Charging puzzle

This has always puzzled me - the tractor has done it since I've had it. IH 886. It is charging the right amount - 14.5 volts or so. At idle the volt gauge slowly fluctuates - maybe 60 times a minute. It is varying from full charge to maybe a volt less. Not down to discharge or anything. If you throttle it up a little it fluctuates faster. When you hit a magical spot (1500 rpm or so) it charges steady. It's not the gauge. The lights visibly show it happening at night. The original owner replaced the alternator in '97 and I assume he reused the pulleys. They seem a bit large to me. I think they are larger than the 4440 with the same alternator.

I've got older machines that idle too low for the alternator to charge. On those it either is or it isn't. None of the others have a voltage swing that matches rpm around idle speed. It's just always kind of annoyed me. At night when you are feeding and idle it down you feel like you are in the twilight zone. The work lights fluctuate in brightness but not enough to be very noticeable. Just enough to make you wonder whether they are or whether you are at some bad nightclub that smells like manure and diesel fumes.

Probably the regulator or diodes.

It probably is a regulator or internal resistor problem.

Do you know if it did it with the original alternator? And is this alternator the same or more amp output as the original? If you are running a lot of accessories, it could be more than the alternator can do at low RPM.

Another thing you might try, the wire on the back of the alternator from the #2 terminal of the plug, typically is jumped to the BAT terminal on the alternator. That is the voltage reference signal. If there is higher than normal resistance on the wire from the alternator to the battery, it could give it a false signal. You could try (just temporary to see if it will work) remove the #2 wire from the BAT terminal and connect it directly to the positive battery cable at the starter. See if that changes the pulsing, could give it a more stable reading without the resistance voltage difference.

Yes this sounds like a voltage regulator malfunction. The alternator is charging fine but the regulator is telling it how much & when to charge. Make sure the regulator is grounded good. One other thing is alternators should charge very well at an idle. One last thing is voltage shouldn't fluctuate as you had mentioned. Amperage will start off high and slowly lower once battery is charged. If you have a temp gun check all your connections while it's acting up. Any high readings will mean a loose or bad connection. Sometimes the two prong plug will have loose connection and cause this problem. It vibrates and gives the readings you're experiencing.

This will cost you a pretty penny, twice as much as your dime store Delco, but replace your Delco with a Nipendenso. Go to Deere and get one for a tractor in the 4440-4450 range and age. The only rewiring you will have to do is to cut one of the small wires and run it to the battery power on the big alternator terminal. I forget which one it is. Someone with more wisdom than me can tell you which wire to reroute.

Notjustair,With the alternator interjized,and engine running remove the 2 prong plug and see if the lights still flicker.If they do the internal regulator is bad.If they stop flickering when the 2 wire plug is unhooked you have a bad connection at the 2 wire plug terminals or at the ignition switch connection.

Den has a good idea. The wires in the flat plug can slowly break from vibration. Yours might be down to the last two strands. It's easy to check. And cheaper than a Nippendenso. LOL

Are the belts in good condition, and SNUG, and are the pulleys OK/not worn and letting the belt bottom out?