Generator pegging ammeter

[Sunny the Model A]

Alrighty y'all, got a good one for you. i'm overhauling a generator for a friend, the old windings were shot so i replaced them with new ones, and i fully reassembled it and tested it on my A, when i did with the diode cutout he bought i got no charge whatsoever, keep that in mind, then i tested it with my known good relay cutout and got a much more interesting result, when the engine rpms went over a certain point the ammeter pegged on a heavy discharge until i returned to idle. now i wired the brushes according to the standard wiring diagram and i put the new windings in the same position as they came out as far as i know, but given the way it's acting to me it's like a reverse polarity in the generator. now it motors clockwise facing the pulley fine, but it refuses to charge. it's being obstinate with me.

[ndnchf]

Please post clear photos of the field coils and how theyare wired, and of the brush plate so we can see what you did.

[Sunny the Model A]

sure, just let me get it off my A and pop it apart, will get some photos for y'all.

[rotorwrench]

This is the second recent poster of similar problems. New field coils and then no charge. It makes me wonder about the coils. One coil is wound in one direction to get a north pole on the inside and the other wound to get a south pole. All I can recommend it that folks carefully inspect the originals for their configuration and make sure the new ones match the originals prior to installation. There could also be some form of internal problem with the magnet wire coating or wire gauge.

We sort of trust manufacturers of this stuff to do a good job of reproduction. A person could wind and insulate their own coils but then they have to source all the materials which is a job in and of itself. I tend to trust them myself so this is disturbing. When I put new coils in, I insure all this stuff as well as connecting things just like Ford or Autolite but what you can't see may be where the problem is. I just don't know.

I polarize the the pole shoes before I put the armature in during assembly. From my Magnaflux experience, this tends to give a better magnetic gauss in the pole shoes than motoring methods folks sometimes use. Motoring applies current to the armature so the field has to absorb it through the commutator to get any magnitisation of the shoes. It's a round about way to do it.

[Sunny the Model A]

well shoot, my phone won't let me get a good shot, but to get a mental image of it, the coils are wired with the connector to the adjustable third brush, the bare end connected to ground, particularly to the case, the wire that joins the coils together is facing the brush end of the generator and is on the bottom side. the brush opposite the ground brush has the wire leading up to the post. all insulators are new and i confirmed that nothing was shorted. i also polished the copper contacts on the armature and ensured the gaps between the contacts were free of copper dust after polishing.

[Sunny the Model A]

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Originally Posted by rotorwrench

This is the second recent poster of similar problems. New field coils and then no charge. It makes me wonder about the coils. One coil is wound in one direction to get a north pole on the inside and the other wound to get a south pole. All I can recommend it that folks carefully inspect to originals for their configuration and make sure the new ones match the originals prior to installation. There could also be some form of internal problem with the magnet wire coating or wire gauge.

We sort of trust manufacturers of this stuff to do a good job of reproduction. A person could wind and insulate their own coils but then they have to source all the materials which is a job in and of itself. I tend to trust them myself so this is disturbing. When I put new coils in, I insure all this stuff as well as connecting things just like Ford or Autolite but what you can't see may be where the problem is. I just don't know.

You know, i thought of that myself. when i wired up the genny i wired it the exact same way as the generator i use on my 31 pickup that's my daily driver, and it has origjnal coils in it with zero issues. I have another generator with good original coils but i don't want to part it out, but i am wondering as well about something funny going on with the coils,

[Sunny the Model A]

postscript to my last comment, i've done a couple generators at this point and never had problems before, the only thing that i can think of is maybe coils wound the wrong way, i'm tempted to flip the polarity of the power and ground brushes and see what happens. but i did wire it the way Henry did it so i'm stumped on this one

[ndnchf]

I restore a lot of generators and use original fields that I refurbish, and new fields. While it is possible to have a new one wound or wired together wrong, I've not encountered a bad set. They are good quality, they just need to have the proper ends put on and wire correctly to the generator. From the description, it sounds correct, but there are many little things that can cause problems. Things like the terminal post being grounded, a long through bolt grounding out a field, weak brush spring tension, brushes not properly sanded in, etc.

There are three possible ways that the fields are grounded. the most troublesome is the type that has a large ring around the terminal post insulator. It is very easy for this to be offset just a little which grounds the output. I prefer to ground the fields via a 6x32 screw near the brush plate end.

Steve

[rotorwrench]

The other poster on this subject finally found he had a flaky armature. Changed the armature and it functioned normally. Some armatures short under temperature changes and some have cracks in the wires that grow apart under higher temps. A growler will generally find these problems but there can be exceptions now and then.

[katy]

Originally Posted by Sunny the Model A

fully reassembled it and tested it on my A, when i did with the diode cutout he bought i got no charge whatsoever,

Did you test the diode cutout? Maybe it's just NG, or possibly it's a Model T cutout which uses a negative ground system.

[Sunny the Model A]

Originally Posted by katy

Did you test the diode cutout? Maybe it's just NG, or possibly it's a Model T cutout which uses a negative ground system.

The diode cutout is a positive ground diode, tried it on my own personal genny and it worked fine. i prefer a relay but it works as intended. i discovered the problem with the genny being the terminal wire being a little too short and it shorted out on the through screws causing it to go bonkers. i also discovered that the flag terminals on the said wire and the terminal on the coil were barely hanging on. so i fabricated custom ones that were made of thicker metal and soldered them on for good measure. when i test the generator i will report back with the results

[Sunny the Model A]

Results are in, the generator works beautifully. i made a new terminal wire and fabricated new flag terminals. turns out it was shorting on the through screws. i set the generator to full amperage and it registered a 5 amp charge on high beam with my 32-50 headlight bulbs. I set it to a standard 6 amp charge rate as per the service bulletin and it's ready to go

[ndnchf]

Glad to hear it! Usually these problems are caused by small things like this. Good job!

[JoeCB]

Many times a perceived electrical problem turns out to be a mechanical problem. Start looking for shorts, bad grounds, loose screws etc.

Joe B

[30Tudor]

A recent comprehensive article on Generator Troubleshooting can be found here.

Model A Generator Troubleshooting - Tips and Tricks by Michael Hill & Steve Blancard