wiring dual batteries, part II

[goose70]

In case you haven't guessed from my first post, I know next to nothing about electronics, so please forgive my ignorance.<br /><br />I recently replaced one starting battery with a deep cycle and cleaned the terminals on the remaining starting battery. I marked the wires so I'd remeber on which battery they go (the batteries are hooked up to an isolator switch). But when I finished putting the wires back on, I noticed that the number of negative wires greatly outnumbers the number of positives. I'd think they'd be even. <br /><br />My starting battery has one thick red wire (outboard motor)and two thick black wires (one outboard motor, one connected to second battery). It also has one thin black wire, which I assume is for the other electronics, but no other red/white wires are connected to the starting battery. Yet, when I'm switched to only the starting battery, the bilge pump, electric trim tabs, lights and all cockpit electronics work.<br /><br />The deep cycle batery has one thick red wire (outboard motor), one thin white wire hooked to the positive terminal, and on the negative terminal it has the one thick wire comming from the starting battery, two thin black wires and one green wire. Again, everything on the boat seems to work when this battery is isolated.<br /><br />But this wiring scheme makes no sense to me. I'd think that, aside from the green ground wire, the negatives and positives would need to even-out on each battery. <br /><br />I probably need to have an electrician come out, but am curious if (1) my threshold presumption about positives equalling negatives is correct and (2) if anything about my description raises alram bells for those of you who are wiring experts.<br /><br />Thanks.

 

[Silvertip]

Re: wiring dual batteries, part II

It is highly probable that the numbers will not be the same for the simple reason devices that are mounted at the back of the boat are simply grounded at the batteries. The positive lines however must first run to the console switches which can be fed by individual wires from the fuse panel. A single heavier wire normally feeds +12V to the fuse panel from the battery. A separate ground wire would also be fed forward so devices mounted forward don't need to have their ground wires run all the way to the back.

 

[swist]

Re: wiring dual batteries, part II

That wrting scheme is pretty Mickey Mouse - you should have positive and negative distribution busses which are designed for a lot of wires to be neatly and reliably connected to. The battery terminals should not be used to pile up grounds or whatever.<br /><br />The only exception on most boats is that the bilge pump is usually connected directly to the battery so it always is enabled and there is minimum chance of some connection coming loose.

 

[Silvertip]

Re: wiring dual batteries, part II

Most small boats do not have a ground buss at the stern which would force installers to run the ground wires for accessories located in that area, all the way to the helm or wherever the ground buss is located. There is nothing inherently wrong with grounding at the battery --it is the central ground point for the entire boat. In fact it eliminates three connection points that could potentially create problems (the connection at the buss bar, the battery ground connection at the buss bar, and the buss bar ground wire connection at the battery).