CH740 in new CC XT3 surging & dies (FIXED!)

[stembridge]

One (hopefully final) update that I've mowed a couple more times as well as run the tractor several times for ~30 minutes or longer for other uses with no problems. Seems like it's fixed.

es

 

[stembridge]

UPDATE

After mowing all summer with no issues, the same problem has cropped back up. The first time was while I was mowing recently, and I noticed a LOW BATT message on the LCD as the engine started to sputter. Barely made it back up to the shop before it died. Battery was at around 12.3V. Putting it on a 4 amp charger for a while brought it back up, and it started okay at that point.



Took it to a tractor show along with my 8N, and it died again while driving it down to enter in the slow race, and would not start (not turning over, not even a click from the starter solenoid). Battery was at 12.4V on the LCD screen. Let it sit a couple hours and it started up, which allowed me to get it loaded on the trailer. Would not start when I got home, however. Put it on the charger a bit and it started, so I unloaded and left it in the shop.

Put it on the charger overnight, and when I checked the next morning, it was back to "no start" condition (no click, not turning over), but other electrical equipment worked fine (lights, deck motor, etc.). Battery indicated 12.8V, engine off.

I pulled the engine-to-body wiring harness connector apart and cleaned those contacts up (there was a bit of white 'haze' on them), and put a squirt of OxGard on the pins. The Kohler CH740 service manual has a test that says to depin the white wire from this connector (safety switch ground) and attempt to start to determine if a safety switch is the issue. Tractor started right up, so I reinstalled that wire in the connector and the tractor started again without issue.

I mowed the grass later in the day and the tractor ran fine the whole time.

After I was done mowing, I let it cool down, then ran the tests in the service manual for the voltage regulator/rectifier, to see if I have an insufficient charging issue due to observation of the battery voltage repeatedly getting low. I initially couldn't even find the rectifier (!), but after searching pictures of the CH740 online, saw that it's mounted on the side, down low at the flywheel end of the engine. As installed in the XT3, it's located on the engine such that it's mostly hidden by the tractor frame, and I ended up removing the black plastic filler panel below the rear of the hood (left side, facing forward) to gain better access. All tests passed without issue, but the connector itself had a lot of crud in it, so I scraped it out as best I could and put a shot of Oxgard into each pin, then put it back together.

After sitting overnight, the battery was reading 12.6V, but it started and ran fine so I moved it back into the garden shed. After shutdown, the battery read 13.4V on the readout, but was dropping - same thing I saw with it in the shop. Don't know if that's a clue or not, but thought I'd include it.

Appreciate any suggestions based on the info provided.

es

 

[bertsmobile1]

Sounds like a duff rectifier / regulator
Note there are 4 electrical connections for the rectifier, the 3 pins + the body ( ground )
Kohler like to use a brass strip in the blower housing to do this which is prone to work hardening and cracking .
The simple test for a duff rectifier is to run the mower so the battery is fully charged then remove the rectifier plug
If that stops the battery drain or slows it down drastically the rectifier or stator is duff
Fully charge the battery on an external charger then take voltage readings every few hours
Strait off the charger it should read 13 V to 14 V ( over voltage is needed for charging ) which should drop down to around 21.6 V ( a lead acid cell is 2.1 V ) and stay there
IF it drops down to 12 V or less over 5 days the battery is duff & self discharging .

 

[stembridge]

It will be at least 4-5 days before I mow again (we need rain!), so I'll keep an eye on it. What you described matches what I'm seeing - battery is at ~13.8V immediately after shutdown, then drops to around 12.6-12.8V over the next minute or so. The last couple times it died (after I realized the LCD shows battery V for a couple seconds on start sequence), it's been as low as 12.3V, which seems to be around the point the LO BATT message is triggered.

I did check the rectifier-to-ground wire as well (measured between rectifier body and engine block) - no issue there.

es

 

[VegetiveSteam]

I did check the rectifier-to-ground wire as well (measured between rectifier body and engine block) - no issue there.

es

Curious, what did you check between the regulator body and engine block? Thanks.

 

[stembridge]

Curious, what did you check between the regulator body and engine block? Thanks.

Ohms, read 0 or maybe 0.001 or something like that.

es

 

[VegetiveSteam]

What do you have at the battery with the engine running full speed? It should be between 13.8 and 14.7 VDC. If you have that, then the charging system is working correctly.

If lower than 13.8 turn the engine off and then turn the key back to the on position. Unless you have a 20 amp charging system or greater the B+ wire at the center terminal normally runs through the key switch so with the key off there is no connection to the battery. With the black lead of your voltmeter connected to the negative terminal of the battery, touch the red lead to that center violet colored wire in the regulator plug for DC volts. It should read within a couple of tenths of what you read at the battery. If you have good battery voltage there, reconnect the connector to the regulator if you've disconnected it. Now with the black lead of your voltmeter still attached to the negative terminal of the battery and the key switch still in the on position, touch the red lead to the metal case of the regulator. If you read battery voltage, the regulator isn't grounded. Simply fix the ground.

The last thing to check, again this is if the voltage at the battery is below 13.8 at the battery while running is the stator output. With the engine running at full throttle, turn your voltmeter to AC volts. Now go to the regulator where the spade terminals meet the connector. Touch the leads of your meter to the spade terminals the white wires connect to and take an AC voltage reading. It should read more than 28 VAC. There is no maximum so it could read 40 plus VAC but it needs to be 28 or above. Typically they read in the mid to high 30s.

Hope this helps.

 

[stembridge]

What do you have at the battery with the engine running full speed? It should be between 13.8 and 14.7 VDC. If you have that, then the charging system is working correctly.

If lower than 13.8 turn the engine off and then turn the key back to the on position. Unless you have a 20 amp charging system or greater the B+ wire at the center terminal normally runs through the key switch so with the key off there is no connection to the battery. With the black lead of your voltmeter connected to the negative terminal of the battery, touch the red lead to that center violet colored wire in the regulator plug for DC volts. It should read within a couple of tenths of what you read at the battery. If you have good battery voltage there, reconnect the connector to the regulator if you've disconnected it. Now with the black lead of your voltmeter still attached to the negative terminal of the battery and the key switch still in the on position, touch the red lead to the metal case of the regulator. If you read battery voltage, the regulator isn't grounded. Simply fix the ground.

The last thing to check, again this is if the voltage at the battery is below 13.8 at the battery while running is the stator output. With the engine running at full throttle, turn your voltmeter to AC volts. Now go to the regulator where the spade terminals meet the connector. Touch the leads of your meter to the spade terminals the white wires connect to and take an AC voltage reading. It should read more than 28 VAC. There is no maximum so it could read 40 plus VAC but it needs to be 28 or above. Typically they read in the mid to high 30s.

Hope this helps.

Going from memory here, but engine running voltage was 13.8 or 13.9. I'm pretty sure DC volts at the regulator plug were 0.1 difference from battery voltage. I'll have to do the regulator ground test you suggest for an answer there - all I looked for was a good ground from the regulator body to the engine block. AC voltage off the stator was ~40V.

Appreciate the suggested procedures to run!

es

 

[VegetiveSteam]

If you’re getting 13.8 or better at the battery, the regulator is grounded. Sounds like the charging system is fine.

 

[stembridge]

Used the XT3 to pull my yard wagon yesterday (starting to clean out the garden), and it fired off fine. Battery was indicating 12.5V before I started it (after sitting for five days). I let it run at full throttle while I was working (maybe 45 minutes), and it hiccuped once or twice toward the end of that time. We'll see how it does when I mow again (and put it under load), which may be a few more days due to it still being dry.

es