Understanding my boat's wiring (or not)

[ghostlymoron]

Its one one of using a 1-2-both switch and perhaps best used with some form of split charging, be that diodes, vsr or something more sophisticated

Its also possible to feed everything from the switch which then merely selects which battery is the one in service and being charged. Appropriate perhaps when no split charging is involved.

I've never had a 1-2-B-O switch and don't want one but lots of boats I've sailed on have had them. I've never really understood how they work except that the owners all get a bit twitchy when you go near them. Do they switch both the feed from the alternator and the feeds to the starter and domestics? If so - how?

[VicS]

I've never had a 1-2-B-O switch and don't want one but lots of boats I've sailed on have had them. I've never really understood how they work except that the owners all get a bit twitchy when you go near them. Do they switch both the feed from the alternator and the feeds to the starter and domestics? If so - how?

The most basic and simplest system is just one battery that supplies everything

No need to debate the shortcomings of such an arrangement


So you add a second battery .....you don't separate the domestic and engine circuits ... you fit a 1,2, both switch to simply select which battery to use and charge. See below.

From then onwards you can separate the domestic and engine systems to make the batteries dedicated to each add split charging etc etc making progressively more complex systems

[ghostlymoron]

The most basic and simplest system is just one battery that supplies everything

No need to debate the shortcomings of such an arrangement


So you add a second battery .....you don't separate the domestic and engine circuits ... you fit a 1,2, both switch to simply select which battery to use and charge. See below.

From then onwards you can separate the domestic and engine systems to make the batteries dedicated to each add split charging etc etc making progressively more complex systems

Thanks Vic, a bit clearer now. Does the 'Engine' connection on your diagram go to the starter and the alternator?

[VicS]

Thanks Vic, a bit clearer now. Does the 'Engine' connection on your diagram go to the starter and the alternator?

The very heavy cable from the isolator will so to the starter solenoid.
In the absence of any split charging system or other fancy gizmos the alternator output will probably go to the same point, possibly only a few inches away.

[ghostlymoron]

The very heavy cable from the isolator will so to the starter solenoid.
In the absence of any split charging system or other fancy gizmos the alternator output will probably go to the same point, possibly only a few inches away.

The mystery is finally explained. Thanks

[Stu Jackson]

Shouldn't be a mystery at all.

http://forums.catalina.sailboatowner...d.php?t=137615

You should really trace your own wiring to understand what you have, as previously suggested.