Kent and list,
And I was half awake this morning and realized my error in yesterday's post to which you responded... I said
"A battery is considered empty at 10.75V (12V), or 1.79 VPC."
No, it's at 10.5V, or 1.75 VPC, as you have correctly stated. Sorry.
Allan
On 3/26/2011 12:01 PM, Kent Osterberg wrote:
Wrenches,
I noticed an error in my reply below when Allan's second comments
arrived. Correction: the battery is considered 100% discharged
(not
80%) at 10.5 volts (1.75 vpc) under the conditions of use.
Kent
Kent Osterberg wrote:
William,
I'll try to add a little to Allan's and Ronald
Parades'
comments. Nearly every battery manufacturer specifies a
maximum 80%
depth of discharge (DOD); that corresponds to about 10.5 volts
for a
nominal 12-volt battery. Notice how close that is to the
default
setting used by many inverter manufacturers for starting the
generator
right away. For deep-cycle batteries, a cycle life in the low
hundreds
should be expected for a battery that is routinely discharged
to 80%
DOD.
Designing for a lower DOD will result in longer battery life.
I've got
a table from Ronald that shows the L16RE battery life
expectancy is
about 7 years for a 25% daily DOD. Since that is their
warranty target,
it seems like they should specify a 25% daily average DOD in
the
battery instructions.
If charging primarily with a generator, 50% DOD before
starting the
generator is good compromise (but the generator shouldn't have
to start
every day, every other day maybe). Fuel economy really falls
off the
chart while charging above 90% SOC. So if you are starting a
generator
at 75% and charging to 100% it'll use a lot more fuel that
using the
generator to charge from 50% to 80% or 85%. Trouble is that
routinely
charging to only 85% SOC will lead to sulfation problems. That
can
shorten the battery life too.
Kent Osterberg
Blue Mountain Solar, Inc.
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