Slimline
™
Power Inverters by Wagan Tech
®
www.wagan.com
7
CONFIGURING THE BATTERY BANK
To determine the minimum battery ampere-hour rating that you will need to
operate appliances from the inverter, and any DC appliances powered by the
battery bank, follow these steps:
(The following calculations are specific to 12V systems. For 24V or 48V systems,
a different calculation is required but the same principles should apply.)
1. List the maximum continuous wattage that the inverter has to supply.
2. Estimate the number of hours the appliances will be in use between
battery recharges. This will vary depending on appliances.
For example, a typical home-use coffee maker draws 500 watts during its
brew time of 5 minutes, but it only requires 100 watts thereafter to maintain
the temperature of the pot. Similarly, a typical use of a microwave oven is
only for a few minutes. Some longer operating time appliances are lamps,
TV’s, computers, and refrigerator/freezers.
3. Determine the total watt-hours of energy needed. This is done by
multiplying average power consumption in watts by hours of run time. For
example: 1,000 watts for 10 hours = 10,000 watt hours.
To get an estimate of the maximum current (in amps) that a battery bank must be
capable of delivering to the inverter, divide the load watts by 10. For example a
1,000 watt appliance load will need 100 amps at 12 Volts DC.
Using the 1,000 watts for 10 hours example as above, then 100 amps is
needed for 10 hours. This provides us with the basic amp-hours (Ah) of battery
that is required. Ten hours at 100 amps equals 1,000 Amp Hours (Ah). This
answer is just a beginning of configuring the battery bank because there are
additional factors that determine actual run time. These include:
• AC appliance load and time in use (basic Ah)
• Cable gauge and length (cable losses)
• Charge level of the batteries (between use, chargers have to be able to
fully charge the batteries)
• Temperature of the batteries (colder batteries provide fewer amps)
• Age and condition of the batteries (older batteries lose Ah capacity)
• Compliance with turning off unnecessary AC loads
• Use of DC appliances and compliance with turning off unnecessary DC
loads
