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Old 07-08-2020, 09:36 PM   #1
Tman62
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Default 1931 Generator needs rebuilt ?

I have read a lot of posts and have done a number of steps but i am still having issues and i am thinking i need the generator replaced or rebuilt.
I cant seem to get more than 6.1 volts from the generator when the car is running.
I don't think that will keep the battery charged.

This is what I have done so far

1 - it's only putting out about 6.1 volts when it is running.
2 - i did a "motor" test of the generator and it spins.
3 - i replaced the cutout, still 6.1 output.
4 - i adjusted the 3rd brush all the way down.
5 - i polarized he generator

After doing all this it's still only outputting 6.1 - 6.2 volts when the car is running

am i missing something here or could it be the generator needs rebuilt. If so i need recommendations on who rebuilds generators.

Thank you
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Old 07-08-2020, 10:15 PM   #2
Kurt in NJ
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Default Re: 1931 Generator needs rebuilt ?

What is the beginning battery voltage?--- before starting the engine
What reading are you getting from the ammeter?
Are there modifications from stock in the wiring?

If the battery is low on charge the voltage could be lower until the battery is closer to full charge, on a stock model A the battery regulates the voltage, the 3rd brush sets the amperage
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Old 07-09-2020, 08:19 AM   #3
Tman62
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Default Re: 1931 Generator needs rebuilt ?

Quote:
Originally Posted by Kurt in NJ View Post
What is the beginning battery voltage?--- before starting the engine
What reading are you getting from the ammeter?
Are there modifications from stock in the wiring?

If the battery is low on charge the voltage could be lower until the battery is closer to full charge, on a stock model A the battery regulates the voltage, the 3rd brush sets the amperage

Beginning volts is 6.1 same as it is started
Ammeter says at Zero, shows no charge (ammeter is working)
no mods its all stock
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Old 07-09-2020, 10:02 AM   #4
Purdy Swoft
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Default Re: 1931 Generator needs rebuilt ?

Is the cut out working .
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Old 07-09-2020, 10:07 AM   #5
Tman62
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Default Re: 1931 Generator needs rebuilt ?

Quote:
Originally Posted by Purdy Swoft View Post
Is the cut out working .
HI Purdy, yes the cutout seems to be fine, i have tried 3 different cut out's with the same results
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Old 07-09-2020, 10:18 AM   #6
Badpuppy
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Default Re: 1931 Generator needs rebuilt ?

Before rebuilding you should clean between the commutator contacts and replace the brushes if worn down. Easy job.
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Old 07-09-2020, 01:02 PM   #7
Patrick L.
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Default Re: 1931 Generator needs rebuilt ?

If the ammeter is working [ showing discharge under a load/lights] and the generator motors, it seems as though things should be working fine as long as the cut-out is doing its job. The ammeter should show some charge at a fast idle. Is the battery going dead ?

Looking into the generator is probably warranted if the above isn't happening. Maybe there is a movable brush issue.
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Old 07-09-2020, 01:10 PM   #8
Tman62
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Default Re: 1931 Generator needs rebuilt ?

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Originally Posted by Patrick L. View Post
If the ammeter is working [ showing discharge under a load/lights] and the generator motors, it seems as though things should be working fine as long as the cut-out is doing its job. The ammeter should show some charge at a fast idle. Is the battery going dead ?

Looking into the generator is probably warranted if the above isn't happening. Maybe there is a movable brush issue.

Thanks Patrick, the ammeter does not show any charge at all. The battery has been replaced so i don't think it is the battery. i have replaced the cut-out with a couple others i had and still only meters 6.1 - 6.2 at any given time.

i am really leaning towards the Generator being the issue.
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Old 07-09-2020, 02:04 PM   #9
rotorwrench
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Default Re: 1931 Generator needs rebuilt ?

If it has a diode that looks like a cut out on it, isolate the connections on both sides and ring the diode through with an Ohm meter. It should pass the current one way but not the other. If it's not a diode but a real cut out relay then it needs to be tested. They can be tested with an 8-volt battery with a quick connection to see it it closes the points and allows voltage through.

If the generator motors then it has field and brush connections but it may still have a problem with the 3rd brush or armature. A person needs a growler to test the armature. The rest can be easily tested for field ohms and shorts to ground anywhere.

The ammeter should show a healthy discharge when you turn the lights on with the engine off. If it doesn't, you need a better ammeter. I don't trust the reproductions. They have poor quality control and are not sensitive enough to give a correct indication.

Your battery has to be in good condition or a 3-brush generator won't hold good voltage. The battery controls the voltage of the system. I worry more about the amperage output than the voltage. No amperage output equals a generator that is not working for one reason or another. Check all your wiring over. It had to have good connections between the ammeter load and battery sides. Any bad wires or loose connections will be a problem.
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