ORIGINAL: jdetray

Switching from 3 cells to 4 cells without reducing the prop size can be a motor killer, too.

Let's say you have a motor rated for 250 watts.

If the motor/prop combination pulls 20A and you are using 3 cells, that's:
11.1V x 20A = 222 watts.

You are safely under the power rating of the motor.

Now switch to a 4 cell battery without changing the prop. You are still pulling 20A, so:
14.8v x 20A = 296 watts

Now you have exceeded the power rating of your motor, which means it will be running hot, perhaps hot enough to melt the insulation on the windings.

- Jeff