<VV> What *could* be damaged by reversing the battery?

[Tony Underwood]

At 07:16 hours 08/24/2005, Jim Houston wrote:
>On any DC motor, if you reverse both the field and armature, it 
>rotates the same direction (I think it works that way)..


This works with any series-wound motor such as a starter motor.   By 
the way, since such motors don't observe polarity, they will also run 
off AC.   Many old series-wound motors for light appliances like desk 
fans or sewing machines etc would run off 110 volts AC or DC and were 
branded as such... had an ancient GE desk fan that looked like 
something out of a Phil Marlowe movie that was like this.   A buddy 
has a 75+ year old compressor with a *huge* series-wound motor on it 
that's labeled AC/DC.
Shunt-wound motors do the same thing but they're not used as starter 
motors because series would motors make more starting torque while 
shunt wound motors tend to be more "regulated" and don't change speed 
as much with a varying load.

>Same with the heater motor, wiper motor, etc....


*Sometimes*.   Such motors anymore have permanent magnets for fields 
and if you reverse the polarity they spin backwards since the 
armature field reverses but the poles field does not.   Heater and 
wiper motors today use PMs in their poles.    It wouldn't be 
extremely difficult to modify such a motor although it could require 
dismantling and switching a couple of wires.


>I had a 1951 Chevy that I converted from 6volts to 12volts.. never 
>changed the starter..  you're right, it would spin like crazy!!  I 
>figured I would replace it when it burned out, but it never did..


Likewise a '51 Dodge with flathead 6 that belonged to a guy, 
converted to 12 volts and all he did was change the light bulbs, 
starter would crank it up *right now*, all it took was a quick bump 
of the starter and it was up and running.

I should have asked him about the gas gauge...  then again a dropping 
resistor or a regulator to feed 6 volts to it would be easy... simple 
LM-7806 would be all it would take since all it would have to do is 
handle a gauge.


tony..