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watts consumed range as recorded by an APC UPS unit

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bjf

Jan 1, 1970
0
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
 
V

Vaughn Simon

Jan 1, 1970
0
bjf said:
what might be the reason the watts "change" by this range of about 20 watts?

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
 
M

M Q

Jan 1, 1970
0
bjf wrote:

....
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?
....
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.
 
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