Hitchcocks Forum

I have a 1965 Crusader, which was originally a 6 volt, on dismantling it most of the wiring was found to be removed, there is a 12 volt coil, an aluminium plate with a connector which looks like a heat sink diode, there are no clues on the bulbs and the number on the stator of the alternator is not the 6v number in Hitchcock book.(Number on stator is 47137A160,number on Rotor Lucas 4661) Can anyone help me to establish if this is a 12 volt alternator. - Thanks Pete

Alternators are rated in Watts, not Volts. Since these are unregulated devices, they'll put out any voltage you desire. It's the battery, bulbs and Zener diodes that do the regulation. So you have a choice. Do you want 6V or 12V electrics?

It sounds as though your bike has been converted to 12 volts, and has a zener diode fitted. If two of the three wires coming from the alternator are connected together then it is definitely 12 volts.

Thanks Barry Q & John M for the quick response, looking at the alternator the wiring is pretty ropey, but it looks like two wires are wired together, but I think a new one will be required. Think it was converted so I guess I may as well go the 12v route as I have most of the parts. Thanks again for the advice - Pete

When you buy a new alternator you'll need to select one with which can cope with the electrical requirements. As a rough guide; Add the Wattage of the main beam bulb to the wattage of the tail light bulb and go for an alternator that's roughly 5 Watts higher (So your battery will continue to charge while on main beam). You're looking for an alternator with an output between 60 and 80 Watts. Any higher than this and you'll need a triple pack Zener to burn off the unwanted juice.

Using a zener as a regulator is a pretty crude way to create a good charging and regulation scenario, it may produce a controlled voltage but it does so by dumping any excess output from the alternator.
In simple terms, it allows (or rather causes) the alternator to run flat out until equilibrium is reached between what current comes out and what is almost shorted to earth.
A better way is to incorporate a rectifier/regulator which controls the current drawn so as to maintain the charging voltage. I am aiming to do this at some stage, but I have yet to do it so cannot give any specific info on what to buy or how to wire it.
For occasional use, a zener is OK, if you want to get the bike going you have all you need.