That's because [most] starter motors have a series-wound field coil,
rather than the permanent magnet field in smaller motors. Reversing
the armature current direction as well as the field current direction
results in non-reversal of the motor. Same thing happens in universal
motors, though they have shunt field coils (connected in parallel to
the armature,) IIRC.
> Date: Fri, 27 Dec 2002 06:53:31 -0500
> From: "Nolan Penney" <email@example.com>
> You know, I hadn't thought of power window motors.
> Engine starter motors don't care which way they're wired. Positive or
> negative ground, they spin the same way regardless. But power windows
> do reverse. Huh, going to have to give that some thought some time.
> >>> Alan Lemen <firstname.lastname@example.org> 12/26/02 11:57PM >>>
> If it did, all those toy trains, remote control cars etc. would have a
> problem and my electric windows (not Spitfire) would only go down and
> never up.......
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