Generator Field Coil Question

[Colonel Biggs]

A couple of months ago I posted a question about a generator armature that suffered water flooding. Where there was supposed to be no continuity contained lots of continuity. But, after two months, a few oven treatments and periodic containment in white rice, the armature has returned to normal. The next test will be to place it in my next generator rebuild to see if it functions as designed.

In my current rebuild, I had to purchase some new field coils (Bratton's). Because the coils are thicker than the originals, I am unable to snug them up against the casting, preventing the armature from being able to be inserted. I have even used bolts to attempt the tightening. If install just the shoes, they snug right up and the insertion of the armature does not present a problem. Has anyone else run into this? Is there another supplier of coils, carried by one of the vendors? I have tried some bending/pressing of the coils to re-shape them, but I don't want to damage them, particularly if I have to return them.

[Tom Wesenberg]

Yes, I've had to take them to a generator shop that has the correct tool to get them very tight.

I'd spray a heavy coat of clear lacquer on the armature coils before you install it, but be sure to spray only the windings, so you don't coat the outside diameter of the core, or the commutator. Spray the windings good so it helps lock them in place, and hopefully won't short again.

[Colonel Biggs]

Hey, Tom --

I use CRC Red Seal Coat, a urethane spray, which Bill McCree put me onto. You can purchase it online through Amazon.

What you're telling me, though, is that no one is making a decent field coil?

[redmodelt]

You need a pole shoe expanded to do the job right. You really can't just pull them into place using the pole screws. It's a standard tool for generator rebuilding. We get our windings from Snyders and more then likely they come from the same place. The pole shoe expanded helps press the shoe and windings into place.

[RonC]

You may be able to get a muffler pipe expander tool at harbor freight to work as a pole expander.

[lindy williams]

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Are you sure that the coils are too thick or are they just not bent enough to fit the curvature of the case? That's the problem I had and I had to curve them more. Then I was able to get the armature to clear the coils by using a hex head bolt with a flat washer to pull them up very tightly.

[Colonel Biggs]

Who might sell a pole shoe expander? Harbor Freight has exhaust pipe expanders.

[RonC]

Originally Posted by Colonel Biggs

Who might sell a pole shoe expander? Harbor Freight has exhaust pipe expanders.

Just bring it to a starter/alternator repair shop and have them installed.

[Tom Wesenberg]

The pole shoes will easily pull the coils to the right curvature, if they are slightly off, but the pole shoe expander is a MUST HAVE tool. I haven't tried the tail pipe expander, but later I will try to make a correct expander.

Also, make sure you have the coils on the correct side of the case. If they are half way around, the generator will not work, and it will spin in reverse when you polarize it.

[Colonel Biggs]

The repro coils are noticeably thicker in spots than the originals, and I miced both sets. I have done some bending of the repros again, and I can get the armature in, but there is not much tolerance. As you know, each pole shoe has two extensions that retain the coil in place, and one of them has broken off on one of the shoes (just my luck). I can probably drill out what is left in the shoe, and cement in place a small dowel as a replacement.

Of interest, I purchased an armature replacement from PV Antique and Classic Ford (a supplier to Bratton's). The diameter at the armature segment of the armature is .005" greater than the one I had in there, but that could be a cause from wear over time. I suppose that there should be no contact at all of the armature segment to the pole shoes when installed, so I just may have to assemble to see how it spins.

[RonC]

There is a "go" and "no go" clearance between shoes and armature. Does anyone know those values??

[KR500]

Tom, I have a couple of questions for you regarding generators. 1st if I get a generator to motor, what would be a reasonable rpm to expect it to spin at on 6-7 volts and does the position of the 3rd brush have, if any, effect on it's spinning? 2nd What if any effect on a generator would one brush have over another if one is in poor condition ( not conforming to radius of commutator, or oil on it, or just poor connection) whether motoring or on a car charging? Would a motoring generator be expected to draw about 6-7 amps when motoring at 6-7 volts? What would a normal set of field coils read in ohms if in good condition? With a few knowledgeable members we have been experimenting with 2 generators. One we have done a growler test on a 701 Weidenhoff growler and failed the hack saw test and another which passed on the hack saw test, but motors rather slowly. Is a battery charger with at least 20-25 amps what should be used to check a motoring generator? What is, in your opinion, thebest test of aset of field coils,(installed or out of the generator frame? Thanks in advance.

[Tom Wesenberg]

I always use my 6 amp battery charger to test field coils. Putting a current through the coils is a better reliability test than just an ohm reading.
I don't know the RPM when motoring, but it is rather slow, nothing like an electric motor.
I've never moved the adjustable brush to check for a speed change while motoring the generator.
Amps and ohms for generator field windings should be:
5 brush powerhouse about 1 1/2 amps, 4 ohms
3 brush powerhouse about 2 amps, 3 ohms
Long generator about 4 amps, 1 1/2 ohms