stepping down US power to 8A 120V

Discussion in 'The Projects Forum' started by second.exodous, Jul 20, 2013.

  1. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    This is probably below this forum since it is a question for fixing a box fan but I have one that quit working and not sure what burned up. The switch still clicks and NONE of the 3 positions work on it. The motor is fine, it runs directly off of power, so I think it is the switch. I thought it would be ok to try off of direct power because the three setting of the switch are:

    6A-120V
    3A-240V
    8A-120V

    So only the Amps differ but wasn't sure if I could directly wire the motor up to the outlet, I'm worried that over time putting 15A through it all the time will burn it up.

    So, if it will burn it up, is there just some simple cheap part that will step down the just the amps?

    I found out that the manufacturer has the fans assembled in the US so they should have boxes of these switches so I e-mailed them asking for one. I'm not sure they will since A: they're a company and B: they're in a union state they might not want to give/sell me a switch and want me to buy a new fan instead. So, I'm asking here also if that is the case.

    Any help would be appreciated.

    Thanx

    EDIT: Oops, the hight setting is what I'd want it constantly set at which I think would be 8A-120V, so I'd have to step down the voltage also.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It sounds like you have the impression that 15amps will automatically flow it you run it off a 120v socket?
    The fan will only draw the current it demands, not 15amps delivered automatically, if that was your reasoning?
    Depends on the technology of the fan, the switch could well have a dropping resistor etc?
    But I am not sure about the double current value on 120v?
    It might be possible to reverse engineer the switch arrangement?
    Max..
     
  3. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Well, upon further inspection I can not run the power through the regulator, a little black box to the side with:

    4 uF +- 10 5%
    250V AC 70 C CF

    written on the side.

    The '+' and '-' are above each other as are the '10' and '5' before the %. The 70 is degrees Celsius. I hope that all made sense.

    Anyway, I now think this is the part burred out. That is the part that steps down voltage/amps? I probably sound like such a noob because I am.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That indicates it is a 4µf 250vac capacitor, IMO that would not be any kind of voltage regulation, although unusual, it sounds as if you could have a split phase induction motor there?
    Is there any other components?
    Can you tell how many connections to the motor?
    Max.
     
  5. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Well, wow, kinda hard to explain but the power is two wires, no ground, one goes directly to the switch the second wire goes into what looks like a mess of wires. I can't see it unless I unbind them, and it goes from there to the capacitor. . .

    Well, I could take some pictures, maybe that would be easier?
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    yes, please.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Plus any info on the motor plate, if it has one?
    Max.
     
  8. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Motor Top

    [​IMG]

    Motor Bottom

    [​IMG]

    Housing removed

    [​IMG]

    Capacitor

    [​IMG]

    Switch top

    [​IMG]

    Switch bottom

    [​IMG]

    I included those pics of the switch just in case and the bottom setting is 8A not 6A, it looks like a 6 on the pic but it is an 8. Hope these are clear enough to see. The wires look like they go into the motor so not sure if I can unbind them.
     
  9. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Just noticed something printed in the motor itself, I'm taking a picture now. Hard to get.

    This was in the motor, the bit at the bottom covered is COM-WHT.

    [​IMG]
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Those current readings are just the rating of the switch, that is a simple el-cheapo on/off sw.
    The motor is a 120v split phase induction motor so you probably just need a decent switch.
    if you measure resistance on the wires, you can detect the two windings, in all probability the windings are identical, which in that case you can use either winding for the start and run.
    If you know from previous observation which winding the cap was connected to, it would pay to observe it, just in case.
    It looks like a 6 lead motor, so it could be dual or 3 speed?
    Max.
     
    Last edited: Jul 20, 2013
  11. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Well, when it worked it had off, low, medium, and high. However, we only use it in the summer on high in a window at night, so If I could somehow wire it up to just run on it highest setting somehow then that would be ideal. We can't even reach the switch from where it is on the rear so we just unplug it to turn it off. Maybe that is why it burned up?
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You just need a 3 posn switch and you should have three speeds.
    If you need it on high then connect the wire that went to L to 3, leave the others disconnected.
    Max.
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    What I see is a 3 speed motor and a 3 point multipoint selector switch to select one of 3 winding taps. Just replace the switch. Check Newark or mouser for the multipoint selector of proper rating (120v, 8A).

    Edit: sorry, I didn't see the second page. All you need to do I connect your 120 v to the black and white wires of the motor if you don't need multiple speeds. You could put a simple on/off toggle in series with it to turn it off.
     
  14. second.exodous

    Thread Starter New Member

    Jul 20, 2013
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    Ah thanks, I'll give it a try. This was a cheap fan, under $20, but I made up my mind to try to at least fix everything that breaks in my house before throwing it out from now on.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would suspect that the gray wire was the L and 1,2,3 were Red,Blue,Black?
    Alternatively gray connected to black for full single speed?
    Max.
     
  16. WBahn

    Moderator

    Mar 31, 2012
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    My best guess is that you have a motor that has two windings, a low power and a high power one. At the lowest speed setting, the switch only powers the low power winding. At the medium setting, it powers the high power setting, and at the highest setting it powers both.
     
  17. WBahn

    Moderator

    Mar 31, 2012
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    Ah, I didn't see second page, either. My vision is bad enough that I didn't even see the gray wire and thought there were only three total.

    @ strantor and maxpower: Would it work to use just two windings as I described? If not, why not? It seems like it would cost less, which would be desireable for a cheap box fan.
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The traditional way is a start winding with the cap permanently connected.
    There would be one main winding and two auxiliary windings, connected what was known as consequent poles.
    On high the main winding would be across the supply and the two aux windings, on MED the run the main winding and half the aux winding connected in series, the other half of the aux winding is connected in series with the start winding.
    On LOW speed the running winding is connected in series with both auxiliary windings across the line.
    The end result is that the 3 speed can be be controlled with a single pole 3 position switch.
    There are a couple of variations, but I suspect that motor conforms to the above?
    On an induction motor the effective pole count has to be increased to reduce RPM.
    Max.
     
    Last edited: Jul 21, 2013
  19. Pencil

    Active Member

    Dec 8, 2009
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    I didn't see if you actually tested the switch.

    If the switch checks good, the thermal fuse in
    the motor is possibly open (blown).

    I suspect the thermal fuse is in contact with
    the windings inside the motor case. You will have
    to carefully clip the wire ties and gently move
    wires and or insulative covering to find the fuse.
    Be very careful that the windings do not become
    dislodged, nicked, or broken.

    Radio shack sells thermal fuses.

    The switch may also be able to be replaced with
    a toggle switch of the SPDT (single pole double throw)
    with center off type for a two speed operation.
    Looking inside the switch will reveal which wires
    are connected for each speed.

    Safety note: Any appliance running off of mains power
    is potentionally dangerous to your safety (you can be killed)
    and can be a fire hazard if not handled properly. PLEASE
    seek advice from a qualified person if you are unaware of
    correct procedures when dealing with such appliances.
     
  20. LDC3

    Active Member

    Apr 27, 2013
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    160
    I found this bit of information here.

     
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