Variable Temp Heating Element (noob)

Discussion in 'The Projects Forum' started by cl8390, May 18, 2010.

  1. cl8390

    Thread Starter New Member

    May 18, 2010
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    0
    First of all, I want everyone to know that I'm a noob to the world of circuitry... I'm a mechanical engineering student and haven't completed my E&M course yet, but want to get my hands on a project I have in mind. I have a project that is very similar to this: http://forum.allaboutcircuits.com/showthread.php?t=25912

    I've read through the post a few times and don't have the knowledge to completely follow everything that's being discussed, so I wanted to know if anyone could read over what I have in mind and give me some feedback/advice (while bearing with my inexperience). I want to make a heating element to put over the bowl of my hookah so that I would eliminate the need for a burning coal to produce smoke (the idea is discussed on another forum, but it's not a very technical forum and it doesn't seem like anyone's gotten anywhere with the idea)

    Through my initial research I came up with this idea: hook a potentiometer up to the gate of a TRIAC, which would be connected to the power supply and a heating element (NiCr wire) in order to create a variable temperature heating element. I need the temperature of the heating element to reach up to 400 degrees Celsius, which shouldn't be an issue if using NiCr. My problem is that I don't have the knowledge to pick out the parts I'd need in order to make such a circuit.

    My other idea would be to use a household light dimmer to regulate the heat of the wire, but again I don't have a very solid knowledge of household dimmers and their functioning. Do they variably limit the amount of amperes flowing through them?

    Here's a chart containing useful information about NiCr wires of different diameters:
    http://www.wiretron.com/nicrdat.html

    For my first idea, I was looking at this TRIAC, but it's rated at levels much higher than what I'd need (I'm looking to use a standard 120V, 15 amp wall socket as my power source):
    http://www.alliedelec.com/search/productdetail.aspx?SKU=9356521
    would this be overkill?

    Any advice would be helpful... I'm not really trying to use the limited knowledge I have and trial and error to try to go about doing this. Thanks for your patience
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It sounds like the heating element may be exposed to the point where a human could touch it. In that case, you must not use mains power directly. You must use a transformer to isolate mains power from the heating element.

    A likely candidate would be this Radio Shack transformer:
    http://www.radioshack.com/product/i...3732&filterName=Type&filterValue=Transformers

    You could then use small-gauge Nichrome wire wrapped around a flat substrate that has holes in it. Ceramic would be a likely candidate.

    Use Ohm's Law to determine the length of Nichrome that you will need to limit the transformer current to achieve the temperature you want. You will have to inquire what the resistance per foot of the particular Nichrome wire is.

    Attaching wires to the Nichrome would be somewhat problematic. You would not want to use a lead-based solder, as the term "hookah" implies that the smoke will be injested.

    Note that use of your project will likely result in bodily harm due to smoke inhalation, when used in the intended manner.

    However, in the interests of your safety, do not attempt to use mains power directly on Nichrome where it will be exposed.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If at all possible use a " Cal-rod " type heating element where the Ni-Cr wire is encased in a stee tube, as a replacement stove replacement, 1000W @ 240V, operated at controled 120V AC. A standard 600W incadescent light dimmer should work.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bernard,
    The OP wants a heating element that is sized in the range of a sewing thimble. A Cal-Rod element would be far, far too large for the application.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    Thanks Sgt. I thought he was heating hooch. I use .029 Ni-Cr , 18 in long with a "Variac " feeding a 120 to 24V, 3A transformer for foam cutting. It can go to red hot- not good for the foam.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    just go buy a vaporizer and be done with it.. happy smoking!!
     
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