Be happy you don't go to school now.
The whole "online test and homework" thing is completely asinine in most
implementations.
The kids spend more time trying to convince the computer that "A+B" is
correct when the computer insists it's only correct as "B+A".
It's really nice when it's a test and 20% of the correct answers are
marked wrong.
Most of the software is so poorly done it's ridiculous. I have seen the
kids spend 50% of their time manipulating correct answers to get the
computer to accept them.
Mark
On 10/28/14, 11:35 AM, Chuck McCown via Af wrote:
I am still pissed at getting marked wrong on an exam in college.
Freshman EE class.
The question was: What is Power Factor.
My answer: Cosine of the Phase Angle
I was right. They were wrong. I was robbed of some points. Somebody
has to pay someday...
*From:* Mark Radabaugh via Af <mailto:[email protected]>
*Sent:* Tuesday, October 28, 2014 9:32 AM
*To:* [email protected] <mailto:[email protected]>
*Subject:* Re: [AFMUG] APC "load in watts"
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
[email protected] 419.837.5015 x 1021
--
Mark Radabaugh
Amplex
[email protected] 419.837.5015 x 1021
