User Manual

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Calculation of battery size required for Constant Power load conditions.
Using Table 5 “Watts/Cell/Ah”, map the required load time to the specified end of
discharge voltage. The figure obtained is the Constant Power available from each 1Ah
of NP type cell. Divide this number into the required wattage load per cell to give the
minimum value of capacity required to supply the required load.
Example: 5.3kW load requires 30 minutes standby operating from maximum 272V
down to end of discharge 204V at 25°C.
1. Recommended float voltage for NP batteries at 25°C is 2.26volts per cell. To find
the number of series cells required, divide the maximum load voltage by 2.26v.
272/2.26 = 120 cells
2. Divide the end voltage by the number of cells to find the value of end volts per
cell 204/120 = 1.7vpc
3. Divide specified load by number of cells to find load in watts per cell
5,300/120 =44.17wpc
4. Map end vpc “1.7” against required load time “30 mins” in Table 5:
1.872watts per cell per Ah
5. Divide load in wpc by value from Table 5
44.17/1.872 = 23.59Ah
6. Select the battery from the list on page 3
20 x NP24-12 is the minimum requirement