Unfortunately striaght load testing won't catch intermittent problems. Best way with typical tools is either use a DMM that has min/max capability or the likes of a foxwell scanner and graph the voltage during a test drive. The main symptom of worn brush/slipring end of life is a trrottke off coast to a red light the voltage will dip.

I would not even consider putting an alternator not even a brand new one before in take it to auto part store for a free load test.

It was fun taking my 17 yr old oil stained alternator to test after replacing the sliprings. The guy was sure that old as hell looking unit couldn't pass but did of course flying colors. Still going strong 3.5 years layer.

Did wife's last year hers failed fast and hard. Just stopped putting out enough voltage at the end of a 7 hr round trip from Chicago to Indianapolis.

I didn't want to wait the days for the slip ring kit, and found a hardware store locally that had the correct size brushes so I bought them and did a brush only swap.

Since one bush/slip ring pair takes 70% of the wear, I swapped the polarity so the opposite slip ring will now take the abuse. I was considering doing the polarity swap before the brushes wore out it should add 50% to the lifespan but I missed the opportunity.

If I ever have an option to get an alternator out and swap the polarity, when the alternator is about 5000 hours I will definitely do it.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)