7
Sizing the Battery Bank
To determine the minimum battery bank ampere-hour (Ah) 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 wattage that the inverter has to provide (as above).
2. Estimate the number of hours the appliances will be in use between battery
recharges. This will differ depending on appliances. As an example, a typical home-
use coffeemaker draws 500 watts during its estimated 5 minute brew time; it main-
tains the temperature of the pot at about 100 watts. Typical use of a microwave
oven is only for a few minutes. Some longer operating time appliances are lamps,
TVs, computers and refrigerators / freezers.
3. Determine the total watt-hours of energy needed. Then multiply the average power
consumption in watts by the number of hours of run time. For example: 3000 watts
for 10 hours = 30,000 watt-hours. Using the 3000 watts (or 300 Amps) for 10 hours
example as above, then 300 amps are needed for 10 hours. This provides us with
the basic amp-hours (Ah) of battery that is required. Ten hours at 300 amps equals
3000 amp-hours (Ah).
This is just an approximate estimation, as there are other conditions that determine
the actual run time. These include:
•
AC appliance load and time in use (basic amp-hour)
•
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 capacity/amp-hour)
•
Compliance with turning off unnecessary AC and DC loads. If there is any
doubt about sizing the battery bank, it is safe to overestimate the amp-hour
requirements of the battery bank.
Note:
The type of batteries you use to power your power inverter is important. Operating a high-
power inverter will routinely discharge batteries and they will require frequent recharging.
Batteries used to start engines are not designed to repeatedly charge and discharge. Enerwatt
recommends using “deep-cycle” or “marine” rated batteries.
Cable Gauges
When connecting the inverter to a battery bank use the thickest stranded insulated copper
wire available, in the shortest practical length. Recommended cable gauges are as follows:
Model
EW-1100
4AWG (3 ft. included W/ 110A inline ANL Fuse)
EW-2000
2AWG (3 ft. included W/ 200A inline ANL Fuse)
EW-3000
0AWG (3 ft. included W/ 300A inline ANL Fuse)
EW-4000
0AWG (3 ft. included W/ 400A inline ANL Fuse)
Recommended Gauges
