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Alternator issue


Super Moderator
Staff member
Apr 3, 2007
I'm looking into the charging system in my Hatz. I was having trouble starting; the trouble seems to have been fixed by replacing the battery, but I’m still not sure about the rest of the system. The charging voltage is 14.2-14.3 volts, which is normal, but the AGM batteries (Odyssey PC680) really want a 14.7 charging voltage. The alternator has a built in regulator so there’s no adjustment.

The alternator is a Lecce-Neville Prestolite model 8AR2169F (sales no. 110-629) which although still available I can find very little on… anybody know anything about these? Is it an aircraft part or an automotive part? It seems to be used on some diesel trucks but we all know many aircraft accessories are repackaged auto parts with expensive paperwork… though all over the Prestolite website it says, “Warning: Prestolite products are not approved for aviation applications!”

Anyway, I don’t think there’s necessarily anything wrong with the alternator, but I’d like to bump the voltage a bit to keep the battery happy. I’m not clear if the wire going back to the master switch is just a sense wire or if it handles the field current, but if I add an appropriate resistor there to drop ~0.4V, it should raise the alternator output by the same amount, no? Or is there some other reason this is a bad idea?

One document on the Prestolite website says:
“A warning light (where applicable) with a minimum rating of 2W or an equivalent resistor must be connected to the alternator to provide initial excitation current from the battery, this is necessary to ensure correct excitation. The warning light has the advantage of indicating failure of the charging system. Normally the warning light will be illuminated when the ignition switch is on and the alternator stationary. As the alternator speed is increased the warning light will go out when the cut in speed is reached.”

However, it’s not clear where that light should be connected and there is no such light on my plane.