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Anonymous Poster #1

UPS Input Power

10/17/2018 5:02 AM

I have a 2 kVA UPS - I assume this is rated output. Say, I have a load of only 1kVA. What is the Input power to the UPS?

Input Power = Rated output Power / Efficiency of UPS
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#1

Re: UPS Input Power

10/17/2018 5:17 AM

<...Input Power = Rated output Power / Efficiency of UPS...> gives the answer. The numbers can be determined by simple measurement. The heat that is rejected by the UPS added to the dissipation of the <...load of only 1kVA...> to give the input power. Or, the input power minus the <...load of only 1kVA...> gives the heat rejected by the <...UPS...> and other arithmetic gives the efficiency.

It's rather like asking the following question:

  • One has a 100W tungsten light bulb that is dimmed by a commercial lighting dimmer so that the bulb gives an output power of 25W. What is the input power to the dimmer?
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#2

Re: UPS Input Power

10/17/2018 9:37 AM

Your load will always change. People will in the future plug more things into this UPS, too. RTFM on the UPS to find out what input power the designers planned for.

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#3

Re: UPS Input Power

10/17/2018 10:49 AM

If the UPS is sustaining the <...load of only 1kVA...> during a power outage, then the <...input power to the UPS...> will be zero. After all, that is its only real purpose.

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#4

Re: UPS Input Power

10/17/2018 11:38 AM

Depends....

https://en.wikipedia.org/wiki/Uninterruptible_power_supply

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#5

Re: UPS Input Power

10/17/2018 10:06 PM

As long as you know the efficiency at the 1 kVA operating point. The marketeers always tout the 'peak' of the efficiency curve. If you operate a typical UPS at 2% of its rated capacity, its efficiency will be VERY low.
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#9
In reply to #5

Re: UPS Input Power

10/18/2018 9:37 AM

True, the efficiency will be low but the actual power draw will be less than when it is most efficient.

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#6

Re: UPS Input Power

10/17/2018 10:38 PM

Is that a single phase UPS or 3 phase UPS and what is your UPS input voltage

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#7

Re: UPS Input Power

10/18/2018 9:15 AM

Is it on-line or off-line? If off-line, the input power will be equal to the output power (when the mains power is on (obviously), and when the battery is fully charged).

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#8
In reply to #7

Re: UPS Input Power

10/18/2018 9:31 AM

But what will the power draw be just after going online as the battery charges and the fans cool and vent whatever outgas is produced by a charging battery? This is why the OP should RTFM.

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#10

Re: UPS Input Power

10/19/2018 11:44 AM

you cannot use the formulae directly.UPS is having a battery charged at the constant flow rate. you can use maximum power of 2 KVA for a programmed hour of usage depending on the capacity of the storage battery.

You can think of an analogy of water tank in your house. Suppose you have a water tank of 2000 Liters. You have a pump which delivers water at the rate 500 litres per hour.

You are drawing water in the outlet pipe at the rate of 1000 litres per hour.

The water inlet is not changed with reference to your outlet.

The delivery depends on the storage on the tank and not directly linked to your inlet flow

UPS functioning is also similar to this analogy
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Brave Sir Robin (1); JohnDG (1); panneerselvam (1); PWSlack (2); redfred (3); Simon Wan (1); SolarEagle (1)

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