Calculation Methods
Information required for battery capacity calculation
We need below basic information for a precise battery capacity calculation.
- nominal voltage of the system - load current
- standby period - maximum voltage (for charging)
- minimum voltage - temperature range
- battery layout and available space - physical condition

Float Voltage Operation
In these conditions the float voltage,being the voltage at which the general load circuit will operate,then a decision will have to be reached on the cell float voltage needed to maintain the battery in the required condition.

Number of cells required =

Circuit voltage Cell Float voltage

Minimum cell voltage=

Minimum D.C. Voltage Number of cells

The most commonly used float voltages are 1.40-1.48 voltage per cell,but the exact figure has to be related carefully to the circumstances.

Example
An Changhong battery is required to maintain an inverter load of 50KVA at 0.8 power factor for a back up time of 30 minutes,at normal temperature. The D.C.voltage to the inverter operates within the limit of 265 voltage.
with the battery on float charge to a minimum of 202 voltage at end of back up time. The inverter has an 85% efficiency.

- Number of Cells(at recommended float of 1.44v.p.c.)

265 1.44

=184cells

- Minimum cell voltage=

202 184

=1.10voltage per cell

- Maximum Battery Current =	Inverter load in KVA x power factor Min.cell voltage x number of cell x inv .efficiency
=	50KVA x 0.8 1.10 x 184 x 0.85
=	232.5Amps

We shall choose the battery with capacity equal or just above.
Determination Battery Capacity-KPM range.Form our catalog date(PAGE7) the cell type is KPM300.
Battery would comprise 184cells type KPM300.

The Number of Cells in a battery
The number of cells in a battery may be determined by simply dividing the nominal voltage of the system by the voltage of a cell(1.2V).

 

System voltage	Number of cells	Spread in the practice
24	20	18-21
36	30	27-31
48	40	36-41
110	92	88-93
220	184	180-186