12v generator won't charge

Automotive Stud

Automotive Stud

Well-known member
I have a 1947 6v generator that I bought 12v field coils and new brushes for. I tested the armature with a growler and with a multimeter and it tests good. I followed the Tardel book on assembly, but it still doesn't charge. I hooked it to a battery to motor it and it will not motor either, the pulley just wobbles a little. I even took it to a local generator shop and they couldn't find what was wrong. Any advice on where I may have gone wrong?
 
I'm not a fan of motoring a generator for one. I've never had a need if I know all things are good. Make sure you field coils meet the Ohms specs for a 12-volt generator, are properly wired in, and have a close relationship with the pole shoes to armature gap. Make sure all your terminals are well insulated from the housing. Make sure the brushes are making good contact and that commutator is smooth and has proper undercut. If all this meets the spec then it has to have the polarity set in the pole shoes by flashing the field to get a good residual magnetism. If using an old style 3-pole regulator then make sure the cut out is functional. If not properly polarized, it won't generate enough on residual to even close the cut out points.

The 6-volt armatures have heavy windings compared to the 12-volt types so this will affect the output amperage by somewhere near 20%. At 12-volt, it should'nt matter much but it does have limitations depending on how much the system has for an average load at night when a lot of electrical power is needed.
 
Are the fields soldered togetter the correct way ?
You will still have connection checking with an ohm meter but will not work if hooked up backwards.
If you look at the field windings they should be a continous rotation from one side to the other...if they change rotation you have an issue.
 
Motoring the generator is sometimes a useful field expedient, and also accomplishes polarization or "flashing the field" at the same time. How are you connecting it when trying to motor?

Jumper the ARM and FLD and motor the generator pulley with a drill, or install it and idle the engine at 2000 RPM. Voltage should spool up well above 12 volts connected between GND and ARM. Only perform this test long enough to verify voltage output.
 
If all things are hooked up correctly, sometimes there can be a brush seating problem.
With the generator spinning, push the brushes into the comuntater with popsicle sticks.
This being said, I've done this on the test stand... it will be harder on a car.

Karl
 
Just to update, I found the problem. The armature was worn around the front bearing, so even with a new bearing there was too much play and the armature was shorting against the fields. Thanks for the tips everyone!
 
Glad to hear you got it figured out. Love it when a threaad closes out, we can all learn from each other.
 
I'm curious about how it wears around the armature, I've heard this kind of problem before.
Generators are primitive but it's interesting to learn about them. Maybe not by the side of the road.. but.
 
I assume the forward bearing failed, causing the armature shaft to machine itself down by friction against the failed bearing. You can see it in this picture. The replacement armature I have is actually knurled where the bearing sits. I'm not sure if this is factory or not, but it was a very nice snug fit on there.
 

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The knurled armature shaft was a repair job to salvage a worn shaft by an auto electrical shop. Armature shafts were not knurled when manufactured. So are you saying that the armature was hitting the field pole shoes because of excessive armature side movement ? We call this "poling" and it is not shorting as such but rather disrupting the magnetic field and no output is the result. Regards, Kevin.
 
The knurled one was likely just chucked in a lathe and a knurling attachment pushed into it. It'll allow them to turn a few more years. The other one may have too much wear to get away with that but just depends on how far it was worn down.
 
Probably not worth the trouble but something similar to a "speedi-sleeve" might give the armature a new lease on life.
 
The stuff isn't getting any easier to find, so I'm going to hang on to the worn armature. Perhaps it could be turned down and an oversized bearing found to fit, or a sleeve as you mentioned.
 
Exactly what I was thinking, parts that we throw away today would get a second look when the supply dries up.
 
My spare generator actually came from an old junkyard last year. I really needed the special nut and square washer for my build, but at that point I figured I might as well grab the crusty generator since it was basically off anyway. I'm sure glad I had it this week.
 
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