Batteries are usually connected in Series as in Series Voltage get added up and current remains the same.
BATTERY RATING CALCULATION
The formula employed rating calculation is as stipulated below:-
Capacity of Battery (AH) = (DC Current X Duration in Hrs)/( %age capacity utilization)
Where, DC Current = (UPS (KVA) x 1000 x Load Power Factor (=1))/( Inverter efficiency x End Voltage)
Hence, VAH = AH x Nominal Voltage
For e.g.: for 3 KVA UPS, 1 hour Backup having 18 no. batteries:
DC Current = (5 x 1000 x 1)/ (0.95 x 10.5 x 18) =27.85A
Battery “AH” = (27.85 x 1.0)/ (0.62) = 44.91
Hence , 18 no.s of 12V/42AH batteries will suffice .
TOTAL VAH = 18 x 12 x 42 = 9072 VAH
The following assumptions have been made in the above calculations:-
1. DC Voltage – 216 for 5 KVA
2. End cell voltage / battery of 10.5 V
3. Load Power Factor = 1.0
4. Inverter efficiency = 95%
% Capacity utilization is:
Duration % Capacity utilization
½ hr (30 min’s) à52%
1hrs à 62%
3hrs à83%4hrs à85%
- The amp-hour is a unit of battery energy capacity, equal to the amount of continuous current multiplied by the discharge time, that a battery can supply before exhausting its internal store of chemical energy.
- An amp-hour battery rating is only an approximation of the battery's charge capacity, and should be trusted only at the current level or time specified by the manufacturer. Such a rating cannot be extrapolated for very high currents or very long times with any accuracy.
- Discharged batteries lose voltage and increase in resistance. The best check for a dead battery is a voltage test under load.