Measuring VA

[vicw]

Hi,

I measured the DC output power of my power supply, so I can find an UPS for my system. How can I find VA? I read that I can multiply my DC output power by 1.4. Can anyone justify this?

Thanks,
Vic

 

[daKlone]

Hi vic, see the IEEE(electrical) forum!!

 

[jbartos]

Suggestion: These multipliers are somewhat justified (could be higher than 1.4) in Standard Handbook for Electrical Engineers by Fink and Beaty, 13th and 14th Editions. However, do not take any chances. The proper way is to see power supply or UPS output specifications, which must meet your load requirements. Then, if you like it, you have to settle for the input VAs.

 

[comander]

List all equipment that will be on the UPS, Check the name plate on each device and record its voltage and amperage requirements. Multiply these figures together to get the Voltamp ( VA ) requirement for each device.If the name plate lists the figure in watts then multiply the watts figure by 1.4 to receive the estimated voltamp figure.
Add up all the voltamp totals NOTE ( 1000 voltamps = 1 KVA ) then divide by 1000 to get to the KVA total. Multiply the KVA total by 1.25% to allow for growth.

Example 120 volts X 15 amps = 1800 voltamps ( 10 units the same )= 18000 V/A
Divide by 1000 = 18 KVA X 1.25 = 22.5 KVA rated UPS.

Any questions let me know

 

[jbartos]

Small encore: The previous posting is addressing the load growth. If the UPS is not dedicated to a specific system (no load growth anticipated or possible), then the 1.25 multiplier has to be carefully applied since the load growth can be bigger. This depends a lot on the system that is not described in more detail.
My suggestion is to reassess the 1.25 multiplier according to nature of the system. Also, either the manufacturer's tech support or literature for the UPS might be useful.