battery discussion [RE-wrenches]

[Todd Cory, Bald Mtn. Solar]

I have always used good old L-16 style, lead antimony cells in RE
systems. While best case life expectancy can generally be in the 10 or
so years range, the more expensive upfront costs of the better cells (C
& D, Edison etc.) often negates their increased longevity benefits.

At the power plant I work at we have a bank of lead calcium cells. I
don't know much about these guy's chemistry. What experiences do list
members have with lead calcium batteries? What is they general best case
life and advantages over lead antimony.

Our bank is 15 years old now and last time we had to really cycle them
down (2 years ago), we did get their rated capacity, so I imagine they
are still doing ok. (I know it is bad to take batteries below 50 to 70%
DOD.) I am curious how other than capacity testing one determines
current health and remaining life span?

The bank is 10, 12 volt batteries, so ~120 VDC. Their self discharge
rate is s-l-o-w-l-y increasing. They are being kept at around 70º F. The
charge voltage set point at 135 volts. Any higher and the inverter kicks
off from over voltage, so it is hard to do an equalization charge and at
present they do not consume any water at all. I am thinking about
removing one battery (6 volts) to lower the pack voltage so I can
effectively raise the per cell charge voltage (without upsetting the
inverter) to attempt to keep them a bit happier. Any comments on this
plan?

Thanks for the feedback,

Todd

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