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Batteries not charging over 3k RPM

Posted: Fri Oct 16, 2020 1:11 pm
by Texas710
Good afternoon all. Thankfully, my truck doesn't give me many issues, but this one came up over the weekend.

Had to drive my truck about 200 miles round trip. First issue I noticed, my speedo was not working (not sure if related). About halfway through, my generator light started flickering intermediately at highway speed, then at some point it just came on. I have two digital gauges hooked to each batteries and this showed the charge drop from about 13.5 each down to 12.5 each (give or take a few decimals points). I exited, slowed down and the light went off, battery's back up to fully charging.

The truck ran fine, read-out on batteries were in spec, so I continued on. Completed my day, started/stopped, everything was normal and I made it back home. Was not much of an issue until dark, when the headlights started draining the batteries pretty good, but was close enough to home that it wasn't a problem. I have a voltage converter for my SSI and really did not want to drop lower than 24V.

I have done some research on the site, and found an old post on this issue that Jim M post that was talking about "non concentric slip rings" or possibly loose fan belt/bad wiring.

I have taken off the front air cover (behind fan) to get at the wires. These look okay, nothing loose or obviously fried. The fan belt seems tight (no different that before). I am pretty sure this is a newer SAV alternator (built in regulator?) installed by the previous owner in 2010. Been happy so far with this alternator, no need for extra power or amps, so not sure if rewinding it is the way to go?

Main question: Anyone have this happen, any easy fixes or other things to look at? Or am I looking at biting the bullet and getting a new alternator (about 400 bucks from SAV)

Any help is great, thanks in advance.

Re: Batteries not charging over 3k RPM

Posted: Fri Oct 16, 2020 2:32 pm
by Texas710
Looking again at the issue over lunch, I noticed cylinder 1 is missing both nuts that hold the intake manifold on, conversely, where my alternator is grounded. I will source some nuts and see if that fixed the issue.

Re: Batteries not charging over 3k RPM

Posted: Sun Oct 18, 2020 4:13 pm
by VinceAtReal4x4s
Any decent alt/elec.motor shop can tell you whats wrong with it or rebuild it, if it happens to be the alternator.

Re: Batteries not charging over 3k RPM

Posted: Mon Oct 19, 2020 11:34 am
by Texas710
Man, I feel like I dodged a bullet here.

Sourced a few grade-8 metric nuts from Napa and reassembled (after cleaning up the grounding points). The charging light is off and the batteries are charging again.

Love when it's easy but still fell a little silly for posting this!