Bench testing a generator

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heck91426

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My dad’s flathead. Generator question. i was checking to see if the generator will motor. If I put 12v to the output /armature, and connect the negative to the case , I just get a spark. If I connect a jumper from the field terminal to the output/armature, and put 12v to the armature it will spin. (Doesn’t seem to be very fast tho). Am I checking this correctly?

It wasn’t making voltage when it was mounted to the engine, although I might not have hooked up the regulator properly.
 

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heck91426 said:
My dad’s flathead. Generator question. i was checking to see if the generator will motor. If I put 12v to the output /armature, and connect the negative to the case , I just get a spark. If I connect a jumper from the field terminal to the output/armature, and put 12v to the armature it will spin. (Doesn’t seem to be very fast tho). Am I checking this correctly?

It wasn’t making voltage when it was mounted to the engine, although I might not have hooked up the regulator properly.
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to test a generator, it might be better to turn its pulley with something like a drill and then measure its output voltage. although the fact that it spins when electric power is applied may well indicate that it would generate electricity if connected properly to the car.

to diagnose problems when installed, i find it effective to test at the output of the generator, and if good, the input to the voltage regulator, and if good, the output of the voltage regulator, and if good, at the battery.
 
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The fields in a 2-brush generator are relatively fine gauge wire so they don't motor well. A 2-brush generator that has had the field properly flashed to match the battery polarity as connected, will have enough magnetic gauss in the field pole shoes to generate a pretty good unregulated voltage/amperage if turned with say a buffer wheel on the pulley or installed on the engine with the belt in place. A test light can be installed to see if it lights up when the pulley is turned. Just don't forget that it's unregulated. A good generator will put out it's full amperage capability and then some pretty quickly so don't over amp it.

The voltage regulator has three basic functions. #1. It regulates the voltage through a vibrating circuit that opens and closed very fast to hold the voltage stable. #2. It limits current output through the limiter pole. #3. It has a cut out pole to bring the generator on line as soon as it reaches a voltage just above battery voltage. If it doesn't come on line then it won't generate.
 
Thank you for the responses. If i spin it with a drill , I get less than 1 volt output. If i put a jumper wire between the Field and the Output , and spin it with a drill i get 9 - 10 volts.
 
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