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Discussion Starter #1 (Edited)
Hi all.. I have a John Deere l120 mower with a 20hp Briggs and recently while mowing, the stator burned up and popped the main fuse with a short to ground. I traced the short to the stator by unplugging all the harness connectors, replacing the fuse, and plugging them back in one by one.. when i got to the stator connector, it popped. So I ordered a new stator.. installed it, and she ran fine.. for about 15 minutes.. then the fuse popped again.. once again, traced the short.. and it came back to the brand new stator!

I then got out the test light to be sure, hooked it up to the positive of the battery, and touched the ends of the stator connector, and sure enough it was pulling a ground.. I added additional shims, and checked the stator wires to make sure they weren't shorting against the chassis or flywheel.. all clear. In fact, even when the flywheel is off, the stator still shows a ground on the test light.

If I lay the stator on the motor, there is no ground. The minute I bolt it on, the ground travels through the screws and and the stator is grounded..

What could be causing the stator to ground out? a faulty stator? is there another part on the mower that could be causing the new stator to burn up in 15 min? voltage regulator?

Thanks for any help and ideas!
Nick
 

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I'm not familiar with your particular setup, but it sounds like you have either a bad regulator (if you have one) or a bad diode. A diode is placed in line from the stator to give you direct current to charge the battery, and to act as a "check valve" to keep the battery from discharging through the stator. It sounds like the battery is feeding back through the stator, thus burning it up.
The regulator does the same thing, but also regulates the voltage going to the battery.
Disconnect your battery, and check for a ground from the hot lead to ground. I'll bet there is a short to ground through either the diode or regulator.
On my Vanguard, the regulator is a small item, about 1.5" square, that sits on the side of the engine. It uses the sheet metal as a heat sink to keep itself cool.
The stator itself should show low resistance from its hot lead to ground - that is normal, since one side of it needs to be grounded in order to work. What shouldn't read to ground is the hot lead from the battery, as I said above.
Check this out, and let us know what you find.

Oh, almost forgot:
:MTF_wel2:
 

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Discussion Starter #3
so to be clear.. if i have a regulator (which I do).. i won't have the diode right? the stator has a two-prong plug, both of which plug into the regulator. So I am assuming the regulator prevents the backflow?

I was guessing it may be the regulator, but i wanted someone elses opinion before i ordered it at $72...
 

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The regulator serves as a diode of sorts, so if you have a regulator you will not have a separate diode. Before spending the money on the regulator, take a multimeter and see if you have continuity from the battery connection (output) to one or both of the stator terminals (all on the regulator itself). You might show continuity one way, but shouldn't have it both ways.
I'm not 100% certain that the stator with two leads should have a ground or not. I think it should, and the fact that it ate up the new stator means the problem is elsewhere. I am about 98% sure, though.
I don't know just what's inside the regulator. It might just be a bridge rectifier with a zener to regulate the voltage. That would necessitate the heat sink, since excess voltage from the stator would just be shunted to ground. Inefficient, but effective. Older motorcycles used that system, and newer ones may also. It's not a regulator in the sense that it controls the stator's output (like a car's), just bleeds the excess to ground.
Hope I haven't confused you...but thought a little background might help you figure it out.
 

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I went out and took some readings on my Vanguard. The stator wires measure around 1 ohm, one to the other. They both read open to ground, so the stator is not grounded. The battery lead on the regulator to each of its input wires (that connect to the stator) read open one way, and conduct the other way, using the diode function on the meter. All leads on the regulator show no connection to ground (or extremely high, that the meter couldn't read).
Hope this helps!
 

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Discussion Starter #7
update!

it was the voltage regulator gone bad. i replaced the stator first time, and it ran ok for 20 min til the ground? or voltage leak? burnt out the new stator. after replacing the voltage regulator .. plus a stator (again).. i noticed the old voltage regulator was melted when i removed it..

now its back running good. thanks for all your help.

to everyone else.. if you are popping fusing and stators.. it may be the regulator burning the stator out!
 

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And thank you for getting back to us!
 
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