Re: Charging a battery backwards

Posted by John T on July 06, 2007 at 11:53:42 from (66.244.83.147):

In Reply to: Charging a battery backwards posted by marvin johnson on July 06, 2007 at 10:37:39:

I agree with Old n the other gents, no harm in trying to revive the battery, you got nuttin to loose by a slow discharge and then hook her to a charger n see what happens?????????

The reason the starter still turns the same direction regardless of polarity is that its NOT a permanent (always same North/South polarity) magnet field motor like small low torque motors but relies on a current induced electromagnetic field.

Most tractor starters are SERIES WOUND MOTORS instead of shunt wound like a tractors DC Generator. The current flows though the Field and Armature wired in series. To reverse its direction (typical DC reversible motor) you would have to reverse the direction of current flow in ONLY one of its windings but in that series starter motor if you swap polarity you DO NOT change the North/South magnetic polarity of the field in relation to the armature, i.e. she still turns the same direction.

Some higher torque DC motors may have Compound windings in which some windings are series but others shunt, but I think the typical tractor starter is SERIES WOUND.

John T

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