Prepare Me For Battle--HAVE to 2nd Battery

[Jeff T]

I'm mostly just worried about the battery cables. I've wired up amps before, so I can take care of that. I have just never wired up battery circuits.

[dogbert]

Originally posted by Jeff T
I'm mostly just worried about the battery cables. I've wired up amps before, so I can take care of that. I have just never wired up battery circuits.

It's really no big deal. Depending on what you do, you'll be just moving cables around. Battery isolators are nice, but they're not really redundant. That's why I have a switch. If one of my batteries goes dead, I've got an identical one to back me up. I know that starter batteries are not ideal for running amps, but I just don't run the kind of system where I need a deep cycle battery to keep up with it.

As I mentioned, I'd measure where you want the batteries to go, and then measure the cables to have them made. I was able to wire tower, install my amp and wire the second battery in a few hours, even with a couple of trips to the dealership. Adding the second battery was the easy part.

[talltigeguy]

I bought battery cable from Ebay and they even heat shrunk the connectors on for me. I couldn't find the exact people I bought from, but have heard good things about these guys, and the price is very competitive. The cable that connected the two batteries that I already had was 0 gauge, so I went with that.

http://cgi.ebay.com/ws/eBayISAPI.dll..._promot_widget

Chpthrl - I was referring even to getting different models of the same type of battery. My concern with one deep cycle and one not, is that when the isolator is open and the alternator is working both batteries, the charge will not distribute evenly because they don't charge or discharge at the same rate due to differences in internal resistance in the battery itself. It may not make a difference in real world applications, but it makes sense to me to have all of the batteries IDENTICAL.

[dogbert]

Agreed. Two batteries of the same type is key.

[chpthril]

I get my marine rated black and red primary wire and ends fromWEST MARINE . They are more resistant to the marine environment (heat, flame, gas, oil) than auto wire. A little safer IMHO, but they both will work.

Deepcycles and starting batteries will charge, and discharge, at differant rates. That what makes them work so well in the correct application.

Alternators output is based on load. It will always be charging, but it's rate (amps out) will go up and down as load changes. The Isolator will act as a 'filter' between the alt and the batts. The alternator will not see 2 differant loads at 2 differant resistances. The Iso will, in a sense, split the differance. The starting battery has a faster charge rate and the deep has a slower charge rate. Currant takes the path of least resistance, so the starting batt will draw more currant first. As it reaches full charge, the Iso will tapper off the flow to it and send more currant to the deep. Because the deep charges slower, the alt will sense this and reduce it's output.

Houseboats and yachts have been running Multiple banks of house and starting batteries seperated by Isolators, some using duel alternators, for many years.

[Jeff T]

Awesome Information. Thanks.

[Jeff T]

Originally posted by chpthril
I get my marine rated black and red primary wire and ends fromWEST MARINE . They are more resistant to the marine environment (heat, flame, gas, oil) than auto wire. A little safer IMHO, but they both will work.

How I determine what guage to use?

[chpthril]

I went with 2ga for my 3rd battery install.

[Jeff T]

Is there a rule of thumb to determine what guage?

[talltigeguy]

It should be as big as your thumb. Just kidding. I chose 0 gauge because that is what the factory used to put the two existing batteries together. I know it cost more than 2 gauge but my 3rd battery is about 8 feet of cable away from the 2nd, so I overbuilt it a little. I felt that all batteries should be connected with the same gauge. If you can afford it go big. In theory, if you have them closer, you can get by with less size (resistance increases with longer wire).

Chpthrl - that is the kind of information I hoped you would give. Assuming he is right, his starting battery will charge faster than the stereo batteries (I'd rather have the stereo dead than the starter). I still opted for simplicity.

[xpjim1]

I have not read this much since College. This is a much better educational tool.

[lee]

Originally posted by Jeff T
Is there a rule of thumb to determine what guage?

When we do a additional battery install, we use 2/0 wire for both batteries.

[chpthril]

http://en.wikipedia.org/wiki/American_wire_gauge

Here is a link to a chart that shows size, resitance, and currant ratings. It's the best I could come up with, as I have never used a chart to calculate wire size. I always go with my gut (and 17 years experiene).

It's like we used to say in the shop when we had to fix someones 'homebrew' :

WE WIRE FOR FIRE

[lee]

Wire Size Guide

[chpthril]

here is one at west marine

another

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