Weird battery wiring

[kwaltersmi]

I've finally got some time to go through our boat's system more closely and am trying to figure how our batteries are wired.

All three batteries are linked via the black/neg wires, but all red/positive wires are separate.

For some reason, the boat has two battery selector switches, each with 1, 2, all and off. The "1" post on the first selector has two of the red/positive wires. The "2" post on the first selector is wired to the "1" post on the second selector. That's all I can remember about the wiring at this point, but will examine more closely the next time I'm back at the boat.

All 12v systems function when the first selector is on "1" or "all", but nothing works on "2". However, if the first selector is on "2" and the second selector is on "1" or "all", all 12v systems function. Anyone have an idea why it's wired this way?

I can't seem to understand why there are 2 separate selector switches with only 3 batteries. Ideally, I'd like one battery on position "1" of a single selector (engine), and batteries 2 & 3 in parallel on position "2" of the same selector (house).

[scotty]

One of the "electrical guru" guys can help you more, but it sounds like you have one battery switch as a motor start switch.  The wiring is so that you can isolate your house bank (two batteries) from your start - or emergency - battery.  In different combinations you can start your engine from the starter battery, or the house battery, or both.  you can find explanations of these on the electrical 101 threads here on the tech wiki.  For many people, this seems to be fairly easy to understand, but for some (like me) it is pretty complicated.  Don't give up if it seems like Greek.  After studying it over and over, it's starting to make sense even to a illlitterate like me!

[Stu Jackson]

kw, if you go to the "101 Topics" it includes an "Electrical 101" subtopic.  Scroll down in the "Electrical 101" to the Basic Battery Wiring Diagrams, there are two of them.  It's all explained there.  Any more questions, come on back here.

I noticed that you also posted this over on sailnet, and Maine Sail answered weith his diagrams.  Those diagrams are also right here.

[lazybone]

Difficult to know exactly from the description but it sounds like the PO repurposed two (1 2 all off) switches as two plain off-on switches?

[kwaltersmi]

I'll have to take some time to trace the wires back to the switches, but I'm hoping MaineSail's explanation/diagram from over at SailNet is what's going on: The second switch is serving as an "on/off" switch to isolate the start/reserve battery.  In other words, when the primary switch is in the "1" position, I'm getting power from the two group 27 12v batteries. When in the "2" position and the secondary switch in the "1" position I'm getting power from the group 24 starter/cranking battery. Not sure if that's exactly what's happening, but I'd sure like to be able to isolate the 27's from the 24.

[Stu Jackson]

ok, KW, those sailnet diagrams are the very same ones we have here on our 'site, with even more backup explanations.

Please, use them.

And, yes, YOU need to do a wiring diagram based on what you have or all else is pure speculation on our part, and yours.

No need to guess, or else you get sparks.   

Good luck.

PS  Why anyone would use sailnet instead of this website is beyond me....

[kwaltersmi]

Agreed, the 101 series about batteries was very useful and contained the same diagrams and tons of details from MaineSail and others, so thanks.

I've got friends and trusted sailors on Sailnet, so I often hang out there too, but wouldn't use SN instead of c34.org but rather in addition to.

[patrice]

HI,

Quick way to find out which batterie is being used with the two different selectors 1/2/B. position.
Put both selector OFF.
Disconnect Pos on each Batt. exept one.
Turn selector until you get power to your panel.  Now you can identify one batt.
Do same with the others.

Unless you can follow the batt wires easily.

[kwaltersmi]

Thanks for the tip, Patrice.  I'll definitely give that a try next time I'm at the boat before I attempt to follow any wires under the sole through the other obstacles on their way to the panel.