I recently purchased some geared DC motors that will be controlled via relays and an Arduino. The leads from the motors are labelled on the motor housings as positive and negative poles. I am planning on running these motors in both directions by reversing poles. To achieve this, I will be using a couple of relays to act as a switch to reverse the poles as required.
I have many old DC motors from printers scanners etc., but none of them have the poles labelled. The fact that the motors I purchased are explicitly labelled makes me wonder if there is a type of DC motor that can only be driven in one direction?
It could be that the leads on motors are labelled simply for convenience, but I'd like to get some feedback before I reverse the poles and possibly damage the motors.
I suspect they are just labelled for convenience so you will know which way it will rotate without having to experiment. Well, you probably need to experiment with the first one but when you get to 10,473 on the production line it would be nice not to have to.
The timing is often set on a DC (or universal) motor for maximum efficiency in one direction,
by angling the brushes 10 degrees or so. This allows for the lag in current
build up in the armature windings due to inductance when running at
high speed and gives a higher maximum speed. The fact a motor has polarity
marked doesn't prove its asymmetric of course, but run it unloaded and measure
the top speed in either direction should soon show if its skewed like this.
MarkT:
The timing is often set on a DC (or universal) motor for maximum efficiency in one direction,
by angling the brushes 10 degrees or so. This allows for the lag in current
build up in the armature windings due to inductance when running at
high speed and gives a higher maximum speed. The fact a motor has polarity
marked doesn't prove its asymmetric of course, but run it unloaded and measure
the top speed and current in either direction should soon show if its skewed like this.
The no load current can also be used to set the brush neutral position and is probably easier to measure than the speed. While I doubt that you can change the setting and optimize the motor for bi-directional operation, at least you'll know if the motor is capable. If the no load current is significantly different in the opposite polarity, it is a sign that motor brush life will most likely be poor.