Help diagnose charging problem

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doitmyself

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Hi guys,

My compact John Deere tractor is not charging. The battery loses charge while operating it several hours. I replaced the battery last September and everything seemed o.k..

The new battery reads 12.7 volts after being charged up. When the tractor is turned on, it reads 12.5 at the posts. It should read 14.5 Volts +/-.

I did have electrical problems in August. A wire in the rear flashing lights pinched and shorted out to ground. We blew several fuses while diagnosing the problem. The tractor would not run with this problem.

Could this fry the alternator? The fuses are good now and the alternator belt is not slipping.

How do I diagnose the problem with a multimeter?

Thanks.
 
I would start by checking the battery voltage with the meter while the engine is running. Leave the black wire on the negative terminal and move from the positive post to the terminal on the alternator. If you have 14.5 at the alternator but not the battery, you have a bad connection or wire between the two. If you only have battery voltage at the alternator, chances are, the alternator isn't putting out. MAYBE it charges through the ignition switch and you have a bad contact?? Just start at the battery and work your way around with the red meter wire.
 
The small alternator on this 25 hp diesel is hard wired inside the unit. The two wires coming out of the alternator have a molex (sp?) plug that I can disconnect.

If I attach the meter directly to the two wires out of the alternator, should I get 14.5 volts? Am I missing something here? When I tried this, I got zero volts.
 
Worst part about these small scale charging systems is that they usually have a fuse on the positive charging wire. When that blows, you immediately fry the alternator diodes, thus bye bye alternator. Not sure about your particular situation, but let’s hope that’s not what happened.
 
what model tractor ? I have a 3year old 4310 and other than no forward or reverse if the tractor gets wet and the factory has no idea what is the cause{nothing runs like a Deere untill it is wet} I fixed the problem so far ..Have you checked the fuses , just guessing ,there should be volts on on the wires you checked probably 1 wire to the battery always hot and the other volts when the key is on. I wonder if there is a fuseable link . come to think is there a heavy gauge wire to the battery and 2 lighter wires at the plug? I will have to look at mine.be back.
 
Do you see any corrosion on the battery connectors or the terminals ? If so clean with a solution of baking soda + water and refit the connectors.

It was a very enlightening, learning and humbling experience for me what a little corrosion can do. I will quote my experience though unsure if it will help you or not.

The battery, charging system and starter on the Acura work perfect but still had a starting problem! It wont start as if the battery's dead!
Turns out the problem was corrosion. Think of corrosion as resistance(electrical) between the connector and the battery terminal. That corrosion was just about right to create a big enough voltage drop across that resistance, but only when the started was keyed i.e. huge current draw.
The resistance is insignificant at normal current draw (lights, fan, radio,etc..) but at 80 or 100 Amps(starter) it becomes significant (simple Ohms Law).

Turns out that after having removed the negative battery terminal a couple of times to reset the ecu, I thought I had it fit snug and good everytime. Not so. The corrosion creeped in due to sparking between the tiny gaps left between the connector and terminal. Ofcourse a little petroleum jelly or vaseline helps avoid that. No problem so far.
 
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This is a 4115 tractor.

Here is another clue/symptom: There is an alternator/battery charging indicator lamp on the instrument panel. The light is supposed to come on when the key is turned to the "on" position, engine not running. This light is normally off during engine operation and should come on with insufficient charge.

The light does not come on in the "on" position, engine off. The bulb is good.

If the alternator circuitry is fried, would this not allow the panel light to go on. Or, do I have other alternator circuit problems?

Maybe I will disconnect that molex at the alternator, jump it, then test the light.
 
you mentioned you had electrical problems after replacing the battery, right ? if that new battery was discharged considerably when you had the problems, and looks like that might be the case from what you have described(short) then its very likely the battery is the problem.
Lead Acid accumalators dont like getting discharged below a certain point and if they do its the point of no return.
Some auto and battery stores will test your battery and charging system for free.
 
No.

Wire to flasher light shorted. Blew fuses in August. Fixed.

