dual battery setup and use question

I've searched the group and found a lot of answers, but......

I have two questions that I can't seem to find,

1. I have a starter battery attached to a perko switch with an unknown size gauge wire. I am planning on adding a deep cycle battery with a #4 gauge wire. Does the wire gauge in a dual battery setup to a perko switch have to be the same? Any potential problems with the different sizes?

2. In a general dual battery setup, battery one (switch 1) is to start the boat and battery two (switch 2) is for accessories etc. I've read that when you start the boat, you switch to one. When you are on your way, you switch to both to charge both battery. My question is why don't you switch to both when you start your boat? Then you won't have to worry about accidentally switching to off.

just need a little clarificaiton.....thanks for you help!

Re: dual battery setup and use question

How you use the switch depends on why you installed it in the first place. People generally install one because they have a gazillion watt stereo system or a lot of high current draw items like fishing lights, trolling motors and other stuff operating while the engine is NOT running. Others install one as simply a backup for starting the engine if the starting battery takes a dump. So in your scenario, setting the switch to BOTH puts both batteries on line whether the engine is running or not. If one battery goes bad (as in not just dies) it sucks the life out of the other one. The idea here is to protect the start battery from discharge (accidentally or on purpose through forgetfulness). You can certainly start the engine on BOTH and run it. But I would bet a dollar to a donut within a month you will have a situation where neither battery starts the engine - especially if you have two different size batteries. You can't get to OFF without going through BAT 1 first so switching it OFF should not be an issue. Just don't switch it off with the engine running.

Wiring between batteries and the engine must all be battery cable size or larger. Use of smaller gauge wire means trying to start the engine in BOTH will cause that smaller wire to go up in smoke. The starter draws a huge amount of current and in the BOTH setting both batteries feed it. Smoke and fire will follow. There are ample drawings and descriptions in this forum about how this works. Use the SEARCH function (Dual Battery Switch). You don't have to look far as diagrams have been posted at least three times in the last week.

Re: dual battery setup and use question

Ok, so if i got it straight, if i have a #6 gauge battery wire and use a #4 gauge battery wire, then I won't have a problem because both are battery wires and won't be too small for the amps being pulled.

I regards to my other questions, my plan was to use switch 1 to start the boat and use switch 2 when I beach camp. I was wondering if I could just switch from 2 to ALL to start the boat when I am done camping.

thanks for your response....

Re: dual battery setup and use question

Six gauge is smaller than four gauge -- not larger. If you set the switch to BOTH or to whichever battery is wired with six gauge, you will have a problem. Battery switches MUST be wired with the same size wire used in the engines battery cables. If not, the first time you forget what you are doing and try to start the engine off the wrong battery you go up in smoke. If you should have a bad start battery and try to start using BOTH you draw nearly full start current through BAT 2 and if that battery is wired using too small a wire again you go up in smoke. To put this another way -- the jumper between the ground terminals on both batteries MUST be the same size or larger than the battery cables going to the engine. The cable running from the POS terminal of BAT 1 to the BAT 1 terminal on the switch MUST also be the same size as the engine battery cable. Likewise the cable from the POS terminal of BAT 2 to the BAT 2 terminal on the switch must be the same size as the battery cables for the engine. The engine POS battery cable gets connected to the COM terminal on the switch. The engine ground cable gets connected to the now joined NEG terminals on the batteries. ALL accessories are also wired to the COM terminal on the switch with one exception. An automatic bilge pump gets wired directly to the larges capacity battery (usually the house battery which is a deep cycle).

You should look into a VSR as well. It's automatic and doesn't require switching. You just can't start the engine from the house battery unless there is a COMBINE feature.

Re: dual battery setup and use question

Thanks Silvertip,

that answers my questions.