Battery Bank – Parallel or Series - SailNet Community
Junior Member

Join Date: Mar 2013
Posts: 2
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0

Battery Bank – Parallel or Series

I know this question has come up before which I’ve read many post and have become more confused. I currently have two batteries / two bank system (one battery per bank). Bank one for engine, bank two for house. Both are 12V deep cycle marine batteries. I’m wanting to add an additional battery to bank two, so I will now have bank one – one battery, bank two – two batteries. Assuming both batteries are 12V and same amperage rating (twin batteries), what is the best way to tie bank two together – my instinct says parallel, however, my dock neighbor suggest series which I don’t understand. I thought series would double the voltage and not give me any longer time without charging.
I thought it would be better to go positive to positive, and negative to negative for the two bank batteries??
Any thoughts would be greatly appreciated.
Rogre is offline

Old 03-26-2013
Senior Member

Join Date: Aug 2006
Location: Norway
Posts: 945
Thanks: 9
Thanked 77 Times in 71 Posts
Rep Power: 11

Re: Battery Bank – Parallel or Series

Quote:
Originally Posted by Rogre View Post
I know this question has come up before which I’ve read many post and have become more confused. I currently have two batteries / two bank system (one battery per bank). Bank one for engine, bank two for house. Both are 12V deep cycle marine batteries. I’m wanting to add an additional battery to bank two, so I will now have bank one – one battery, bank two – two batteries. Assuming both batteries are 12V and same amperage rating (twin batteries), what is the best way to tie bank two together – my instinct says parallel, however, my dock neighbor suggest series which I don’t understand. I thought series would double the voltage and not give me any longer time without charging.
I thought it would be better to go positive to positive, and negative to negative for the two bank batteries??
Any thoughts would be greatly appreciated.
In parallell you get 12v
In series you get 24v not any good on a 12v system..
knuterikt is offline
Old 03-26-2013
Senior Member

Join Date: Apr 2007
Posts: 309
Thanks: 1
Thanked 1 Time in 1 Post
Rep Power: 11

Re: Battery Bank – Parallel or Series

Rogre,

Take your two old batteries and connect them pos to pos, neg to neg and make them your house bank. Connect your new battery to the engine. This is assuming your old batteries are of similar age and amp hours. You want the new battery as your engine battery so you always have a dependable start. The old batteries will double your house bank capacity.

You are right, your dockmate doesn't know what he is talking about.

Scott
Gemini Catamaran Split Decision
NautiG is offline

Junior Member

Join Date: Mar 2013
Posts: 2
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0

Re: Battery Bank – Parallel or Series

Thanks for the responses back!
Rogre is offline
Old 03-27-2013
Senior Member

Join Date: Sep 2007
Location: Pasadena Md - Magothy side
Posts: 5,979
Thanks: 10
Thanked 31 Times in 31 Posts
Rep Power: 12

Re: Battery Bank – Parallel or Series

Clear as mud

Lessons learned are opportunities earned.
chucklesR is offline
Old 03-27-2013
Señor Member

Join Date: Sep 2007
Location: North Florida
Posts: 1,457
Thanks: 8
Thanked 22 Times in 21 Posts
Rep Power: 10

Re: Battery Bank – Parallel or Series

Take note of Chuckles' diagram -- you want the run the positive load off of one battery, and your run to ground off of the other battery. If you run them both off of the same battery, you will get unbalanced charging on the second battery.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
________
'85 BYB Vagabond 39
PorFin is offline
Old 03-27-2013
Senior Member

Join Date: Jun 2008
Location: Tampa, FL
Posts: 1,223
Thanks: 0
Thanked 37 Times in 37 Posts
Rep Power: 9

Re: Battery Bank – Parallel or Series

A little mnemonic that I use to help me remember is pac-n-sav. That is the name of a grocery chain I used to shop at, so it's easy for me to remember. What it means is...

denverd0n is offline
Old 03-27-2013
Senior Member

Join Date: Apr 2007
Posts: 309
Thanks: 1
Thanked 1 Time in 1 Post
Rep Power: 11

Re: Battery Bank – Parallel or Series

Quote:
Originally Posted by PorFin View Post
Take note of Chuckles' diagram -- you want the run the positive load off of one battery, and your run to ground off of the other battery. If you run them both off of the same battery, you will get unbalanced charging on the second battery.
Really? I'm not an electrical maven or anything, but it seems to me that it wouldn't make a difference which battery you connected the leads to, as the batteries are parallel. I've had a two battery bank for years with both leads off one battery and they seem to be fine. But I'm prepared to be educated that I am wrong.

Scott
Gemini Catamaran Split Decision
NautiG is offline
Old 03-27-2013
Asleep at the wheel

Join Date: Sep 2011
Location: Pennsylvania
Posts: 3,014
Thanks: 71
Thanked 117 Times in 115 Posts
Rep Power: 6

Re: Battery Bank – Parallel or Series

Scott,
It's just a guess, but abstract this out to be 10 or 15 batteries instead of only 2 or 3. If you have a bunch of batteries daisy-chained in and only attach your charter to the first battery, you have increased impedence due to the cable connecting each subsequent battery as you walk down the chain. Electricity, like water, tends to follow the path of least resistance, which means that the battery at the end of the chain will see the least amount of charge. With Chuck's set-up, the current has to flow through all of the batteries, and the entire bank is essentially at the same impedence from the charger's perspective.

- Jim
Home: Western Philly 'burbs
1980 Allmand 31
1975 Albacore 15

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
jimgo is offline
Old 03-27-2013
Senior Member

Join Date: Apr 2007
Posts: 309
Thanks: 1
Thanked 1 Time in 1 Post
Rep Power: 11

Re: Battery Bank – Parallel or Series

Hey Jim,

I'm familiar with the water analogy, but I don't think it applies in the manner you indicate. If you extrapolate to a large number of batteries and there is resistance between the wire connections between them, I would think the solution would be to connect the main positive and negative leads to each battery to compensate for any volt or amp drop.

I would think that connecting the pos and neg to the separate ends of the battery bank would be ineffectual and maybe even counterproductive. But maybe there is some principal I'm not accounting for. In any case, I think it's all theoretical in a two bank system, as the resistance would be minimal.

Scott
Gemini Catamaran Split Decision

Last edited by NautiG; 03-27-2013 at 06:40 PM.
NautiG is offline

Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.

## Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
OR

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

 Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)