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Generator overcharging


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I know this has been covered before but after reading the posts I am still confused. My car has the 6V generator, 12 V battery and 12v regulator. This is because I have read a 6V generator will produce more than enough volts but not as many amps as a 12 volt generator, plus all i have one the car will be lights, so no heavy loads on the battery. The regulator is new, the wiring is new and properly connected, I have checked and made as sure as i can the grounds are good at all connections. The field coils are attached in series, one end goes to a generator brush, the other goes to ground. The generator commutator is clean and looks in very good condition. I have checked each and every section of the commutator and none of them are shorted. The generator wildly overcharges., near 20 volts at 2000 rpm. What else do I check and how do I check it. I have the top off the regulator. At idle the battery coil has its circuit open, just off idle that circuit closes and it starts overcharging and as I said before the voltage gas gone to nearly 20 volts. 

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Rusty, thanks for the response,

Two things, how will I determine which coils will work correctly? and , Its making over 18 volts now at 2200 rpm.

Will normal driving speed be more than 2200 rpm?

I really do want to change the field coils, I just haven't found anyone that can tell me how to determine what is correct.  

Any help is greatly appeciated

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If you need answers to antique auto electrical systems give Jason Smith at:  Advanced Electrical Rebuilders a call.  Jason posts here and has helped many with their problems.  Check out his web site at: http://aerrebuild.com/index.php/home.html .  You will get professional and helpful advise to solve your problem.



Jason Smith

Phone: 517-345-7272

Phone: 866-228-0218

Email: jason@aerrebuild.com


16574 S. Bauer Rd
Grand Ledge, MI 48837
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Why are you trying to make a 6 volt generator make 12 volts? Either switch to a 12 volt generator or alternator, or take the whole system back to 6 volts as original. Trying to do a hybrid system is a recipe for headaches and future problems. Pick one or the other, but don't try to reinvent the wheel. Unless you're planning a big stereo or power windows and A/C, 6 volts will work just fine and will be reliable. Don't be fooled by the old myth that you need 12 volts to make a car work properly.


Good luck!

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  I do agree with Matt, on a stock car a 6V system will work fine.

 This looks like a classic regulator issue, the voltage section is not cutting out properly, and is letting the voltage soar as the revs go up. I cannot see how changing anything on the generator will help, if the voltage is not being limited to spec by the regulator.

 Personally I have had very little success repairing these devices, I think you need a new one.

 The revs at driving speed are mainly dependent on gear ratios and driving style. You don't say what the car is, or what your intent is with it.

 On my '41 Roadmaster for instance, accelerating through the gears, I might go to 3,000 rpm, then down to a cruise of 1,500 or less at city speeds, but on the highrway, with gearing at say 20 mph per 1000 rpm, at 60, you'd be spinning at 3,000 rpm, which will burn the whole system up in no time if its' overcharging.

 Also, if the system is running at 12V, all the lights and fan and heater motors will need to be changed over too.


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Ford used basically the same generator for years, even after changing to 12 volts. The field coils out of a 12 volt generator will fit your generator.


An auto electric shop can install the coils as part of a rebuild. Or you may be able to get them from an auto electric parts supplier or Ford vintage specialist. They are not the sort of thing auto parts stores carry.

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Harwood, not reinventing the wheel, updating to one newer spoke as the rest of the wheel has been modernized.


Buick, its a 42 Ford Fordor with the original  6 G series engine which poses its own problems, changing anything is one of them, and this is the last of the challenges I will be facing as far as anything that connects to the motor


Thank you Rusty, that was the answer I was looking for. I will look to people who do that sort of thing to have it changed to 12 v coils

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I don't know the exact model but Ford used the same diameter generator with the same size field coils up to the mid sixties or until they went to alternators. Probably on Falcon and base model vehicles with a small generator.


You can't use the whole generator because of different mounting, pulley etc but some parts interchange.

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