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Voltage too high

T

Tree-Farmer

Member
I have a John Deere lawn mower that won t charge the battery, STX38. The mower works if I remove the battery and charge it before I use it.

I found the repair manual online. It says to remove the connector from the voltage regulator, start the mower and
Then check the AC voltage across the outside connectors.
I did this and am getting 42 Volts AC.
The manual says it should be 28 VAC.

It says: If the reading is LESS than it should be then replace the stator
If the voltage is OK, then replace the voltage regulator/rectifier.

It doesn t say what to do if the voltage is MORE than it should be.

Anyone had any experience with this?
If the AC voltage is more, if it s waaaay too high, does that mean it s a bad stator?

Can the voltage regulator convert and regulate the voltage if it s higher than it s expecting?

Thank you!
 
A permanent magnet alternator isn't going to suddenly produce 1.5 times the voltage it was wound to produce. NOT gonna happen.

It's possible your (digital???) meter is confused by the waveform it is "seeing", or freaked out from ignition system "noise".

Connect the wires back up to the rectifier/regulator, and measure again.

Then check the DC voltage reading on the rectifier/regulator's third/output terminal.

Also, the "case" of the rectifier/regulator must be grounded, it mounts to sheet metal, and problems with grounding have occurred. The system can't produce charging current without a good ground there.

If it doesn't already have one, run a ground wire from one of the rectifier/regulator mounting bolts to a GOOD ground.
 
Just mentioning this, as a shot in the dark, but I had a 76 Dodge pickup, that overcharged, and burned out the head lights. It turned out to be a bad ammeter.
 
Don't over think it, just replace the voltage regulator.

The AC voltage is created by magnets on flywheel. Slow the engine and voltage will be less.
 
(quoted from post at 00:08:09 07/30/19) A permanent magnet alternator isn't going to suddenly produce 1.5 times the voltage it was wound to produce. NOT gonna happen.

It's possible your (digital???) meter is confused by the waveform it is "seeing", or freaked out from ignition system "noise".

Connect the wires back up to the rectifier/regulator, and measure again.

Then check the DC voltage reading on the rectifier/regulator's third/output terminal.

Also, the "case" of the rectifier/regulator must be grounded, it mounts to sheet metal, and problems with grounding have occurred. The system can't produce charging current without a good ground there.

If it doesn't already have one, run a ground wire from one of the rectifier/regulator mounting bolts to a GOOD ground.
Click to expand...

Here's the official Kohler word on the voltage you measured...note the "conclusion" to Test #2, it's worded a bit differently than what you posted.

"If voltage is 28 volts or more, stator is OK.
Rectifier-regulator is faulty. Replace the
rectifier-regulator."

ptR9tlM.jpg


Link to official Kohler CV-12.5 manual...

http://resources.kohler.com/power/kohler/enginesUS/pdf/tp_2339_d.pdf
 
With the regulator disconnected, the stator output voltage will be dependent on engine speed. It's not possible for the voltage to be too high; that's what the regulator is for.

Something to check for is that the regulator case is grounded. A neighbor's ZTR quit charging, and after checking the stator voltage I told him to replace the regulator. That made no change to the battery voltage, so I checked the regulator output and discovered it wasn't grounded. He added a ground wire from one of the regulator ground screws to a good ground and it has worked fine for over a year. The shroud on that engine was plastic and didn't provide a ground. I have no idea how it was originally grounded as there was no sign of a ground lead anywhere.
 

The regulator must have solid connection back to chassis/ground/negative or the regulator s zenor diode can not pull the voltage down to 13.8V
 
I am not an electrically skilled person. I had a 165 Hydro that wasn't keeping the battery charged. It was my fault. I wasn't running the engine at full throttle. The electric clutch takes a lot of amps to stay engaged. At less than full throttle, the battery would not get enough juice to be charged.
Just my experience.
SDE
 
Cheap (non RMS) AC voltmeters are not very accurate. High AC voltage reading is no concern. All that counts is you have AC going into the
rectifier or rectifier/regulator, and DC coming out. Some of those smaller systems have no regulator at all. Larger systems do. Charge your
battery and then hook things up. Start the engine and see if the voltage rises. Anywhere from 13 volts to 15.5 volts is fine. If it goes to
16 volts or higher - you can have issues with battery life. Best way to check is with a amp gauge, but a DC volt reading can work well
enough.

On the same subject - I have two 9000 watt gas generators with electric start. Both are charging the batteries at 16 volts which is a bit
high. Both generators are from Harbor Freight. I don't know if there is problem with quality control in China or they really want battery
charge at 16 volts? It is fine for a short time, but not good when done steady.
 
I wouldn't worry much about about the AC voltage from the stator. it is above the 28v minimum.
I would check that the voltage regulator is grounded well, as has already been stated. it would not hurt to added another known-good ground
to the regulator.

Then I would start the engine and check with my from the battery neg. to the output post on the regulator. The output post is the one where
the wire goes to the chassis wiring harness. It should be something over 13v and no more than 15v. That would mean that the regulator is
doing it's job and the no=charging issue is somewhere else in the wiring harness.

It is also acceptable to run a jumper wire directly from the regulator output to the battery + cable and measure the charging output across
the battery posts. The thing to be aware of is the diodes in the regulator have to be in good shape, or the regulator itself will kill the
battery while it sits around.
 
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