Trying to help a friend with a 2003ish Lomatsu PLC210lc-7 excavator 16k hours. Earlier this year the machine stopped charging and actually drained the batteries while running to the point where the machine wouldn't shut off due to low voltage. They pulled the plug off the back of the alternator and wiggled it a bit and recharged the battery. They told me it seemed to be charging but the light is still on. Troubleshooting steps and results so far: 1: checked excitation voltage at alternator, it read same as battery 2: checked battery voltage not running, it read 25ish volts 3:checked battery voltage running with some revs, reads 28.4v(with .2 or .3v fluctuation) 4:back probed L terminal on alternator while plugged in and running, reads nothing(did not check continuity to ground which I probably should have) 5:at the connector for the safety relay that passes a signal? to the alternator checked for voltage and continuity there and got nothing running or not 6:brought up battery voltage(ID 32) and battery charge voltage(id 43) on the lcd monitor, reads battery voltage correctly, reads 0.0v for battery charge voltage. I think the safety relay is meant to provide a sub 1v signal to the alternator? not sure exactly why the alternator is connected to the safety relay like that. Not sure what to do other than toss an alternator at it(and maybe the start safety relay?), though the alternator looks pretty new and seems to be charging correctly. also not positive what sort of signal should be going to or coming from the L terminal of the alternator. Also who the hell can read those tiny wiring diagrams in the manual, had to use a magnifying glass to get anywhere. Thanks so much for any help or advice!
Im not sure the wiring diagram i have is a match for what you have there buts probably close. The safety relay is not meant to provide any voltage, but monitors the L voltage and if it sees battery voltage there it assumes the engine is running and prevents the starter from being energized when the engine is running. The L terminal should have battery voltage there when the alternator is operating so if you pull the plug off and put a temp wire on it and measure with meter. If it is charging and no voltage there something is wrong in the alternator. Should be only a minor bad connection issue which is why they got some action when they wriggled the plug. See how you go Cheers
That explanation really makes the wiring diagram make sense. This makes it seem pretty obvious that the alternator isn't quite right and should be replaced, charging or not. I backprobed the L terminal with the engine running and got 0 voltage out of it. Thanks for the response, and I'll update after the alternator replacement.
(I backprobed the L terminal with the engine running and got 0 voltage out of it.) And i hope you mean there was 28V at the B terminal when you did this and the plug was pulled off so no external wiring could influence it.!!! I would pull the alt apart and have a look see before buying new one but each to there own.
I only tested with the plug and wire connected, I'll try independently powering B and testing L with everything disconnected today if I get a chance. Thank you
Tried it today, ran a jumper for the excitation voltage, and put a meter on L terminal, got 0v, verified ground and that alternator was charging while this was happening. So, problem is hopefully in the alternator, my friend is going to pull the alternator and get it rebuilt/replace it. It's a pain enough to pull it that he'd rather do that than pull it apart and attempt a fix. Thank you so much for your help I could not for the life of me understand why the alternator was connected to the safety relay until you explained it.