....Test a generator by running it as a DC motor. You ground the frame, hook the hot lead from the battery to the the armature and jump the field to ground and it should spin like a motor, lift the field and it should stop. We had TWO generators that would run without the field grounded. (Shorted feild) The result would be a full charge no matter what. 

JP  Jul 2003

====================================

First make sure and polarize the generator then with the car running put a
volt meter to the battery with the engine around 1200+ RPM this should give
you about 6.7+ volts, have a friend turn on the headlights that shouldn't
drop the voltage more than 0.2 volts (and no drop in voltage at all is best)
then do the same test at 2400+ RPM this should give you about 7.2 volts and
do the same headlight check and watch for a voltage drop. Then proceed to
what John Paulos recommended "Ground the field wire on the generator, if it
charges like mad it's the regulator, if not, the generator is shot".  Next,
disconnect the belt and unhook the wires from the generator turn the pulley
by had to feel for any strange noises, roughness, etc.  If that seems to be
ok take a charged 6 volt battery with the generator STILL DISCONNECTED (like
the one in the car)!  and using jumper wires connect them to the generator
and then the hot wire to the battery then hold the other cable to the
negative (USE RUBBER GLOVES or make sure your holding insulted wire) and
KEEP EVERYTHING AWAY from the generator and the generator should run like an
electric motor.  If it doesn't pass the voltage test or the 'electric motor'
test it likely just the brushes.  But don't forget the basics, new battery
or not check the water level of the battery first, a low battery can't hold
a charge for very long.  Hope this helps, by the way you don't have to do
every test here if you've found the problem!  : )\



----------------------
Brushes- Aug 2004 
With a new generator or turned commutator, it seems to me that when
the brushes are new the contact area is smaller due to the brushes not
having worn in to match the commutator diameter. (Seated)
The spring pressure is also highest at this point. Wear will be
greater.

After the brushes are seated and worn a small amount by the smoothing
action of the brushes riding on the commutator, the best point is
reached.
Under the best of conditions (daytime highway driving at least one a
week with good cooling air flow, and so on, you should get well over
40,000 miles before new brushes are needed.

As the brushes wear toward the end of their life, the spring pressure
will decrease, perhaps causing a little bit of arcing, which is good
for neither brushes or commutator.

Somewhere along the line, maybe at 30K or before, measure and record
the height of your old brushes in situ before they get too bad. Pull
them and examine the commutator and mica insulation between the
commutator segnents for condition. If good, change the brushes. If
not, get it turned by an expert.
(While the brushes are out, turn the rotor and listen for bad bearing
sounds.)
If the bearings sound good and the commutator is good, replace the
brushes.

midlant@earthlink.net (karl haas)
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