Generator charging problem update

Attachments

  • fields.jpg
    fields.jpg
    17.5 KB · Views: 12
Bob C, Good link, thanks.

In regards to flashing the generator, that sets up a small amount of residual magnetism in the field windings. The armature then supplies current to the field windings through the third brush after it starts turning. If the field windings are wired backwards, I think this causes the generator to produce voltage opposite to the way it was flashed. But Marshall said it showed a charge so that confuses me. He also said that the generator continued to motor when the hot lead was disconnected. I am wondering if the cutout was supplying enough current to slowly turn the generator. But that would raise the question of why the cutout had not cut out. It also raises a ground question because why would the generator stop turning if the ground lead was disconnected? I would like to see some voltage readings while the engine is off and while the generator is generating. Voltage at the generator post and the cutout battery side with respect to the generator case and with respect to the ground side of the battery.
 
Last edited:
I hadn't read through the step-by-step repair of generators in the Model A generator book for 9 or 10 months because all rebuilds went smoothly, so I skimmed through it again a few minutes ago. Instead of the following sentence appearing in the trouble shooting section where its presence would have been of great benefit, I found it in the testing section. A good place for it, but the information would have been just as welcome in the trouble shooting list.

Anyway, the sentence reads: "If the generator motors, but does so in a counter-clockwise direction, the field coil leads are installed backwards." That pretty well sums up what I have been fighting for 10 days now: incompetence at the factory level in that these field coil leads were incorrectly oriented from the manufacturer and should have been just the opposite. Jeez, you had one job to do and you screwed it up with a 50-50 chance of getting it right. How many other field coil sets are out there now with the same problem because some nincompoop at the factory was more interested in going to lunch than doing his job properly? Now this country can't even make something as patently simple as field coils. Yeah, my 10 day frustration point has been reached and surpassed because of yet more inferior repo parts. 'Really getting old recently with a spate of poor repo parts I've been stuck with from more than one national vendor. Anyone else experiencing this alarming trend?
Marshall
 
Last edited:
The wire winding around an iron or steel pole shoe is using DC amperage to magnetize that shoe. I used a DC coil to magnetize parts for magnaflux inspections. I used an AC coil to demagnitised the part.

The direction the wire is wound around any given shoe will designate what the pole direction is, ie north or south of the inside surface of that shoe. The outside surface will be the opposite of the inside surface. One is wound clockwise and the other is wound counterclockwise so that the insides of the two shoes will have opposite polarities.

Reassociating wire ends won't change the polar relationship. The two coils either got swapped or one was not wound correctly.

Tom's thread on reverse motoring gives the best info on testing field polarity. A person can check a single coil and shoe the same way before installing it in the case. Both coils & shoes can be tested together as well prior to installing in the case.
 
Last edited:
One thing I learned in designing manufacturing equipment is to make the assembly equipment fool proof. This involves making it so that things cannot be assembled wrong. This is done, for instance, by making fixturing so that parts can be placed only one way, the correct way. People make mistakes. It is up to the engineer designing the assembly equipment to make sure that the parts come out correctly 100% of the time. The assembly must not be dependent on someone remembering to do it right. In this case, the fixturing must be designed so that the windings can only be put on in the correct orientation. I don't know how to to that without learning how it is done now and doing some design work.
 
Bob, If you change the electrical polarity of the wires the magnetic polarity of the electromagnet will change. Google "Faraday right hand rule".
 
Last edited:
Yes, just flip the field wires. But if you are curious what's going on in the coils and want to make them right. Then unwrap them and correct the orientation.
 
O.K. I just flipped the field wires and although the armature now spins in the correct clockwise direction (looking at the generator's pulley, the direction of engine rotation), the generator does not charge, no matter which cutout I use. I even "flashed" between the terminals using the old points cutout and also against the generator body. Normally, this kick starts my generator rebuilds. But not this time. The generator motors clockwise easily when the jumper cables are connected to it, but no charge registers on the ammeter, which is in perfect working order. Moving the 3rd brush up or down affects the speed at which the armature turns, slower or faster. So, all the boxes have been checked and the generator passes the motoring and variable speed tests. Theoretically, the generator MUST then charge, right? At least before I switched wires around, the old cutout would allow juice to flow to the battery, but not any of the three electronic cutouts. Now I've got zero charge no matter what I do or which cutout I use.
I am just about at my wit's end with this ^%$#* generator and almost ready to give up. But I have got to solve this problem or it will haunt me, whether we stick with this generator or not. THIS frustrating experience is why I have avoided repairing Model A generators for almost 55 years! And apparently with good reason. They'll drive you nuts!!!
Marshall
 
Last edited:
Do you mean running the hot wire directly from the generator's terminal post through the terminal box junction up to the ammeter? Hmmm...That never occurred to me. Could doing this possibly damage the freshly rebuilt generator? I should think if one did this only for a few seconds, nothing would get burned up or shorted out. Has anyone reading here done this before?
M.
 
