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Popper Pot specs?

Discussion in 'General Electronics Discussion' started by Greg J., Apr 7, 2015.

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  1. Greg J.

    Greg J.

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    Oct 8, 2013
    I am trying to use an air popcorn popper to roast coffee (a not unusual use for air poppers these days). However, the temperature is too high. I thought I could put a rheostat in the hot wire to the heating element. My concern is in choosing a pot with an appropriate power rating and resistance. While I found formulas, I wasn't able to figure out how to use them properly. Can someone help? Any comments appreciated. The popper is labeled as 1440 watts, 120 volts @ 60 Hz. (The instruction manual seems to only be useful for user operation: http://www.gopresto.com/downloads/instructions/04821.pdf.) If you can suggest a pot or two from Mouser, that would also be helpful, since there are so many.
     

    Attached Files:

  2. duke37

    duke37

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    Jan 9, 2011
    You will need a very big rheostat to handle 1440W (12A). I would go for a simmerstat as used on a cooker. This will turn on and off but the time constant may be short enough to generate a fairly constant temperature.

    Half power can be obtained by putting a diode in the supply.

    The fan motor appears to be DC, it is not clear here it gets its power. If in series with the heater, then messing the heater supply will also affect the motor. Also if the motor is tapped across part of the heater winding. If you are capable of measuring fan voltage without killing yourself, it would be interesting to know what it is.
     
    davenn likes this.
  3. Greg J.

    Greg J.

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    Oct 8, 2013
    The fan is in parallel with the heating coil. When the fan is running the voltage is 18.75 RMS.
     
  4. duke37

    duke37

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    Jan 9, 2011
    If the heater runs on 120V, them how can the fan get 19V if it connected to the same place?
    Hair dryers often have a 12V motor in series with the heater. I suspect that this is the case here but the diodes look small for 4A.
     
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  5. Greg J.

    Greg J.

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    Oct 8, 2013
    Yes, sorry. It is in series. The two white, thick wires in the upper left of the photo run directly to the wall outlet.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    still doesn't sound right ... that would mean the poor fan is passing the full current needed to heat the element, and that isn't going to happen

    how about some sharp and well lit wide and close pics of the internal wiring of this popper unit
    the one you gave in your first post doesn't tell us too much

    those 2 thick white wires going to mains power in, which is phase and which is neutral ?
    the bridge rectifier is proving a dirty DC to the motor and much be around 110V as there would only be
    around 2V drop across the diodes

    Dave
     
    Last edited: Apr 8, 2015
  7. Greg J.

    Greg J.

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    Oct 8, 2013
    Attached is a schematic I drew from what I can see in the popper. Also attached are various photos of the internals. Since the full size of each is 6M, I just uploaded versions with a smaller file size. I can provide full resolution for zooming in upon request. I may have made errors. For example, I'm assuming the "Wheatstone"-formation passives are diodes, but I can't read enough of the labeling on any of them. I can only tell they are polarized. The resistor+relay is presumably an overheating cutoff, but that's just a guess on my part based on its electromechanical appearance.

    Popcorn-Popper.png
     

    Attached Files:

  8. Greg J.

    Greg J.

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    Oct 8, 2013
    Any help?
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    hi Greg,
    sorry I am out of ideas :(
     
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