positive to negative ground

Moondoggie · Feb 4, 2013

I am curious about the change over from 6volt positive ground to 12v negative ground. I thought reversing the polarity on a DC circuit would cause certain DC motors to reverse rotation. On a reverse of the + to - grounds, does a change have to be made to the starter so it doesn"t operate in reverse?

Zachary Hoyt · Feb 4, 2013

The starter rotation is not affected. I have no idea why, electricity is a closed book to me except for the few things I have specifically learned to do.
Zach

David G · Feb 4, 2013

It will reverse permanent magnet motors, starters are not.

John G. Hasler · Feb 4, 2013

> It will reverse permanent magnet motors,
> starters are not.

It will reverse PM DC motors and also shunt-wound DC motors if both field and armature are not reversed. It will not effect series motors such as starters because in them the armature and field are internally wired in series so you can"t reverse just one.

David G · Feb 4, 2013

agreed, thanks

teddy52food · Feb 4, 2013

When you reverse the current in both the armature and the field, the rotation stays the same. In a starter with permanent magnet fields, if you reverse the armature current, it will turn backwards.

John T · Feb 4, 2013

As posted below, the direction of rotation in your electromagnetic field starter tractor WILL REMAIN THE SAME REGARDLESS OF SWAPPING POLARITY.

To reverse its rotation you have to change the polarity relationship between the Fields and Armature.

If it were a Permanent Magnet motor (NOT electromagnetic field) and you change polarity IT WOULD RUN THE OPPOSITE DIRECTION

John T

Jon Hagen · Feb 4, 2013

No, motor rotation only changes with polarity in a motor with permanent magnet fields. You only find those on small engines and a few modern automobils.
A conventional starter motor with field coils will rotate the same normal direction when wired either pos or neg ground.

mkirsch · Feb 5, 2013

There are no magnets in a starter motor. BOTH the armature (spinny part) and field (outer can part) are electromagnets, and they're connected in series. Hence the term "series motor."

You'll also notice there are no magnets in generators, or alternators. The only place you'll find a magnet on an antique tractor is the magneto.

Because the armature and field are wired in series, when you reverse the polarity of the battery, you reverse the polarity in the stator, and you reverse the polarity in the field. The starter turns the same direction no matter what.

It has the same effect as a "double negative" in a sentence:

I know something. = I don't know nothing.

positive to negative ground

Moondoggie

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David G

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John G. Hasler

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