If things are symmetrical at the commutator end of the dynamo then it would likely run either way . Whichever way it runs then you will still have a + and a - , just that they will not be the same way around . The two wires to the dynamo are one of the main output wires , and the other is one end of the field circuit . In both cases , output and field ( marked D and F by Lucas ) , the earth connection completes the circuit .
On an automotive dynamo you will need a CVC box to control the voltage , otherwise it will rise too high if you over rev the engine , and then it will blow the bulbs . There are two coils and some points in the CVC box . The coil with the points on top cuts in when the dynamo voltage reaches charging speed , about 12+ volts . This can be jammed closed with a matchstick if you are not connected to a battery . If you are , then the battery will try to drive the dynamo as a motor if you hold the points closed when not up to charging speed .
The other coil will start to vibrate when the voltage rises too high , This intermittently puts a resistance in the field circuit to reduce the voltage and hold it steady at about 14 and a bit volts .
If your dynamo will not charge then you may have it connected with the wrong polarity . The simple answer to this used to be to touch the cutout points together momentarily , when the battery will reverse the polarity of the dynamo . The same applies if the dynamo has lost all its residual magnetism , which will mean it will not charge until you energise the field coils by touching the points in with a battery in circuit .
This is from memory of old Lucas Magdyno sets on motorcycles , and Morris minor electrics .
No responsibility accepted !
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9th August 2017, 10:40 PM
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