Trouble charging batteries from alternator

[LJH]

My batteries have stopped accepting a charge or my alternator has quit. I have AGM house battery bank that ran down while I was away from our boat for an extended period of time. They are about 50% charged. When I ran the engine there was no voltage rise and the batteries showed a dicharge. The voltage regulator is providing field voltage. The alternator is a Balmar 70-110 that has less than 500 hours in service and not showing any output!. The belt tension appears good and the belt shows no abnormal signs of ware. I replaced the alternator with a Bamar 95-70 and still no output! Two bad alternators in a row!

[Captain Bill]

Where are you measuring the output at the alternator or the battery. I would suspect a bad wire either the field connection is not getting any voltage or the output wire is bad, if you are measuring at the battery.

Another possibility is if you have a switch between the alternator and the battery perhaps it has gone bad.

[Vasco]

Have you checked the regulator? This alternator takes an external regulator.

[LJH]

Originally Posted by Captain Bill

Where are you measuring the output at the alternator or the battery. I would suspect a bad wire either the field connection is not getting any voltage or the output wire is bad, if you are measuring at the battery.

Another possibility is if you have a switch between the alternator and the battery perhaps it has gone bad.

With the field voltage set at 12.8V from Start Bat, I measured Alt+ to Alt-, Bat+ to Bat-, Alt+ to Bat- and Bat+ to Alt- All we 12V. No measurable voltage drop across the Alternator shunt. If I put an isolating diode between the alternator and the battery bank the measurements are Alt+ to Alt- and Alt+to Bat- 12.6V,
Bat+ to Bat- and Bat+ to Alt- were 12V. Voltage drop measured across the diode as .6 volts. So voltage at the alternator, but no current flow.

[LJH]

After another day's troubleshooting, it turned out to be a faulty cable.

Thanks for your help guys.