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In article <1k68g7INN2ei@gap.caltech.edu> carl@SOL1.GPS.CALTECH.EDU writes:
>In article <C1IpIq.DFF@usenet.ucs.indiana.edu>, amirza@bronze.ucs.indiana.edu (Anmar Caves) writes:
>>>If you use a 12 volt system you can start out with one set of batteries
>=>and add capacity in parallel.  If you are on 120 volts dc you have 10
>=>times the number of cells.  The initial cost for a 120 volt system will be
>=>much higher. 
>=
>=In addition, there will be ten times the number of cells in series.
>
>But the same total number of cells in your storage system.

Yep.  But, you can get away with mixing different aged banks in
parallel.  It's not the best for a system, but it isn't too
detrimental.  Replacing one cell in a series system *can* be
detrimental and can lead to reverse charging and increased sulfation
if lead acid cells.  It's best that all cells in a series system be
the same type, capacity and age.  It's not absolutley ruinous to
replace one cell (or one battery if using 6 or 12volt batteries to
make up the 120 volt battery, hmm, a battery of batteries?) in a
120volt battery, but it is more so than replacing once battery in a 10
12volt battery system.

>=Any one cell failure can ruin a bank.
>
>The same is true if the cells are connected in parallel:  One shorted cell can
>load the rest enough to damage them.

I wasn't talking about a shorted cell.  In a bank of 60 cells
connected in series a shorted cell would hardly be noticed.  The
charge/discharge voltage fluctuation is much higher than that (like
around 10 volts).  In a bank of 60 series-parallel cells working at 12
volts it could blow up the cell (more likely it wouldn't happen
because most shorts would get burned away before they became serious).
But shorted cells in a lead acid bank for that type of application
rarely happen unless you drop your wrench on them (shame on you! why
didn't you insulate all exposed leads!).  On that I speak from
experience. 
With lead acid banks in stand by or home use configuration the most
common failure mode is sulfation.  I generally try to avoid this by
dropping the acid content on the cells to about 1.2 sp. grav. fully
charged.

-- 
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