Dynamo testing

[Tiger]

           

This is how I tested the spare Dynamo 
Only started generating when speed was 2500 rpm

My previous attempts were using a drill which I think too slow

[leaf200]

Is this a standard 3 brush Dynamo. If so be careful if testing not connected to a cutout and battery as it will damage it.

[Bob Culver]

For brief testing joining the output and field terminals and connecting a 12v lamp to earth or just reading volts is fine but if run in this condition as can occur if the car battery connection comes adrift the dyn will eventually cook.  Can drive thru a piece of hose or somesuch, or a loose socket to allow misalignment. 2500 rpm is quite high for a lathe.

[Parazine]

This is a good test; I use a 12V, 36W bulb, with a voltmeter in parallel, keeping the voltage down below 15V. The test will verify that the dynamo can generate power, i.e. V x I. I find that my cordless drill spins sufficiently fast to test the machine.

[Tiger]

Thanks for the replies gents.
The Dynamo which was on test has not been used for years.
So possibly lost residual magnesium
Which is possibly why it takes such high revs to start generating.
Once started a speed of about 500 will light the 12 volt bulb.