watts consumed range as recorded by an APC UPS unit

Posted by bjf on July 31, 2008, 6:52 am

can someone comment on this observation:

I replaced an aging UPS which provides some power backup/surge control for a
digital
cable box and television, bought this unit
Model: BR1300LCD (APC BACK-UPS RS 1300VA LCD)

When both the cable box and tv are on, the watts on the LCD display alternates
between
a low of 87 watts, up to 107 watts at somewhat random intervals but all within a
few
minutes.

what might be the reason the watts "change" by this range of about 20 watts?

I have the unit set on a permanent LCD display turned on so it works similar to
my
Kill-A-Watt display, though much nicer

Posted by BobG on July 31, 2008, 8:19 am

On Jul 31, 6:52 am, "bjf"

==========================
==========
Stick the voltmeter on the battery. Maybe the trickle charge turns on
and off every couple minutes?

Posted by Vaughn Simon on July 31, 2008, 8:28 am

I have actually seen the same effect on the KAW when it is connected to an
electronic appliance with a switching power supply. What you are seeing is an
artififact of the sampling rate of the wattmeter trying to make sense of the
ragged load presented by a switching power supply. If you stop to think about
it, it is not surprising that a switching power supply "switches" on & off
rather than presenting a steady load. In fact, they work very much like the
mechanical voltage regulators found in the cars of my youth.

Vaughn

Posted by M Q on July 31, 2008, 9:44 am

bjf wrote:

...

The brightness of the picture displayed on the TV at the moment.
You didn't say if the TV was a CRT or newer technology.
CRT uses more power to produce more light, as would, I suspect
plasma, but not LCD.

Posted by Neon John on July 31, 2008, 11:46 am

On Thu, 31 Jul 2008 13:52:58 +0300, "bjf"

digital

between

a few

What does your KAW say at the same time?  Could the UPS display be noisy?

If the power fluctuation is real then it's probably the TV.  Is it a CRT or
flat panel TV?  Plasma or LCD?  A CRT TV draws a bit more power when
displaying white than black.

It could also partially be the cable box.  Given how hot these things get, I
could see chip power dissipation changing, depending on what task it was
executing.

I suggest separating out the two and using your KAW, see which one is
responsible for the fluctuations.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
In theory, there is no difference between theory and practice.  In practice,
there is.