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Thanks Jack and Chris for setting me straight on this one. I had always assumed that a motor would spin backwards if you reversed the polarity. Never tested it though, which I suppose proves the old "never assume..." adage. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
Think someone else will step in here but is my understanding that it depends upon the type of motor, ie how it is made. But then I am not an engineer, maybe someone can tell us about this.
 
Is it because Lucas starters are series-wound? I'm a software guy.
 
If a DC motor has a permanent magnet as the magnetic source in the field or armature then reversing the polarity of the supplied power would reverse the direction of the motor. Drew, I suspect this is what happened in the IH tractor.

If the field coil and armature are both electromagnets with a common feed source then changing the polarity of the supply will not change the rotation because the relative current flow for the field and the armature will be the same as before. To change the rotation on a motor like this the field and armature need to be separated so that there are two distinct supplies, then the polarity of one of the two supplies could be changed to reverse direction.
 
See that, we got folks with book learning.

Thanks guys.
 
Impressive aint it. We'd be lost without the knowledge base found here!!!
 
If a motor has a wound field (like the starter and wiper motors)then it doesn't care about polarity. If only the armature is wound Like on a kid's toy motor with a permanant magnet for the field then a change of polarity will change direction. On the starter and wiper motors both the field and armature change polarity and cancel each other out so the direction stays the same.
Bill
 
Thanks Chris and Bill for the clarification. I think I get it now.

I'm a software guy too, Tunebug is my first experience with hardware. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
My head hurts already. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
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