no alternator output >1820 rpm

RV community,

A friends RV-6 has a peculiar behavior. It has a Vans standard 35a alternator w/external regulator and only charges (as indicated by an increase in voltage) when the engine is operating from idle rpm to about 1820 rpm. Above that rpm it does not charge. External voltage regulator is mounted on the engine side of the firewall and r2'd--same symptoms. Another related symptom is that there is static on certain frequencies when the alternator is not charging. Pulling back the rpm below 1820 silences the radio static as well as increases the volts.

Things have been going okay since we've been in the pattern a lot lately with regular ops below 1820 rpm. But today, two hours of cruising at 2400 rpm dropped the battery down to about 11 volts.

Any ideas of what's going on here? Anyone seen this one before? I did some searches but didn't find this one.

Thanks in advance for your time!

-Jim

I've never heard that one, but my worth-what-you-paid-for-it guess would be that you've got some sort of arcing or loose ground going on above 1820 RPM? That would explain the radio noise and the lack of charge. Check all connections and grounds for security, and if that doesn't work I would swap the alternator.

I would also check that your voltage indications are correct, using a multimeter on the ground. Doubtful that's the problem, but worth a check.

brushes. I bet the brushes are worn.

Given my experience with washing machines I would check the brushes too.

I had two washers that would not pick up revs as they should (low revs ok, but just would not spin up). In both cases it turned up to be worn brushes. And since altenators and motors are not to far apart...


jm2c, and not very scientific...