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Fan Power Consumption

Discussion in 'Electronic Repair' started by Joe, Jul 17, 2007.

  1. Joe

    Joe Guest

    I have a Lasko Premium 20" three-speed box fan. I'd like to know how many
    watts it uses, but so far I can't find any good info.

    No wattage info on the box or the fan, no wattage info on the Lasko website.

    Googling gets me wildly disparate numbers on wattage for "portable" fans.

    Does anyone have reasonably accurate info? It would be nice to know how
    many watts for each of the three speeds.


    --- Joe
  2. Vey

    Vey Guest

    If you really want to know the real numbers, rather than theoretical
    book numbers, which are next to useless, you can buy clamp-on amp meters
    for really cheap now. Then you would need an extension cord, where you
    (carefully!!) split the wires, leaving both insulated, so that one could
    be clamped around. These amp meters only work if one of the wires are
    clamped. If you use an extension cord, you can use it for all sorts of
    things around the house to see what they use too.

    I was really surprised at how cheap these amp meters have gotten to be.
    They are accurate, too. I took one over to a certifying lab and they
    wanted to test it for free on a lark cause they couldn't believe
    anything that cheap would be worth a damn. Not many years ago, they cost
    hundreds, now they are down to $20 or so from here:
  3. ian field

    ian field Guest

    Put a low value resistor in the neutral lead and measure the volt drop, if
    its an AC supply and the fan is an inductive load this won't be exactly
    accurate - but probably close enough.
  4. N Cook

    N Cook Guest

    With nothing much , other than clocks on in the house , take a reading on
    the billing consumption meter and then 10 minutes later. Then time for 10
    minutes each of the 3 settings and consequential consumption readings
  5. Guest

  6. Vey

    Vey Guest

    This is the next to useless number I mentioned in my post. It is the
    theoretical maximum amount based on the theoretical voltage. In the
    field, voltage can vary and so can the usage. I know it sounds nutty,
    but I've seen variations of more than 15% from the theory and that, to
    me, is unacceptable.
  7. Guest

    If +/- 15 % is unacceptable then the clamp on ampmeter you suggested
    from Harbor Freight would also be unacceptable.
  8. For an actual measurement, you could plug it into one of
    these meters:
  9. Vey

    Vey Guest

    Don't assume. Buy it and test it like I did. The lab said +-3%. I
    consider that to be acceptable. If you don't like those numbers, then
    buy one for $300 and compare it to what you suggest the "book" numbers are.
  10. Vey

    Vey Guest

  11. Ken Weitzel

    Ken Weitzel Guest

    Hi Joe...

    It's going to continue to be a bit confusing... google lasko fan watts
    and you'll find several entries that include comsumption.... but most
    say 170 watts, one says 165 watts, and yet another 70 watts.

    There must be a rating plate somewhere on the machine or motor,
    though... isn't it a legal requirement?

    Take care.

  12. James Sweet

    James Sweet Guest

    There's much better solutions than that, especially for the novice.

    I have one, it does a good job of measuring voltage, amperage draw,
    volt-amps, power factor, watts, and cumulative kilowatt-hours.
  13. James Sweet

    James Sweet Guest

    You still don't know what the power factor is with that route, a lot of
    cheap motors are closer to 0.5 than to unity, so the calculated wattage can
    be nearly double what the motor actually draws.
  14. The Phantom

    The Phantom Guest

    I have an older GE 20" window fan. It only has two speeds, but here are
    the measurements:

    Speed True watts Amps Volts Power Factor

    Low 94 1.18 121.8 .6535

    High 194 2.38 121.3 .672

    Power was measured with a Yokogawa analog wattmeter; applied voltage and
    current with a Fluke 189.

    This power factor is probably typical for an induction motor of this size.
  15. ian field

    ian field Guest

    If its a ventilation fan exposed to the great outdoors, wind direction could
    easily account for a 15% variation in power draw.
  16. Bill Jeffrey

    Bill Jeffrey Guest

    I have a 20" Lasko in front of me at the moment. My Kill-A-Watt says

    99/136/196 watts
    129/175/248 volt-amps
    at 121 volts

    And no, there is no electrical info plate or marking on any of several
    of these cheapie box fans that I own.

    Bill Jeffrey
  17. Joe

    Joe Guest

    Thanks a lot, Bill. Is your Lasko a model 3723? That's the one I have
    (two of, actually).

    Also, I went to the Kill-A-Watt web site. It looks like you can't measure
    any appliance running at 220 volts, correct?

    I have a wall A/C unit in my apartment that plugs into a 220 outlet. I
    read somewhere that even a fairly small one of these units uses 3500
    watts. I imagine that the 3500 is only when the A/C is running the
    compressor. So the average wattage would depend greatly on the outside
    temperature, I would think.

    --- Joe
  18. James Sweet

    James Sweet Guest

    I have the UK version which is not even branded, but looking at it, it's
    obviously internally identical to the Kill-A-Watt. It's designed for 240V
    but works fine all the way down to 60V so I suspect the 120V model will work
    on 240V but have not opened one up to compare. At any rate the power supply
    is a simple capacitor and zener arrangement so it would be easy enough to
    modify with a lower value capacitor if the zener heats up too much on 240.
    If in doubt, it shouldn't be too hard to get the UK model and build some
    plug adapters as I did, back before it was widely available in the US.

    I used mine to measure the draw of my 3 ton (36,000 BTU) central AC and
    found that the outdoor unit draws about 3500W with a power factor of 0.91.
    You're correct that current draw varies with head pressure which varies with
    outdoor ambient temperature. I doubt your window AC is bigger than 1 ton, so
    even with the indoor fan, I'd be shocked to see it drawing more than 2KW and
    really it's probably closer to 1200W.
  19. Bill Jeffrey

    Bill Jeffrey Guest

    Hey, I found the "electrical info plate" on the Lasko. It was stamped
    into the sheet metal on the bottom of the fan. After being stamped, the
    sheet metal was painted, which obscured the stamped info so completely
    that the only way I can see it only with a bright light held at an
    angle. As near as I can tell, it says
    "Model 3723 (last two digits very unclear, could be almost anything)
    Style EC437 (again very unclear)
    Type 1
    Listed 154C (UL symbol)
    120v 2.2amp 60hz

  20. Having some issues with the landlord over your utility charges?

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