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power supply for a printed resistive flexible heater

Discussion in 'Power Electronics' started by sidneo, Jun 14, 2013.

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  1. sidneo

    sidneo

    3
    0
    Jun 14, 2013
    Hi I am a newbie I would like to get an advice for a printed resistive heater I am working on . The heater is a heat resistant thin film on which I printed patterns made out of resistive ink carbon/ graphite/ ferrous material each connected to the power supply via a more conductive ink (silver ink).
    My goal is to do some kind of multiplexing to turn on and off certain areas my patterned circuit .Here is my questions is there an idiot proof way to calculate the power needed to turn my half millimeter resistors red hot ?

    I Have Seen people turning graphite leads into incandescent light with 24volt 2 amp
    How can one build a simple power supply to produce the Power Required will A joule thief do The Job ? If yes how ?Because I have tried I don't know what I am doing wrong I am getting 5 volt from a 9 volt battery the only think getting hot seem to be my transistor . My ideal solution would be to pulse high current to the resistors from capacitors connected to a usb power supply but I don't know if that's possible and I surely don't what Kind of capacitors to use


    Apologise for my lack of knowledge and I hope to get a feedback soon .
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    Can you post an approximate circuit diagram of what you have?
    You would need to figure out the resistance and area (and thickness if possible) of your "resistor" that you want to get red hot.
    A 9V battery is not going to be able to provide nearly enough current to make anything other than say a small bit of steel wool red hot.
     
  3. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Hi :)
    For something to glow red hot it must have reached a temperature of 500*C to 800*C. But the question of how much energy is required to maintain your resistor at that temperature goes far beyond electronics.
    The material which is used to make the heater elements; the thickness of that material; the exact shape of the heater elements; the film on which the elements are printed; the ambient temerature; airflow; ... all these have some influence on the final heat of the elements.
    The experimenter sometimes needs to actually experiment.Off the cuff, I think you'd do well to start by learning to power a very small heater that requires a relatively low current and voltage to operate. That way you'd learn quite a lot without anywhere near the expense or trouble of full-size appliances.

    If you could print up a small heater and measure its resistance, you could show us a bit more and we might be able to guess how much voltage and current it is likely to require to get it to your temperature.

    I am not really all that confident that printed carbon can survive at 800* but that's your party I guess, Sidneo.
     
  4. sidneo

    sidneo

    3
    0
    Jun 14, 2013
    Hi thanks for your responses each of the resistors are about half a millimeter square . The material is a ink Made from graphite and metal powder my goal is not to maintain the heat it won't be possible . I am just pulsing in and out the power to create some kind of incandescent display effect to get an idea of what I am doing just imagine an led matrix I am replacing the leds with tiny resistors . It doesn't really matter if the material survive my temperature goal is 300c.

    I was just worried that the size would reduce the resistance and require more power .someone suggested a laptop power supply I happen to have a 18 volt 2 amp I will try that and update.
    Here is how the ink look like under high power.
    http://www.instructables.com/files/deriv/FWM/DF1Y/HGU2EYGN/FWMDF1YHGU2EYGN.MEDIUM.jpg
     
    Last edited: Jun 14, 2013
  5. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Fortunately, the smaller the resistor (all other things being equal), the higher the resistance.
    The photograph I found at the link showed only the burnt remains of what must have been the lights you want to make.
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    The resistance of a square of conductor is independant of size.
    The required power will be proportional to area.
     
  7. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    aww Duke
    Any 3D shaped resistor, reproduced in a scaled-down version, has higher resistance.
    But I accept the telling-off.
    :)
     
  8. sidneo

    sidneo

    3
    0
    Jun 14, 2013
    Thanks guys for your advices I used a 18 volt 2 amp power supply from a laptop it worked exactly as I wanted the material for the resistors doesn't survive after more than 10 seconds of continuous power but I have been pulsing it to achieve a reasonable level of heat without burning off my millimeter size resistors :) . Perhaps I should find a way to reduce the power I Tried using a 9 volt battery it didn't work i am Thinking about The possibility of using capacitors to pulse the power required but I have no ideas on which type of Capacitors will allow me to Send Into my circuit a little less than 18 volt 2 amps while being charged from a regular USB power supply.

    How Does One calculate the voltage and the amperage from a capacitor?
    Thanks again :)
     
  9. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    dV/dt = I / C

    But that won't help you much. A circuit to make pulses is a little more complicated than just a capacitor.

    Bob
     
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