3930 alternator

[professor]

I had my alternator rebuilt by a reputable shop and after I ran the tractor for an hour the battery (alternator) light begin to flash. I turned on the lights and the blinking stopped. I seem to remember sometimes generators would overcharge and the lights could be turned on to help. The alternator is a Delco. Any suggestions as to the problem will be appreciated.

 

[WM75Guy]

Very possible. Check the voltage at the battery. A fully charged 12 volt battery should have from 12.8 to 13.2 volts. The alternator charges 1 volt above what the battery is at, so with the tractor running you should be between 13.8 to 14.2 volts. Anything higher will overcharge the battery and ruin it.

I also use a DC amp clamp to check the alternator amp output. I have seen alternators show OK voltage but only put out 3-5 amps. The battery is used to start the tractor. After that the alternator powers everything and charges the battery.

 

[professor]

I was at the farm this week and I checked the voltage from the alternator.

14.46 volts lights off
14.26 volts lights on

The tractor will run approx. 10 minutes before the light flashes. Turn on light flashing stops.

 

[jinman]

I think your rebuilt alternator is putting out too much voltage. I'd talk to your alternator repair shop and ask them if they have a regulator that puts out closer to 14 vdc. As it is, you are going to cook your battery and you'll find your lights don't last as long either because the high voltage is making them brighter/hotter. Any other component that uses battery voltage directly without regulation is going to be overheating a bit.

 

[WM75Guy]

Jinman,as usual, is right. The alternator is recharging the battery for the 10 minutes. When the battery is charged it should stop climbing. The longer it runs I suspect the higher it will climb. Take it back to the rebuild shop.