Creating Button Sized Heating Pad

Discussion in 'The Projects Forum' started by Michael Cibene, May 30, 2015.

  1. Michael Cibene

    Thread Starter New Member

    May 30, 2015
    4
    0
    I have an idea for a product but don't know how to get started with it. I don't know anything about this stuff and will be doing as much research as I can but would appreciate any help anyone is able to give me.

    My idea is to have a small (button sized) heating pad (probably metal or some other material) that is powered by a AA or AAA battery. I would like to develop it eventually to be rechargeable (so have a small lipo battery or similar) but for now, I want to be able to test it and have AA and AAA batteries readily available.

    I want to press a button, have the battery heat up the small pad for 15 to 30 seconds and then turn off. Also, I would like it to gradually heat up the pad to where it is safe to touch but around the temp of hot water from a faucet (not sure the exact temp).

    Again, any help is very much appreciated!
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Welcome to AAC

    I doubt you can get that temp from a button size heater.

    but I might be wrong.
    Q, is do you have the heater ?
     
  3. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    What are you wanting to heat? Getting something button-sized hot is probably not terribly hard, but keeping it hot for any length of time as that heat is transferred into its target (air, human body, water?) or radiated out into its surroundings could be unrealistic.

    If my calculations are right (that's a big if) then a 1.5V battery with 2.2Ah capacity would have 2844 calories of energy, enough to heat 1 oz of water by roughly 95°C.

    So if you need to heat more than the equivalent of a few ounces of water, AA batteries probably won't get you there. Even if it's a smaller amount, whatever you're heating will presumably be radiating off heat even while it's being heated by your button, so it would be hard to maintain temperature for any length of time before depleting the battery (or in your case of 30 second pulses, you might get VERY few such pulses out of each battery.)

    Even if my calculations or assumptions are off, you should probably consider doing this sort of analysis before going too far down the road of circuit design.

    Another thing to consider is how fast any given battery can deliver its power. Even if the total available energy is acceptable, a battery may not be able to deliver enough current to heat something that quickly.
     
    Michael Cibene likes this.
  4. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,060
    A flashlight is close. The bulb gets fairly warm. Depending on what you are heating, you might consider an array of IR LEDs in an LED flashlight configuration. It would deliver warmth without getting terribly hot itself.
     
    Michael Cibene likes this.
  5. Michael Cibene

    Thread Starter New Member

    May 30, 2015
    4
    0
    I am looking to heat up human skin (I know that sounds so strange - but it's just based off a theory I have that isn't so strange haha). The heating pad area would be about 1/4inch diameter. And for the temperature, I don't mean scolding hot water - just water that is hot to the touch.

    I really like the idea of the ir led. I think that would work for my purposes.

    Does anyone know if the brightness of an ir led bulb can be controlled - Therefore controlling the heat?

    Can the bulb be powered from a cellphone battery?

    Thanks again for all of the responses. This has been very helpful!
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,060
    Ahh, that's smaller than I was picturing. That's roughly one single LED. I think you'll need a relatively high power LED to get much sensation of heat out of it. Sorry I don't have experience with such a thing.

    There might be a way to wrap heating wire around a pencil-shaped metal rod. This would conduct the heat along the rod to the skin surface, and the other end could be inside a wooden handle. I have no idea how to get temperature "control" without testing various options (length of resistance heating wire, resistor in series, battery voltage, etc.).
     
    Michael Cibene likes this.
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    Michael Cibene likes this.
  8. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,060
    Or maybe a surface mount resistor (because it has a flat surface), with a small metal button on top of it.
     
    Michael Cibene likes this.
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Main issue is to deliver the power via AA cells.
    Li-on could do the trick but it won't last long
     
    Michael Cibene likes this.
  10. Michael Cibene

    Thread Starter New Member

    May 30, 2015
    4
    0
    These were all really helpful comments! Thanks again guys :)
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
    834
    Have you considered researching e-cigarettes? They faced many of the same design challenges. Small form factor, sufficient battery source to provide heat, providing enough heat to vaporize liquid... How do E-cigarettes work
    [​IMG]
     
    ebeowulf17 and Michael Cibene like this.
Loading...