Battery Bank Sizing; Estimating Battery Requirements - Trace Engineering LEGEND II Manual

the battery. If the batteries are insulated, the heat can be kept in the batteries to keep them warmer.
This will substantially increase the performance of the system.
Insulated battery enclosures also ensure that the temperatures of the individual battery cells are
more consistent, preventing unequal charging which can cause battery failure (some cells will be
overcharged while others are undercharged).
The batteries should also be protected from high temperature as well. This can be caused by high
ambient temperatures, solar heating of the battery enclosure, or heat released by a closely located
generator. High battery temperatures will result in short battery life and should be avoided by
ventilating the enclosure and reducing the external heat sources by shading and insulation.
Batteries are the inverter's fuel tank. The greater amp-hour capacity of the batteries, the longer the
inverter can operate before recharging is necessary. An undersized battery bank results in reduced
battery life and disappointing system performance.
Batteries should not be discharged more than 50% of their capacity on a regular basis. Under
extreme conditions cycling to a discharge level of 80% is acceptable. Totally discharging a battery
may result in permanent damage and reduced life.

Estimating Battery Requirements

In order to determine the proper battery bank size, it is necessary to compute the number of amp-
hours that will be used between charging cycles. When the required amp-hours are known, size the
batteries at approximately twice this amount. Doubling the expected amp-hour usage ensures that
the batteries will not be overly discharged and extends battery life. To compute total amp-hours
usage, the amp-hour requirements of each appliance that is to be used are determined and then
added together.
You can compute your battery requirements using the nameplate rating of your appliances. The
critical formula is WATTS = VOLTS X AMPS. Divide the wattage of your load by the battery voltage
to determine the amperage the load will draw from the batteries. If the AC current is known, then the
battery amperage will be:
(AC volts X AC current) / Battery Bank Voltage X 1.2 (efficiency loss) = DC amps (Battery amps)
Multiply the amperage a load requires by the number of hours the load will operate and you have,
reasonably enough, amp-hours.
Motors are normally marked with their running current rather than their starting current. Starting
current may be three to six times running current. Manufacturer literature may provide more
accurate information compared to the motor nameplate. If large motors will be started, increase the
battery size to allow for the high demand start-ups require.
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