John Deere L111 PTO Clutch Voltage

GreasyfingersApril 21, 2011

I have an old ('80s) model J. Deere L111 with a new battery. After mowing and shutting off the engine, the battery is too low on voltage to restart. I tested the charging voltage with the PTO off (with the engine running at operating speed), and the voltage reaches about 14 volts. Leaving everything in this condition, when the PTO is started, the voltage starts to drop, until it reaches about 12 volts. With the PTO off, charging voltage again climbs to 14 volts.

Is the PTO drawing too much voltage?/Is it rebuildable?/What is the correct charging voltage with the PTO on? Simply, what are my options, assuming I have narrowed this down to the PTO clutch. Thanks for any help.

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mownie(7)

Click the link below (posted in another thread by justalurker)
and download your copy of the PTO troubleshooter PDF.

While your initial voltage test seems to indicate the charging system is OK, that might not be 100% true.
Some charging stators ( the alternator) have more than 1 independent set of coils (feeding into a "regulator/rectifier") and are capable of showing 14 volts with no load applied, even if 1 of the coils is defective.
But under a load (PTO engaged), there is insufficient Amperage output to adequately operate the PTO clutch AND recharge the battery simultaneously, so the battery voltage falls and soon the PTO disengages.
The amp draw test in the PTO manual will determine if the PTO is actually drawing too much amperage.
If the PTO amp draw is within specs, your charging system might be the issue.

Here is a link that might be useful: PTO troubleshooter

    Bookmark   April 21, 2011 at 12:24PM
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Greasyfingers

Thanks so much. This document is probably just what I need and have been looking for. Hopefully it solves my issue.

    Bookmark   April 21, 2011 at 12:47PM
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justalurker

When diagnosing a charging problem always start at square #1. You need to know that the battery is good... not think it's good.

What is the static voltage of the battery? Should be 12.7 volts DC. If the static voltage of the battery is OK then take the battery to an auto parts store and have it load tested. If the battery passes a load test then it IS a good battery and you move on to square #2.

Most people don't understand how a charging system works. The battery starts and runs the tractor and PTO. The charging system charges the battery. If the battery is marginal the charging system will never charge the battery to full charge and you're in a kind of a deficit spending situation. The longer you run the marginal battery the harder you make life on your charging system until you have earned yourself a more expensive repair that was unnecessary because you're going to buy a new battery one way or another.

Buy a battery with as many CCAs as you can find and for sure above the tractor manufacturer's specs and don't buy a battery from a store that won't or can't load test it right in front of your eyes and show you that it passed. You wouldn't believe how many marginal batteries come down the production line and get bought by unsuspecting customers.

It sounds more like you have a battery with a marginal cell then a problem with the PTO. Electric (clutch) PTOs are a go or no go piece of hardware. They usually short open or short to ground or seize. Since electric (clutch) PTOs draw a lot of current they will amplify a charging system problem into a glaring problem.

    Bookmark   April 21, 2011 at 3:21PM
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BriggsGalaxieman

"If the battery is marginal the charging system will never charge the battery to full charge and you're in a kind of a deficit spending situation."

Yeah, that's true, but as Washington has taught us.....just turn the screw marked 'Raise The Debt Ceiling' clockwise and everything will be fine....

    Bookmark   April 22, 2011 at 2:56PM
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justalurker

"Yeah, that's true, but as Washington has taught us.....just turn the screw marked 'Raise The Debt Ceiling' clockwise and everything will be fine...."

So the answer is an 18 volt battery?

How about we keep politics and social comment on a forum where it belongs and try to help the OP?

    Bookmark   April 22, 2011 at 3:05PM
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BriggsGalaxieman

"Jokes of the proper kind, properly told, can do more to enlighten questions of politics, philosophy, and literature than any number of dull arguments."....Isaac Asimov

"I think the next best thing to solving a problem is finding some humor in it."....Frank A. Clark

    Bookmark   April 22, 2011 at 4:40PM
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mownie(7)

I like humor!

    Bookmark   April 22, 2011 at 4:44PM
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Greasyfingers

Back to the issue, fellas. The new battery was load tested yesterday and it is in perfect condition. A resistance test indicated that the clutch coils have 0.9 ohm. The document I downloaded from mownie7 says the coils should be 2.4-2.9 ohms, assuming this clutch is a Warner model. So, I can either remove and recheck the clutch before a new one is ordered up, or, I can run the PTO for awhile, then shut it off and let it the engine recharge the battery. Decisions, decisions...

On another note, the only time politicians tell the truth is when they're calling each other liars! A good day to all!

    Bookmark   April 22, 2011 at 5:18PM
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mownie(7)

At .9 ohm you would certainly have an increase in amp draw on that circuit, probably to the border line of blowing a fuse or having a PTO switch burn out. You haven't replaced the OEM fuse with something larger, have you?