Replaced battery in September because it wouldn't stay charged.

Now, doing same again. Didn't do any diagnostic work in Sept., but battery guy bench tested it and said it was bad. Haven't run tractor a lot between Sept. and December.

Still not getting 14.5 volts at battery while running. Panel lamp doesn't light.

I need to confirm if alternator is good/bad. Then, work from there to see if there is a wire problem.
 
You should raise the idle when checking the alternator output.
If you need better output at idle, an overdrive [larger] pulley on the alternator will help.
Your ground and power leads must be perfect - both ends of each. You may need new cables or add an additional cable. Factory wiring is often weak.
The alternator can be removed and bench tested, as an option.
 
I think I got it, with some help from tractorbynet.com (and you BITOG'ers, of course).

This tractor has a separate voltage regulator. When I tested the alternator correctly this time, (measure AC, not DC), it was kicking out the correct voltage to the regulator.

I do not get any 12 V DC from the regulator going out. I also checked various wire continuity and grounding to hopefully rule out fried wiring.

I ordered a new regulator ($200, ouch) and hope this is it.

Thanks everyone for some great ideas. I will follow up if the outcome is different. Another great example to not jump to conclusions....I was determined that the alternator was bad.
Knock on wood, many times.
 
Maybe. But, again, the alternator seems fine.

Unlike a car, the voltage regulator is a separate electronic piece (parts sealed in resin with large heat sink fins). It is hard wired with a six wire pig tail that has to match the tractor. It can't be rebuilt.

It's not like it's a Chevy or Ford. The JD tractor is really a Japanese Yanmar. The chance that a local alternator shop could get an exact replacement seems iffy to me. But, who knows!

Thanks. Maybe I will check, just for fun.
 
$200.00! Gosh, I'd make a cheap Ford or GM unit [regulator] work by splicing/wiring it in.
An hour with wiring diagrams should tell you if this is possible, and is worth checking in to.
Also, a stand alone alternator from a car with the regulator inside can be fitted to the engine, as another option.
It is stone simple wiring, but may need a bushing or spacer to make it fit and align right.
A used alternator can be obtained from the boneyard, and traded in for a rebuilt one at a parts store. You local rebuild place may have options for you concerning changing the system to a stand alone unit.
Good luck!
 
Oops,

I should have told you guys this is my work place tractor. Repairs are covered by the loyal tax payers of Michigan. In this case, I have to balance repair time vs. parts cost.

Donald - thanks for the tip. Too late this time, but the single alt. shop in my town said he "might" be able to match the part. I may follow up just out of curiosity for future work.

Another Todd - the unit I am replacing is actually a combined rectifier and regulator and it has other circuitry such as sensors, etc..

Mechtech2 - are you related to Red Green????? Stone simple wiring? I am electrically challenged - ie., setting my meter on DC to measure AC out of this particular alternator! Today's tractors are not Ford 8Ns. Chock it up to another learning experience.

Thanks again everyone.
 
Quote:
funny the fault was in the charging circuit yet the tractor didnt show the "charging" light ??


I agree. I am concerned that there still may be some other cause of this regulator/rectifier problem.

Could someone explain: if the fuse blew during the original lighting wire short, wouldn't that protect the other circuitry? Or, are there damaging surges involved here. Both headlights blew out too. One poster above said diodes could be fried in a fuse blowing situation.


My "smallish" Graingers battery charger has a boost setting on it designed for a quick start. I read somewhere that it could damage electronics and I urge people not to use it. Any comments.
 
People say the same thing about welding on a vehicle without disconnecting the battery and ignition harness , but welding is done all the time on vehicles without disconnecting anything, and nothing seems to ever be harmed.

A short caused both headlights to blow out, blew a fuse, and wrecked the rectifier/regulator...hmmmm... did you call John Deere and ask them about it? It is not a standard charging system (external rectifier), so conventional wisdom (automotive) may not apply. I suppose you could have briefly got AC voltage through the system when the rectifier blew.
 
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