Altenator question

[deere755]

I went to start my tractor Saturday and it had to be jumped. I tested the Batteries and they both tested bad. I replaced them and it started like always. Tonite I had it running at a idle for a few minutes and when I went to shut it off the Battery light was on real dim. Hooked my meter up to the batteries all is good. Started it and checked the charging system all is good. Turned on the headlights and all is good. Shut the lights off and the needle went to 15 volts and stayed there. Battery light on the dash was dim. I can make the light go out by speeding up the engine. If it was daylight you would never see the light. Is 15 volts a little too much. Never noticed the light before the battery change.

[KYErik]

15 volts is a little bit high- I think 14.5 volts should be about as high as it should go.

What was the voltage when the dash light went out (when you revved the engine)?

To high of a voltage can heat up the batteries and bake out the water- were the old ones still full of electrolyte?

[ModMech]

Normal charging voltage for an alternator with a "12V" system is 13.6V Min to 14.5V max although most are capable of over 15V as you have discovered, it is TOO HIGH.

Check the voltage with the lights on and the tractor at 1200 RPM both at the alternator terminals and battery terminals. The voltage measured at the alternator and battery seperately must be within 1/2V of each other or you have a wiring problem. If that checks out, but the voltage is higher than 14.5, the regulator has failed (internal or external).

[professor]

I had a similiar problem with my 4WD NH 3930. The tractor was equipped with a Delco alternator (internal reg.). The alternator went bad and I had it rebuilt. The rebuilt alternator was putting out 14.7-15 and the alternator light would flash and the battery would heat. With the lights on the voltage would drop to 14.3 and the alternator light would go off. The rebuilder tried to find another regulator without luck. I bought a new aftermarket alternator and problem solved and now voltage reading 13.7.

[deere755]

Thanks for the input on this. I went back out and checked all the connections at the altenator and batteries and retested every thing. Same thing as before. Charging system was running at 14 volts without lights off and at 14 with the lights on. I shut the lights off and the needle jumped to 15 volts. After a couple of minutes it dropped back to 14 and the light stayed off. I did this at 1200 rpms.

[mscheer772]

I have available for sale a 40 amp alternator from a 4310 JD. I went with a 55 AMP.
Any interest. PM me

[BobRip]

Thanks for the input on this. I went back out and checked all the connections at the altenator and batteries and retested every thing. Same thing as before. Charging system was running at 14 volts without lights off and at 14 with the lights on. I shut the lights off and the needle jumped to 15 volts. After a couple of minutes it dropped back to 14 and the light stayed off. I did this at 1200 rpms.

I don't think a short time at 15 volts is going to hurt anything. If you are not loosing a lot of water from the battery you will be fine.

[jonyyuma]

If it is over charging you will notice sulfur odor and gassing from the caps or vents? heavy overcharging will cause a bulge in battery. I caused one of these alternators to do this by jumping and it blew out the diode bridge causing swelling...Be very careful of polarity..