Most common failure on any alternator should be diodes, (since there aren't any brushes.... right George?
). I would be suspicious of the regulator. We know that, for a short while anyway, the alternator is capable of putting out sufficient voltage which tells us that it's output should be
good. Check wiring for clean connections first. I also like the idea of hooking up a meter too. I am running the same Jasco 50a alternator and skytronics regulator.
Alternators have brushes. (Although I've never seen inside a Jasco unit, I've never seen an alternator that did not have brushes...I suppose it's technically feasible.) Dick is technically correct as regards "commutator" (normally used in conjunction with generators)... in alternators they are usually referred to as "brush rings" or "slip rings" but they serve the same purpose of transferring (or "commuting") current to/from a rotating armature or rotor. The term may be used with either type of generator, including "AC generators".
Worn rings (or commutator) will have slight irregularities (not perfectly round) and a worn brush will have less mass and less brush-spring tension to keep them in contact with the rings/commutator.... so higher rpms may cause the brushes to "bounce" and reduce the transfer of current....resulting in a loss of efficiency or "discharge" indication.
Here's an illustration of two popular Cessna Alternators. You can see the two brushes within their holders on the right end of the rotors.
Skytronics claims to be the only authorized Jasco overhaul/repair facility in the U.S.
You may contact them at:
227 Oregon Street
P.O. Box 807
El Segundo, California 90245
Phone:(800) 421-6846 US/Canada (310) 322-6284