May 6, 2020 Power Supplies

A low noise resistive load

A resistive load to test power supplies

A low noise resistive load

I needed a load to test my power supplies without worrying what noise it introduced to the measurement. I had a bunch of power resistor from a previous project and a box from a switching power supply. So I combined the two.

The resistors have a mediocre TCR (100ppm/°C). But that's OK. They can also operate up to 200°C which is also good. The cables are 1,5mm² silicone

Exploded view
The schematic


Test setup

Now let's see if the heat sink can handle the power. I loaded the load with 6A. This amounts to about 140W according to me Rigol DP 832. I recorder the heat sink temperature until it flattened out (about 50 minutes). Here are the results:

Heat sink temperature with a 6A load - Diagram from FlukeView Forms

Looks like with less than half of the resistors nominal load the heat sink flattens out at about 100°C (environmental conditions 20°C, 50% RH). Also the metal feet were not a very good idea. Their temperature was 50°C. I need to insulate them somehow.

Feet temperature

Maybe the 350W claim is marketing bs but all-in-all I am happy with the result. It also makes an excellent hand warmer!