    Bookmark   April 22, 2011 at 5:41PM
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Greasyfingers

No, the fuse hasn't been replaced. Matter of fact, this model uses a circuit breaker. If there's less resistance through the coils, wouldn't that indicate a short in the coiled wire�essentially making the circuit shorter and indicating less resistance? If so, I would think the only option would be to replace the clutch. Thanks for your help.

    Bookmark   April 23, 2011 at 10:20AM
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mownie(7)

Your thoughts on the resistance are correct and for the reasons you state.
But I still maintain that the condition you are documenting here is right on the border line of causing some other problems as well and not just having the battery run down from excessive current draw.
It may be that the PTO switch Deere chose back when this tractor was built is heavy enough to endure (for a little while) the extra load without burning up. I believe if "today's switches" were in place you would probably have reported a problem with burn out of the PTO switch before you reported a draining battery in use.

Anyhow, you know you have a problem (battery going dead) and have found a defective condition in the tests to the PTO clutch which is probably causing the problem.

It's a bitter pill to swallow, but clutches do fail...........and you get to swap money from your pocket to someone else's.

    Bookmark   April 23, 2011 at 10:50AM
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justalurker

"It may be that the PTO switch Deere chose back when this tractor was built is heavy enough to endure (for a little while) the extra load without burning up. I believe if "today's switches" were in place you would probably have reported a problem with burn out of the PTO switch before you reported a draining battery in use".

It would be easy and cheap enough to install a fuse of the same value (or 1 amp lower) as used today in similar JD installations in the circuit and see if it pops. If the fuse pops that would confirm Mownie's theory and be another indication of a faulty PTO.

If you have to buy a PTO it would be nice to have as many indications that the old one has failed as you can get cause they are rarely returnable.

    Bookmark   April 23, 2011 at 11:33AM
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BriggsGalaxieman

Before you shell out the big bucks for a new PTO there is one more thing you might want to check. PTO coils are huge inductors. They should have a diode across them to protect the PTO switch from the inductive kick that happens when you turn off the PTO. Without the diode the switch will have a short life.

I don't know how your tractor was made. If it has a diode it could be someplace in the wiring harness or built into the PTO itself.

If you did your resistance check properly, you disconnected the PTO completely from the harness when measuring. Then you would have gotten a good reading provided there is not a diode built into the PTO assembly.

If there is a diode built into the PTO assembly you have to be aware of the meter polarity. One way the diode is not a factor and the other way the diode would likely cause a lower reading, like you measured.

One more possibility exists, if the diode is built into the PTO. The diode itself could be bad! If you have a good schematic of the wiring it should indicate where the diode is located.

    Bookmark   April 23, 2011 at 3:55PM
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mownie(7)

Well now, BG brought up a good point there. You do need to check the ohms and then reverse the leads and check again.
If you consistently get .9 ohms no matter which way the leads are applied, it would indicate the coil is most likely shorted. The diode (if present and if good) would cause your ohmmeter to show practically no resistance in one direction (because it "bypasses" the coil that way) but would show some resistance when the leads were swapped around.
I also second the suggestion for replacing the circuit breaker (temporarily) with a fuse of the same ampacity and giving the tractor a test run.

    Bookmark   April 23, 2011 at 10:41PM
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justalurker

The presence of a diode in the PTO circuit is a good catch, Reversing the ohm meter leads is an EZ thing to do.

If there were a diode in the clutch I would expect the tech info to indicate that and neither the Warner nor the Ogura troubleshooting info does.

A diode elsewhere in the circuit should be indicated on the tractor wiring schematic.

    Bookmark   April 24, 2011 at 12:03AM
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rdaystrom

I had a Cub Cadet do this very thing. It was drawing the battery down but in addition it burned out the PTO engagement switch, and started blowing fuses quicker and quicker. With .9 ohms (instead of the normal 2.4 to 2.9 ohms) the clutch is bad and should be replaced. A new clutch fixed my problem.

    Bookmark   April 24, 2011 at 2:21AM
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Greasyfingers

Thanks for all the feedback. As I recall, I did check the clutch connector in both directions and got the same ohm reading. So, I'll follow up on this thread when I get the situation fixed. It may be awhile before I can get the mower into my shop for a little teardown and TLC (time, labor, cash).
In the meantime, I will use my other mower (GX85), but the old L111 will get repaired, as it was my fathers, who always referred to it as "Little John." He always claimed it was the best mower he ever owned, and after nearly 30 years of service, I can't argue with that. Lots of steel and a bit of fiberglass bodywork. Looking at the quality of new mowers is always a disappointment. I bid you all good health and wealth.

    Bookmark   April 26, 2011 at 10:10AM
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Greasyfingers

Just a followup on the clutch. I took it to a J. Deere shop and they tested it for amperage, which turned out to be 18 amps! The original clutch was an Ogura and the replacement clutch is made by Warner. The resistance in the new Warner clutch is 2.7 ohms. If this doesn't solve the problem, I'll post it here. Thanks again to all.

    Bookmark   April 27, 2011 at 1:36PM
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