Quote:
Originally Posted by 30 Closed Cab PU
I've seen this expressed before, and assume it is true but do not understand why the starter does not run backwards and be a problem, since it is a DC motor.
Can you/someone please explain?
Thanks
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What drives any electric motor is magnetic attraction and repulsion. Like poles repel and opposites attract. There are two major parts to a starter motor - the armature and the field windings. If you reverse the polarity of both, it runs in the same direction. Reverse only one of them, it will run in the reverse direction.
The field windings set up a magnetic field and the armature sits in the middle of it. Another magnetic field is created by the current flowing through the armature. That causes one side ot eh armature to be attracted to the field, the other is repelled by it. The direction of this field changes as the current reverses direction. That is achieved by the way the commutator is connected to the armature windings. That is, as the armature turns, the brushes are connected to different windings by the commutator. When the timing of the changes is right, the armature spins.
This clip probably explains it better than I did.
https://www.youtube.com/watch?v=CWulQ1ZSE3c
When I was in secondary school, each year we had to make something for display to parents on open night which demonstrated something we had learned that year in our science class. When was 14, I thought I was clever making an electric motor, only to be well and truly trumped by a couple of friends who teamed up to make a device which carried their voices on a beam of light. That might not sound overly impressive now, but in 1962, it was more than most parents could comprehend.