TESTING THE DYNAMO

From a DA7C Technical Forum clubnight demonstrated by Roger Ballard

1. Testing the armature circuit.
Remove the wires from the dynamo and connect a volt meter between the “D” terminal and earth. Start the engine. At charging speed (1000 – 1500 rpm) the volt meter should show approximately 2 volts. If 2 volts is shown it confirms that the main brushes are contacting the armature and the armature is probably serviceable. If the voltage increases with speed, this would indicate that the field winding is connected to the “D” terminal. If there is no voltage try the other terminal.

2. Testing the field circuit.
Leave the volt meter as in the previous test. Connect an ammeter between the “D” terminal and the “F” terminal. Start the engine and slowly increase the engine speed until the volt meter reads battery voltage (6 Volts) the ammeter should be reading 2 amps, a higher reading indicates an internal short in the field windings. If there is no increase in voltage above 2 volts this would indicate a break in the field winding or the field (third brush) is not contacting the armature.

3. Setting the maximum output, (3rd brush adjustment)
Connect “D” and “F” terminals together, Connect an ammeter in the dynamo output lead and turn on all the lights. Run the engine at 2,000 rpm approx. Ammeter should read 8 amps. If it is less the 3rd brush should be moved towards the earth brush. Conversely if the output is above 8amps the 3rd brush should be moved away from the earth brush.