Home Forums Hunting & Shooting Hunter's Campfire Any mechanics out there? Alternator ?

My John Deere 2750, 86 H.P. tractor has the Alternator light on the dash and it is "ON" , can I check this while it is in the tractor running or do I just take it out and replace it ?

As with everything John Deere Parts are not cheap ! Any Ideas ?

Put a volt meter across the battery and see if the voltage goes up when you start the tractor, if it reads 14 or move volts your alternator is good... if not there may be a solinoid to check... or you can just put the meter on the back of the alternator and see if it’s putting out... if not you done.

Often it’s the solinoid / relays between the battery and alternator... and those are cheap.

Spitballing here.

Learn a little about your alternator.
There is a good chance it's not a JD specific part.
If not, then you can buy a replacement at an auto parts store.

Is there someone near you that rebuilds them.
If the armature and statutor are good, brushes, bearings, contacts,
won't cost much.

Usually your indicator light is tied to a diode trio inside the alt or on a bridge outside the alternator. If you get the model #?off your alternator, or a year tractor I can tell you exactly how to test.


It looks like you will have a B+ and a small terminal D+ that will excite the unit and control indicator light. Take a test light or voltmeter and confirm battery potential on your main B+ post (use alternator case as ground) . Should read 12 volts not started.

Then with key off your d+ the smaller post should not light test light or read 0 volts with voltmeter. Turn key to on position. D+ should now read 12 volts.


If it doesn’t, you are not exciting the alternator . Start tractor and Jump it between battery terminal and d+ , if it after jumping it you read 14.7 volts at battery your excitation wire is the problem. Could be fuse, wire, dash circuit.

If D+ does read 12 volts, the diode trio in alt is usually the problem.

Please listen to Jeff.

The tractor is a 1986 model 2750 with 2200 hours on it . There seems to be a drain on the batteries, it has two , as we use this tractor so little, but usually a quick charge and its good to go this time it would not start after sitting since this spring, so we pulled it to start it, after an hour or so of driving it home I noticed the light on.

Pm sent

It sounds like Jeff knows his stuff and I'm sure he's telling you right. I'll just chime in that I have an old school generator and starter repair shop near me that if this happened to me I'd take the alternator off and get him to test it. He could tell me in about two minutes what's wrong with it and likely fix it for not too much money.

The alternator on my Kubota L2550 quit charging. This system has an external regulator. I got troubleshooting info and started going through it. I found some of the wiring was corroded pretty bad, one was broken at the regulator. I bought a single wire alternator from Amazon, a Denzi model. It actually lined up very well, the original wire to the battery was good, and it has been great. I installed a volt meter to monitor it instead of a light. The only issue is the dash has all red lights on now that everything is bypassed, but the charging is perfect.

This:



And this:





I owned an auto repair shop for 35+ years and rebuilt my own alternators/generators and starters.

If your alternator is charging (14+ on voltmeter or appx 30 amps on ammeter) than most likely diode trio. Simply ignore the light and continue using.

-Ken

Ken if you have a bad trio most likely the unit can not excite to charge to begin with.
if you read his reply, he also has a battery drain. That could be the drain from his diode trio or he has a key off drain that caused his problem to begin with . Which will perpetuate problems as every time he uses the tractor it will be with low battery voltage. As you know, alternators are to maintain battery levels not to recharge dead batteries . Jump start a tractor with a low or dead battery and you eventually blow a diode or two in your rectifier.

Also a voltmeter test alone at battery is not conclusive that the charging system is ok. It is possible to produce voltage and still have a bad diode in your rectifier.

I had a bad alternator that would randomly drain the battery when the tractor was sitting. The new john deere re-man is complete junk. Made in China. Went through 3 starters on a 9520 this year.