Dynamo Testing

[DaveT]

I want to test and check a spare dynamo for my 1935 Ruby which is a Positive earth car.

How do I check a dynamo on the bench for voltage?

I can run the dynamo in the correct direction using a drill with everything secure. But when running at speed how would I check it with a voltmeter? would I put the voltmeter across the two top terminals?

If so is it +ve to the left hand and -ve to the right hand or does the +ve go to the casting and the -ve to the Field (rhs) terminal or visa versa?

Finally what voltage would I expect to see? and is there anything else that I should check while it's on the bench?

All comments most welcome

[Peter Clayton]

If you connect the two (D and F) then put a volt meter between them and the dynamo body, you should get a voltage. This will be an unregulated output and will rise with revs to probably around 20 volts if the unit is good. DON'T run it for long, as it could overheat. My 6volt dynamo has happily been putting out 12volts with electronic regulation.

[dickie65]

i have run them as a motor to test them.

[DaveT]

Hi Peter, 

Thanks for the info, I followed your advice and ran the dynamo and it produced 15v at the max speed of the little drill, is there anything else that I can check on the dynamo before fitting it?

[Nick Turley]

Hi Dave if it is doing that it is working.