An Electric Motors Uses MORE Current When Stopped. Here’s the Physics.

Photo: Rhett Allain. DC Electric Motors.

Here’s a fun question. Imagine I have a small DC fan that’s on and spinning. I can measure the electric current going into the motor. Let’s say I get a value of 0.6 amps. Now, if I stop that fan motor the electric current will increase to something like 1.0 amps. Here’s a quick experiment to show that.

But why? Why does a motor draw more current when stopped?

Electric Motors

I guess we should still start from the beginning. What exactly is an electric motor and how does it work? There are many different types of motors, but I’m going to be looking at the standard DC motor with brushes.

A DC motor consists of a coil of wire (with electric current) and a permanent magnet. When electric current runs through the coil, it creates a magnetic field. This magnetic field then interacts with the magnetic field from the permanent magnet to produce a torque. The torque on the coil causes it to rotate in an attempt to line up with the external magnetic field.

There is a small trick to get the coil to continue to spin. In order to allow the coil to rotate…