Generator question

Since it worked before with the crappy looking field coils and does not work now with the new field coils, then logic would say there is something wrong with the new field coils. Are the screws that hold in the field coil segments really tight? I use an impact screwdriver to tighten the screws on starters. Just a thought, but if the magnetic path is poor maybe that could be the problem.
 
nkaminar said:
Since it worked before with the crappy looking field coils and does not work now with the new field coils, then logic would say there is something wrong with the new field coils. Are the screws that hold in the field coil segments really tight? I use an impact screwdriver to tighten the screws on starters. Just a thought, but if the magnetic path is poor maybe that could be the problem.
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nkaminar, suggest that you re-read post #13, the original field coils are back in the generator.
The field coil screws are TIGHT, I use a large exhaust pipe expander and a drill press to hold pressure on the screw while tightening.
 

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The Autolite generators used on the Model B were the first ones to have two wires exiting the case. Model A units just have the single power terminal with the field ground internal to the case. Many of the rebuilt generators supplied as spare parts over the years could have been changed to the external wire configuration so this is just added information. They can work either way.

The two field coils packs are wound in different direction so that they can have both a North and South polar capability. Insure they are wound as they should be. Use a compass if you have to. A complete connected field coil system should have 2 to 8 Ohms according to information that I have. A reading outside of this range may indicate a problem. This information comes mostly from the generator and starter overhaul manual by Paul & William Mcree.

The old 3-brush generators have to be well connected to the 6-volt battery. It's the only limiting factor on voltage output. With no voltage control, the generator will over volt and damage itself.
 
Katy, Sorry, I see that you tried the old field coil wires. The exhaust pipe expander looks like a good tool to assure that the field pieces are tight.

Here is another thought: The Model T generator has a third brush to adjust the output like the Model A. But it also has a way to move the whole bush assembly. I put together a generator for a Model T from various parts and could not get good output after adjusting the third brush. I finally saw that the whole brush assembly could be adjusted and doing that give me the required output. I wonder if there is a way to adjust the whole brush assembly on the Model A generator.

The armature has a position on the circumference where the voltage is the highest. It has to do with the how the magnetic lines of force line up. As a test, maybe you could use an old brush and a voltmeter to search for the optimum spot on the armature while the generator was rotating and the back cover off. If you find the optimum (highest voltage) spot different from where the brushes are maybe you could modify the brush locations.

OR. Has the brush locations changed somehow during your rebuilding?

Other than that, I am out of ideas.
 
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Please post photos of your brush plate and the fields inside. If you are using a later vented brush plate, these have 2 alignment pin holes. If you are not using the correct one, the brush position will be way off.

Here are two sets of field coils showing the ohms reading through each. The pink set are new and read 0.8 ohms. The other set are originals from a 1929 generator. I just refurbished them today. They read 1.1 ohms. The difference is insignificant in regards to generator operation.
Steve
 

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rotorwrench said:
The Autolite generators used on the Model B were the first ones to have two wires exiting the case. Model A units just have the single power terminal with the field ground internal to the case.
Click to expand...

Somewhere I heard, I think it was on the santaanitaas generator overhaul video where it was said that the late '31s had one field wire exiting the case for grounding.
 
The field wire coming out and grounding via a cutout mounting screw began around March 1934 with introduction of the optional 2-charge oval shaped regulator. When the regulator was installed, the field wire connected to a terminal on its base. When a standard cutout was used. The field wire was simply grounded via a cutout mounting screw.
Steve
 
I made a mistake, the rear plate is perforated, I just hadn't paid attention to it previously.
Here's the pictures you requested:
 

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I can't see the output wire, but it looks like the fields are wiired wrong. I noted on your photo where the field wires should go. Also adding a photo of mine showing these wires. The positive brush should have its own high strand count, 12ga wire going to the cutout.
 

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Katy, The correct position for the brushes on the armature depends on the rpm of the generator. That is why the 3rd brush works. As the rpm increases the third brush is further away from the maximum voltage point so the current levels out. So when you first start the car it is possible to get a higher charge.

I am very interested to see what Mike says.
 
Hi All - Katy and I had a look at his Generator using my generator test stand. As Steve noted above, the coils were wired backwards. With that fixed, the generator would still not run - it was actually drawing 5A rather than producing 5 Amps at the lowest third brush setting. After scratching my head for a while, I swapped the armature from a good generator and it worked properly. My guess is there was a "flying short" in the armature even though it apparently tested well on a growler.

Anyway - it is working great now! Yay!
 
Well done Mike, thanks for the follow up. I knew the field wiring was wrong, but when compounded by a bad armature, troubleshooting is difficult. I have seen a few flying shorts, they can be hard to diagnose. Good job!
 
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