How to calculate the ratings of UPS against different power units with respect to battery back ups?

Question

when we are going to calculate the rating of UPS for X watts with the battery back up is 5 hrs ,we can say the rating of UPS is Y KVA.if we want to increase the battery back up to 8 hrs means what will be the KVA ratings.

my doubt is

X watts for 5 hrs battery back = Y KVA

X watts for 8 hrs battery back = ? KVA

and also how we can calculate the UPS ratings for any power systems,it means any house,industrial area,

please clarify this doubt.

Answer 1

i think what you're questioning is battery performance.

Batteries are less efficient at higher loads, (drain rates).

So yes, the same battery pack will give you more

KW/Hr.s at a lower loading.

The battery manufacturer should provide performance data

at various loads if asked.

For more info, Go here;

www.windsun.com/batteries/battery_FAQ....

Answer 2

Not sure what you are asking.

I think you are confused between KVA and KVA-hours.

KVA and KW are units of power. This is the rate at which the unit delivers energy. Multiply by time to get energy.

KVA-hr and KW-hr are units of energy. divide this by the time to get power.

So a 1000KVA unit will deliver 1000KVA as long as the battery lasts. Changing the battery size doesn't change the 1000KVA.

A unit that can deliver 1000KVA for one hour can supply a total of 1000KVA-hr of energy. If it can supply it for 2 hours, it can deliver 2000KVA-hr of energy.

Watts and VA (or KWatts and KVA) are both units of power, one is for real resistive load and the other is for reactive load.

To calculate the UPS size, add up all of the loads in watts*. Convert to kwatts by dividing by 1000. Add some margin. That number in kW is the amount of power the unit should be able to deliver.  I'd ignore the KVA rating, it doesn't mean much.

Now look at the time. How long do you expect it to deliver that amount of power? That determines the size of the battery.

* if the load is listed as amps, multiply that by the voltage to get watts.

Warning: UPSs are not intended to supply power for long periods of time. For that you need a motor-generator set.

Hope this helps, contact me if not.