Re: Before you start your prize, POLARIZE!

["Melissa & Jim" <jadney@vwtype3.org>]

On 10 Nov 97, DILLARDP@edu-suu-lifac.li.su wrote:

> Ah dear friends, if you disconnect your generator from the voltage
> regulator, be absitively posolutely sure to POLARIZE the generator
> before re-connecting it and starting your engine.

There may be more misunderstanding of generators and charging systems 
than any other part of the car.  Perhaps it's just because people who 
get "into" cars tend to be more mechanically inclined and less 
electrically aware, or whatever.  

Anyway, polarizing the generator is one of those "mystical" processes 
that seems to have a special attraction to people.  In reality, it is 
VERY seldom necessary.  There are only two times that I would even 
consider bothering with it.

1)  After I have COMPLETELY disassembled a generator, including 
removing the field coils from the generator body.  In this case it is 
possible to accidentally switch the two pole pieces and neutralize 
or reverse the residual field.

Note that commercial rebuilders will have to repolarize 
their rebuilds before they test them, so you don't need to worry 
about this when you take a "new" unit out of the box.

 2)  After someone has accidentally installed a battery 
backwards.

Of these two possibilities, I have had to do #2 one time in 30 years 
and #1 never (probably because I've never had to remove any field 
coils ;-)

Polarization is just a matter of making sure that the residual field 
in your generator is in the right direction so that when it starts up 
it will generate the right electrical polarity.  There is no need to 
re-do this periodically because normal operation "refreshes" this 
field strength every time the generator is operated.  In fact, 
"refreshing" is not really necessary.  The residual field is quite 
stable and will hold for decades in a stored car or just a generator 
on the shelf.

When the engine is off, there is no current in any of the wires 
between the generator and the regulator, so it really doesn't matter 
whether they are connected or not.

The one time I had to do this came just  a couple of years ago with a 
Karmann Ghia that someone had installed the battery backwards in 
several months before.  The battery problem had been fixed, but the 
car had never been able to keep its battery charged after that.  When 
they asked me to look at it I was puzzled at first because the 
battery voltage went DOWN as the rpm went up.

I finally disconnected the generator from the battery (which they had 
been keeping on a charger) and watched the generator output alone.  
It was negative!  I repolarized it quickly, reconnected the wires, 
and sent them home.  I was really surprised, but the generator and 
the regulator were both fine.  I suspect that the battery, which was 
new, had taken a beating, however.

Jim
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       Melissa Kepner                                    Jim Adney
                             Laura Kepner-Adney
                         jadney@vwtype3.org      
                             Madison, Wisconsin
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