Ken: I've played with the low voltage units, and was not impressed. I used them in generator control / battery bank systems. The problem is they are not very accurate (at least the one we used). Seems like every time you tried to adjust it, the next time was different. One time it would kick out a 12, the next time 10.5, etc. Your idea is good, if the low voltage relay can be set that accurately.
I agree the timing function is minimally necessary. I just suggested those relays because they are relatively cheap, I've used them, and you can easily get them. They only come in the timer format. I also agree we don't know if his current alternator will completely fail....but I'm most concerned about the NEXT one. Using a SS relay with very little load should prevent it from failing again.
Dave: The key to how that works is what kind of circuit is in the alternator. As Ken pointed out--an unknown. My theory is that the "control wire" can actually be Ground or 12V depending on if the alternator is working. When the alternator is not working, the internal circuit grounds the control wire and turns on the LED (12V to ground). When the alternator is working, the control wire is (or should be!) 12V, turning on the relay (coil hooked to ground).
The above kind of circuit (called a dual state output or high/low driver) is very common in modern control circuitry. Think of it like there are two relays inside the alternator...one to ground and one to 12V. Which one is closed depends on the charge state of the alternator.
The test I suggested above should tell us if the theory is correct or not. But it remains a theory until we get data....
Last edited by Jeff-C-IL; 11-22-2018 at 10:58 AM.