Correct amperage output?

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    I’ve had my generator rebuilt twice on my Series 81 because it seems to be either shorting out or the amperage is too high. After having the generator completely rebuilt the first time, I’ve watched the amp meter like a hawk. When operating at comfortable cruising speed, about 40mph, it typically would read about +12 amps. Then one day, only a few hundred miles after the rebuild, it just stopped charging. When we opened it up we found that the armature was cooked and it had flung solder. I had it rewound and I just put it back in the car. Now at 40mph, it’s showing 20 amps. This seems much too high. What should the reading be at normal operating speed? Any other ideas on what could have caused the armature to get so hot? I don’t think I have any shorts.


    Hello Mike,

    I went back to the reference material and I show that the Maximum charging rate for a cold Series 81 generator is 24 Amps at 1600 RPM. A couple of other data points are given as normal operation:

    5A @ 800 RPM

    11A @ 1000 RPM

    15A @ 1600 RPM with 7.5V – 8.0V output

    Based on this data, your observations of current output appear to be in the ball park. You can adjust the current output of the generator by moving the 3rd brush position inside the generator. You gain access by removing the commutator cover band on the body of the generator. Shifting the 3rd brush in a counterclockwise direction increases the charging rate. Moving it the opposite way decreases the charging rate. The brush is usually secured by an adjustment screw. If you are seeing 20A, you could lower the output a little by moving the 3rd brush to take some of the load off of the system. Unless you are running extra lights or electrical accessories, getting every last amp of output from the generator is not that important, especially since your car was not built with voltage regulation or overcharging protection for your battery.

    I have had one generator fail, similar to how you described by the cutout relay failing, sticking closed, and allowing the battery to discharge through the generator. This ruined the battery and heated the generator to the point where it had flung its solder and discolored the windings. Verify the action of your cutout relay that it definitely is disconnecting the battery from the generator, say at idle, when the generator output is reduced, or when the engine is stopped. There should only be battery voltage on the battery side of the cutout relay and the generator should be isolated. I have seen large diodes successfully installed inside cutout relay bodies to eliminate the electromechanical relay action and replace it with a solid state diode.

    I assume that the bearings in the generator were replaced when your generator was rebuilt. If you have sealed bearings, which are permanently lubricated, you don’t have to worry about filling your generator oil cups anymore. If they used non-sealed bearings in your generator, they will continue to need lubrication through the oil cups at each end of the generator. Dry bearings will generate heat, but their failure will usually be accompanied by noise or seizing.

    Good luck with resolving your generator questions.

    Happy Motoring,




    Thanks so much for response, and please accept my apology for taking so long to get back to you.

    Since I posted my inquiry, it’s happened again. The armature is cooked and it flung solder.

    I’ve already been through what you suggest. Sealed bearings were installed when I had it rebuilt. I’ve tested the cut-out and it’s fine. I adjusted the third brush to the lowest setting. It brought the amperage down closer to 10 amps at normal operating speed. I did this almost immediately after re-installing the generator after having the armature rewound again. I then drove the car for no more then an hour and a half (split up between three or so short drives) when the ampmeter started to show a weeker charge, only a few amps. I removed the band to find that it flung solder again and the armature looks cooked. This is the second time this exact scenerio has played out. Everything working fine, no sign of any shorts, amperage starts to get low, and I find that it’s flug solder and the armature looks like someone spilled black coffee on it. I feel confident that the guy who rebuilt it is very competent, and I can’t find any dead shorts. I’m at a loss.

    Here’s something: With everything in the off position in the car and the ground side of the battery disconected, I put a voltmeter between the positive post and ground. I get about one and a half a volts. This suggests a mild short. But when I remove both battery cables and put my ohm meter between the two cables, I get no reading. It seems that there should be some resistance of the car is drawing voltage. I then put my voltmeter beween the two cables, battery totally out of the picture, and got about a half a volt. That must be from dissimilar metals in the car.

    Either way, if the car is drawing 1.5 volts, it seems there must be a mild short, but it doesn’t seem like that would be enough to fry the generator so quickly. I am of course on a mission to find the short(s).

    Thanks again.



    You can put a regulator on the unit. the ford 6 volt regulator works great. I removed the 3rd brush(field coil)inside the generator and routed the wire outside to the regulator. I buried the regulator in the frame where it is out of sight. the system has been in use since 2001 with no problems. one of the pa service bulletins describes how to do it. if you need I can locate it at home.


    The information for the upgrade is in the 1967 issue 4 service bulletin.

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