Dumb Generator Question
 

My generator is not putting any current out (it had supposedly been rebuilt some time ago and has not been run since).

It is a 12 volt General Motors 4 brush type. Taking it apart I find two brushes (marked 'A' on the photo) are attached to the armature and only one (marked 'F') to the field. The last brush has no wire attached to it and does not appear to be 'grounded' to the generator body. So, my dumb question is what should attach to the 4th brush? Nothing? (assuming the last guy who had it apart knew what he was doing), a wire to the 'Field'? (to match the one opposite it) or a wire to ground? The manual says to make sure you carefully re-attach the wires as they were, which is a little help at this point.

I'm hoping it's as simple as this and I don't have to rig up a 110 volt growler or other dangerous looking apparatus.

2 Pole Shunt Wound
 

Hmm Bruce...

By the (Chev CMP) book you have a two pole, shunt wound generator (You in fact, have three poles) Hence two poles are the armature. The other provides excitation via the Field.

Remember ANFEE+ (Mike Kelly will know the good old Morris theory) Armature, Neutral, Field, Earth. Floating earth...

Do not connect the third set of brushes.. They will alter the charging circuit. They are just a redundancy option if you stuff/wreck the field windings.. or they burn out.

As I do not have a Chev & I presume this is a CMP generator, then I guess that the two poles are the correct number of windings.. This should give you the desired output.

Otherwise you will have to do a trial & connect the third set of windings & measure Voltage output, & current output. Rotating the generator at the 6 cylinder engine RPM of about 800-1200 RPM (around average charging cct). Which is easy with a washing machine motor bolted onto a test bench. Then you can determine if you have sufficient voltage to charge your battery.. (this is done connecting the third set of field windings, which in your case should NOT be necessary!

A Growler will only determine if the windings are serviceable..not the output..

How will that output look????
It will be a very ripply DC as each rotation induces the voltage to the armature. You wont notice that with a multimeter (selected ON DC VOLTS) but with a Cathode Ray Oscilloscope it will show up as a positive ripple voltage.

Gee you blokes test my electrical theory!

Hmm don't ask me about Ward Leonard lifts.. I had to learn them for Aircraft carrier theory :teach: Now 26 years on I am teaching generator theory! :thup2:

Ian

I agree with Ian
The second set of brushes is unusual ,normally only have the one pair
Of these pair ,one brush will be grounded to the case
the other will connect to the A terminal
also coming off the A terminal is one side of the field wiring
Off the F terminal will be the other side of the field wiring

Bearing in mind these are not a permanent magnet generator you do require an excitation voltage which is supplied from the regulator to create an induced voltage
The wiring of which is BAT terminal to the battery via the Ammeter
GEN terminal to the A terminal of the generator
And F to F on generator

So bearing this in mind if the generator was indeed reconditioned correctly the most likely cause of your grief usually comes from stuck or open points on your regulator ,ineffective insulating blocks at connection points or an open circuited ammeter

Thanks guys!!
 

The generator is back together according to your instructions and 'motors' so it ought to work in reverse. I suspect dirty contacts were the worst of the problem and I apologize for doubting the last guy mucking about with it. If I still don't get a charge then I suspect the regulator; the ammeter and battery do what they're supposed to.