multiple battery setup

I've read a bunch of threads in the archives, but im still kinda confused.

To setup multiple batteries so that your accessories run off the other batteries, you can

- get a perco switch
- get a perco switch and a battery isolator
- get a perco switch and a relay
- get a hellroading isolator/combiner

I bought a guest battery isolator from skidim before I realized that it wasnt an all in one solution, and I still needed a switch. So I bought a perco switch (1,2,all). Do I still need the isolator? Im running a fairly large stereo system (3 amps, 2 subs, nvs..etc)

any input is appreciated

You’re opening a can of worms on this one. I think I have one of the simplest setups and it works. I use a perko only, I’ve used other methods in the past, but I prefer this one. I have two 6 volt batteries in series as bank #2, one starting batteries as bank #1. All stereo equipment is directly wired to the 6 volts as is all boat power. My switch stays on battery # 2 all the time. If I need to start the boat b/c of low power on #2 I switch to #1 and start or switch to both and start, and then back to #2. (I turn my boat off when I have to switch, but I’ve never had to thus far) I have two separate trickle chargers that get plugged in every nite on each battery bank. Mikeski has another great battery hookup system using a combiner and a switch. Email me and I’ll send you the pdf file.

I agree with Adam-Perko is all you'll need.

In my old boat I just went to an auto parts store and user a "Continuos Use Solenoid". This combines the bats when the engine is keyed and seperates them when the key is off.

Solenoid only cost me like 40 bucks but that was also about 7 years ago... Just a thought

Thanks Adam, thats really what I wanted to hear. nice and easy and I have all the parts.

Is it bad to switch from "Both" to one of your batteries with a Perko switch while the boat is running? While the stereo is on?

I haven't had any problems yet...but I'm not sure if it is a good idea to keeping doing it.

Some perko's have a saftey built into them some don't. the ones that do don't "switch" the power untill it connects to the other contact. You probably have one of those, if not you would have already fried your alt.

Dj, are you driving to the trinity for Roundup?

Adam,

I had planed to, but than a friend of mine decided to get married this weekend, and im in the wedding . I reserved a camp spot and everything

The common battery switch has positions 1-BOTH-2-OFF

You can rotate the knob either direction, full rotations. If you go either battery through BOTH then you are safe, connection to the other battery is made before connection to the previous battery is lost.

If you rotate the switch so that you pass through OFF then it is REALLY IMPORTANT that the engine be off! ALternators have the electrical equivalent of momentum, they can not stop the flow of current instantaneously. If your batteries were low, and the alternator was pumping out maximum current, and you switch to OFF you will create a very bad situation. It is very likely that you will damage the alternator and it is also possible that you can destroy all the electronics in your boat.

Some battery switches have a "field disconnect" option that will shut down the alternator as you rotate towards "OFF". This requires additional wiring, and it also requires a voltage regulator and/or alternator setup that gives you access to the alternator field windings, which is not common.

As long as you pass through BOTH, however, everything is fine.

Back to the original subject:

The "battery isolator" will at least provide protection for the alternator/electronics as it prevents any damage from my above described scenario because alternator current will always have a path through the isolator to the batteries. The down side, which I think is very significant for most of the people on this forum, is that the isolator will also dramatically reduce the effective output of the alternator unless you get a voltage regulator with "remote sense" (more wiring, harder to install, requires non standard alternator with remote voltage regulator).

A battery disconnect switch (such as the brand name "Perko") is a very good idea in general, IF it is properly installed. Since all the battery current must route through the battery switch, including the starter current, you must use heavy gauge wire (#4 AWG minimum, #2 preferred). The switch wiring will certainly increase the wire run to the starter so you may need to increase the size of the wire over what it currently is to compensate for the extra run.

The major problem with the battery switch is that you have to remember to operate it. It must be on "BOTH" while you are running so both batteries will charge. You must switch to either "1" or "2" when you stop otherwise you might run down both batteries and leave you stranded.

If you add the battery combiner then you simplify the operation. Just set the battery switch on either "1" or "2" (I would pick the battery that had the shortest wire run) and leave it there. The combiner will connect the second battery when the engine is running and the alternator is working.