【 Weak current College 】 Watt (W) and VA (VA): confusing two concepts

Many people can't figure out should use Watt or should use the VA to represent UPS capacity. Many of the UPS manufacturer can't tell the difference between the two concepts, even W and VA equating the two nouns, that increased understanding of confusion.

Large-capacity UPS capacity is always expressed by VA; small-capacity UPS (less than 1000VA) W indicates that capacity.

Capacity in 1KVA--500KVA ups with VA and not W to indicate the capacity. Use W represents the small capacity ups may be due to the small capacity, UPS users become more familiar with the concept of a Watt. However with the VA to more accurately represent UPS and load capacity of the match, because most fundamental decisions UPS output capability is the current value (A), it is natural to use VA represents more appropriately.

The w value is always less than or equal to the value VA

Conversion formula is as follows:

Watts (w) = VA * PowerFactor = Volts * Amps * PowerFactor

Typical = 120 Volts or 230V

Amps = load current

PowerFactor: power factor with a value between 0 and 1

Power factor in 0-1, which indicates that the load current to do useful work (Watts).
Only electric heater and lamp, power factor is 1; for other devices, some of the load current is only the internal circulation in load, without work. This current is harmonic or reactance current, it is caused by the load characteristics. It is important to understand because this part of the current, so the VA W value greater than the value, the value W is considered to be the value when the VA power factor is a special case.

Computer w W value is its value of VA 60 ~ 70%

In fact today all modern computer charger are capacitive, the power factor value of 0.6--0.7. PC tend to 0.6, mainframe tend to 0.7. The recently developed a known as a power factor correction feature of the new power, its power factor value of one. The future is likely to be the full use of this power, but the market also rarely see this kind of power supply.

The load on the computer, the UPS W value is its value of 60 VA--70%

Because all computers of the power factor value of 0.6--0.7, load on the computer, the UPS W value is the value of 60 VA--70 per cent.

Most UPS manufacturers use W indicates that capacity, and in fact they are VA value

When UPS manufacturers have rated the w value that without the power factor and rated VA value, a user can assume that this is the power factor of 1 W values (equal to VA value), and the fact that manufacturers are rated VA UPS. The actual load on the computer to the W value in the value of 60-70%, a nominal value of 100
W ups can drive a bulb of 100W, but can only drive a 65W computer.

Most computer equipment with the VA that capacity

Most computer equipment capacity, said recently some VA computers began W indicates that capacity (the most famous DEC and IBM). But overall, or VA. So the VA UPS with that capacity to better reflect its and load match. All UPS APC are at the same time provides the w value and two values VA. Product models include VA value or a value by VA multiplied by 0.65 converted into W values.

The rated value for VA UPS to avoid confusion

When a UPS label out of the W value that the load on your computer's actual W capacity the mark value of 60-100% (usually 60%) and the value is 100 VA--130% of rated W values. But when one ups marks the nominal VA value that the load on the computer of the actual value is equal to the VA flag value, the value for the W value of 60-70%.

For example:

One of the following configured criteria: NEC Compaq386 machine with colour display, hard drive, a streaming 120M tape drive, an Ethernet card and a Logitech
Bus mouse, 120VAC power measured at its W, current AVA values are as follows:

Total Watts = 230W

Total Amps = 3.04A

120V AC voltage =

Total V-A = 365VA

Power factor = 0.63

In 230VAC and other configuration of the computer power factor value of similar (see "PCMagazine on 9/16/1986)