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Old 03-26-2013
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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.
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Old 03-26-2013
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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.
Trust your instinct
In parallell you get 12v
In series you get 24v not any good on a 12v system..
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Old 03-26-2013
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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
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Re: Battery Bank – Parallel or Series

Thanks for the responses back!
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Old 03-27-2013
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Re: Battery Bank – Parallel or Series



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Old 03-27-2013
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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.
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Old 03-27-2013
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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...

parallel adds current - n - series adds voltage
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Old 03-27-2013
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Re: Battery Bank – Parallel or Series

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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.

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