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Household outlet, how much power can you get from?

Discussion in 'Electronic Basics' started by CJ, Dec 6, 2003.

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  1. CJ

    CJ Guest

    The standard household outlet is 120V,

    but it surprises me that I have a gas powered (powered by a weedwacker
    motor) snowblower that can move 300 lbs/min.
    yet I see electric models that can move 700.
    interestingly no electric weed-wacker seems to outpower my 1 hp gas
    unit. (uses the same motor and has a cool snow blower attachment).
    this raises some questions.

    1: if they can make a more powerfull snow blower, why not a more
    powerfull electric weed-waker?

    It seems that they can just keep putting on bigger motors and making
    devices such as snow blowers more powerfull.

    2: What are the limits to the power in watts that can be derived from
    a standard outlet?

    My calculations.

    Horsepower = =Watts/746
    R: R = E / I
    I = W / E
    W = (I^2)*R
    E R I Watts HP
    120 1 120 14,400 19.3

    So if we raise R to only 2,
    E R I Watts HP
    120 2 240 115,2 154.4

    That means that Just by adding resistance we can get infinitely more
    So I guess there is a limit to how high the I/R ratio can get on a
    normal household circuit (but that always equals 120)

    So for our One HP snowblower,
    one HP=(750Watts) if we have 120 V, then I=6.25 (do to W = (I^2)*R)
    This means we only have .052 Ohms on our one HP snowblower. Doesn't
    ..052 seem a little low to derive such power?


  2. E/I=R 120/240=0.5ohms
    Make that lowering resistance.
    The normal household receptacle is rated at 15 amps, but a single
    device plugged into that receptacle is allowed to pass only 12 amps.

    120 volts * 12 amps = 1440 watts, about 2 hp.

    If you go with a higher current receptacle, you might as well also go
    with a 240 volt receptacle to get twice as much horsepower per amp.
  3. 120 volts with 1 ohm gives 120 amps

    120 volts with 2 ohms gives 60 amps

    Current goes down as resistance goes up, I = E/R

  4. N. Thornton

    N. Thornton Guest

    Re: Household outlet, how much power can you get from?


    You _can_ get around a megawatt out of a 240v hosehold receptacle -
    but not for long! Theyre rated at 240v x 13A.

    Regards, NT
  5. B Fuhrmann

    B Fuhrmann Guest

    "CJ" wrote ...
    Maybe there isn't a need for a more powerful weed wacker?
    It takes a lot less energy to cut weeds than to throw snow.
    Until you run into the power limitations of the circuit that you are on.
    Most household circuits (United States) are 15 ampere at 120volts.
    Watts = Volts times amperes = 1800 watts
    Ever wonder why there are so many hair dryers and other portable appliances
    are rated at 1500 watts?
    It lets you plug them into a circuit that has a light bulb on it without
    blowing the breaker.

    Kitchens will have a couple 20 amp circuits because they tend to have large
    power devices on them.

    You could install a 20 amp circuit for your portable tool, but you will have
    a hard time finding an extension cord that is rated to carry 20 amps. Get
    beyond 20 amps and the wire starts to get really heavy and well beyond what
    you would want for a portable tool.

    The other alternative is to increase the voltage of the circuit. This is
    what is done for the typical very high loads in houses (electric stove,
    central air conditioning, and large shop tools.
    My stove is on a 50 amp 240 volt circuit (12,000 watts)
    My air conditioner is on a 30 amp 240 volts circuit (97,200 watts)
    You really would not want to lug an extension cord made to carry the power
    for those circuits.
    Do you realize the size of the wire you would need to provide 120 amperes?
    Look at the wire running into your house from the power company.
    Many houses only have 100 amp services.
    Only if you supply the additional voltage to keep the current constant.
    This is the reason that large household items are powered by 240 volts, you
    can supply more power without increasing the current to numbers where the
    wiring is huge.
    You are thinking backwards on that one, and your math is off.

    You do not derive more power from more resistance on a circuit. If you keep
    the voltage constant, lower resistance will cause more power dissipation
    (FYI: on an AC circuit, it is technically the impedance instead of
    resistance and it is related to the resistance and inductance of the

    P=E*I and E=I*R thus P=(E^2)/R
  6. CJ

    CJ Guest

    And I was hoping to outfit my wacker with a 450 HP V8 from an old
    mustang. :)
    BTW, if you can find a way to use your weed wacker to blow snow, I
    strongly recommend it. It works great.

    Really though,

    thanks for your reply and all the others too, very informative.

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