The automatic combiner doesn't necessarily eliminate anything *except* the need to select batteries while you are charging. Not using--just charging.
The Yandina/West unit is normally installed in a system where there is one engine-mounted alternator, one starting battery, and one house battery. In that application, when you run the engine it will wait until it sees 13.5V at the starting battery, indicating the starting battery has a reasonably full charge or is getting one. At that point, it automatically adds in the house battery, allowing both to charge as long as 13.5v is still available.
When the engine is off, the voltage on the starting battery (even fully charged) will drop below 13.5 in a minute or so, at which point the batteries are isolated again. That means you can run house loads off one house bank, and know the starting battery was charged first and kept separated so it is available again for starting.
There's no provision for switching or multiple house banks in that scheme.
If you have two house banks, instead of one starting battery plus one larger house bank...yes, some type of switching to a/b or combine your banks would still be a good idea. (Dare I say "needed" ? ) And obviously, even with a combiner you might want the option of an a/b/all switch since something like a bad alternator diode could still wipe out your starting battery, even when isolated from the house bank. There are still many options. The advantage to the combiner is simply that, in its most basic installation, it ensures that the "Number One Wife" gets full and prompt attention whenever the engine is running, and is left in splendid isolation the rest of the time. As a means of protecting Number One Wife, and doing nothing more, it can still be a good idea.
Incidentally, there are also three extra contacts on the combiner, which can be manually jumpered, or connected with two switches, so that you can manually FORCE the batteries to be combined--or isolated--regardless of engine operation. So in theory, you could add two small panel switches ($1-2 each kind) and add some manual switching with it as well. In practice...that's just more switches to accidentally trip and "oops" with, isn't it?
I went online looking for aircraft type switch safety covers, the kind you have to lift in order to flip on a switch? Ouch, ten bucks each, surplus, even without the switch!
Last edited by hellosailor; 01-13-2007 at 06:42 PM.