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IGNITION CUT-OFF SWITCH - ALTERNATOR DIODE FAILURES

Posted: Sun Nov 08, 2009 9:14 pm
by Tom Styczynski
I am asking the collective technical genius of the PHA to solve a dilemma. At Weatherly I noticed my voltmeter was indicating approximately 10-11 volts DC and it never moved to the 14 volts DC post-start battery charge mode. Fortunately my battery is larger and newer then my Bugeye engine so it never failed to start even after I returned home. Having some retirement time on my hands I decided to look into the problem. I could find no circuit faults plus the battery was obviously strong. I took the alternator and a shelf spare to an automotive electric shop in Catonsville, MD. A quick test and both alternators were bad. This had happened last year explaining the bad shelf spare. Yes, they are Lucas single wire units so let us get the Prince of Darkness/If Lucas Made War They Would Never Start jokes out of the resolution process. A rebuilt alternator solved the problem plus a new rectifier diode pack fixed the shelf spare.

I have the correct cut-off switch with the alternator bleed down load resistor circuit. I can only think that I pass the annual inspection with the circuit shut off verification but this must weaken the diodes to ultimately fail later in the season.

Is there a solution to keep the alternator alive longer then a few events?

Re: IGNITION CUT-OFF SWITCH - ALTERNATOR DIODE FAILURES

Posted: Sun Nov 08, 2009 10:36 pm
by Sue Salsburg
Tom - not sure what a bleed down resistor is but we wired the switch in the Jag following the kill-switch instructions. It was messy, with extra wires going back to the battery. I think there's something in the Pegasus catalog/website. We use a Chevy alternator, if that makes a difference. Sue

Re: IGNITION CUT-OFF SWITCH - ALTERNATOR DIODE FAILURES

Posted: Mon Nov 09, 2009 5:05 pm
by Richard Elliott
The big #10 wire from the alternator needs to go to the battery and no where else. This will give the last spike from the alternator some where to go when you shut down the electrics. Works for me.

Re: IGNITION CUT-OFF SWITCH - ALTERNATOR DIODE FAILURES

Posted: Fri Nov 13, 2009 11:20 am
by GeoffCraig
Hi Tom,
An alternative to cutting off the alternator circuit would be to isolate and cut off the ignition power with the cut-off switch, much like you would if the car had a magneto.
Geoff Craig