# Watt meter

Discussion in 'Electronic Basics' started by [email protected], Jan 11, 2006.

2. ### A ManGuest

On 11 Jan 2006 10:38:50 -0800 in article <1137004730.093965.80770
An appliance, like your fridge, will tell you how many watts it uses (which
is watts per hour). But it isn't on all the time so you really don't know how
much energy it actually uses. This looks interesting. I'd be curious to know
how much power my notebook uses in sleep mode while it's plugged in to the
wall. I also want to know how much my VCR uses, since power has to always
flow through it to know when to turn on and record a program.

I read an article that if you sum all the power used by built-in clocks in
your house, like on the stove, microwave, TV, VCR, etc that you have
significant power uses. But what does "significant" mean? Does that mean if I
turned them all off I'd save \$1 per month? Or save \$2? In Feb 2005 my
electricity alone cost me \$250, so \$2 is not going to break me. And I have a
tiny house (850 sq ft).

3. ### Guest

Once you know the average for a certain appliance over a typical day
you can certainly calculate the cost. Your electric bill should list
your rate per KWH (KiloWatt-Hours). If your rate is 10 cents per KWH
then a 100W bulb will cost 10 cents for every ten hours of use. A clock
or sleeping VCR would only be a tiny fraction of the amount used by a
single 100W bulb, so what you read is not true.

4. ### Bob MastaGuest

Steve Ciarcia, the publisher of Circuit Cellar magazine, related
his experience with this last year. He figured we was burning up
around \$100 per month this way. However, after reading his
I'd say he has a serious reality disconnect! ;-)

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

5. ### Guest

Oh boy, I'll bet Ciarcia has a real "typical" house. Is is true that
things that run 24/7 will add up. A typical clock is going to draw
maybe a few Watts. If you figure that for each Watt the item will
consume 8.76 KWH per year then each 24/7 Watt at 10 cents per KWH will
cost you 88 cents per year. So a typical clock might cost \$2-\$6 per
year to run. A 4 Watt nightlight is \$3.52 cents per year.

6. ### Rich GriseGuest

Watts per hour would be a rate of change of power. What it shows is watts,
which is watt-hours per hour. Watt-hours are what accumulate on the energy
meter, that you pay for. Power is a rate of doing work, power times time
is the total amount of work done. Energy == Work. (well, the kinetic kind.)
Yes, you do. However many watts it consumes, in one hour it will
use that many watt-hours. Energy is Power * Time. So, watts times
amount of run time gives energy.
If you're spending \$250/month on electricity, you must have an electric
driveway heater or something! Geez!

Yeah, get the little power meter and find out what the power hog is!

Or, if it's something like the A/C, you'd be able to meter that by
watching the house KWH meter while it's running.

Good Luck!
Rich

7. ### JohnGuest

If you have a Palm PDA, you can download a calculator that measures
current electrical usage by timing the rotation of the meter disk
(North American power grid - don't know about any others).

KW Calculator http://www.jecarter.com/nsbsource.html

John

8. ### Guest

Sure, if you want to look at the draw of the entire house. This thing
saves you the trouble of shutting off everything else in the house and
then standing outside with a stopwatch.

9. ### Homer J SimpsonGuest

I read an article that if you sum all the power used by built-in clocks in
In winter, all that 'waste' energy just helps to heat to house so you get
double benefits. What is your heat source? If it's electricity, or if gas is
not that much cheaper, forget about it.

10. ### Serious MachiningGuest

Hi guys, I find this discussion to be quite interesting and it got me
wondering about the workings of the typical USA residence watt-hour
meter (2-120V poles, single phase, 60hz).
Does the meter somehow 'average' the current draw of the two phases or
does it react based only on the highest drawing phase at any given time
? I'm thinking that if someone does not have their 120 v circuits
evenly allocated (not by # of circuits but by actual amount of current
running through them in a typical day) between the two phases (poles),
will the watt-hour meter overstate the amount of electricity consumed ?
- Dennis Anderson

11. ### John FieldsGuest

---
The residential watt-hour meter is a marvel of clever engineering.

Not only will it not overstate the amount of energy used, it will
compensate for the reactance of the load and not charge for anything
but the resistive portion, so it's truly only tallying up
watt-hours, not volt-ampere-hours.

Google watt-hour meter for a lot of information.

12. ### Jasen BettsGuest

I expect it sums the currents (which is basically the same as averaging them)

they'd do this in the old mechanical meters by putting both current measuring
windings together but oppositely oriented so that a load current in either
would have a similar effect

in modern microcontroller based meters it'd be done either by measuring each
phase separately or by passing both phases in opposite directions through
the same current sensor.. (so the magnetic fields would add)
I don't think so...

13. ### Guest

Yeah the 'waste' energy warms the house but I'm pretty sure the
price/BTU is is lower for natural gas meaning, he'd be money ahead if
he wasted less electricity and heated the house with gas.

GG

14. ### Rich GriseGuest

This is true, and I have no argument with it. But "Serious Machining"'s
question has piqued my curiosity - is the incoming KWH heter "smart"
enough to meter true watt-hours when one side of the line is loaded
much more heavily than the other?

In the US, power typically comes into a house as 240V, center-tapped,
with the center tap grounded at the entrance panel, and called "neutral".
But typically, only a few houses are fed from any given distribution
transformer, so the load should "balance" upstream, but - I'm trying
to visualize - on the house side of the pole pig, if only one side/leg
(which some people mistakenly call "phase") is being utilized, will
the entrance meter know the difference?

Thanks,
Rich

15. ### Jasen BettsGuest

if it's heavily loaded enough that one side has a significantly different
voltage to the other side maybe.
basically the two currents either drive separate motors attached to
the same shaft or drive antiparallel windings in the same motor.
so their effects add with pretty-much perfect arithmetic precision.

Bye.
Jasen