Size the UPS

Size the UPS so that it will supply you a current of 6.3 amp at 230 vac for a period of 40 minutes. The extra 10 minutes is for "academic spare."

here it is.

How to size a UPS

Step-1 : equipment
step-2 : Amps x Volts = VA
Step-3 : Total All Equipment VA * 1.2
Step-4 : Grant total VA = UPS Size

An easy way to size it is.

The load is 6.3 A 230vac and you have the time 30 minutes.

So say you have a 12v dc 100 Amp Hour battery.

20 times approx voltage so now the battery will be able to supply only 5 Amps (20 times less current) for that Amp Hour but as you only want half an hour you will be able to get 10 Amps per half hour from that battery which is fine for me.

Now you will have some losses (especially if you put a rectifier in the battery line to run an ammeter which would be a strange thing to do...so I don't recommend it.)

Not a totally accurate system of sizing a UPS but it is what I would do.

UPS capacity is mentioned in KVA. Per your load, the required capacity is 230 x 6.3 = 1,449VA or 1.5KVA (assumed yours is single phase system). With contingency, you can select 2 KVA capacity.

For calculation of battery capacity and charger capacity, this previous thread may help. Especially look into the comment # 9. There is a detail calculation (including UPS capacity, battery sizing, charger capacity etc.) of a 3 phase industrial UPS. It will help you.

http://cr4.globalspec.com/thread/38821

There are many other threads for UPS calculation available in CR4, you can search for them.

- MS

6.3A x 230V = 1449W

Asssuming power factor of UPS at 0.8.

1449/0.8 = 1811 VA

Optimum UPS operation is at 80% load, so i guess a 2kVA UPS is fine.

To size battery, you need to know the no. of cells per string, which is dependant on your UPS type (DC output at rectifier charger)

THen assuming inverter efficieny at 0.9, calcaulate the watt per cell required

2kVA x 0.8p.f / 0.9eff / no. of cells = wpc value.

Select your battery brand and with the wpc value, there should be a table which gives you the batt required for 30min discharge time.

visit http://hbl.in from where you get lot info. You can free download UPS & Battery sizing calculator. Good Luck!

Get an equivalently rated inverter for your application, with a continues duty cycle, coupled it with a battery rated to provide continues supply of current for at least twice the amount of expected length of time of operation.