battery discussion [RE-wrenches]

Sun May 6 11:34:50 PDT 2001

-----Original Message-----
From:	Todd Cory, Bald Mtn. Solar [mailto:toddcory at jps.net]
Sent:	Sunday, May 06, 2001 12:30 PM
To:	Wrenches
Subject:	battery discussion [RE-wrenches]

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.
A lot of the C-D cells are designed as a shallow cycle, float service
battery and will NOT hold up in the type of service we give them.

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.
Best bet is to call the manufacturer and talk to them and / or have them
send you the chart for the battery. What you might find is that they are
similar to some batteries a distributor was passing out in my area. They
were promoting them as power system batteries.
After speaking to the manufacturer I found that they had a cycle life of 50
cycles and were designed to put out some unbelievably high discharge rate
for 15 minutes or so. Then they were spent. They were from a military base
radar system back up (or something like that) and were just to cover power
needs till the generator started......

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?
Do you have a load tester available? (sorry stupid question) See if you can
(Choose one) beg, borrow, steal, or if all else fails, rent one from a
company that works on fork lift batteries or something similar. That is the
only way to really tell. It is hard to find one to handle that high a
voltage. You will probably need to rearrange them to a 48 volt pack to test
them. If you don't know the procedure I can send it to you privately unless
the list wants it.

At any rate you will need the load specs from the manufacturer to do the
test.
The last one I did was 6 hours at a 85 Ah load. So this is a long process.

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. These sound like a float
service battery. If so I would avoid them like the plague.
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?

If things screw up when you are testing there will be no backup, Can it
create a dangerous situation without the batteries in the system?

Later,
Bob

RE. Ellison
Supplier of;
Diesel Generators &
Alternative Energy Systems & Supplies
34642 Countryman Road
Theresa, NY. USA
                              13691-2076

Thanks for the feedback,
It is free and some say worth everything you pay for it........

Todd

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