With the cutout removed and battery disconnected, I laid the hot wire connector over the exposed generator terminal post. When I tried to drop the battery cable over the positive post, it sparked. Should it? Or is there something wrong inside the generator or with the terminal post? It's new and has rubber O-rings over the shank to insulate it from the steel generator housing, as well as rubber washers beneath the terminal post head and between the case and lower post nut. Would fiber washers be better or even make a difference?
With the points cutout in place and the engine running, I jumpered between the terminal post and an engine stud nut to test for spark. None. I touched the end of the wire against various other engine parts with the same result - no spark. That means nothing is going from the generator to the ammeter, which is why no charge registers. But the generator still motors merrily along via jumper cables. That means, the generator must be o.k., yet it won't charge, no matter where I set the third brush. Flashing the cutout still doesn't help kick start the charging.
Help!
Marshall
 
I just tried the hot wire hookup to the terminal post of a known good generator and the battery cable also sparked when trying to connect it. So, apparently we can cross that off the list for tests. It won't help and is impossible to connect without sparking, a no-no in electronics.
Next?
M.
 
Time to take it to a shop and get it tested. Parts stores in my area test for free. Unregulated the generator puts out a lot of volts.
 
The only generator-starter shop left around here is a joke and run by an incompetent low-grade moron, who sits at the front desk talking to friends all day. I've had to reclaim generators from him that were sitting in the same place gathering dust where I had left them for repair six months earlier. Taking this thing to a local "professional" is therefore not an option.
If the darned thing didn't motor properly now or respond to moving the adjustable brush, I'd agree that it's time for a TRUE professional small motor person to check it out. But this thing passed the bench test that would convince any rebuilder it is o.k., so it should work. There must be one little thing I am overlooking that would cause the lack of charging ability. Does this sound like a generator that won't charge, given the tests it passed? Something's going on here that positively eludes me.
M.
 
You are stumping me. Can you put a cut-out with the cover off on it and see if it is pulling the points closed? That would tell if there was any juce being made. A NAPA parts shop should be able to test your generator, or an O-Riley. Where is a Western Auto when you need one?
 
Good suggestion, J Franklin. I, too, am stumped and finally have to admit defeat. Even though I've had good success rebuilding about a half dozen generators this year alone, I think I am over my head on this one. We do have NAPA and O'Reilly stores here, so if I can't resolve this problem on my own in the next day or two, I will take the generator there for testing. But all of this should be completely unnecessary. I will also call the vendor who sold me these suspected defective field coils and see about rectifying the situation with a PRE-TESTED replacement pair. The basis of the non-charging issue has almost got to be traceable to the improperly-wound field coils that make the armature spin in the wrong direction. Even switching the two leads around in function does not help restore charging.
One final question for everyone following this thread: if 12-volt field coils for a negative ground electrical system were packaged and mislabeled as 6-volts, would that cause this situation? I mean, would the armature motor spin as fast as it does if the field coils are actually intended for 12-volt application? Would 12-volt field coils explain the reverse armature rotation with the lead wires attached normally (plain wire to ground, sheathed wire to the 3rd brush)?
Marshall
 
Last edited:
'Sorry to keep extending a thread that should have been able to provide a solution after five or six posted suggestions. The problem turned out to be thornier than anticipated. NOTHING is simple anymore. :( I tried almost everything suggested so far, limited by available testing equipment and a narrow base of electrical knowledge. When something like this problem gets stuck in my craw, I can't let go until it's been resolved. So, here's some more background information on this generator that may or may not be helpful in deducing the cause its problems.

A friend acquired three non-functioning Model A generators a while back from a now-deceased fellow club member. So, their histories are unknown. I offered to rebuild them for my friend. Two of the generators were savable (one of which became a successful rebuild right off the bat), but the third one was so bad, that it will serve as a parts generator. This particular generator that is driving me nuts now had a note attached to it that said it pegged the ammeter needle when charging. It was a Frankenstein mix of Model A generators with a 1929-30 long nose/rear bearing armature and accompanying brush plate for a rear bearing, but the case was from a 1930-31 generator with the terminal post on the opposite end of the case. So, we know right away that it's been messed with. What I DON'T know is, could this generator possibly have been converted to 12-volts via an armature and field coils swap? The coil wrappings were almost non-existent and many of the wires were exposed, so I ordered and installed the now-infamous new field coils for a 6-volt system. That's when my nightmare began.
If the field coils and armature had been changed to a 12-volt system, wouldn't that account for the field coils now not being correctly oriented and why the armature spun in the wrong direction after the rebuild? Were long nose/rear bearing armatures even available for such a conversion? A 6-volt armature converted to 12-volts? How can I tell if that is the case? It passed a growler test, but that only told me the armature was still good, not whether it is 6-volt or 12-volt. Is there some telltale way of determining if the armature is for a 12-volt conversion? I shouldn't think it would spin as fast as it does when a 6-volt battery applies juice if the armature was a 12-volt. Would it even function inside what are supposed to be 6-volt field coils? My abysmal lack of experience in this area of Model A restoration really shows up here.
Marshall
 
The 12V coils have smaller diameter wire, more turns. I'm not sure about the armature, more segments perhaps.
 
Of course, without removing the wrappings around the field coils, I don't think I'd be able to compare wire sizes. The number of segments on the armature's commutator appears to be the same as on my other 6-volt armatures.
Marshall
 
You must log in or register to reply here.
Back
Top