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Heat wire to ~45 degrees with batteries

Discussion in 'Electronic Basics' started by [email protected], Jan 21, 2007.

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  1. Guest

    Here's kind of a wierd question. I would like to try to heat wire (any
    kind) to ~40 - 50 degrees for a sustained time with batteries. I would
    love to get 10+ hours out of C or D batteries. My question is, is
    there an easy way to determine how thick the wire should be, and how
    many batteries I would need to do this? The temperature does not need
    to be exact, just within 10 - 15 degrees.
     
  2. The problem has very little to do with the wires and
    everything to do with how much insulation you wrap around
    them. That insulation will have to be pretty good, to keep
    even a short length of wire (or other resistor) above 50C in
    a much cooler environment for 10+ hours. For instance, a
    millimeter length of bare wire (submerged in 25C water)
    would take many times the power to sustain a 50C surface
    temperature than a kilometer of fine wire (wound on a small
    spool that is enclosed in close fitting Styrofoam box a few
    centimeters thick surrounded by 25C air) would need.

    So lets get started with what you actually need to have
    happen (not how you envision doing it), and we can work
    towards a means to that end and see if that means is
    practical with power available from some number of C or D
    batteries.
     
  3. Chris

    Chris Guest

    This isn't a weird question at all. The whole point of resistance
    heaters is precisely that.

    But you didn't mention what length of wire you wanted, whether it would
    be in free-standing air or another medium, whether the air or other
    medium was still or moving and at what speed, and whether the wire
    would be actually doing any work or heating something which might
    change the temperature. Kind of difficult to give you any advice given
    those constraints.

    Another difficulty you might have is load life for your batteries,
    which might be the final determining factor. A couple of D alkaline
    batteries can light a 1/4 to 1/2 amp bulb for 8 or 10 hours. That will
    limit you to 3/4 to 1-1/2 watts, which isn't much power. However, your
    temp requirement might not be that strict if you're talking about 20
    degrees C ambient in still air.

    What you might want to do is scrounge some 22 to 220 ohm, 10 watt power
    wirewound resistors and gently tap off the ceramic overcoating so as
    not to break the resistance wire. If you then break the ceramic core,
    you can unspool it and have several inches to a foot or so of high
    quality resistance wire. Connect alligator clips to your battery
    wires, then starting with the 22 ohm wire, clamp the clips to the wire,
    let it stabilize, and measure temp. For the 22 ohm resistor, your
    minimum length would be around 1/4 of the total length of wire, or
    about 6 ohms. More than that will use the battery up too fast. Do the
    length calculations for the longer lengths of wire so minimum
    resistance doesn't go below 6 ohms or so. Then just find what you're
    comfortable with.

    As I said, if your project requires that the wire actually heat
    something, or if you're working with something besides free still air,
    you might have to get more complicated. Feel free to post back with
    more info.

    Cheers
    Chris
     
  4. Chris

    Chris Guest

    Forgot to mention that the above is based on *two* D sized alkaline
    cells. Sorry.

    Cheers
    Chris
     
  5. Guest

    What I would like to do (if humanly possible), is make something like a
    heated driveway, only smaller, using wire and batteries. I was
    thinking of putting wire between two sheets of plastic and connecting
    them to a battery pack. The wire would have to be warm on the outside,
    even at very cold temperatures. Am I wasting my time, or could this be
    done?
     
  6. Guest

    I forgot... maybe the most important part... I would like this to melt
    snow, and further more, continue to melt snow as it falls on the
    plastic. That's probably an important detail to leave out!
     
  7. Okay. This is a pretty demanding requirement, since ice
    absorbs so much energy per gram to melt. What area would
    you like to have this melting action take place? A pea
    sized area may be practical.
     
  8. Alison

    Alison Guest

    Apologies for sounding blunt. But I think you would have more success with
    eating a bannana and going out there with a stiff sweeping brush. Alot more
    environmentally friendly too.

    A chemical solution could also work. Very salty water has a lower freezing
    temperature than water/snow alone.
     
  9. You are looking at an area of maybe 1 sq mm in that case.
     
  10. neon

    neon

    1,325
    0
    Oct 21, 2006
    a "D" battery is ridiculous 20 is ridiculous. "D" is capable of 2 amps into a short circuit and then throw them away. you need microme wire like on discarded hair blowers and you need a lot of them. this whole thing is totaly a wet dream. and if it is -20 degrees you need to raise it to 32 and that will make nice ice i ruther have snow don't you agree? at least think about installing the wires into the ground then let me buy stock on your power co.
     
  11. Guest

    Huh. Thanks for the blunt replies. That is what I was looking for!
     
  12. If you could let up in on the planned use we might be able to come up with
    good, workable suggestions.


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  13. Rich Grise

    Rich Grise Guest

    Hmmm. they've got 6 watts per foot stuff here:
    http://www.deanbennett.com/wintergard-wet-heat-tape-for-eaves.htm

    I don't know how long you can get 6 watts out of a few D cells, but they
    do sell battery-powered socks and gloves. ;-)

    Cheers!
    Rich
     
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