Generator question (3 brush, type A circuit, 12v, neg. gr.)

Hello all, I have what I believe to be a Delco-Remy generator on my TO-20. The thing wasn't charging, turned out to be the voltage regulator field points were not grounding the field coils.

But, while I was at it, I got into the generator, which is a three brush generator, circuit A type. I dug up as many specs as I could find, according to them, the field coil is separated from the armature.

With a DMM I measured the resistance from the field post on the gen. to the armature brush on the commutator, expecting that if I did see some current flow, all I would have to do is raise the field brush and break the circuit.

Well, I did, and it didn't... Confused

There was an increase in the ohms when I lifted the field brush, but still there was a connection between the field post and the armature brush. btw, there was around 7 ohms with the field brush connected to the commutator, and about 10 ohms when I lifted the field brush.

Now, this sounds like the field coil is close to shorted, and the voltage would run high. But the thing works....

Low RPMs the charging relay will not even close in the voltage regulator, medium RPMs, 14.0 volts, full throttle 16 volts output from the generator.

So, my question:
Is the field coil on some of these generators connected in some manner to the armature without going through the brushes?

Since it is working, and has been for years, should I leave it alone, employing the "if it ain't broke, don't fix it" strategy?

btw, I've looked the generator over, there are no numbers on it at all. But, I think it is a Delco.

Thanks in advance!

The generator is a Delco-Remy, I don't have D-R part number for the generator but the MF part number is 181674M91 for the generator.

MF part number is 181674M91 for the generator.

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Thanks for the help, but I'm a little confused. Isn't the 674M61 a 6 volt generator?

Back somewhere, the original was replaced and switched to a 12 volt system. I was thinking this is from a TO-35, but that is just a guess.

However, the generator is a 12 volt output gen.

(I have looked all over this thing to try and find a number or model; no tag, no numbers, nothing...)

Thanks again!

There is no 674M61 listed in the Ferguson parts. On another note a lot of generators (6 and 12 volt) that's used on a lot of different equipment look pretty much all the same externally. I know of a couple of people who works on starters, alternators, and generators for a living who can look inside the generator, and tell you pretty much what the model of it is (or close to it, a good rebuilder doesn't really need the tag). Since yours is still working I wouldn't worry about it until it quits working.

(quoted from post at 00:07:37 04/17/16) There is no 674M61 listed in the Ferguson parts.

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Sorry, I didn't catch that typo, I meant (181)-674M91, I was in a rush and tried to drop the 181.... Sorry.

The only thing that worries me is at low rpm, the charging relay in the voltage regulator will not close. At medium rpm's the generator will put out 14.0 volts, but at full throttle it puts out 16.0 volts.

All the stuff I've read from Delco-Remy says at 2300 rpm the regulator should be set no higher than 14.5 volts to keep from over charging the battery. But those specs are talking about generator rpms. My old beast will go up to 2200 rpms at full throttle, but the pulley on the generator is turning almost twice that.

This all could be normal behavior for a generator. But, I don't know.

However, the thing has been working for years, so with no more information than I've been able to dig up, it is "do I fix it, and really fix it, (as in break something that can't be replaced?) Or, leave well enough alone?

I would love to talk to someone who is like you say, who "knows" and is a "good re-builder."

I just don't want to damage the battery.

Thanks again for your help!
kr

I'm lucky enough to have a old "mom, and pop" starter, generator, and alternator rebuild shop close by. If the battery is being overcharged it will slowly boil the acid out of it. What is the outside diameter of the pulley on the generator? A bigger diameter pulley will slow the generator down so it won't charge as much.

The original generators on my OC-3's were 3 brush 6 v., with a single coil cut-out relay. Remaining one has been converted to 12 v alternator after failure would have cost a fortune to rebuild.

The third brush was moveable to adjust charging current. No experience with the 12 v 3 brush - all my 12 v units on the masseys were 2 brush, but all have been converted to self-energizing alternators after the originals died.

But it might be worth looking to see if that third brush will rotate, and playing with it a bit. And keep using it (and replacing brushes) until it dies from armature failure! The problems I had when converting were fabricating mounting brackets, finding a proper pulley and rewiring to negative ground. (And replacing the 6 v lights on the OC-3 after that oops. . . All three were SO bright - for a split second . . .!)

I had a third brush generator with vibrating voltage generator on my MH55 and I converted it to two brushes. I found info online, but does not remember where.
Then I put a full voltage, and current regulator on it. I bend up the spring support in the regulator to obtain correct maximum current and correct maximum voltage. It is fairly easy to do. Hope this helps.
It would be nice if cheap solid-state regulator for those old generator existed. Those old generator are very reliable, but the regulator and its points are not.

Those old generator are very reliable, but the regulator and its points are not.

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That is the TRUTH!!! I've had two new voltage regulators in the past 12 years, the first was around $35, the one I have on there now, was not grounding the field coil. New aftermarket, $164...
(So, I cleaned the points!!! )

What I'm really worried about, and you mentioned this, is the generator is getting old. There is a current path between the field coil and the armature. (it measures about 8 ohms)

I've attached a schematic of the generator, I don't see a path where I could connect to the field terminal, and the armature positive brush, then lift the positive field brush,,, and still measure about 10-12 ohms...

So I'm really worried that the generator is close to a short...

One point was made to me, that copper dust will provide a path, but doesn't really mean the generator is bad.

Thanks again for all your help!!!