For what it's worth since most people are not used to power factor (PF)
Power is measured as volts * amps * PF = Watts
VA ratings are volts * amps
For DC the power factor is effectively 1 and can be ignored (we are
talking supply power here... you RF guys don't need to go off on a
tangent here...).
The current draw of a load does not always track the voltage supplied.
If the load is purely resistive (no inductors, no capacitors) then
rising voltage and current track linearly. Most AC loads are not purely
resistive and the current may lag or lead the voltage - meaning the
current rise lags behind what would be expected for the voltage
applied. The power factor (PF) is the ratio between the (expected)
current and voltage and it's expressed as a number between -1 and 1.
Old switching power supplies have a PF around .8
A 500W, 120V power supply with a PF of 1 draws: Voltage: 120V, Current
(500/120) = 4.16A
A 500W, 120V power supply with a PF of 0.8 draws: Voltage: 120V,
Current (500/120/.8) = 5.21A
The power supply with the PF of 0.8 requires considerably more current
from the UPS than the power supply with a PF of 1 ~ 25% more.
UPS manufacturers rate power supplies based on VA rather than Watts
since (take your pick here...) they don't have control over the power
factor of the equipment you are adding, or the VA number is bigger and
looks better on the box.
You can get more runtime out of your UPS if you pay attention to the
power factor of the computers you attach to them. Better power
supplies have better power factors. They cost a little bit more but
can save you money on your UPS.
Mark
On 10/28/14, 10:35 AM, Robbie Wright via Af wrote:
Under, about click on UPS. You'll see apparent power rating in VA and
real power rating in watts. Under status>ups, you should also see
output voltage and amps so you can figure out watts if you want. It
also logs your usage in kWH as well.
Robbie Wright
Siuslaw Broadband <http://siuslawbroadband.com>
541-902-5101
--
Mark Radabaugh
Amplex
m...@amplex.net 419.837.5015 x 1021
