ADDING STORAGE BATTERIES to the NEXTEK POWER MODULE

A lead-acid storage battery connected to the power module allows power to continue to the load in the event the primary power is interrupted or as a means for accumulating solar energy when complementing an alternative power source. The power module serves as a battery manager, insuring an optimum state-of-charge. In such modes its is recommended that deep cycle, maintenance-free, lead acid, storage batteries suitable for building applications be used. Batteries of this type are designed for hundreds of deep discharge and charge cycles. They are generally sealed and do not required routine service and may be installed safely in all approved occupied locations without concern for odor and acid spilling problems. Such units are approved under UL 94V0 for building applications and are commonly used in small and large-scale computer UPS systems.

BATTERY STORAGE CAPACITY

Most deep-cycle batteries are sold with a rating indicating the storage capacity of the battery under discharge conditions. Two ratings are commonly used. One is ampere-hour capacity and the other is the reserve capacity (RS). Of the two ratings, the RS value is a more reliable indicator for predicting how long the battery will supply stored energy during periods of discharge.

The RC rating is determined based on the number of minutes of battery operation that can be expected at a constant current drain of 25 amps, until the battery is considered deeply discharged. For example, if a storage battery has an RS rating of 100, and an application current of 25 amperes, the battery would sustain the load for about 100 minutes before being considered discharged. In another example if the application load requires 12.5 amperes of current, the battery with the RS rating of 100 can be expected to service the load for more than twice the period or about 200 minutes. The lower the current drain for a given battery RS rating, the longer it will last. As a point of reference a battery with the RS rating of 100 will support a 20 amperes lighting load for about two hours. A battery with an RS of 180 may be expected to sustain the lighting for about 225 minutes or about 4 hours.

CALCULATING the REQUIRED BATTERY RESERVE CAPACITY VALUE

To estimate the required battery RS value:

Determine the running time required under battery power = (T) in minutes.
Determine the application DC load in amperes = (A), in amps.
Determine RS with RS= AT/25 and T with T=25xRS/A
Select a battery from the manufacturer's list that exceeds the required RS value.

Sample calculation:

Load current estimated or measured at A = 16 amps.
Required battery "running time" T = 90 minutes.
Calculated RS value required RS = [(16)(90)] / 25 = 57.6

CONCLUSION: Select storage battery with a RS rating of 60 or greater

ESTIMATING THE BATTERY RUNNING TIME FOR A SPECIFIC LOAD CURRENT

Sample calculation:

Load current estimated or measured at A = 19 amps.
Given manufactures RS value RS = 160 minutes.
Calculate battery "running time" T = [(25)(160)] / 19 = 211 minutes

CAUTION: Two 12 volt batteries in series are required for the NPS 660 power module and four 12 volt units in series are required for the NPS 1000. Also the battery system must have a fuse in series with the circuit connecting it to the power module not to exceed 30 amps for the NPS 660 and 20 amps for the NPS 1000.

Home Company How it Works Products Applications Distribution News-Articles Contact MyNextek