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post #8 of Old 11-08-2012
Maine Sail
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

Originally Posted by asdf38 View Post
Just remember that there are two main advantages to the single large bank:

1) A single large bank means each battery sees a lighter load. Ah's are specified at certain load current (the 20 hour rate) - anything more and you get less Ah's, anything less you get more. So for any given load when you add batteries you always get 'extra' capacity as the load for each battery goes down and therefore it's effective capacity at the new lower discharge rate goes up. It's like 4 lightly loaded horses pulling a kart will take it more than twice as far as 2 heavily strained ones.
This is called the Peukert Effect.

Two smaller banks will always see more use and cycle depth than a single large bank.. You also have charge inefficiency issues too. It is more efficient to charge one bank than two unless using 100% free energy and even then "finishing" two banks is less efficient due to the longevity of the time acceptance limiting and "finishing" takes.. The larger bank will also not be as dramatically affected by Peukert and you'll actually get some more amp hours out of a larger bank with the same load than you do with a smaller bank with the same load.

For example a bank with a Peukert of 1.2 and a average load of 8A it looks like this..

100Ah bank, Peukert 1.2, load 8A = 91Ah's
200Ah bank, Peukert 1.2, load 8A = 209Ah's
400Ah bank, Peukert 1.2, load 8A = 480 Ah's
600Ah bank, Peukert 1.2, load 8A = 782Ah's
800Ah bank, Peukert 1.2, load 8A = 1104 Ah's

This means that your bank will have shallower discharges, not just because it is one large bank, but if the load stays the same and you increase bank size you will actually get more out of the larger bank due to Peukert.

-Maine Sail / CS-36T

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Last edited by Maine Sail; 11-08-2012 at 07:13 PM.
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