Powering your Motors

Motors are power hungry devices. They are also not very well behaved loads and can cause supply fluctuations that disrupt other devices powered from the same supply. Many difficulties with motorized projects stem from power supply problems.

Voltage

It is important to choose the right voltage for your power supply. Too low will result in reduced performance. Too high will cause damage to the motor and/or the controller.
  • Make sure that your power supply voltage does not exceed the rated voltage for your controller.
  • Unless you have a current limiting controller, make sure that the voltage does not exceed the voltage rating of your motor.
Too high a voltage can damage your controller and/or your motor

Current

Current draw is determined by the motor. As long as you stay within the voltage rating for the motor, the motor will only draw a safe amount of current. To protect the power supply from overload:
  • Make sure that the current rating for the power supply is at least as high as the motor.
  • Keep in mind that stepper motors are rated 'per phase'. To calculate the current demands of a stepper motor, multiply the current per phase number by 2.
Understand the current ratings of both motor and controller

Safety

"The greater the power, the more dangerous the abuse."


I don't think Edmund Burke was referring to motors when he said that. (In fact, they hadn't even been invented yet!) But his wise words are still applicable.

If you experiment with motors long enough, you will probably burn out one or two in the process. For smaller motors, this usually just means some very smelly smoke. But larger motors and their associated circuitry and power supplies can become a real hazard if you are not careful.

Be careful around live circuits and moving machinery

Protect yourself

Use caution when handing high current power sources, circuitry and attached machinery.
  • Avoid skin contact with live circuits. You can get a pretty nasty shock from a 12v circuit!
  • Short circuits in batteries and power supplies can result in fire and/or explosion. Always double-check polarity and use caution when making connections.
  • Beware of loose wires and stray tools that can cause short circuits or get caught in moving machinery.
  • Wear eye protection.
  • Stand clear of moving parts such as robot arms and other machinery when applying power. Unexpected rapid movement can cause injury.


Check that your power supply, controller and motor are compatible before applying power to the system

Protect the Electronics

Understand the capabilities of the components you are using and use care when connecting them:
  • Make sure that the motor is matched well to the controller. If you try to pull 3A from a controller rated for 2A, you will likely end up with a burnt controller.
  • Make sure the power supply is a safe voltage for the controller. Feeding 24v to a controller rated for 12v will kill the controller.
  • Make sure that the power supply is the right voltage for the motor. Unless you have a constant-current controller, doubling the voltage will double the current to the motor, risking damage to both motor and controller.
  • Don't make connections to live circuits. Make all connections first before powering up the system.

Overloaded circuits can be a fire hazard

Protect the Wiring

Overloaded wiring can quickly turn red-hot and burn through insulation and whatever else is nearby.
  • Always use a wire gauge large enough to handle the expected current. This chart from Georgia State University is a handy reference.
  • If your power supply is rated for more current than the wire, add a fuse to protect against short circuits.
  • If you are powering several circuits from one large supply, fuse each one separately to protect the wiring.
This guide was first published on May 21, 2014. It was last updated on May 21, 2014. This page (Powering your Motors) was last updated on May 04, 2015.