Magnet Wire as Heating Coil?

Discussion in 'General Electronics Chat' started by js_530, Mar 4, 2004.

  1. js_530

    Thread Starter New Member

    Mar 4, 2004
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    What's the proper way to use magnet wire to make a heating coil? What kind of voltage/amperage should I use and how can I avoid shorting the power supply?
     
  2. Harlan

    Active Member

    Feb 26, 2004
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    Hey ya JS;
    Well you got me on this one for sure! I have never heard of using standard magnet wire for heating purposes. Everything I have had to work with for heat applications has been with wire that is designed to tolerate heat in its chemical composition, like the Nichrome and tungsten wires. My experience tells me that the magnet wire would cause problems for both the supply and the wire itself. With magnet wire, the heat wil cause a change in resistance to a greater degree than the materials specifically designed for this. Maybe you can share with me the source for this application and how magnet wire came to be suggested, maybe there is a new wire I am not aware of here. You have me curious now!!! :rolleyes:
    Harlan :)
     
  3. js_530

    Thread Starter New Member

    Mar 4, 2004
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    lol, a friend of mine has suggested using magnet wire for heating. I have no commercial application for this, I'm just thinking of a way to heat up my keyboard when it's cold in my house. Are there any sites that sell Nichrome or tungsten wire in small quantities, and how much does it cost?
     
  4. Harlan

    Active Member

    Feb 26, 2004
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    AHHHHH ok
    heated mouse and keyboard
    http://www.theheatedmouse.com/
    :blink: :unsure:
    IF!!! you are going to heat your mouse, the plastics used to make the standard keyboards and mice are NOT thermal plastics and you may end up with a melted mouse or keyboard. There is another place that sells a heated mouse pad too but I can not find the site. Just search for Nichrome wire in any search engine and you will come up with a lot of sources. My local radio parts jobber has Nicrome replacement wire in stock all the time. Also some appliance repair depots have the right wire, since they repair toasters and such. Be careful though, and once you have the idea formed, tested, and ready to apply, get a current measurement and get a fuse in the circuit quick! heated wires are a real fire hazard. Safety first , Safety!!
    Harlan :)
     
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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    :) hi,

    you can use a 3 or 4 turn 600w nich wire and power it with a 12v transfo. it will glow after 3 to 5 seconds.

    you didn't mention how long you want your pad heated up. further details would give us a clearer picture of what you want. :)
     
  6. Harlan

    Active Member

    Feb 26, 2004
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    Ok I had to try this, anddddd
    Laughing here, I took an old mouse pad, decided this would be fun, and wound #28 magnet wire into a coil that was very loose in the turns, so the turns start at the middle and work out to the edges of the pad. I measured the DC resistance and it was too low for my meter. I am guestimating this to be around 0.01 ohms. I decided to go for a current of 20 mA to see what happened, so knew I would need a series voltage drop to adjust the heating element. From my computer I stole the 5 volts and wired in a 500 ohm rheostat and a 100 ohm resistor to limit this to 50 mA maximum. I adjusted the current flow for 5 mA first and let it sit, and to my surprise, the dang thing was warm and nice and toasty and dang it actually felt good on my heel of my wrist that is always in contact with the pad. THe reason I decided to try it out is that in my telescope days, we would use a bank of resistors to heat the tube to prevent fogging, and all we wanted was a one egree rise over ambient, and running 1 mA current seemed to be fine.
    But to the humor of all things, I also will share this with everyone.
    http://www.halfbakery.com/idea/Winter_20Mouse
    Thanks for the Inspiriation JS, next test, 12AX7 mounted inside mouse! :lol:
    Harlan
     
  7. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    :lol: Good stuff! :D

    *Goes to dig out magnet wire!*
     
  8. js_530

    Thread Starter New Member

    Mar 4, 2004
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    Ironically, I melted my keyboard just a few days ago. I used two heat lamps, suspended about 5 inches away to dry it after cleaning it. The plastic melted after less than five minutes.

    edit:

    How did you put the magnet wire in the mousepad? Was it just underneth the mouse pad?
     
  9. Harlan

    Active Member

    Feb 26, 2004
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    Hey JS
    Ok I used and exacto knife and made a cut from the center of the pad outwards in a circular motion, from the bottom and made the cut about 75% deep. Leaving the slit as a form I laid the wire into the channel with a pencil, and attached a connector to the ends of the wire, I think I have about 40 to 50 turns and made 5 layers of the windings, connecting them in series. I am Kicking the current on now so will know how well this works in a few minutes. TOASTY Mouse Pads!!!!!!
    This is a kick!!
    Harlan :lol:
     
  10. js_530

    Thread Starter New Member

    Mar 4, 2004
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    I tried using 20 guage magnet wire with 10 mA at 5 volts and I didn't feel any difference after 10 minutes. I measured the current, so I know there is current flowing through it. How long did it take for yours to warm up? I'm only using about three feet of wire, but I've also tried using about 6 inches, still with no affect. It could be possible that it's just too warm to notice a difference here in Texas.
     
