I am using one of those small yellow "robot" DC motor like this one, on a circuit where the motor will turn on a couple of times under certain circumstances.
I am thinking of designing a normally-closed circuit where both poles of the motor are shorted at all times to keep it stopped.
When a sensor goes off, one of the poles will be grounded and the motor will spin until the sensor goes on again, shorting the motor and braking it.
My question is: is it bad to keep the poles shorted for a very long period? Both in terms of damaging the motor and power consumption.
The "very long period" would be 24/7, with the motor turning on for ~5 seconds every 6 hours.
EDIT: Here's the schematic, haven't tested it yet but this is more or less what I'm planning to do.
simulate this circuit – Schematic created using CircuitLab
Best Answer
Shorting a motor by itself is no problem. It only becomes a problem if external forces turn the motor shaft fast enough to cause too much dissipation in the motor. When the motor is shorted, all the mechanical power from external things driving its shaft ends up getting dissipated in the motor as heat. As long as the motor can handle that heat, there is no problem.
It should take no power electrically to keep the motor shorted. You can keep a FET on across the motor using no power. It's only when switching that FETs take control power.
Make sure that the wussy little plastic gears in the yellow part can handle the stresses of the external torque working against the shorted motor. Of course if those torques are within what the motor itself is rated to put out, it should be fine in theory. The reason I only "in theory" is that on cheap motors with plastic gearboxes optimized for price, the motor's full torque for extended periods of time may damage the device too.