Motor Controller Selection

Motor Controller Selection

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A DC brushed motor has several specifications. There are three key areas of a given motor that must be known to properly select a motor controller. The first specification is voltage range. The motor controller must be able to operate at the correct voltage the motor requires to avoid damage.

The second is running current. This is typical the current which the motor requires to spin at maximum speed. The running current is under a no load condition. So the next specification is where we get down to brass tacks.

Stall current is what matters most in pairing a motor with a given motor controller. Any motor when not rotating is in a stall condition. The motor controller needs to be rated with enough current capability to handle the motor in a stall condition. The amount of current will vary based on load.

We often get customer who feel their motor will only operate at light loads and therefor can use a smaller motor controller. This is not true in any way. When starting from a stand still the motor will require its maximum stall current in order to startup and spin. The load will only determine the amount of time the maximum current is required. Once the motor is spinning freely the current will drop proportionally. However if the motor direction is changed without a full stop the maximum stall current will be easily reached. The time it takes for the motor to fully reverse direction dictates how long the maximum stall current will be required.

An example of this would be a DC brushed motor that has a stall current of 100 amps and a running current of 15 amps. The RoboClaw 2X30 has the running current to run this motor. However since the RoboClaw 2X30 is only capable of 60 amps for brief periods it would not be able to start this motor properly.

The minimum motor controller that is required for a motor with the specifications given would be a RoboClaw 2X60A which is capable of 120 amps for brief periods. The 2X60A would be able to easily handle frequent starting and stopping along with sudden direction changes. The only limitation being the heat which is generated. If the motor is expected to be under heavy loads and change rotation frequently then its possible the RoboClaw 2X60 could also be to small and the next size up of RoboClaw motor controllers is required. This is true for all motor controller.

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