Alternator charging at only?
 

Anybody know why the alternator seems to only charge on my 7.4L at idle and then drops off when power is applied. Belt is tight. Wire/terminals are new and clean. Anything that can be rebuilt inside? I am on vacation with the boat and they want $250 for new alt. So far, no problems as there are plenty of no wakes down here at VA Beach to keep the batts charged. Planning some night trips and parties this weekend though that might require more volts for light and stereo.

Re: Alternator charging at only?
 

How dfo you know it's only charging at idle? Did you check it with an ammeter or is it that your voltage drops.
If it's a voltage drop, it could be due to corrosion in the ignition switch.
Otherwise any starter/alternator shop can rebuild for about $100.
Gary

Re: Alternator charging at only?
 

Yes, I used my Fluke77 and at the alternator at idle it is charging at 14.6 and when I open her up the voltage drops off to 12.6. Can a fella buy a rebuild kit like the kits for the older GM AC Delco alts?

Re: Alternator charging at only?
 

I just put a 110 alternator on my 454 mag. I bought a rebuilt 65 amp from the local parts store for 35 bucks (the really common mid 80's chevy truck style) took it to the alternator shop and they bumped it to 110 and made it a one wire and put the marine case on the back for another 40 bucks. Less than a hundred bucks in the whole deal and it has made a huge difference in my charging system. I have two blue top optima's and a huge stereo system and have not had a problem since putting the new alternator on.

Re: Alternator charging at only?
 

I did a search for "One Wire Alternators" and got a couple of good sites with recommends for parts. Talked about taking a cheap rebuild and making it a one wire, like RBake did. But you should be able to find a rebuild shop that will either fix yours or sell you a new one. I think I paid $70 bucks for mine a few years back. They added the screens to make it marine, so it was legal!!

Call around, you can do much better than the $250!!

Good luck and enjoy the trip
Dick

Re: Alternator charging at only?
 

A voltage drop is not indicative of an amperage drop or a no charge situation. The only real way to test the output of an alternator is to connect an amp clamp to the output wire (orange), set your DMM to alternating voltage / peak. Then connect a load tester to one battery in the circuit, I assume you have two connected on that circiut. Start the motor, run at idle perform load test, record reading. Run engine up to 1500 rpm perform load test record reading. If you are running for example a 55a alternator then over 1500rpm you should see 55 + amps being produced during the load test. At idle a minimal amount should be produced during the load test but still noticeable.

The drop in voltage tells me you have a faulty ground or poor wiring.

Or you can take the thing off and take it to your local auto-parts store and they'll check it for free. Whatever floats yer' boat.

Re: Alternator charging at only?
 

Your brushed are shot and they either skip or bounce at higher RPMs.

PUt brushes in it and go.

MAV

Re: Alternator charging at only?
 

I had a big block Chevelle that did the same thing...and the belt seemed tight too. Turned out it wasn't tight enough :rolleyes: .