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Battery Bank Sizing Example
The following battery sizing example illustrates a typical calculation, assuming an
opportunity to charge the battery every three days:
Table 1-1
Battery Sizing Example
This example illustrates how quickly your battery needs can escalate. To reduce
the required battery bank size, you can either conserve energy by eliminating or
reducing the use of some loads, or recharge more frequently.
When sizing your battery, be conservative and resist the temptation to skip the last
step of this calculation (multiplying by 2). 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.
As your power requirements increase, you may need to use more than one battery
to obtain sufficient capacity. Batteries can be connected in parallel, in series, or in
series-parallel to create higher capacity systems. It is not recommended to connect
batteries from different manufacturers, different types, or that have different amp-
hour ratings in parallel. Improper charging and decreased battery life will result.
See “Cabling & Hook-up Configurations” on page 52 for more information about
battery inter-connection schemes.
Appliance
(A) Power
Consumption (Watts)
(B) Operating Time
per Day (Hours)
Daily watt-hours needed
for this appliance
(= A × B)
TV & VCR 200 W 2 hours 400 Wh
Small microwave
oven
800 W 15 min = 1/4 hour 200 Wh
3 lamps, 60 W
each
180 W 4 hours 720 Wh
Coffee maker 600 W 15 min = 1/4 hour 150 Wh
Hair dryer 1500 W 6 min = 1/10 hour 150 Wh
Total daily watt-hours of AC load 1620 Wh
× Number of days between charges 3
= Total watt-hours of AC load between charges 4860 Wh
Battery Ah used between charges (divide by 10 for 12 volt system;
divide by 20 for 24 volt system)
486 Ah
Recommended Battery Bank Size in Ah (multiply by 2) 972 Ah