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Estimating Battery Requirements
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:
1. Obtain the wattage. If the wattage is marked on the
nameplate rating, use that. Otherwise, multiply the marked
voltage and amperage:
WATTS = VOLTS × AMPS.
2. Obtain the Watt-hours by multiplying that amount by the
hours the appliance will be used:
WATT-HOURS = WATTS × HOURS.
3. Obtain the amp-hours that the appliance requires by dividing
that amount by 10 (the factor for the Freedom SW-RVC,
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 on
page 69.
Step 2: Calculate Battery Size
5. Complete the rest of the worksheet; see Battery Sizing
Example on page 68 for an example.
67
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.
Freedom SW-RVC Installation Guide
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