Did I ruin a perfectly good generator?

[KGBnut]

My generator had a funny clicking noise, and I also couldn't adjust the output, so I got a rebuilt one from Bert's (those guys are the greatest).

I put the new one in the car, fired it up, and was getting healthy amperage showing on the ammeter. Time for the test drive.


About five miles from home, I notice the ammeter is now showing discharge, and it starts to run rough.

I pull out the ammeter and double-check it. I check my master fuse between the wiring harness and the battery lead on the starter. I check all the connections on the generator to ensure I had good connections there. I put my multi-meter on the generator and the output is good.

Scratching my head, I decide to go to Pop's house, but, now she won't crank. I hate being stranded, so I try to roll start her. She fires up and now I show charge on the ammeter. I decided to continue to Pop's house anyway, because he is Pop and, by definition, much smarter than I am. Almost immediately she again shows discharge on the ammeter, but is running okay, so I make the five miles to Pop's.

Being much smarter than me, Pop pulls out the floor boards and finds that the negative connection on the battery is quite loose. I'm sure that was the problem the whole time.


Now here is my current problem... Now that the battery connection was fixed, I still am not showing charge on the ammeter. I checked the generator output with my multi-meter and am now getting NOTHING. I quadruple checked it on both sides of the cutout.

Pop seems to think that running it with the bad battery connection gave the generator output nowhere to go, and thus spoiled the generator. Keeping in mind that I only ran it for about 5 miles, a total of about 20 minutes, could that be. If so, just how bad have I damaged it?

[Joe K]

You may have a bad brush (3rd brush) going to the field which caused you to have no excitation. No excitation no voltage - no power out.

Check your brushes to be sure everything is firmly seated on the commutator.

If you had damaged the generator, you likely would have had a smell. Failure is usually accompanied by that burned paint electrical sort of sniff.

You can try to "motor" the generator which will prove everything is working correctly. Remove the belt and jumper the cutout to establish a reverse flow of current. The generator should attempt to "motor."

And while you're at it check out your cut-out. When the engine is running, you can jumper it and effectively take an open circuit that may be there out of the loop. Don't forget to remove the jumper quickly on stopping.

Joe K

[tbirdtbird]

non-mechanical folks need to be careful of motoring generators. they can overheat very quickly doing this. And some will forget to remove the belt and 'motoring' that way will kill a gen. Most likely he just needs to re-polarize the gen, which you have actually described in your last paragraph. try the jumper for just 5 seconds and see if it begins charging again.

[al's28/33]

Somebody better call Tom Wesenberg......he's the Generator Doctor!

[Tom Wesenberg]

You may have cooked the generator windings by running with a loose battery cable. Also check your brake light because the high voltage may have cooked it also. Same with any lights that were turned on.

Do the checks listed above, then remove the band and see if you can smell or see anything burned.

[KGBnut]

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The taillight is LED, and is working fine. The headlights were off when all this took place. However, I did use the turn signals and the interior dome light. None of them burned out.

I did have the band off, and peeked inside. I didn't notice any strong burning smell or burnt look.

If I can get a little sunshine this weekend, I will try and (carefully) motor the generator, and re-polarize it.

[Joe K]

Gosh I always forget - the Model A generator is GROUNDED as 1/2 of the circuit. You need to check ground between the generator case and the frame of the car.

A lot of restorations create problems. Your new Berts generator might have a coating of new paint?

Check the wiring diagram at http://www.webjunk.com/modela/wp-con...amcolor2sm.jpg

And think "circular."

Joe K

[Purdy Swoft]

When the battery cable is loose, If its loose enough it can cause a 40 volt spike. If you are lucky, you may have just cooked the ammeter. No generator can motor with the belt in place, it just doesn't have the power to turn the engine like the starter. When the generator motors, it doesn't turn all that fast or with much power. You could stop it from motoring with your hand easily if you tried.

[Clem Clement]

Think about a couple of more grounds for your A.

[tbirdtbird]

i would re-polarize first and see what happens. then maybe motor it. but if it were me, repolarizing while it is running will tell you very quickly if it is working: just look at the ammeter, or put a volt meter across it and look for about 7 volts with the revs up a bit.

checking grounds is never a bad idea, but it did work in the beginning....until his ground cable bounced loose...

[Willie Krash]

KB, stop light not tail light. Typically if the generator is open circuit you will blow the stop light, tail lights are normally off but at night.

Tom asked an important question. If it did blow the STOP light, it will be apparent you did run in open circuit. The generator can tolerate that short term but....heat can build fast and variables exist such as engine RPM.
If that stop light is intact it is a good indicator but not definitive, that you didn't run open circuit.
A 6v bulb at 40v+ as indicated will last less than a millisecond. LED I don't know but I would guess they (it) would blow too.
My point is if it went open circuit you lose, if not it may be a warranty question.

Also I'd ask what is loose? The car did start so that loose connection was passing 100amps (?) plus. That kind of current requires a good connection. 10 amps not as much.
If it is on you I would take it to a generator shop. Might be less than a replacement. I own such a shop and really I try to help people and often fix units that are really not very old, often for little money.
Best check with the vendor. Good luck.