistors in parallel, each 1 ohm rated at 100 watts. This results in a 0.1 ohm shunt rated for 1000 watts. Ohms law says for every 1 amp, I should see 0.1 volts across the shunt. 100 amps will result in 10 volts across the shunt. This voltage is sensed by an op amp which is used as feedback and error correction. The op amp will attempt to adjust the output to get the negative input feedback to match the positive input voltage, which in-turn controls the power mosfets. So the amount of current allowed to pass by the mosfet is directly proportional to the voltage on the positive input pin of the op amp. a 2:1