Resistive heater dummy load

While testing moteus controllers, it is often necessary to experiment with high power conditions. For short durations, any decent sized brushless motor can work, as the windings have a non-zero thermal mass and take a little bit to warm up. However, when testing at high power for extended duration, it can be hard to find a way to get rid of all output energy. Even blowing a fan directly onto a motor only gets you so far when you are trying to get rid of 1kW.

Thus enter my resistive dummy load:

This is just a block of DC water heaters screwed into a plastic container. They are wired in series with some high current inductors to roughly approximate the inductance and resistance of a motor in the range of what is normally driven by moteus. When conducting a test, the container can be filled with water to greatly increase the available thermal mass (and if need be boil away the water).

Parts and Assembly

I have used this fixture with two different elements, a 24V 900W one, and a 12V 600W one depending upon what resistance I want to test with:

The container is just a basic polyproplene plastic one, so that it should be safe up to at least the boiling point of water:

The inductors are 33uH, 30A:

To assemble, I used a 1.25″ hole saw to cut each of the holes, then used a 1″ NPT nut to fasten each element in place. Each phase connected to 3 of the inductors in parallel in series with 4 of the heating elements. All three phases were tied together in the center to form a wye topology.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s