Oliver L

Li-ion battery types place a significant strain on an alternator due to their low internal resistance; however, in most cases, the alternators then break down and fail to shut off. Unfortunately, we haven’t heard back from the person who asked the question... but if he’s actually using lithium batteries as service batteries, that could explain the problem: the isolator switches to the service bank, the BMS shuts down the battery due to overvoltage, and the ping-pong effect begins...

Or to put it more simply: Disconnect the cable from the alternator that was connected to A and connect it directly to the cable leading to the starter or test bench. I’d prefer to use the partially drained service battery so the alternator has something to work with. And if it’s the isolator, just remove it—isolator diodes are very “old school.”

Without a meter and on-site, all I can do is guess. First off: In my opinion, these “charge disconnect switches” are, technically speaking, complete junk. Either install a second alternator or have the alternator charge the service battery directly, and then use a DC/DC charger to charge the starter battery from there—that only requires a few watts. But that’s a different topic and not the subject of your question ;) The alternator might have a temperature sensor that cuts off the excitation current if it gets too hot. Check the datasheet. In my opinion, the alternator isn’t defective—otherwise, it wouldn’t be charging at all. Is the V-belt slipping? I could imagine that the rather old cut-off switch is defective and is switching back and forth erratically, or perhaps there’s a broken wire or something similar somewhere. Maybe you could temporarily bypass the cut-off switch and let the alternator charge only the starter battery.