Propshaft Alternator

[Tom Hildebrandt]

OK you technical types, I need some help.

I had a prop shaft alternator that died some time ago, the builder of the old one is no longer around.

To recreate what I used to have I have been given a "special winding" that is reported to allow full voltage out put at low rpm, I have the casing that the winding is go into, I have the large pulley for the shaft, I have the small pulley for the alternator, I have the bracket and the pulley. So the system is ready to be put back into service.

The difference in the new/old systems as best I can tell is the alternator is a Delco which is internally regulated, and the old one was an Ingram with an external regulator.

On my last system, there was a switch that normally was kept in the off position when at rest or when the engine was driving the prop. With the switch in the off position, the DField did not have power, so even though the alternator shaft was being driven the shaft alternator was not putting out power. When you switched the switch on when sailing, the dfield would recieve voltage, the alternator would then start producing output voltage so long as the boat speed was sufficient to turn over the prop, usually at about 3 knots. Full out put, about 20 amps, was achieved at 6 knots.

Now I have been told that such a system is likely to burn up the diodes unless you have a "special" alternator. The argument goes that when the switch is off, with the shaft turning but the df ield not recieving power, the diodes can still be fried. My non technical mind thinks that the diodes can only be fried if there is power output, so if the dfield is not powered, there is no output power, therefore the diodes can not be blown.

Yes or no??? Or is this one of those, I do not know it depends on....!! I sincerely hope you do not ask me too many more technical questions about this because I have just about exhausted my technical knowledge in decribing the system!!!.

Regards

Tom