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3.2 Configuring the Battery Bank
To determine the
approx’ minimum
battery amp-hour rating that you will need to
operate appliances from the inverter and any DC appliances powered by the battery
bank, follow these steps:
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. It maintains the
temperature of the pot, requiring 100 watts. Typical use of a microwave oven is only
for a few minutes. Some longer operating time appliances are lamps, TVs, computers
and refrigerator/freezers.
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: 500 watts for 10
hours = 5000 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 ten.
For example a 500 watt appliance load will need 50 amps at 12 volts DC. Using the
500 watts (or 50 amps) for 10 hours example as above, then 50 amps is needed for 10
hours. This provides us with the basic amp-hours (AH) of battery that is required. Ten
hours at 50 amps equals 500 amp-hours (AH). 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.
3.3 Battery Wiring Examples
In renewable energy systems, batteries are connected to each other in one of three ways:
•
Series (voltage increases, amperage stays the same as a single battery)
•
Parallel (voltage stays the same as a single battery, amperage increases)
•
Series/Parallel (both voltage and amperage increase)
