My Tractor Forum banner

L118 battery draining

13302 Views 14 Replies 4 Participants Last post by  davidg
This mower has a new battery, probably 5 hours mowing on it. A couple of service hours after the new batt was installed it came up dead. While charging it I noticed the water level was about 1.5 inches low or so. Filled it up and finished charging. Ran the mower another 2-3 service hours, now its come up dead again.

I've looked over the posts here about battery charging problems - and learned a bunch... This is a great forum you have here. But, I'm still not confident enough to make a call. It looks like the alternator or regulator. But I don't know how to test and be absolutely sure of which parts broke. Alternators and regulators are not cheap, too expensive to start part swapping.

Engine is: Briggs n Stratton Intek with 1 red wire, 1 gray wire, and 1 black wire.

What I've done so far:

- charged battery, checked voltage across battery with the engine off - was 12.8
- started engine, checked same - was 12.4
- found red wire coming from engine and checked voltage - was 12.4
See less See more
1 - 15 of 15 Posts
Re: L118 battery draining - update

Found the regulator, in plain sight, DOH! So the wires of interest are, 2 yellow and 1 red.

teh alternator is part number AM132174 and costs 33.50
the regulator is part number LG691185 and costs 92.00

was the 12.4volts with it running at WOT or just idling? you need to check it with the throttle wide open.

as to possible problems, it could be either of the above or could be a bad cable. remove and clean teh ground wire from teh battery at BOTH ends. also clean the positive battery cable and the smaller charge wire. recheck your voltages and see if it has come up now with the engine wide open.

it should have no effect, but make sure the lights are off when testing. then turn them on, if the voltage drops big time or the lights do not work, then the alternator is the likely problem.


goto and click on teh left where it tells you to "Start Here" you then enter your model number and see the parts breakdown. this is where i got the numbers above.
See less See more
Yes, the engine was running at full throttle. This time around the post to post voltage was 12.7, with the lights on 12.6.

Checked the cable connections, they look new and tight. I know appearances can be deceiving - gotta do the cleaning in a little bit. I skipped that, for now, cause I got 12.8 (DC with no AC measured there) coming off the red wire from the engine. That voltage comes from the alternator?

Theory.. I very new to this so...don't laugh. To produce greater than 12 volts, the alternator gets "tweaked" by the regulator? If thats true, then a bad regulator would cause the alternator to output 12v instead of the 13-14v you need. But then again, if the alternator is defective, the regulator can tweak all it wants and the alternator might not boost the voltage. If all the above be true then it we need more information/diagnostics.

I have a hunch my "theory" is sorely lacking... How does the regulator regulate? (my carburetor won't carb, my pistons won't .... )
See less See more
teh alternator will put out anywhere from from 20-30 volts AC. the regulator regulates and rectifies it to 13-14VDC. you need to check the AC side of the regulator to seem what that voltage is to determine if it is the alternator.
Ok, measured some more. This regulator has 1 red wire connected to the rest of mower (battery, etc), and 2 yellow wires connected to 2 black ones which lead to the engine.

with mower running full throttle:

- red wire from the end connecting to the regulator is 3-4v dc
- either black wire from the side connecting to the engine are 7-8v ac
See less See more
i will shoot Walt or Red a PM to make sure they see this. i am on some sinus meds right now and my mind is a fog.

were those voltages with the regulator hooked up to the battery or disconnected from it?
I missed your question. The voltages were unhooked from the battery - the red wire is the connection to the battery and I had it unplugged so I could test.

Update. Went to the local lawn mower shop and found an BS engine repair manual for $13. It has test procedures for the stator and regulator.

The stator test:
- Run the engine at 3600rpm (full throttle is the best I could do).
- Unhook the regulator's yellow connector, which connects 2 yellow wires
from the regulator to 2 black wires from the stator.
- Measure the voltage across the 2 black stator wires. Should be 20v AC
for engines with a 10Amp alternator. Should be 30v AC for engines with
a 16Amp alternator.

The 10A versus 16A alternator both use the same stator - the flywheel magnets are different sizes for each. Don't know how to tell what an engine has, large or small magnets.

My voltages using the above test were 8v AC. Turns out to be the same as my previous test, only difference being where I grounded my multimeter.

The other test, the regulator test, needs a way to measure up to 16 amps current, they advise using a special shunt tool to keep your meter from getting fried. I haven't done that test yet and maybe don't need to if I'm sure the stator is the culprit.

Next, open up the engine top and check wires and connections going to the stator. Or, b*tch and complain to John Deere and get some action there. This mower is only ~4 years old with 116 hours on it.
See less See more
you have the 10A alternator according to the jdparts site. so you should have seen 20VAC. i would say the alternator is the problem.
It sounds like your alternator has shorted windings. They are quite simple, just a coil of wire around an iron slug, and when the magnet flies by, it induces current into the coil. More coils mean more voltage. Short half of them out some way, you get what yours is. If it ran hot, or got overloaded, it might get an internal short. Hopefully your regulator is still okay, and that it wasn't the victim of excessive current draw.

Either way, your alternator sounds cooked. First, check to be sure it is the right distance from the magnets if it's adjustable though.

Wait! Something else just jumped out at me. You grounded your multimeter? I would expect you to measure the voltage from wire to wire. That by itself might get you up to 16 or more volts. If you measured with respect to ground, who knows what it would read.

Hope this helps a bit.
See less See more
"First, check to be sure it is the right distance from the magnets if it's adjustable though."

Well it isn't adjustable. Sorry for the delay, been out of town, just got back. To get your correct AC voltage, go from one alternator lead to the other.

I suspect you may have a bad cell in your "new" battery, Auto Zone will check it free.

Walt Conner
See less See more
I did the alternator test right out of the repair book - ac voltage across the two alternator leads. Which was 8v AC.

My battery and/or regulator may be bad - but, this "book" test for the alternator definitely proves that the alternator *is* bad. Right?
Re: UPDATE: L118 battery draining


Took the machine apart and found a stator with 3 or 4 burnt looking magnet stacks. The regulator also looks bad. There is a black stain running down from the box as if something inside melted and ran...

Looks like this happened when I jumped the mower - what else would shoot enough amps thru the system to do that? There is a 20amp fuse on the mower I woulda thought that would protect me from myself. Fooey!

Thanks everyone for helping with this problem!
See less See more
if it happened during a boost of this tractor, you may have hooked the cables up backwards. no other reason voltage would have went backwards thru the regulator/rectifier.

if it happened using this tractor to boost something else off, then you learned the lesson the hard way! if you use a l/g tractor to boost off something, disconnect the booster cables or turn the engine OFF before trying to start the other machine. i blew the fuses in my L130 trying to start up a generator i have!
See less See more
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.