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post #15 of Old 09-05-2006 Thread Starter
Join Date: Apr 2006
Location: Spokane, WA
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BTW Hellosailor, I’ve been meaning to ask. A single point of failure for a connection will render the single bank as you advocate useless. A parrelled bank has a greater chance of being at lease partially usable, if at a lower capacity.

“I'd been told that's not the case, and that is the problem. They WILL equalize, yes. And then as each battery is different, and has a different rate of self-discharge (among other things caused by the physical changes and sulphation happening differently in each battery), as soon as they have equalized they begin to drift apart and the current loop between them starts to flow again. This process does not stop, it continues and it drags them down.”

Agreed, each battery will have a different open cell voltage and they will drift apart if they are not connected. This drift will cause a small current to flow until the equilibrium voltage of both batteries are the same. This will NOT however drag the batteries down. What is removed from one battery will be stored in the other. Discounting self discharge, the amount of charge will remain constant. The current will be very small and eventually stop. The total charge capacity of the battery bank will not change.

And just to clear it up, full discharge is whatever you define it as. The more and deeper you discharge your batteries the faster they will loose capacity. I routinely discharge batteries at work to 1.75V/cell (10.5V) to get full capacity out of the battery. (I say routinely, by that I mean during each discharge cycle, maybe dozen times per year.) However, being cheep and not wanting to replace my batteries all that often, I also use the 50% discharge point as fully discharged, about 11.25V (1.88V/cell) under load.

There are two types of fools...

One says this is old, and therefore good..

The other says this is new, and therefore better...
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