Dynamo Motor Test

Dynamo Motor Test

'Motoring' is not a conclusive indication that a dynamo will work as a generator but it is a good starting point. Failing the motor test shows that there is a problem whereas a successful motor test will, if nothing else, polarise the dynamo ready for a test on its performance as a generator. To carry out a motor test, the dynamo drive needs to be disconnected - the dynamo will not be able to turn the engine over! If the dynamo is removed from the vehicle, clamp it firmly in a vice before  trying to motor it otherwise it may fly across the bench when it starts to turn. 

First thing to do is to determine whether the dynamo is wired in 'shunt' or 'series' configuration as the test connections are slightly different.

Join the 'F' (brown wire) and 'D' (yellow wire) terminals together and connect to the non-earthed side of the battery. 

Connect the 'F' (brown wire) to the dynamo case (earth). Then connect the 'D' (yellow wire) terminal to the non-earthed side of the battery.
With both configurations, connect the earthed side of the battery to the dynamo case.

The dynamo should turn in the same direction that it would turn when being driven by the engine. If it motors successfully, test to see if the dynamo generates. To do this, remove the two wires from the battery and connect them to a dc voltmeter. Leave all other connections unchanged. Now spin the dynamo  to see if there is an output. This could be done by reconnecting the drive and starting the engine. Alternatively, if the dynamo is off the vehicle and firmly clamped in the vice, use an electric drill. Make sure that the dynamo is rotated in the correct direction - you may need a reversing drill if  it is an anticlockwise dynamo. The drill can be connected to the dynamo using a short length of rubber hose and some jubilee clips. This will provide a flexible joint which allows for any mis-alignment. If the meter shows no output then it's time to strip the dynamo down to find out why. We can help with that!
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