Can anyone explain how the Firefly ignition works?

[billirwinnz]

Hi Vic
Sorry I didn't see this until now. After speaking to Jaqueline Bickerstaff it seems that most Firefly owners have resorted to battery ignition. I haven't unsoldered and tested each coil but I did put a meter across each and got the same very low resistance.

I have since purchased a Zundapp primary coil to go with an external secondary and am in the process of trying to fit it in the very narrow space available behind the flywheel. I had to remove some metal from the flywheel casting around the hub so that it will fit inside the flywheel but I haven't yet got around to to trying to mount it on the bike. Other more urgent work.

I hope it will fit and that the Firefly magnets are strong enough to get a spark. I'll use a bicycle dynamo for lights which I'll never need anyway.

Bill

 

[billirwinnz]

This seems to be the theory for the Firefly alternator. Notice the winding orientations and the orientation of the magnets.

Single Phase Alternator

Since the e.m.f. induced in the armature of a generator is alternating, the same sort of winding can be used on an alternator as on a dc generator. This type of alternator is known as a single phase alternator, but since the power delivered by a single phase circuit is pulsating, this type of circuit is objectionable in many applications.

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A single phase alternator has a stator made up of a number of windings in series, forming a single circuit in which an output voltage is generated. Figure 9-35 illustrates a schematic diagram of a single phase alternator having four poles. The stator has four polar groups evenly spaced around the stator frame. The rotor has four poles, with adjacent poles of opposite polarity. As the rotor revolves, ac voltages are induced in the stator windings. Since one rotor pole is in the same position relative to a stator winding as any other rotor pole, all stator polar groups are cut by equal numbers of magnetic lines of force at any time.

As a result, the voltages induced in all the windings have the same amplitude, or value, at any given instant. The four stator windings are connected to each other so that the ac voltages are in phase, or "series adding." Assume that rotor pole 1, a south pole, induces a voltage in the direction indicated by the arrow in stator winding 1. Since rotor pole 2 is a north pole, it will induce a voltage in the opposite direction in stator coil 2 with respect to that in coil 1.

For the two induced voltages to be in series addition, the two coils are connected as shown in the diagram. Applying the same reasoning, the voltage induced in stator coil 3 (clockwise rotation of the field) is the same direction (counterclockwise) as the voltage induced in coil 1. Similarly, the direction of the voltage induced in winding 4 is opposite to the direction of the voltage induced in coil 1. All four stator coil groups are connected in series so that the voltages induced in each winding add to give a total voltage that is four times the voltage in any one winding.