On Sat, 12 Nov 2005 19:54:52 -0500, Pop wrote:


"chocolatemalt" wrote in
message
...
: In article ,
: "John Grabowski" wrote:
:
: 24 watts divided by 1000 equals .024 KW times 1 hour equals
.024 KWH times
: 10 cents per hour would cost you .0024 cents to operate for
one hour. I
: think.
:
: Just a nit: You multiplied by 0.1 to get the final answer,
which works
: for dollars but not cents. So, .0024 dollars/hr, or .24
cents/hr.
: Small change either way.
:
: For general electric costs rule-of-thumb, I use the 100W
lightbulb, at
: $0.10/kWH (common rate in the U.S.), and 1 month (electric bill
: frequency), to come up with:
:
: 0.1kW * 1 month * 30 days/month * 24 hrs/day * $0.10/kWh ~=
$7/mo.
:
: So, $7/mo. to run a 100W device all the time. Most appliances
and duty
: cycles can be scaled to this benchmark pretty easily.

Basically true for an incandescent light bulb. I went out and
bought a watt/VA meter one of the guys here suggested - and you'd
be surprised how far off that same 100W calc is if the load is
inductive. Depending, I'm seeing power factors so far as low as
58% to around 80%, which will throw off your calcs over the space
of months or a year.

At least in the US, residential customers are charged for energy consumed.
They are not peanalized for crappy PF. Many corporate customers are.

That meter's a nice little gizmo for $30 and seems to be
pretty accurate to boot. No specs with it, but I did check it against
some calcs, plus what my UPS measures the line stuff at - they lined up
very nicely; less than 4% diff and I'm sure the UPS ain't all that
accurate as a rule either. How's that for a scientific calibration
check g?
Also, if you're playing with duty cycle, you don't multipy by
24 x 7 etc.; that's a 100% duty cycle on your assumption of everything
having a power factor of 1.00.
For an electric bulb though, you'd be real close. But
refrigerator, furnace, flourescent, things like that it's quite a
different story.
It's been interesting if nothing else, and might save a thou
or two over a year; making it worthwhile.

A thou or two over a year? Your bill must be mighty big! ;-) Again, you
are only charged for watts. The PF is irrelevant here (not so for your
UPS though).