  11. Harlan

    Active Member

    Feb 26, 2004
    46
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    Hi ya JS,
    It only took a few minutes before seeing an increase of a couple degrees, but I am measuring this at the contact area of the wire too. Lets look at this as to how much heat you want to generate too. To et a really nice warmth, I am guessing here that you will want somewhere between 1 and 5 Watts of energy dissapating, so next step is too increase the current flow, and figure in some loss through the insulating pad. If we go up to a full watt, watch for fire and smoke, but that can be a gol for now. At 5 volts and 20 mA we find we have a 50 mWatt output, 0.05 Watts, so get to 1 watt using 5 volts we find the current needs to be at 200 mA. This is also for the whole circuit too, so remember the Rheostat is also heating the same, or disappating. If you have a milliohm meter there, you can check the resistance of the wire coil, and calculate teh current needed for a half watt or which ever you choose. The higher resistance types of magnet wire will be easier to get better results with too. That is the type of magnet wire I am using here. Things to watch for is exceeding the ratings of the rheostat, the power supply and the current rating of the wire. I just took a measurement on the outside of my pad here, and I am only seeing a half degree rise after 15 minutes. Later I will run this up some more and post back some more results. As we have been doing this, I have been thinking of a much nicer way to accomplish the heated mouse pad, and if I have enough resistors here I might try this out, to see if I can get an adjustable hot pad for my mouse. I will start with a maximum of 10 watts dissipation but instead of using wire I will use 1/8 watt resistors in series laid inside the cut track. For 10 watts, and at 5 volts the current will have to go up to 2 amps so I might jump jump over to my 12 volt supply basically cutting my current in half. So for 12 volts and 10 watts I will have 833 mA. and only 83 mA at 1 Watt. So for full heating I need 14.4 ohms and I figured spacing them an inch apart so maybe 50 resistors at 0.228 ohms each. The gola will be now to get a 5 degree rise from the "Surface" of the mouse pad here. Later I will run some old calcs on watts to BTU and area to temp rise.
    Harlan :D
     
  12. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    :) hi harlan,

    don't forget to post what happened when you put the 12ax inside the mouse :D :D :D :blink: :unsure:

    the idea of heating a mouse never entered my mind. am in a tropical country.
     
  13. Harlan

    Active Member

    Feb 26, 2004
    46
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    OK! :eek:
    I have an Ignorant Brain Cell here, and need to straighten this thing out and make the cells fly right. How much current can I demand from an USB port???
    I have a few experiments here that I will post later but wondering just how much power is available at the usb port.
    I hope its enough!!!
    :blink:
    Harlan
     
  14. Harlan

    Active Member

    Feb 26, 2004
    46
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    Oh yeah and MOZ!
    NeveR NEVER never place sound circuits inside mice!!!! Oh I gone and done it this time!! Got the 12AX7 installed and the DANG MOUSE TOOK OFF! :eek: I know it is hiding around here somewhere, because well.... I am now missing 4 of my all time favorite CD's and at Night I hear the music playing and so I can not GET MY SLEEP!!!! :angry: ..... Dang mice....... Live and learn!!!!!!! :unsure:
    Harlan
     
  15. Harlan

    Active Member

    Feb 26, 2004
    46
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    Sometimes these experiments take on a twist that makes one really think. :eek: HereI figured a simple resistance network would be just fine, and upon playing with this little project I learned an interesting hurdle :unsure: that has to be dealt with. It is not about the electronics end and getting warmth from the R network, but one of conducting the heat to the surface of the pad and here in lies part of the problem. The mouse pads I have are foam style cloth covered, and they do a really good job of 'Insulating" the heat transfer. I did some basic tests and found I could get a 15 degree rise from 220 ohm across 5 volts. Working with a limited current supply and spreading things out over a square area, say 9x7 inches or 63 square inches, I determined i would need a half watt per square inch. That is 63 watts, and at 5 volts means the current has to be 12.6 AMPS total. :eek: Not available at the USB port. If I go with 12 volts though I will need 5.25 AMPs and again not available in the PC to use. So Next I tried a few things to see how low I could go for current salvation. and with 220 ohms offering a max of 15 degrees at point contact, and a half degree installed 1/16 th inch below cloth in the pad and at 330 ohms only a point contact rise of 5 to 6 degrees and a pad temp of 0.1 on my Fluke. So to make a conservative compromise, say cut the power in half to be required still means a 5 volt 6 amp supply or a 12 volt 2.5 AMP supply. Still out of the range of the PC so even with conservative choices we are talking external supply to really make t his work. My compormise is going to be really conservative and start with a 15 watt supply of 5 volts at 3 amps. This equates to 0.23 watts per square. Tomorrow I will be making a new array of 100 ohm values to see how much transfer i can get through the pad, and taking the temp differential from the material. Maybe time to graph the wattage to temp inside to outside too. determine the temp characteristics of the foam. More tomorrow!!!
    Harlan :)
     
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