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Watt meter

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

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  1. A Man

    A Man Guest

    On 11 Jan 2006 10:38:50 -0800 in article <1137004730.093965.80770>, spoke thusly...
    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).
  2. 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.
  3. Bob Masta

    Bob Masta Guest

    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
    description of all the "gotta have it" gadgets he had running,
    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
    Home of DaqGen, the FREEWARE signal generator
  4. 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.
  5. Rich Grise

    Rich Grise Guest

    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!
  6. John

    John Guest

    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

  7. 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.
  8. 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.
  9. 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
  10. John Fields

    John Fields Guest

    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.
  11. Jasen Betts

    Jasen Betts Guest

    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...
  12. 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.

  13. Rich Grise

    Rich Grise Guest

    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?

  14. Jasen Betts

    Jasen Betts Guest

    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.

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