Generator hot to the touch

30Tudor (Great name....as I have a 31 Tudor)

The armature produces the power and the higher voltage applied to the field winding/coil heats up as it was not designed for the high voltage.

The armature also gets hot, since the higher current into the field coil from the high voltage increases due to ohms law and this higher current is produced by the armature.

Current flowing through copper wires produces heat as a function of the current squared times the resistance.....

In summary, the Model A Generator with the "third brush" method of current regulation will overheat with no load. The high heat is due to the overvoltage applied to the field coil and the high current drawn by the armature.

Interesting stuff. I read a good article about how the third brush method keeps the current constant. Its quite a clever design and for thoses interested its at : http://www.tpub.com/content/automotiveenginemechanics/TM-9-8000/TM-9-80000308.htm

Thanks for the good comments. It all make sense now (at least this problem).

Marc
 
I put it on the car, got it to charge (7-8 amps), charges good but it still gets hot. Maybe like Peter said "How hot is too hot?" I'm going to try one of the infrared thermometers and see what it says. Thanks again to all.
 
I hope the 7-8 amps is with the lights off and engine at cruising rpm. If you're doing this in-car, fully charge the battery first. After starting, keep the lights off until the battery stabilizes from starter use. Bring the engine speed up to about your cruising rpm and turn on the lights. Set the third brush so that your ammeter shows 1-2 amps on the plus side.

If that 7-8 amps is at idle, you'll smoke your generator and probably the battery for sure.
 
marc hildebrant said:
30Tudor and Others,

Yes, I read the section in Les Andrews book and as I thought, the lack of a load on the generator causes the voltage to the field winding to increase higher than designed. Then, using ohms law, the current in the coil rises and with IR losses, the heat bakes the coil and heats the generator. Makes sense.

Thanks for the info as today many electical appliances are made "goof proof" where as the Model A generator needed to have a load on it always.

Interesting.....

Marc
Click to expand...

With the field wire disconnected the generator will put out about 1/2 volt from the residual magnetism in the field poles. Now with the field wire connected to the adjustable brush the field windings will get a percent of the output voltage. The % will depend on the placement of the adjustable brush, but even on the lowest setting a percent will still be added to the residual magnetism, thus increasing the output in the armature. This higher output will then be fed back to the field windings, which will increase the armature output even more, which will again add to the field strength. You can see what you now have is a runaway condition when no load is applied to the generator output, and the output voltage can reach 40 volts. This will overheat the field and armature and burn out the generator.

That's why it's important to make sure EVERY connection and wire is in good condition in the charging circuit. The amp meter nuts and terminal box studs are part of the charging circuit and must be clean and tight. All wire terminals should be soldered to the wire. This makes a better and stronger connection than just crimping. BTW, there is nothing uglier than seeing a bunch of yellow crimped connectors on a Model A!!!!!!!..........A proper harness doesn't cost much.

Another advantage of having an electronic voltage regulator is not having to worry about a burned out generator from a bad connection in the charging circuit. With my EVR installed I've run the generator with no battery for an hour with no damage and no burned out lights. I ran with the lights on for about half an hour and the lights off for the other half hour. The EVR fits in place of the adjustable brush and regulates the output to a safe level, just like a modern generator or alternator does.
 
Tom W.

Yes, I agree with you. In addition, you have a good way of expressing yourself to make a complex subject understandable.

Marc
 
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