Hi all,

I believe that wiring 12 volt batteries together is not well understood by most installers. It is important to “do it right”. If there are only two 12 volt batteries involved then method #2 or #3 from this page will work:

http://www.smartgauge.co.uk/batt_con.html

If there are an *odd* number of batteries then only method #3 will work correctly.

If there are an even number of batteries then method #3 or method #4 will work.

If the batteries are six volt it somewhat harder to “get it wrong”, as there can only be an even number of batteries, and most folks don't get more than four–which makes method #2 correct–and method #1 wrong. The installer is likely to “get it right” when there are only two choices.

So far I've not seen correct wiring diagrams on any of the battery makers pages–so no wonder the installers are unaware of the problem. Most of the diagrams I've found are method #1 which is blatantly incorrect and will lead to early failure of the first battery in the “chain”. Sometimes method #2 is illustrated–which if there are three or more batteries will result in early failure of "end" batteries.

I believe that errors in wiring have helped to create the myth that "six volt batteries are better".

Thanks for that, Don. I wasn't aware of the difference.

--
Dave

Can you mix both 6 volt in series with 12 volts?

You would have to have even number of six volts. Not recommended. All your batteries should be exactly the same (model, amp hour, etc.) and the same age.

Hi Krazy Koach,

You can do so--but really ought to have separate battery banks for each voltage which are independent of each other. That adds unnecessary complications to the system, and is expensive--I don't recommend it.

Yeah maybe I had better especially when I want to add a sine wave invertor right?

Hi Krazy Koach,

Sine wave inverters cost a lot more and are less efficient than Modified Sine Wave inverters. There are a few quality MSW inverters around such as Cobra which are rated to run things such as microwaves, and motors.

I could live with the five to ten fold difference in price...but the difference in efficiency is a "deal breaker" for me. I have as much storage as I can cram into my RV. It is a limited resource.

don, my golf cart has 6 batteries. i'm assuming the best way to hook them up is either 3 or 4. they are hooked up like 1 now. i can follow 3. all the cables coming off all the battery terminals going to the main cables are the same length. ex 8 cables 12" long. correct? 4 is tougher with 6 batteries.
which is the better way between 3 or 4. i have the room and can make up my own set of cables.
thanks in advance. bob

sorry guys a got dumb for awhile. after i posted i realized the cart batteries are hooked up to give me 36 volts. tried to delete post before anyone saw it. at least it is multiple batteries. duh.

bob

Hi dog bone,

I've done the same thing. You can't delete--but you can edit it to "post removed by sender". Sometimes my fingers move faster than my brain too! LOL!

in the motor home, I used the factory wiring, I have not modified the power supply - yet.

HOWEVER, at home, I use version #3.

My computer network is battery backup suppied.
My ham station is battery suppied
The emergency lighting is battery supplied
The emergency sump pump is battery supplied.

All of my devices that require battery are supplied by a large bank of 12v AGM batteries - and I just added two Trojan 105's that will be added as a 12v battery.

Each battery is connected to a copper buss bar via a #2 copper cable.
Each cable has an eye ring that has been crimped then silver soldered.

I am sure that not everyone has access to copper buss bar... since I used to work as a telephone tech, I had access to all kinds of neat things when we would pull old PBX's and replace them with digital.

I wired my 12v batteries similar to the way the telco wired the PBX batteries.

There is something that a lot of people forget. The interconnection cable is a resistor. It is a small resistor, but it still has a voltage drop.

I use a millivolt meter across a jumper so that I can measure the voltage drop and convert to amps, so I know how much current is being drawn thru that circuit.

By parallel connections, you drop the resistance, so #4 would be the way I would wire batteries if I did not have buss bars.