LT155 Charging Problem (15 Amp System)
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Thread: LT155 Charging Problem (15 Amp System)

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    LT155 Charging Problem (15 Amp System)

    Hi, I'm working on a friend's LT155 who is having problems starting his machine. He did get the machine started for the season (sat all winter in a shed here in PA) using a quick shot starter. After mowing the lawn (about 2 hrs), the machine seemed to charge the battery enough for one start. Second start failed...got solenoid clicking. I put my VOM across the battery. With key off got 12.4VDC; with key turned to start and solenoid clicking I was showing about 5VDC. All consistent with a low/dead battery.

    So we fired up the machine again using the hot shot. With engine running I'm seeing 12.4 VDC across the battery terminals. I was expecting at least 13.5VDC, consistent with a charging circuit working properly. Tells me the charging circuit is not working.

    So here are my questions: Can you verify my troubleshooting and conclusion that the charging ckt is not working? If you agree, how can I verify what has failed in the charging circuit so I replace the right part? I'm thinking it must be the stator and/or voltage regulator. How can I isolate the problem? Really hoping its the regulator (easier to replace). I think this comes down to what I should be able to see on the stator terminals at the regulator with either a VOM set in AC mode. I have an oscilloscope if needed. If I know what to look for on the stator terminals, I might be able to isolate the problem to the regulator. Or better yet, maybe there is some simple diagnostic you have from experience to isolate the problem.
    In any event, any help/advice would be much appreciated!

    Jeff

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    Captain Hook Kennyd's Avatar
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    Welcome to DT Jeff
    Kenny

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    Quote Originally Posted by Kennyd View Post
    Welcome to DT Jeff
    KennyD...any idea how long it might take to get a response to my question? THis is my first time to DT.

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    Captain Hook Kennyd's Avatar
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    Quote Originally Posted by jrapp View Post
    KennyD...any idea how long it might take to get a response to my question? THis is my first time to DT.
    Sorry man...I was in a rush earlier, I will do my best. Hopefully Kevin will chime in soon as well- he is a JD mechanic and has access to more tech docs than me.

    I agree that you should be seeing 13 plus volts while running to charge the battery. As for the reading on the stator that is definitely a Kevin question!

    Below are some pics from JDparts


    I assume the obvious has been checked like the battery cables tight and the battery load tested? How old is the battery? If it's original-know JD battery's aren't well know for their longevity!
    Attached Thumbnails Attached Thumbnails lt155.jpg
    Kenny

    -John Deere 3720 Deluxe Cab TLB
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    NP...just trying to move forward on this one. Yes, all connections are tight and clean at the battery. But as I write this, I realize I should do a continuity test from the center connector on the voltage regulator to the plus side of the battery terminal (with the red connector disconnected from the battery or course). It could be a broken wire or something disconnected in the wiring harness. I'll check that tomorrow.

    What I'm looking for is some way to determine if the regulator is bad or the stator is bad, or both.

    Thanks again for the help!
    Jeff

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    Jrapp, I'm away from my computer, but I think we can wing it. You should have a three wire regulator. The 2 wires that go to your stator should give you 30-35 vac at mid rpm. Those should be the outer wires on the regulator. The center wire should put out 13-14.5 vdc. The online parts catalog in Kenny's signature will help identify the regulator, if you have trouble finding it. Holler if you have more questions.

    Sent from Kev's EVO.
    Thanks,
    Kevin

    Master Service Technician, John Deere AG, North America
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    We, the unwilling, led by the unknowing, have done so much, for so long, with so little that we can now do anything with nothing.

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    Ken, many thanks for the info. I know where the regulator is and will check it tomorrow and message back with the results!
    Jeff

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    I am just a novice, but I had a similar problem and I also thought it was the charging system or battery. It turned out the be the valves needed adjusted as they were causing a lot of back pressure that just made it hard to turn over the motor.

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    Test Results: Engine off, voltage across batt terminals is 12.7VDC (freshly charged battery). Engine on at near full throttle, voltage across outside terminals of voltage regulator is 13.7VAC and voltage between center terminal of voltage regulator and batt negative terminal is 12.7 VDC. Also verified the resistance between voltage regulator center terminal and batt positive wire terminal is about .2 ohms (no open circuit here).

    So, looks to me like the voltage regulator is fried...or at least isn't putting out anything to charge the battery. We all agree that the next step is to replace the voltage regulator?

    Really appreciate all the help here! Loads of fun!
    Jeff

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    Actually, your AC voltage is low. You said 13.7 volts. It should be 30-35 volts. That would indicate a bad stator.

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