02/11/98
9
BATTERY CAPACITY TESTING
Your
Link 1000
can be used to conduct periodic capacity tests that tell you the
actual amount of energy your batteries can store. A capacity test should start with a battery
that has been properly charged and equalized. The objective is to find the maximum
available capacity.
Deep cycle battery capacity is usually stated as a 20 hour discharge rate. A 100
A hr battery will provide 5 amps for 20 hours. At discharge rates above 5 amps, the battery
will not supply 100 A hr. For example: If you are drawing 100 amps out of the battery
it will last less than half an hour. Consider the following table:
CAPACITY AT VARIOUS DISCHARGE RATES
(As a percent of 20 hour rate)
Hours to Discharge Capacity (percent of rating)
20 100%
10 89%
5 78%
3 66%
1 45%
To test battery capacity, charge battery until charge parameters are met. This resets
Amp-hours to zero. Positive Amp-hours will be zeroed when you begin to discharge.
Turn on a load that draws approximately 5% of the expected battery capacity.
Check the current with the Amps display. The load should be constant, such as
incandescent lighting. Now put the
Link 1000
in the Volts display mode. When the
battery voltage drops to 10.5 volts (or 21 volts if you're testing a 24V system), hopefully
about 20 hours later, turn off the load and look at the A hrs display on your
Link 1000
.
The A hrs displayed is your actual battery capacity.
If less than 20 hours passed before the battery voltage fell to 10.5V you can still
determine the capacity with some arithmetic. For example: Assume a 12V battery rated
at 100 A hr. Apply a 5 amp load. Suppose it only took 10 hours for the voltage to reach
10.50 volts. The
Link 1000
would display -50 A hr. This is the 10 hour capacity. Dividing
50 by 89% (10 hour rate) from the table above, you determine that the actual 20 hour
capacity is 56 Amp-hours. You could repeat the test at 5% of the tested capacity (2.8A) to
verify the actual capacity.
USING YOUR
TO TEST BATTERY CAPACITY
Your
Freedom
inverter makes testing the battery capacity easy. First, fully charge
(and Equalize if necessary) the battery to be tested. Use a load like incandescent lights
running on the inverter whose amperage consumption is 5% or less of the battery capacity.
Let the load run until the inverter shuts down on low voltage (about 10.2V). Read the
number of Amp-hours that have been consumed from the battery. If it is not close to the
expected number use the procedure outlined above to estimate the capacity.
CAUTION! Be sure to completely recharge your battery after a discharge test.
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