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I have three generators I just refurbished from the 1950-1953 era I believe. I checked continuity between the field windings and the case. There were no shorts. I also checked the armature windings through the commutator segments. No shorts and good continuity. I figure these are 30A generators. Two of them have bearings on the pully end and bushings on the opposite end. The other has bearings on both ends. The field winding resistance was twice that of the other two. I'm thinking it maybe a 12V generator? I replaced the brushes on all of them. I tried to test the generators by spinning with a drill but I can only get to around 500RPM. I tried 0.2 ohm resistance load for the 6V generators and 0.4 ohm load with what I think is the 12V generator. I also tried just a light bulb. I was unable to measure any current or voltage output with load between the Field terminal and Armature terminal.

Is there a way to bench test these. Are there specifications available for the generators such as winding resistance? Any suggestions or assistance would be appreciated. Thank You.

You'll need a lot more power than a drill motor to test the output. The 1/2 HP motor on my lathe struggles to do any voltage testing on the checking fixture I built, and it's not able to do a full current check- - - -not enough torque. The Sun generator/regulator tester I used to teach charging system maintenance with for several years used a 2 HP electric motor. I'd suggest a small HP gas engine- - - -maybe 3 HP or more. Wire the test fixture up with a regulator and a battery and be aware that any adjustments you make with the cover off the regulator will drop slightly when the cover is replaced due to better magnetic conduction of the steel cover. PM me if you want to discuss specific testing and adjustment procedures- - - -I've been doing it since the early 1960s. In 25 years or so on the stovebolt site, I've only known two members who have been willing to go to the effort to listen to my advice on testing DC generators properly.
Jerry

The Chevy truck shop manual has a procedure for testing generators when rebuilding. It entails wiring it to a battery and running it like a motor. But to measure the amp output you’ll need to install it and measure with an amp meter.