LT133 wires burned
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Thread: LT133 wires burned

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    LT133 wires burned

    I recently had an issue with my LT133 regulator wiring. Some of the wires to the regulator burned. See photo:
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    I resolved the issue by replacing the regulator and making sure that it had a good ground. I replaced the regulator connector housing but did not repace the pins. When I fired up the mower everything seemed to be working great....until eventually everything fried again even worse than the first time. See photo:
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    This time I'll be replacing the X4 connector housing and pins, as well as any wire that has burned. I'm ditching the regulator connector housing and I'm going to use new quick disconnect crimp terminals instead. Also will replace the regulator as resistance readings tell me it's bad according to the manual.

    My understanding is that what has caused the overheating and burned wires is the fact that there may have been some bad connections. The first time I believe it was a bad ground connection. The second time I believe it was because of charred connections in the regulator housing connector and in the X4 connector. I did try to clean them up but evidently not good enough.

    My questions are:

    Are there other problems (other than bad connections) that might cause the wiring to overheat? I need to replace all of the above anyway but is there is something else I can look for that might have caused the overheating? I would hate to get this all wired up just to have the same thing happen again.

    Also, would anyone recommend leaving out the X4 connector and just hardwiring to the regulator?

    Thanks.

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    1010's Avatar
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    Is that ground wire bolted to a plastic flywheel cover? Or is the other end of that wire grounded? I'd start there for sure.
    Last edited by 1010; 07-10-2018 at 03:35 PM.

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    I have observed many times when resistance builds at a connector that the resulting heat travels into the wires themselves and seems to change the conductive properties of the copper resulting in higher resistance in the conductor.

    It is then a cycle of more resistance = more heat = more resistance.

    Often cutting the wire back from the hot spot or trace and it can still be used if it is long enough.

    The things that could lead to the burning wires:

    The connector resistance which you already diagnosed.
    Undersized wire for the current demand. Unlikely as this is a simple matter handled by experts during design.
    Faulty regulator allowed excess current?
    JD4044M likes this.
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    xcopterdoc's Avatar
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    I would pull the covers and flywheel then have a look at the stator.

    Sent from my LGL52VL using Tapatalk

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    Quote Originally Posted by 1010 View Post
    Is that ground wire bolted to a plastic flywheel cover? Or is the other end of that wire grounded? I'd start there for sure.
    The ground wire is bolted to a plate that looks like it is threaded into the block and supports the throttle linkage. Resistance reading from ground of regulator to battery ground is 0 ohms.
    JD4044M and 1010 like this.

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    Quote Originally Posted by xcopterdoc View Post
    I would pull the covers and flywheel then have a look at the stator.

    Sent from my LGL52VL using Tapatalk
    Stator resistance across leads should be between 0.1 to 0.2 ohms according to manual and infinite from leads to ground. I read about 0.8 ohms across stator leads and infinite from stator leads to ground. Seems pretty close to me. I don't have a flywheel puller so removing stator is not an option for me. I'm hoping for a simpler solution.

    In case I do need to go this route, what would I look for when inspecting the stator? How might it cause excessive current?
    1010 likes this.

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    Quote Originally Posted by Jeff B View Post
    I have observed many times when resistance builds at a connector that the resulting heat travels into the wires themselves and seems to change the conductive properties of the copper resulting in higher resistance in the conductor.

    It is then a cycle of more resistance = more heat = more resistance.

    Often cutting the wire back from the hot spot or trace and it can still be used if it is long enough.

    The things that could lead to the burning wires:

    The connector resistance which you already diagnosed.
    Undersized wire for the current demand. Unlikely as this is a simple matter handled by experts during design.
    Faulty regulator allowed excess current?
    I was wondering if the ignition switch could cause overheating. I think mine is faulty as I sometimes need to jiggle the switch housing to get the engine to turn over. I'm guessing there is not much current running through the switch but thought I would ask anyway.
    JD4044M and 1010 like this.

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    Thought I'd post a few photos of my new wiring job. After rewiring as shown in photos below, everything seems to be working fine. Mowed the lawn yesterday and today. Will finish up tomorrow. So I learned my lesson: be sure that you have good, clean wiring connections!

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    The last photo shows the extra ground wire I added from the regulator case directly to the battery ground terminal. Also, for anyone interested, I used quick connect terminals with a barrel crimp. I also soldered the ones I could for extra security. Some of the wires started to melt before I could apply enough heat to the terminal with my 100W soldering gun so I just left them crimped. Also some of the wires are a tad long but I wanted to have some extra in case they started to melt again. Will probably shorten them up when I have some time.

    Thanks to all who responded to this thread!

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    bloodrunsgreen's Avatar
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    In order for more current to flow, it is usually a drop in resistance ( ie short to ground thus the wire because a heating filament). So besides, VR and fixing wires, I would also check on the other end of what normally consumers power and the path to them ( battery, PTO). So you need to check for a bare or pinched wire in the safety switch(s) circuit. PTO coil going bad (less than 3.8 ohms resistance), PTO switch. Then the Key switch, if you have to wiggle it to get it to start, it is failing (falling apart inside), thus shorting to ground.

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