Table of Contents
Advertisement
4.1 Battery Information
4.1.1 Battery Size
Batteries are the Inverter's fuel tank. The larger 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.
Avoid discharging batteries to more than 50% of their capacity too often. Under extreme conditions,
such as a severe storm or a long utility outage, cycling to a discharge level of 80% is acceptable.
Totally discharging a battery may result in permanent damage and reduced life.
For stand-alone applications, battery size should provide between 3 and 5 days of storage before
needing to be recharged. The power contribution from other charging sources is not included in this
calculation to duplicate the conditions present during a cloudy or windless period. This is often
referred to as the "number of days of autonomy." If the system is a hybrid system with daily generator
runs periods then the battery size may be smaller. During cloudy periods the generator would be
expected to run longer. Utilities back up applications often have very small batteries. The minimum
recommended battery capacity is 100 amp-hours@24vdc, and 50 amp-hours@48vdc.
4.1.2 Battery Bank Sizing
To determine the proper battery bank size, compute the number of amp hours that will be used during
charging cycles. 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, determine the amp hour
requirements of each load and total them.
You can compute your battery requirements using the nameplate rating of your appliances. The
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 as follows:
AC Current x AC Voltage / Battery Voltage = DC amps.
Multiply the amperage by the number of hours that the load will operate, and you have a reasonable
estimate of 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's literature may provide more
accurate information than the motor nameplate. For larger motors, increasing the battery size
indicates that the high demand for start-ups should be required.
Follow this procedure for each individual load. Add the resulting amp hour requirements for each load
to arrive at a total requirement. The minimum properly sized battery bank should be approximately
double this amount. This will allow the battery to be cycled only 50% on a regular basis.
4.1.3 Monthly Maintenance
The level of the electrolyte of a flooded battery should be checked monthly. It should be about 1/ 2"
above the top of the plates, but not completely full. Don't overfill the batteries or the electrolyte will
seep out during charging. Refill the batteries with distilled water. Avoid "spring" water and regular tap
water as they may have high mineral levels that can affect the battery chemistry and reduce life.
Check the battery interconnections for tightness and corrosion. If corrosion is found, disconnect the
cables; clean them with a mild solution of baking soda and water. DO NOT ALLOW THE SOLUTION
TO ENTER THE BATTERY. Rinse the top of the battery with clean water when finished (replace the
caps first.)
- 12 -
Hide quick links:
Advertisement
Table of Contents
