Testing a generator armature

[Will N]

Originally Posted by Joe K

...I will add to be sure in reassembly of a generator to have the field poles oriented correctly - you have a 50-50 chance of connecting them "opposing" - which will give you a generator that CAN'T be flashed.

Joe K

Joe, How can you know that you have the field poles oriented correctly?

[Kurt in NJ]

I found this old "book" wandering online, the LeJay manual
http://www.scribd.com/doc/3093121/LeJay-Manual

many interesting things from rebuilding a battery to making a outboard motor for a boat from a T starter, plan 28 tells about testing armatures and fields --including polarity of field coils, and going to plan 35 it shows the "wiring" of ford armatures so you can pick what "bar" on the commutator to best test each winding, ---there are even instructions in other "plans" to rewind your own armature

[Joe K]

Joe, How can you know that you have the field poles oriented correctly?

I do this by tracing the wiring. Poles are opposing (i.e. on opposite sides of the case) but are actually wound in the same "direction" (i.e. wire should go "in and around" on the same side and the same direction and exit by the same thought)

While the coils are separated into two coils physically - magnetically (and electrically) it's all one coil. So where one coil leaves off, the other coil should pick up the same way.

Another way which I have not done is to use a compass. As the coils are energised and in the case, you should be able to hold the compass needle against a pole next to the armature and read one pole (either north or south), held against the other pole, it should read the "other" pole (either south or north.)

I think Tom checks using the compass method?

And this may be different for the powerhouse which I have NOT done at all. Isn't that a four pole generator? I think poles there go N-S-N-S as you go around the armature circle.

Joe K

[Tom Wesenberg]

The powerhouse is a 6 pole generator with alternating north- south poles.

Here's a link to a past thread which shows using a compass. Check reply 8.

http://www.fordbarn.com/forum/showth...+compass+field

[Will N]

What a wealth of information! Thanks guys.

[Willie Krash]

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Hmmm. I don't know that I have seen pole shoes on automotive generators having any orientation. I do mark them regardless but I don't recall seeing it. They may however. I will acquiesce to that point.

Starters however may and many do and if the pole shoes are in backwards they will work fine but will lack power.

Re: gen. armature forgive me for my simplistic approach. Armatures for me are almost completely a visual test. Windings look nice, not burned, still tight in the lams, no dead spots, solder not thrown, I use them.
If they are to be turned and undercut I will use a growler to check for shorts.
It's an odds game and I hedge my bet by running them with an oscilloscope.
Now for those at home, with a high degree of probability if the generator will self excite the armature will be ok.
If everything is good (regardless of testing protocol) and the generator still goes offline and after polarizing works again, it may be a cracked armature winding. Very rare. All IMHO

[Joe K]

Heh. The use of an oscilloscope to check an armature is an interesting test I hadn't thought of. As you turn the armature slowly in a field excited generator case you should see "blips" as each coil comes under the windings? See no blip means you got an open winding?

Tell us more on that.

And this means I might have to scour craigslist for that $15 oscilloscope which I thought was a remarkable buy considering what an oscilloscope USED to cost before the digital age.

And who can argue a reason to buy more toys - er tools.

Joe K

[Willie Krash]

Yep, you'll see the hole. We use them on starters too.
They just don't seem to self excite with open bars.
I failed to mention the obvious visual test is watch the comm as the generator works or is forced to work. Open bars make for a good light show.
BTW Joe K thanks for all your posts, very informative and re charging systems I'll always defer to Tom.
After 38 years I'm like the old man on Pawn Stars. I play in the office.

[Joe K]

re charging systems I'll always defer to Tom

Heh. I'm smart enough to do likewise.

It's one thing to see (and hopefully understand) the theory and practice - it's quite another to have actually done it.

(like NOT the work on two powerhouses currently sitting on my workbench which I can't seem to get back to.)

And Tom has done it on both kinds enough to have seen all the possibilities - and where he excels.

Joe K

[Tom Wesenberg]

Thanks Joe and Mike for the kudos, but I only know enough to keep my finders out of light sockets. BTW, when I was in grade school I stuck my finger into a light socket a couple times to show my brothers ................well, I don't know what the heck I was trying to show them.

