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Topic: UPS for Projector Electronics
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 07-05-2010 05:38 PM
Seems the talk was of VA(=Volt Ampere) vs Watts
From wikipedia:
quote:
A volt-ampere (VA) is the unit used for the apparent power in an electrical circuit, equal to the product of root-mean-square (RMS) voltage and RMS current.[1] In direct current (DC) circuits, this product is equal to the real power (active power) in watts[2]. Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents of the same frequency).
Apparent power is the vector sum of real and reactive AC power vectors. While both the volt-ampere (abbreviated VA) and the watt have the dimension of energy, they do not have the same meaning. Some devices, including Uninterruptible Power Supplies (UPSs)], have ratings both for maximum VAs and maximum watts. The VA rating is limited by the maximum permissible current, and the watt rating by the power-handling capacity of the device. When a UPS powers equipment which presents a reactive load with a low power factor (e.g., a computer), neither limit may safely be exceeded.
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Josh Jones
Redhat
Posts: 1207
From: Plano, TX
Registered: Apr 2000
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posted 07-07-2010 02:28 PM
quote: Robert Minichino
Power consumption in watts is never higher than apparent power in VA. Power factor is the ratio between apparent power and actual power, and is from 0 (no power delivered) to 1 (VA = W).
Note paragraph 2 of the wiki.
quote:
Apparent power is the vector sum of real and reactive AC power vectors. While both the volt-ampere (abbreviated VA) and the watt have the dimension of energy, they do not have the same meaning. Some devices, including Uninterruptible Power Supplies (UPSs)], have ratings both for maximum VAs and maximum watts. The VA rating is limited by the maximum permissible current, and the watt rating by the power-handling capacity of the device. When a UPS powers equipment which presents a reactive load with a low power factor (e.g., a computer), neither limit may safely be exceeded.
The key word here is "apparent power", ie VA. Because of time domain relationships between voltage and current, a device with poor power factor will require more power to do the same amount of work than a comparable device with power factor correction. This is why those silly twister bulbs are only 2X as efficient as a comparable incandecent bulb, rather than the stated 4X. Their power factor sucks.
JJ
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![[Roll Eyes]](rolleyes.gif)
let them make up some ludicrous standard like the "power ratings" of automotive amplifiers. Remember the "300 watt per channel" in-dash stereos operating from 12vdc with no switch mode power supply? 
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