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Power Resistor As Heating Element

Discussion in 'General Electronics Discussion' started by muashr, Jun 24, 2015.

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  1. muashr


    Feb 11, 2014

    A 25W/12 Ω resistor is to be used as a heating element. It is desired to get it hot up to 100°C. The questions are:
    1. Can it be connected directly to the output pin of a microcontroller (which can only output upto 5V) or an additional cicuitry is required (for more voltage and current)?
    2. How much current and voltage is required in general for such purpose?
    3. Which quantity plays more important role in such cases: current or voltage?
    In case of additional circuitry please mention it or provide schematic.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    No microcontroller pin can output 25W. From P=V²/R it follows that you will need 17V at 1.44A to drive that load. A driver circuit is required, see here.

    See above.

    AS P=V*I both are equally relevant.
  3. duke37


    Jan 9, 2011
    1. You will need to determine the output current which the microcontroller can provide. I have never used a microcontroller so have never bothered to look up their specifications. I very much doubt that a microcontroller will provide anywhere near the power required.

    2. The current and voltage required will depend on the amount of heat which is wanted. The temperature obtained will depend on the heat loss.

    3.Look up Ohms law. You cannot have voltage across the resistor without current.
    In your case 25W dissipation will need 17V and 1.4A.
    5V, 0.4A will give 2W.
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