BATTERY SIZING

Let us have total load of 16 kW with 0.8 pf, which needs to be supported by battery backup for at least 1 hr, when the grid fails. Before choosing the battery with respect to cost or brand, there are many questions to be answered

Which type of battery?

C-rating of the battery?

What is the UPS Voltage window?

UPS rating?

No: of Batteries (blocs) required?

How many cells per bloc?

How many blocs in series?

How many blocs are in a string (parallel)?

What is the End Cell Voltage (ECV)?

What is the Temperature correction factor with respect to the ambient

temperature?

What is the Discharge power per cell with respect to ECV and backup time?

What is the Discharge current per cell with respect to ECV and backup time?

What is the aging factor considering the end-of-life criterion?

What is the K factor?

For space constraints, bloc dimensions?

No: of blocs per rack?

Battery sizing calculation differs with respect to the application as well

UPS

Telecommunications

Solar Photovoltaic

REFERENCE STANDARDS / DOCUMENTS:

IEEE 1184-2006 – Guide for Batteries for Uninterruptible Power Supply Systems

Highlighted values are taken from a reputed vendor catalog available on the internet for calculation purposes.

UPS BATTERY SIZING CALCULATION:

The battery load of UPS should be calculated by considering the following 4 margin factors as shown below

Actual load / Inverter Efficiency = Nominal battery load

Temperature correction factor x Design Margin x Aging Margin x Overloading factor = Battery load

Selected Battery type Sealed Maintenance Free VRLA.

UPS Output rating = 20 kVA

Output Power Factor = 0.8

Actual Load = 16 kW

Inverter Efficiency (EFF) = 94%

Nominal Battery load = 17.02 kW