Electronic – Current drawn by a permanent magnet DC motor

currentdc motor

I have been working with PMDC motors for a while now. In these motors, as the load increases current drawn by the motor also increases. I was just wondering what is the theoretical reason behind this change in current?

Best Answer

As the motor spins, the magnetic field induces back EMF in the windings. The induced voltage has opposite polarity than the supply voltage. Theoretically, when no load is present, these voltages cancel out and no current can flow.

When the motor is loaded and slowed down, the BEMF voltage decreases and allows more current to flow. When the motor is stalled, there is no BEMF and current is limited only by winding resistance.