FOXPOWER FULAGDA1512A, User Manual

Page: 47 / 59

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 Ultra UL1741, 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 33).
Step 2: Calculate Battery Size
5. Complete the rest of the worksheet; "Battery Sizing Example" on page
32 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.