Alternator = battery drain ?

[MACH90XJ]

I am hunting down a batery drain without luck so far. This is not a jeep, but I cant find the link to the 12v message board I used to have.

I want to know whats in a alternator that goes bad and can cause a battery drain. Can I test it with a multimeter or do I have to take it off to test it.

I have a dual battery system in a van, the starting batt is draining while no drain on spare deep cycle.

Any tips on this type of system, or a reference for another website for electrical diagnostics being I cant find the one I used to go to.

TIA ,Mike

 

[5-90]

BLown rectifier diodes can cause trouble - it depends on whether they're blown "open" (won't conduct either way) or blown "short" (conduct both ways) - both are possible.

Try disconnecting your alternator lead and rechecking your drain KOEO, and do a separate drain check with the ammeter between the battery and the alternator.

I'd not say it's a rare problem, but I've not seen it very often - when diodes fail, they tend to fail "open" rather than "short." Still, it's a distinct possibility...

5-90