Battery Life in Grid-Tie Systems [RE-wrenches]

Bruce Geddes b.geddes at clear.net.nz
Thu Nov 20 12:08:55 PST 2003


Hi Scott,
             This preocupation with cells being on the negative or positive
end of a battery fascinates me.  The current MUST go through all cells in
the string so it (electrically) makes no difference where they are.  There
may be some environmental difference but this should be taken care of by
good installation.

Also I find the comments from the Trojan rep interesting.  Cycling a battery
to any depth causes stress which ages the battery mechanically.  The deeper
the cycle, the more the stress, the shorter the life.  As pointed out
earlier in posts the only reason to work the battery is to prevent
stratification and inter cell variance.

Batteries such as L16's are not made to last forever.  They are a compromise
between cost, performance and life.  I regularly replace L16's, T105's etc
after 3 to 5 years use.  Hence my love of traction cells which have proven
to last more than twice as long despite severe abuse but at less than twice
the price.  You gets what you pays for.  Mind you, on a hydro based system I
would have expected a little longer than you got.

It all comes down to what the battery is built for.  The longest lasting
batteries (lead acid) are the standby batteries with pure lead grids such as
the old Faurex.  I have seen these still working after 20 years.  Problem is
try to cycle them and they will break up.

If anyone has a good, technical explaination to justify the beliefs about
+ve or -ve ends of batteries failng I would really like to hear it.

Bruce Geddes
PowerOn


> Last weekend, one cell in the battery which is now my main (-), not the
one
> using extra water, died. It would not respond to any charging input from
the
> hydro nor a backup generator while the other two cells in this battery
> quickly attained a 1275 + hydrometer reading as did the other batteries in
> the bank. I spoke with a Trojan engineer at great length about this
> situation and after a careful review of my entire system's parameters, he
> concluded that I did not cycle my batteries deep enough.
>
> In summary, he said:
>
> Minimum 20% - 30% discharge on a regular basis;
> Equalize once a year if hydrometer readings don't indicate to do it more
> often;
> The main (-) battery will use more water; and
> Rotate battery positions once a year.
>
>
> So do I believe him?? and does anyone have other comments on my battery
> situation?
>
> Thanks
>
> Scott
>

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