watts meter

Discussion in 'General Electronics Chat' started by aac9876, Jan 2, 2009.

  1. aac9876

    Thread Starter Active Member

    Dec 9, 2006
    124
    0
    I am using a Kill A Watt EZ meter to measure the power needs of a pellet stove.
    It is brand new. I measured the start, and after. Its needs include an igniter for about 8 minutes, a feed auger, a combustion blower and a convection blower.
    I had the meter on watts. I was pleased to see it was about half the draw I thought it would be. Start was about 360, ( igniter is a watt hog) but when the igniter went off and it settled in
    to the 2 blowers and the occasional auger motor feed, it was about 150 watts.
    I thought it was excellent and I could indeed run this off a battery bank for a couple days easy.
    I then switched it to VA and it said about 280. I switched it to amps and it said 2.6 amps.
    So what is the real story. The factory specs do say that it requires about 300 watts to run
    without the igniter.
    I was hoping they were wrong. Why is VA and the amp so much different than the watts
    reading.???
    The manual for the meter says amps are displayed in true RMS...
    watts are displayed in active power watts.....
    VA is displayed in apparent power VA....
    whats the story????
    thanks
     
  2. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    VA and watts are equal when powering a purely resistive load, like say a heating element or lamps. However when driving capacitive or inductive loads, like motors, the reactive load causes a phase shift between the voltage and the current.

    I guess the key question is does one pay the utility company for the true RMS power consumed or the apparent VA power consumed? I'm not sure, but I'm sure that someone here will bring clarity to the topic.

    Lefty
     
  3. aac9876

    Thread Starter Active Member

    Dec 9, 2006
    124
    0
    the important thing for me is what draw there is on a battery bank and inverter.....
    I want to know how long I can run it when the power goes out......
    If I have 4 L-16 at 24V I have about 11000 watts minus half = 5500 watts.
    with that in mind...?????
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The extra apparent power is stored in inductors and capacitors then is returned to a normal power source but not returned when an inverter is used. Figure on the highest amps.

    Your battery is probably rated at a 20 hour rate. If it is discharged too low then the inverter might stop or the battery might be destroyed.
     
  5. rlewis581

    New Member

    Jan 1, 2009
    2
    0
    Watts are watts and that is what the power company charges you for . Who cares in your situation...you're not paying them. You are using X amount of Amps for X amount of time. Do your calculations accordingly at the DC end to include your inverter in-efficency and that's how long you're battery bank will last.
    Hope this helps. Rog
     
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