I did quite a bit of reading on the ACR over the weekend after I had an issue.Bfun220 wrote: ↑Wed Jul 12, 2017 7:05 pm You are correct. The alternator is not connected to the switch. The rely is wired between A and B battery. Your alternator goes to battery A. Once battery A is charged above 12.9 volts (I think) it closes the rely. Once closed your batteries would be combined at this piont. Battery A while being maintain by the alternator would then charge battery B.
In the video they run the relay back to the switch because it is a shorter distance to wire. It would be the same as going back to the battery.
It looks for voltage on either battery to rise to a charging level. If 13.6V or higher, it closes the connection between batteries after 30 seconds. If 12.9V to 13.6V, it closes the connection after 2 minutes. It senses the charging voltage on battery A or B. It does not care which one. However, if the battery not connected to the alternator drops below some specific voltage, it will isolate that battery to prevent draining the good battery into a bad and/or severely depleted battery, since that could potentially suck voltage from the good battery faster than the alternator could keep it charged, leading to both batteries being dead.
I learned about the isolation feature after running the house battery too low while tinkering around. The radio and GPS gave me a low voltage warning, but I figured once I got out on the water the alternator would charge it back up and all would be good. It didn't, so I was worried until I got to reading about the ACR. I then charged the battery back to normal with a battery charger, and it worked fine next time we were on the water. I'll be wiring in my onboard charger/maintainer this week, so at least I won't need to wheel my big charger over to the marina if it happens again.
The ACR also has a terminal to power a remote LED. Just like the LED on the ACR, it just illuminates when it has combined the batteries and goes off when they aren't combined. I'm thinking about putting an LED somewhere on the dash for this.