Battery Sizing Calculation

Battery capacity =
The UPS capacity in VA x the time required in Hrs
The DC voltage of the UPS

Example 1 : 10kVA(240V), 2Hrs
= 10000x2 = 83.34Ah

Now you need to consider the battery efficiency for getting the proper back up, after some usage. Battery efficiency is considered as 80-85 % for practical purposes.

Therefore, it will be, (83.34x100) / 80 = 104.18Ah

The nearest capacities available in Tubular or SMF types are 100Ah and 120 Ah. Here we can select 100Ah.

The no of batteries can be decided by dividing the DC voltage by 12. So, here you will need 240/12 = 20 batteries.

Ie., 20 nos of 100 AH batteries will give 2hrs back up with a 10kVA UPS.

Example 2 : 800VA(12V), 2Hrs
= (800x3) / 12 = 133.4Ah

With 85% efficiency factor, = (133.4x100) / 85 = 156.87Ah Nearest capacity is 150Ah. You may also select an 120Ah, if price is a consideration, since the load usage in a house will not be altogether.
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