DaveM wrote:

"default" wrote in message
...
On Thu, 10 Nov 2005 21:21:31 +0000, gastec
wrote:


Every night I need to charge up my works mobile phone / laptop /printer
/ gas detection equipment.......Its a pain.....I was wondering if
anyone knows how i could measure the cost of charging all this
equipment????

keep it simple as poss please

Thanks

Short answer: plug it all into a power strip and measure the current
it consumes then multiply that by the line voltage and you have the
number of watts. Multiply the watts by the time its turned on per
day. Power is billed per kilowatt hour of consumption. You need to
know what you pay for power per kilowatt hour and how many KWH the
stuff you're concerned with uses.

It takes very little electricity to work that stuff, if you look at
each piece individually, it is not worth worrying about. Collectively,
it may be another matter.

I found all the stuff that never turns completely off TV with a
remote, my electronic typewriter, VCR, wall wart chargers etc. were
costing me about $4 a month. Soon to be $5.5 with the new rate hikes.

Spend a day with an ammeter and go around the house - then plug your
findings into a spreadsheet program to calculate usage for an hour,
day, month - its enlightening.

Someone is marketing this gizmo called a "Kill A Watt." You program
it with the cost of energy and then plug an appliance in and tells you
what it would cost to run that appliance. I think its around $30-50,
Learn to read your meter. It's easy enough - and the power company
will usually mail you instructions if you have trouble. Tie what you
do to what you use on a daily basis. For instance I take a shower it
costs me about 37 cents, bake bread 22 cents, wash dishes: about 5-15
cents, brew two cases of beer 40 cents.

snip


Sage advice, to be sure. But the Kill-A-Watt doesn't give you the cost of
the energy you use... it only gives you the quantity of energy units,
such as watts and V-A.
A word of caution about calculating energy... battery chargers are
notoriously reactive. IOW, the standard DC formula for power doesn't
necessarily fly when you're using AC devices.
That's where the Kill-A-Watt shines. It will calculate the energy in true
watts, volt-amps, or KWH. It will also give the power factor of the load,
as well as line voltage, current and line frequency.
Most likely all your chargers together would take several days or weeks to
register one KWH. Not much you can do about it anyway, unless you want
to
hack the chargers to add power factor correction. A ton more trouble
than it's worth.
See a description of the Kill-A Watt at
http://www.p3international.com/produ.../P4400-CE.html. You
can usually find them on EBay for $20 - $30 US.

As an alternative, use a clamp-on current meter to measure the line
current being drawn by the chargers and, as stated, calculate the V-A by
multiplying
line voltage by Amps. remember that you are calculating volt-amperes, not
true watts. You need to measure power factor (or voltage vs. current
phase) to be able to calculate true watts.

Cheers!!!!

Two things:
Power factor correction won't really affect the reading of your electricity
meter. It will keep the power consumption (Watts) about the same, but it
will reduce the reactive current so that there will be less Amperes of
current. The electricity meter will read watts, not current, so the
reading will be pretty much unaffected. The power company will be
grateful, however, because although they receive the same amount of money
from you, the losses im their wires and transformers will be slightly less
because the power lost in the wiring is proportional to the current squared
times the wiring resistance.

The second point: a clamp-on meter probably won't make things easier when
measuring the consumption of ordinary appliances, because you have to
separate the line and neutral conductors and clamp the meter around only
one of these if you want it to read the current. Also most clamp meters
don't work so well below about an amp, so this would be no good for a
charger.

Probable the best option is to either buy a power meter, or read the label
on the appliance which should state the power consumption. Watt meters are
really useful for looking at the standby consumption of TVs etc. however,
because the label on the TV probably doesn't even mention the standby
consumption.

Chris