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(Really simple) Newbie in EE

  1. Aug 29, 2014 #1
    So, I have this Lasko 20" Box Fan that I think is dead; with one of two possible causes:
    One, the motor is bad in which case, new fan
    Two, the switch quit, in which case, I have an AC power line from the wall, with two wires, no ground, connected to the fan. The fan has a rotating-type switch, C is always connected, with L having 1, 2, or 3, for low, medium, high, or no connection on L for off.

    What'd be the best way of going about testing if it's the switch?

    I've already (with the fan unplugged) wired the two wires for C together, using orange caps.

    Would it be (reasonably) safe, to do this on a home circuit with a power strip for a cutoff switch (Since the rotating assembly is busto, and not working at all; plus I lost a part or two to the switch)?
    Or would it be better to use a generator? I'm at a loss here. I'm trying to avoid unnecessary damage.
     
  2. jcsd
  3. Aug 29, 2014 #2

    mfb

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    Unplug the fan, test if the lines have a good electrical connection if the switch is "on". Anything with low voltage will work - a multimeter is the most convenient solution, a flashlight with batteries and some wires will work, too.

    I don't understand what you try to do.
     
  4. Aug 29, 2014 #3

    berkeman

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    Do not re-wire the fan to try to bypass the switch. As mfb says, use a meter of some sort to "beep out" the circuit, to see if turning the switch on shows continuity to the fan motor's various windings.

    There also should be a fuse somewhere inside the fan. See if you can locate it, and beep it out to see if it's still good.
     
  5. Aug 30, 2014 #4
    The fan is really old - it's also really simple; it may not have a fuse? It's a 20" Box fan, if that helps. My apologies for the lack of information.
     
  6. Aug 30, 2014 #5

    jim hardy

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    Typically there's a thermal cutout inside the motor.

    Your local hardware store should have a replacement rotary switch. Ceiling fans use them but have a pull chain instead of a knob.

    A power strip with cutoff switch should be okay for a one time test just to see if motor still runs. If motor smells strongly of burnt insulation dont bother - it is in early stages of failure already.

    Glad to see you used the orange screw on wirenut. Keep it safe.
    Don't touch it while testing. If it hums loud but doesn't turn it has internal shorts and is kaput.



    http://en.wikipedia.org/wiki/Induction_motor
     
    Last edited by a moderator: Sep 25, 2014
  7. Aug 30, 2014 #6
    Yeah, we gave it a test today with the configuration I had, based on what the switch looks like inside I either got it wrong (wiring), or it's dead. The motor had been seizing up for about 2 months and we've been spraying the back cylinder with WD40 and that usually solved it for a week or so.
     
  8. Aug 30, 2014 #7

    AlephZero

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    What berkeman said!!!!

    A few years ago I had an ancient electric heater with a fan that was getting a bit noisy. I assumed was because the fan bearings were just about worn out.

    One day, without any warning, there was an very loud bang, and it stopped working. It didn't just blow a fuse. It completely destroyed the wall socket that it was plugged into. The connections between the socket and the mains cable in the house wall didn't exist any more.

    Mains-powered inductive loads, like a fan motor, need to be treated with the respect they deserve, if you want to live long and prosper.

    I didn't investigate the cause of the fault - some things are not worth the risk of trying to repair them compared with the cost of a replacement!
     
  9. Aug 30, 2014 #8
    The fan is in the trash now, so I'm not worried about it.
     
  10. Aug 30, 2014 #9

    jim hardy

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    They'll do that when they first develop shorted turns inside. They hum loudly and smell, too. Then they burn up and can go pyrotechnic. Electrical winding faults grow exponentially.


    That'd be scary. Sounds like an arc got started behind the socket and some protective device failed to quickly clear it . I had a recent near miss like that on a water heater . A loose terminal had overheated one wire to point about four inches of insulation was crumbling away. The 30 amp breaker would've supported a substantial arc for quite a few line cycles.

    Glad you're safe - you showed common sense.

    old jim
     
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