Would you even notice if the wiper motor ran backwards? Possibly only by a
slight change in park position, if at all. The wiper motor has a permanent
magnet stator so reversing the polarity reverses the magnetic field in the
rotor only making it run backwards. Both my heater fan motors definitely
run backwards if their polarity is reversed, can't comment on positive
ground cars having different heater fan motors, but the Moss catalogue does
show a change in part number at that point. Having to repolarise the dynamo
when switching polarity is for the same reason - the residual magnetism in
the stator is just like a weak permanent magnet, it has to be reversed
before the dynamo will generate voltage of the required polarity. The
starter motor is different - it has a wound stator and rotor, so reversing
the polarity of the supply reverses the magentic field in both hence it
still rotates in the same direction.
PaulH.
----- Original Message -----
From: Bullwinkle <yd3@nvc.net>
To: <mgs@autox.team.net>
Sent: Thursday, July 20, 2000 10:04 PM
Subject: Re: Heater motor
> I would think that all MG's that were originally built with positive
grounds
> have DC motors which are NOT polarity sensitive. I base that decision on
what
> happens when these cars are converted to negative ground. When that is
done, you
> don't have to replace or switch the leads of the wiper motor, heater
motor, or
> the starter. If the starter, a DC motor, was polarity sensitive then it
would
> run backwards after changing to a negative ground. It doesn't!
>
> The generator must be polarized, as it has some permanent magnetism to
insure it
> will energise without the battery.
>
> Blake
>
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