ThirdBird

1989 twin 454 mags, bone stock:

My alternators tend to discharge the faster (more rpm) I go. The condition isn't always evident but most of the time it is. Alternators show about 13-14 volts at idle and slow speed. As I get to cruising speed and higher, they both tend to discharge down to 10 volts, sometimes even less than that!!!!

Took both off and to the alternator shop. Bench test showed both to be working fine. Alternator guy said no sense rebuilding them.

Any thoughts on what the problem could be? I've heard that battery connections can present problems. Heard that we should not use the stud/wingnut connection but rather we should use real post type terminals to assure good contact. Could I be experiencing high resistance at my batteries do to stud/wingnut connection, or is that a bunch of baolgna????

Iggy

When you figure it out let me know, mine does the same thing.
Some times mine won't show that it's putting out more than 10-12 volts. Then there's other times it's showing 13+ volts. What gives???

Im going to pull my alternator off and have it throughly checked.
Maybe something wrong with the diodes?
Regulator?
Both?

mopower

K.I.S.S. ( keep it simple stupid)

I had a similar problem , charged good at idle and not at speed.

Answer , Tighten the belt. At idle it would turn it , higher speeds would cause it to slip
Try this before you get crazy digging into things.

As for the battery connections...does it start ok. When you start , you're pulling a couple hundred amps through the connection and if it were high resistance you would have starting problems as well.

HARRISONMIRAGE

ARE YOUR BATTERIES DISCHARGING.I WAS HAVING A PROBLEM WITH LOW VOLTAGE AT THE HELM.WHEN CHECKING WITH METER I HAD PROPER VOLTAGE IN THE ENGINE COMPARTMENT BUT NOT AT THE HELM.MY BATTERIES WOULD NEVER DISCHARGE BUT ELECTRICAL ITEMS WOULD ACT UP THAT WERE WIRED INTO THE DASH.IF ITS A POS.WIRE ISSUE AT THE HELM ALL THE GAUGES SHOULD READ LOW AS THEY ARE ALL GROUNDED INDEPENDANTLY AT THERE SENDING UNITS.IF ITS A NEG.WIRE ISSUE ONLY THE VOLT METER WILL READ LOW.I RAN NEW 8 GAUGE POS. AND NEG.WIRE TO THE HELM AND THE PROBLEM WAS SOLVED.

ThirdBird

Thanks for the replys. Belts are good and tight. I'll check helm vs. battery voltage, never considered that one. However, I do have other gauges that act a little wierd like my temperature gauges. They don't register any temp until the engine(s) gets really hot for some reason (like when the intakes get partially plugged). So,,,,,sounds like maybe I have the same issue you had Harrisonmarage. Thanks!!!

Audiofn

Another thing that will do this is a faulty regulator. Like has been said however try and test at the battery for your volate. Unfortunatly at the battery voltage changes apear a little slower, so you have to run at WOT for a bit then while still at WOT go back and test. If you can take out the alternator and have it bench tested at your local napa or Alt. rebuild shop.

Jon

formula31

Mine was voltage regulator like Audio said, first one and then the other went too. It wasnt easy to diagnose because of my 3 battery setup with the isolator and 3 bank charger.

Gary Anderson

If you've got good voltage at the alternator, but low at the helm (guages), it's often the ignition switch. Corrosion inside will cause the symptoms you described. The coil is using the amperage flowing through the ignition switch, but the resistance at the switch results in lower voltage to the guage.
Gary

ThirdBird

Hmmmmmm, at the ignition switch eh???? Never would have thought of that one. Thanks for the input, I'll check it out. (Just love this board!!! )

Gary Anderson

Just hook the voltmeter to the hot lead, battery, and go for a run. If it's 13V there and 10V at the guage, you've found the problem. These usually show up at the start of the season, due to corrosion over winter. Also check for corrosion on the input/output leads of the ignition switch.
Gary