6 Volt Marine Battery Conversion

I got into a discussion yesterday about how to convert a 2 battery, 12 volt house battery bank into a 2 battery, 6 volt battery bank utilizing golf cart style batteries. I thought that I’d share it with you here.

And the first question is, why would you want to do this?

A few years back the golf cart people discovered that they could get more run time on electric golf carts by using 6 volt batteries connected in series (which provides 12 volts) than they could by connecting 12 volt batteries in parallel. Recently boaters and RV’ers have discovered the same thing and the 6 volt battery combo has seen a recent growth in popularity.

Before we continue let’s look at a couple of the basic rules of electricity as they apply to battery configurations.

Connecting batteries in parallel (positive to positive and negative to negative) results in the voltage remaining as one battery however the capacity (amp hours) will be the sum of both batteries.

Connecting two 12 volt / 110 amp hour batteries in parallel will result in a 12 volt bank with a capacity of 220 amp hours.

Connecting batteries in series (positive in and negative to positive connecting the batteries with negative out) results in the voltage being the sum of both batteries and the capacity remaining as one battery.

Connecting two 6 volt / 220 amp hour batteries in series will result in a 12 volt bank with a capacity of 220 amp hours.

Hmmmm, what’s the difference you might ask?

Well here it is. 12 volt batteries are comprised of 6 cells and 6 volt batteries are comprised of 3 cells. What this means is that 6 volt batteries have larger cells with plates that are more robust and each cell has an increased electrolyte volume. Because of this they can easily withstand longer and deeper discharges than 12 volt batteries of equal capacity. 6 volt batteries also have a smaller footprint (7.1×10.25”) that a comparable Group 27 12volt, battery (6.75×12.75”) however 6 volt batteries are slightly taller (11.25”) as opposed to their 12 volt counterpart (9.5”). Be sure to factor in this height difference when considering this change. The sizes listed above are an aveage but they should be close.

Also, if you have the larger 4D or 8D batteries fitted, and if you refer to the battery size chart on an earlier posting, from a size and weight standpoint alone, the advantage of the 6 volt deal becomes obvious.

Here’s how you do it.

6 volt batteries wired in parallel

The above diagram shows the two 6 volt (each@220ah) batteries wired in series and connected to bank 1 of the battery master switch. A separate starting battery is connected to position 2 of the switch. This gives us 12 volts and 220 amp hours capacity.

Heres another popular combination if your serious about some extended off shore jaunts.

four 6v batteries

Do the math. On this one we have two pairs of 6 volt batteries (@220 ah) each wired in parallel  and with the pairs wired in series we have a bank that produces 12 volts and a capacity of 440 amp hours.

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