12v or 6v ?

[dakno]

I am planning new dc system . What r pros/cons of 12v vs 6 v. I am thinking of space/capacity for 4 dep-cycles. Maybe one 4 engine and 3 for house! would app. input from u out there.

[By Invitation]

Uh...... What can you get that runs on 6V? Most everything marine is 12V. Why complicate your life. KISS

[denverd0n]

The main reasons for using 6-volt batteries are twofold: 1) 6-volt golf-cart batteries are commonly available and relatively inexpensive. 2) A 6-volt 200+ amp hour battery weighs a whole lot less than a 12-volt 200+ amp hour battery and so by wiring together two 6-volt batteries you get all the amp hours but each one is light enough for one person to lift and carry.

Of course, 6+6=12, so you MUST wire them together in pairs! There is no way to wire three 6-volt batteries together to get the 12-volts that your boat is expecting. That means you either wire four 6-volt batteries all together to make one big 12-volt bank, or you wire up two pairs of 6-volt batteries to make two 12-volt banks, or (if you want to do the three-and-one arrangement) you must use 12-volt batteries.

[jaga]

Still, what can you do with 6v?

If you can't fit a 5th battery for a starter, then you might make two 12v banks and also use them to start, but I'm not sure the golf cart batteries would work for that. My old boat was set up that way using the 'combo' type batteries and worked well for short trips/coastal cruising. Wouldn't want that for longer cruises.

[Pblais]

Two golf carts can be a starter bank. Seems like a not very economical approach but it works. Our first boat had 3 banks of golf carts. One for starting and two for using as a house bank. Our current boat uses a marine staring battery and 4 golf carts. It's cheaper that way and they all fit in the compartment. Fitting them in some space usually is the problem to deal with.

Group 4's can be a space saver and are not as bad to haul as group 8's. Group 8's require a crane. Can be a little dangerous when dropped.

[Tellie]

Go 12V as others said. 6V makes no sense on a boat. Four 6V 200amp gives you 12V 400amp and a smaller 12V separated by a diode for the starter.

[BluesTraveler]

Hello,

You can wire any odd or even amount to 6 volt batteries you want to to achive a 12 volt system, depends on how you wire them; parallel or series. I can explain this in a drawing if you like, just let me know.


Steve

[BluesTraveler]

Connecting Batteries in Series or Parallel


Here's an explanation of how to accomplish your task of getting the right combination of 12 volts out of multiple 6 volts batteries.

Happy sparking

Steve

[Tellie]

I suppose you could series/parallel three 6V to achieve 12V but I've never seen it done or doubt you'll find it in ABYC. But I'd like to see the drawing if you got it.

[BluesTraveler]

Hello Tellie,

Parallel two of the six volt batteries and add the 3rd in series. As far as ampacity goes, you would only end up doubling the amps of the paralled batteries.

[jaga]

I'm trying to vision how you would wire an odd number, say 3, 6v batteries to get 12v, and have it efficient. I know you could wire two in parallel and that in series with on other, but somehow I think you'd lose something somewhere. Like wiring a 200ah and 100 ah 12v battery in parallel. I'd always understood you'd want your batteries in a bank the same or at least nearly the same.

[guess I wrote this the same time BluesTraveler was responding to the first part]

[BluesTraveler]

Yes, I was assuming all of the batteries were of the same capacity. Mixing different amp/hour batteries could be a problem.

[jaga]

Steve,
Yes, but you'd effectively have a 400ah 6v battery from the paired, in series with a 200ah 6v battery. What would your true capacity be? Also, seems like an inefficient solution, based on your link:

"When connecting batteries in a pack you should try to match the capacities as much as possible to avoid discharging one battery quicker than another. A pack operates at a combined voltage so your one cell that discharges quicker will likely discharge deeper than it may be able to recover from."

[BluesTraveler]

I agree, the AH of battery(s) in series must be equal in ampacity as the combination of the paralleled batteries.

I liked what I read in a thread earlier in this forum; the guy said that after hours and hours of research, he concluded that installing two, 12 volt "over-the-shelf" RV batteries (about 60 bucks each) he ran his boat with more than enough capacity at start and the house bank worked just fine.

[jaga]

Steve,
Yep, if he only has space for the 4 batteries I think that would really be the best option.
Scot