BTW, the visual that Mike mentioned is also my first check. I have an armature with 2 or 3 cut wires and the growler didn't work to show the open. But I have a powerhouse armature that you would swear is NOS, and it has several shorts as shown by the growler. When I showed it to an old generator guy in St. Paul he thought I must have made a mistake, so he checked it on his growler also. He said "yes, you were right about the shorts". I was showing it to him to see if he knew of anyone that rewinds them, but no luck in that.

[Willie Krash]

Tom, Romaine might do it........for a price. 1-800-426-5005
Yes to the armatures but as indicated it's an "odds" game. Visual for the guy at home should work pretty well and it's no deal to pull the armature out if it won't work.
BTW re the old generator guy....yep, he's playin the odds as you point out, but you can lose once in a while.

[Joe K]

I own print copy of the LeJay manual referenced earlier - and even played around with a few things they build.

IIRC, a Model A armature isn't that terribly complicated. It's more a matter of studying it and finding out where they "left off" on the outermost coil and then unwinding and working backwards from there. And then once back at the beginning, then work it all in reverse with new wire to bring it back to a complete armature.

Somewhere on the 'net somebody has done this - and IIRC it's like 17 gauge wire - and there isn't all that much wire all totaled - perhaps 60 feet?

Sounds tempting - I have a long generator here that had a bad armature. I replaced it with a nice tested used armature from one of my earliest respondants here on the Fordbarn - that respondant might even have been you Willie.

But that bad armature is still around - one thing you learn in Model A land is you NEVER throw anything away. And it would be interesting to experiment with.

Joe K

[Will N]

Ok, I know it's been a while since I posted on this thread. But after having tested the armature and found no shorts, and finding 6+ volts on the commutator 180 degrees apart while on a growler, and checking the field coils for shorts, and connecting them to a power source and finding they produce a magnetic field, cleaning it all up, assembling it, and connecting it to a power source and finding that the generator motors, I reinstalled it on my car today. It's still not putting out a charge. The ammeter will fluctuate at a a slow idle, but when I rev it up, it will only go to steady 0 amps. So it's putting out a little charge, but not enough. I moved the third brush down, no change. The ammeter works, because it is showing a charge with the spare generator I had on it. When I motored it, I made sure the polarity was correct (+ on the ground), and just to be sure, I polarized it again after installing it. Why isn't this thing charging?

[Bob C]

When it's motoring is it turning the same direction as if
it was installed on the engine?

Bob

[Will N]

Yes, in the same direction.

PS. I tried motoring a spare generator I have, and the spare spins much faster than the one giving me the problem. The problem generator spin quite slowly.

[Tom Wesenberg]

Bring your armature to French Lick. I have my Snap On growler in my suit case.

Did anyone by chance sand or turn the armature steel core on a lathe to clean off rust? This will cause a large air gap and little to no output. I've run across this problem twice on armatures that someone worked on before.

Are you sure the field wire is connected to the adjustable brush? I've seen two generator shops mix up the field and output wires, which resulted in a burned up generator.

[Will N]

Thanks Tom- I'm a bit far from French Lick being located in New York. The armature core was not tampered with. And the field wire is attached to the 3rd brush. This generator was working fine until I messed around with that Voltage Regulator contraption. I mentioned earlier that I found melted wax inside the generator body (it leaked out too), and the commutator had darkened. So the generator had overheated. Would the wax had come from the field windings? I guess I'll try replacing them first, as they're cheaper than a new armature.

[Tom Wesenberg]

Just connect a battery charger to the field windings and if the meter reads about 4 amps, DON'T replace them.

I don't know where the wax like stuff came from, but it shouldn't be from the fields or armature.

[Will N]

Success!! I replaced the field coils, and it's working again!

I tried the battery charger test, and the amperage draw was off the scale. Strange, because there is good continuity through the coils, and they were not grounding out to the body of the generator (tested after disconnecting the field ground wire). I guess the windings in the coil are grounding out to each other. The wax definitely came from the coils, as the cloth covering feels waxy, and there was a build up of the wax between the coils and the body of the generator.