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Old Automotive Generator Trouble

I have an old generator (not alternator) that was overcharging the battery due to the external regulator stuck on. The voltage was reading over 16 volts and rising. I perhaps stupidly removed the B+ armature wire from the generator and continued to run the engine for a few hours leaving the field wire connected. (Perhaps causing over voltage within the generator?). After getting a new external regulator generator is not charging when connected to battery. To test I applied full voltage to field and only get 10 volts with evennothing connected to B+ armature stud with engine running. Increased engine speed and voltage actually dropped. Tried polarizing generator with no luck. Removed belt and applied full voltage to field stud and it spun really fast and disconnected before it maxed out as I think it could have spun too fast. Connected full voltage to B+ armature terminal and generator spun but slower than idle speed but it was spinning none the less. Not sure if this means anything as far as what the issue may be. Also would powering the field with nothing connected to the armature damage the internals in some way?

Thanks in advance,

Practically everything you’ve done could have damaged the internals. Find an automotive electrical shop and have the generator rebuilt. And for Pete’s sake, spring for a new regulator.


I’ll add one vote for auto electric shop. Local small business run by people who know what they are doing and seem to enjoy the work, and helping me, in my experience.

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Thanks old_mapar_guy, I do have a new external regulator but it did not help and thats why I think the cause could have been leaving the field connected without the armature stud connected to the battery. As far as the other testing that is how you test them by applying power to the armature and and if it spins the windings are supposedly good. I was interested in a home repair but not sure what may have been damaged internally if the windings are still good. If the windings are done I will probably just switch to an alternator.


That new regulator could be bad, or needs adjustment.
I’ve encountered “new” external regulators for alternators that were way off right out the box.
Put everything back with the old regulator and see if it still goes to 16V.
If so then you’ll know the generator is still able to put out.

Good idea. I will try that. I did think putting full battery voltage to the field stud would do the same but it is worth a try for sure.


The problem might not be the voltage regulator. Some electrical systems had an externally grounded field and some had an internally grounded field back in the days of generators. I put new brushes in the generator of my 1954 Buick. In assembling the generator, the field coil became grounded through theb
long bolts that ran through the generator. The generator ran wide open and the voltage regulator had no control. I believe GM cars had an externally grounded field. Other makes had an internally grounded field.

Ahh a generator. Remember the oil caps where you were supposed to oil the bearings from time to time? I didn’t think there was a whole lot to them if the brushes were good and the windings and commutator are OK?

Based on what the OP did to this poor generator, he could have bad field windings, bad armature windings, bad commutator, or brush issues.

@FarmerDaveo. What make automobile do you have? Some of those old cars had an externally grounded field and some had an internally grounded field coil. If you have an externally grounded field and the field becomes grounded in the generator, the generator will run wide open and the regulator will have no effect.
If you can come across an old Chilton or Motors repair manual from the old days or find the appropriate book written under the name Bill Tolboldt this would have the information you need. There were three books: Fix Your Ford; Fix Your Chevrolet; Fix Your Plymouth. If your old car was made by Ford, GM, or Chrysler, you will find the appropriate charging system.
You may want to check to see if you have overheated the generator and thrown solder off the armature.
As I said in an earlier post, I messed up putting brushes in a generator. That was back in 1963 so my memory is hazy on some of the details.

Yes @Triedaq, And as I recall that the 2 systems were designated type A and type B but it’s been so long I don’t recall which is which. But my best solution to all problems with generators is to replace them with single wire alternators.

!!! on looking at the part in my link it is spec’d as a 1 wire but it is a Delco housing and the connection for BAT and IGN are shown which is puzzling to me. I have put 1 wire regulators on many Ford and Delco alternators to deal with many problems with 100% success though.

@Rod_Knox. I agree that converting to an alternator is the best alternative. However, if the car has a 6 volt system then everything electrical has to be converted to 12 volts. The issue may be complicated if the car is a Ford or Chrysler product or even an early 30s GM product with positive ground.

I converted a 24v Jeep to a single wire alternator and had to replace the starter and all the lamps but I was happy with the results.

Since you applied voltage to the generator and it ran like a motor, it seems to me that is a sign that the generator is okay. You stated that you removed the output lead, so no current could flow and damage the windings of the generator. I suspect that the something isn’t right with the new regulator…