How to Easily Control the RPM of a DC Electric Motor

By William Kinsey
DC Electric Motor
motor.jpg image by Aussiebloke from

DC motors use direct current to produce rotational motion. These motors have two primary parts: the the stator and the armature. The stator is bolted to the motor housing and does not move. The stator can either be composed of permanent magnets, like in small DC electric hobby motors, or it can be composed of electromagnets. The armature is connected to the rotating shaft and also has an electromagnet. During normal operation the magnetic field of the armature and stator interact, forcing the armature and the main shaft to rotate.

Connect one side of the DC electric motor to the negative terminal on the variable DC power supply, using the #12 electrical wire.

Connect the other side of the DC motor to the center terminal on the variable resistor if the resistor has three terminals. Connect one of the other resistor terminals to the positive side of the power supply using the #12 electrical wire. Make sure the resistor can handle at least the same amount of power as the motor.

Set the power supply at the rated voltage of the motor and turn it on. The motor should start running. Change the resistance of the circuit by rotating the resistor shaft. The motor speed should change. This changes the voltage the motor sees at its terminals. Reducing that voltage reduces the magnetic field at the armature. The same principle holds true if the the voltage at the power supply is changed.

About the Author

William Kinsey lives in Concord, N.C. He started writing articles in March 2009, which have appeared on and He currently holds a Bachelor of Science in electrical engineering from the University of North Carolina at Charlotte and a Master of Business Administration from the University of Phoenix. He also has several years experience as an outside plant engineer and planner with AT&T. He also currently owns and operates Sophisticated Curves, an online fashion mall that caters to the needs of plus size women.