what will over voltage of a DC motor do? like say I have a 12 volt motor and run it at 24 volts. What exactly happens when it "burns out"? too much heat?
if so can I run it in cold temperatures?
The motor will go faster and will generate more heat. Plastic parts might melt. Insulation might melt and fail. If you run it in a cold environment with plenty of cold air circulation that might prevent a catastrophic overheat failure.
Wear on the brushes will be greater, particularly from spark erosion, so the life will be shorter. I don't think cld air will prevent that.
And some very high speed motors might burst/explode if run at twice max rated speed (OK, this is far-fetched)
Bearing wear could be excessive due to much higher vibration levels.
Some motors with permanent magnets could heat enough to approach the Curie temperature, causing the magnetisation to start falling, which will cause the speed to increase (so more friction, more current, more heat, viscious circle).
A motor with integral fan will of course have a much higher flow of cooling air at higher speeds, mitigating the risk of excessive temperature, but not addressing mechanical issues.
Overall useful lifetime of motor could be drastically reduced.
arduinopi:
what will over voltage of a DC motor do? like say I have a 12 volt motor and run it at 24 volts. What exactly happens when it "burns out"? too much heat?
if so can I run it in cold temperatures?
The startup current and stall current will both double, and the heat dissipated within the motor at startup and when it is stalled will go up by a factor of four. It's conceivable that this would be enough to burn windings out.
The mechanical issues from doubling the free running speed have already been mentioned. I would have thought that if the motor was safe and reliable and durable at the free-running speed with 12V then running at twice that speed is unlikely to do anything catastrophic in the short term.
What exactly happens when it "burns out"? too much heat?
Yes
if so can I run it in cold temperatures?
You can but it will not save the motor from burning out.