BATTERIES
Trace Engineering Co. Inc. Tel (360) 435-8826 Part Number 3179
5916 195
th
Street, NE Fax (360) 435-2229 Effective August 6, 1998
Arlington, WA 98223 USA www.traceengineering.com Page
45
Battery Bank Sizing Example & Worksheet
Complete the steps that follow to calculate your battery bank capacity. No two installation will require
exactly the same battery bank capacity. The example that follows will provide a guideline for
determining your needs. Read through the example and then complete the worksheet on the
following page.
Step 1: Multiply the number of hours (or fractions of hours) you will use the appliance each day by
the wattage of each appliance. Total these Daily Watt-Hours to determine your Daily Energy
Required;
Step 2: Multiply the Daily Energy Required by the number of anticipated days of autonomy (days
between charging, usually one to five) to determine your Rough Battery Estimate (example used
three);
AC Appliance
Hours of
Daily Usage
Appliance
Watts
Daily Watt-Hours Used
Microwave 0.5 600 300
Lights (x4) 6 40 240
Hair Dryer 0.75 750 563
Television 4 100 400
Washer/Dryer 1 375 375
STEP 1
Daily Energy Required 1878
STEP 2
Rough Battery Estimate 5634
STEP 3
Safe Battery Size (watt-hours) 13522
STEP 4
Amp-Hours Required 1127
INVERTER
Minimum Inverter Size Required 2000
Step 3: Multiply your Rough Battery Estimate (Step 2) by two. This allows for a maximum 50%
normal battery discharge and an additional 50% for emergency situations. Multiply this figure by 1.2
to allow for an efficiency of 80%. This number is your Safe Battery Size in watt-hours.
Step 4: Convert Safe Battery Size in watt-hours to amp-hours. The formula is Safe Battery Size
(Step 3) divided by DC system voltage (example used 12-volts). This is the Amp-Hours Required
each day from your battery bank without recharging.
Inverter: This is the minimum inverter size required. Add together the appliances that will run at the
same time from Column 3 (Appliance Watts, listed above). You will need an inverter with this many
watts or more.
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