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Battery Information
Estimating Battery Requirements
Calculating Battery Size
Step 1: Compute Amp-hours
For each appliance, compute the number of amp-hours that
will be used between charging cycles, as follows:
Obtain the wattage. If the wattage is marked on the
nameplate rating, use that. Otherwise, multiply the
marked voltage and amperage:
WATTS = VOLTS × AMPS
.
Obtain the Watt-hours by multiplying that amount by the
hours the appliance will be used:
WATT-HOURS = WATTS × HOURS
.
Obtain the amp-hours that the appliance requires by
dividing that amount by 10 (the factor for the
$XWR
3RZHU
, which is a 12-volt system):
BATTERY AMP-HOURS USED = AC WATT-
HOURS/10
For example, a 100 W light bulb that is used for 4 hours will
use 400 watt-hours (Wh) and the inverter will consume
approximately 40 Ah from a 12 volt battery.
4. Enter this information on the blank calculation worksheet
(page 68).
Step 2: Calculate Battery Size
5. Complete the rest of the worksheet; see Table 6, “Battery
Sizing Example” on page 6
for an example.
Size the batteries at approximately twice the estimated total
amp-hour usage. Doubling the expected amp-hour usage
ensures that the batteries will not be overly discharged and
extends battery life.
Do not skip this doubling step. More capacity is better since
you will have more reserve capacity, be better able to handle
large loads and surge loads, and your battery won’t be
discharged as deeply. Battery life is directly dependent on
how deeply the battery is discharged. The deeper the
discharge, the shorter the battery life.
Troubleshooting
If you find that the system shuts down
when appliances with large motors are started, the problem
may be that this motor is too much for the battery. Even
though you calculated the amp-hour requirements
appropriately, the startup of a large motor makes high
demands on the battery. You may find that adding more amp-
hours (in the form of extra batteries or replacement with a
bigger battery) solves the problem.
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