# Calculating battery for UPS

As discussed in Volt Ampere and Watts, we apply the following way to calculating apparent power to match it with its UPS capacity:

VA = Watts / PF

In this equation, PF is the same as the power factor of your UPS, which is available on all devices. In simple terms, it means that all the voltages and current we are able to provide for a consumable device will not turn into useful work.

The power factor can be defined from the perspective of the consumer and the UPS.

In UPS because of output impedance, a part of output power will be lost inside of the device.

**Calculating the capacity of battery**

To calculate the battery capacity for an UPS, check the following tips:

1. Consumption: Naturally, the most important factor, and the first one, is the pay attention to the power consumption of your load or device.

2. Required time for the device after power outage: Title, self-telling. Here you will find this number according to your need and your own set of amenities.

3. Selecting the battery voltage: Note how much your selected UPS charger is and, based on that, proceed with the choice of battery amp. Usually, the amp batteries are up to 12 times higher than the power of UPS charger. That is, for a 4-amp battery charger, it’s better to use batteries with a capacity of 48 amps. But choosing a battery with a higher amp will increase its charging time. This coefficient and calculation is merely a useful and practical recommendation. It’s better to use higher-capacity batteries if you want the battery discharge time to increase and the battery is recharged at longer intervals.

4. Number of batteries: Naturally, this factor is selected and chosen by looking at the spec. of your UPS, which is also dependent on the inverter of your chosen device.

5. Power factor: This is also available in your UPS technical specifications.

6. Battery Type: Usually acid batteries are used for UPS’s, which is better for a battery we consider a coefficient of 1.5.

Here’s an example to figure out how to calculate the battery for the UPS:

Power Consumption: 1000 Watts

The number of your UPS batteries: 3 (in fact 36 volts)

UPS time(in battery mode): 1 hour

Power factor: 90%

UPS charger: 4 Amps

_______________

Load flow calculation:

I = P / PF / V = 1000 / 0.9 / 36 = 30.86 A

That means the first charge for an hour of power was 31 amps. But, as mentioned above, it does not select the equivalent capacity of the battery in a manner that is just as good as it needs. We have defined a coefficient below which we will include in our calculations:

I = 30.86 x 1.5 = 46.29 A

But it is possible that the number we obtain does not fit exactly what is on the market, so we choose the first battery capacity larger and close to our calculated number to find an UPS battery, which in our example can be the number 48 amp. That is, in this example, we can pick three 48-amp batteries for optimal performance.