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Tips for controlling the RPM of a DC motor

DC motors are a vital component in many modern electrical appliances and we all have used them in one way or another. Be it remote-controlled cars, battery-powered fans or even artificial satellites orbiting our planet, DC motors serve many purposes and play an instrumental role in the functioning of many electrical products.

A DC motor can be calibrated for personal use. For this, however, the key lies in controlling the motor’s RPM. By controlling the rate at which the rotating shaft moves, one can virtually use it for any purpose. Without this control, the motor would just rotate at its factory-calibrated rate and might lose some of its utility in various household or industrial tasks.

In this article we will discuss how to control the RPM of a DC motor. For this purpose, we will need the following items:

  1. A DC motor
  2. A variable DC power supply
  3. #12 electrical wires of desired length
  4. A variable resistor

The basics:

A DC motor consists of two primary parts; a stator and an armature. A stator is an immobile magnet or electromagnet fixed in the housing of the motor. It is either screwed or glued to the casing of the motor on the inside. An armature is a part of the rotating shaft, sits right behind the shaft and is also composed of an electromagnet. The motor functions when the magnetic field of these two parts interact, result in rotational motion of rotating shaft through the armature.

The operation:

The following steps will guide you to control the RPM of your DC motor.

  1. Connect one side of your 12 volt DC motor to the negative terminal of your power supply. You will use the # 12 electrical wires in this case. You can either cut the wire for the suited length of purchase a wire of small length, according to your requirement. For this connection though, the smaller the wire the easier it will be for you to set it up and continue using it.
  2. Now connect the unused side of the DC motor to the center terminal of the variable resister (if it has three terminals) otherwise connect it to the one on the right (if it has two). Then connect one of the other terminals to the positive terminal of your DC power supply using the #12 wire. Before this connection, make sure the resistor is calibrated to handle the same power as your motor.
  3. Now set the power supply to the voltage rated on your DC motor. This will complete the circuit and your motor should start running. Vary the resistance of your circuit through changing the resistance from the variable resister. And viola! Your motor should change speed accordingly. This works because changing the resistance of the circuit also changes the voltage, which powers the motor up. The rotational energy of the shaft varies linearly with the supplied voltage because the armature receives a lower voltage that lowers its magnetic field. Conversely, this will even work if the voltage from the power supply is varied.

Your entire assembly will be well connected if your use smaller wires. But you need to make sure they are not completely taut when connected between the components. Additionally, positioning the different components in the assembly is also important so that wires don’t get tangled. This would be a good place to test your Tetris skills.


Choosing the right resistor is important. Resistor’s dissipate heat and it is measured in Watts. When choosing your variable resistor, make sure its wattage is at least the wattage rating of the motor. It shouldn’t be less than the motor’s rating.

Author Bio:

Dawn Gibbs writes about topics such as dc motors and electrical gadgets. Gibbs holds a Bachelor of Arts in history from Virginia Commonwealth University.

About Imwan Xandria

Imwan Xandria is a web enthusiast and blogger who loves all things about design, technology and idea of making money from internet! Love to write and share almost everything using his blog. This blog post is originally written by Imwan Xandria or guest blogger.

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