Understanding the difference between VA versus Watts.
Real power (measured in watts) is the portion of power flow that results in the
consumption of energy. The energy consumed is related to the resistance in an
electrical circuit. An example of consumed energy is the filament in a light 
bulb. Reactive power (measured in VAR or volt-amps reactive) is the portion of
power flow due to stored energy. Stored energy is related to the presence of
inductance and/or capacitance in an electrical circuit. An example of stored
energy is a charged flash bulb in a camera



Apparent Power (VA) vs Real Power (Watts)




Apparent power (measured in VA or volt-amps) is a mathematical combination
of real power and reactive power.
The geometric relationship between apparent power, reactive power and real
power is illustrated in the power triangle below:


Mathematically, real power (watts) is related to apparent power (VA) using a
numerical ratio referred to as the power factor (PF)
, which is expressed in
decimal format and always carries a value between 0 and 1.0. For many newer
types of IT equipment, such as computer servers
, the typical PF is 0.9 or
greater
. For 
legacy personal computers (PCs), this 
value can be 0.60 –
0.75.
 
	
		VA-watts-graph.jpg


Using one of the following formulas, a calculation can be made to determine
the missing quantity:
	Watts = VA * Power Factor 
	OR 
	VA = Watts / Power Factor
	OR
	PF = Watts / VA 

Note:
Thermaltake 430 Watt Smart PF = .86
CyberPower CP1500PFCLCD PFC Sinewave UPS (1500/1000): PF = .666
CyberPower CP1500AVRLCD3 Intelligent LCD UPS (1500/900): PF = .6 
APC UPS BX1500M  (1500VA / 900W): PF = .6
pt 

Since many types of equipment are rated in watts, it’s important to consider the
PF when sizing a UPS. If you don't take PF into account, you may under size your
UPS. As an example, a piece of equipment that’s rated at 525 watts and has a
power factor of 0.7 results in a 750 VA load.
	750 VA = 525 Watts / 0.7 PF

Sizing the UPS to operate at 75 percent capacity results in a UPS with a
1000 VA rating (750 VA / 0.75 = 1000 VA).



Converting amps to VA

Single phase: Multiply amps by voltage (120 volts in the U.S.). 
10A x 120V = 1200 VA.
Three phase: Amps x volts x 1.732 = VA.



Calculating the right size backup power UPS
UPS battery backup are given a power rating in volt-amperes (VA) that range from
300 VA to 5,000 kVA. This rating represents the maximum load that a UPS can
support, but it shouldn’t match exactly the power load you have. To allow room 
for growth, the best practice is to choose a battery back up with a VA rating 
that is 1.2x the total load you need it to support. 

If your UPS will be supporting motors, variable-speed drives, medical imaging
devices or laser printers, add more VA capacity to your requirements to account
for the high power inrush that occurs when those devices startup.  Companies 
that are anticipating rapid growth should use a higher multiplier than 1.2x. 
Newer server hardware tends to have higher power requirements than older models,
so factoring in additional VA will account for adding more and newer equipment.



More




Watts vs. VA: What’s the Difference Anyway
Between the increasingly fragile power grid, the escalating power
consumption of IT equipment and the constantly increasing importance of our
network, it isn't difficult to see the value a UPS (uninterruptible power
supply) has to not only a business, but a home. So have you ever decided to
research some UPSs to see which is the right fit for you, only to be left
asking yourself, "Watts? VA? Huh?"

Most of us have heard of Watts before – and have some understanding that
each piece of equipment has a certain amount of Watts it draws to operate,
but how exactly does that relate to a UPS? And what is a VA anyway?

Electronics have both maximum Watt ratings and maximum VA (volt-ampere) ratings;
and neither the Watt nor the VA rating of a UPS may be exceeded by the attached
equipment (load). Watts is the real power drawn by the equipment, while 
volt-amps are called the "apparent power" and are the product of the voltage 
applied to the equipment times the current drawn by the equipment.
The Watt rating determines the actual power purchased from the utility company
and the heat loading generated by the equipment; and the VA rating is used for
sizing wiring and circuit breakers. Any clearer? Probably not much.

What you really need to know is that for electronics such as computers and UPSs,
Watt and VA ratings can differ significantly; with the VA rating always being
equal to or larger than the Watt rating. The ratio of the Watts to VA is called
the "Power Factor" and is expressed either as a number (i.e. – 0.8) or a 
percentage (i.e. 80%). This power factor is what really matters when sizing a
UPS for your specific requirements.

APC™ by Schneider Electric’s™ latest generation of Smart-UPS™ On-Line now 
delivers innovative features to help you make the most of your energy™. Models 
6kVA (6000 VA) and higher have a unity power factor, which means VA translates 
to an equal amount of Watts (i.e. 6000 VA = 6000 Watts).  Smaller models of the
next generation of Smart-UPS On-Line have a 0.9 power factor or higher, and all
are Energy Star™ qualified regardless of VA.

The difference between 0.8 or 0.9 power factors and a unity power factor (1.0)
may not sound like much – but when you take into account the fact that the 
extra available wattage can be used to support additional loads and extend run
times; it is easy to see how the next generation of Smart-UPS On-Line will 
increase your availability while saving you money.

Please refer to our UPS Selector for help properly sizing a UPS.  Alternatively,
if you are looking to upgrade your current UPS, refer to our UPS Upgrade 
Selector; and don’t forget to utilize our Trade-UPS Program which allows you to 
receive up to a 25% discount on the purchase of a new APC by Schneider Electric 
UPS when you trade in your old model, regardless of the manufacturer.

For further discussion regarding the differences between Watts and VA please
refer to White Paper 15, Watts and Volt Amps: Powerful Confusion.

This pic and run times is for a 1500VA/900W SKE1500 UPS $159 amazon