What causes a resistor to get too hot?

Discussion in 'General Electronics Chat' started by PowerLogic, Jan 7, 2015.

  1. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    Guys seeking for your help!

    What causes a resistor too much heat?

    The unit is working but I have a problem with the resistor its heating up too much!
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Please don't hijack someone else's thread. Start your own thread so that we can focus on your problem there. I will ask the mods to split this off into a thread of your own.
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,715
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    Okay, so now that you have your own thread...

    The reason that a resistor gets too hot is that you are putting more power into it than it can dissipate at a reasonable temperature.

    Without more specifics, that's about as good an answer as you can hope for.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,414
    3,353
    Every resistor has to dissipate power given by the formula IxIxR or VxV/R regardless of the power rating of the resistor.

    That power has to be taken up by the surroundings via conduction, convection and/or radiation. The temperature that the resistor attains depends on how quickly you can remove the heat, i.e. the faster you can cool it, the lower the temperature. If you have a huge fan blowing on the resistor you might not even feel a temperature rise.

    So the bottom line is, if you want to keep the temperature down you have to remove the heat.
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Too much current flowing through it.
    Too much voltage across it.
    It is too close to the electric skillet.
    You used it to stir your boiling coffee.
    It was left out in the desert sun.
     
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  6. profbuxton

    Member

    Feb 21, 2014
    233
    68
    Resistors are designed/manufactured in certain resistance values and power dissipation values. I assume you are aware that the power dissipated by any resistance is the product of the voltage across the resistance and the current passing through the resistance.
    Therefore, if you exceed the power rating of the resistance by trying to pass too much current through it by increasing the voltage drop across it, the resistance will heat up. It will heat up anyway but as long as you do not approach the maximum power rating all will be well.
    Continuing to increase the current through the resistor and at a critical point it will act as a fuse. Or catch fire, itself or anything flammable in close proximity.
    In certain circumstances it may possible to provide extra cooling(heat sink, fan) but its better to design circuits so these do not become necessary.
    I do not know what "unit" you have or what resistor you are talking about but I would suggest you may have a problem or maybe the resistor is actually working within its power rating and just seems hot to you. Make some measurements of voltage and current and work it out.
     
  7. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    Sir WBahn sorry for that, by the way thanks a lot. and all of you guys thanks! more power!
     
  8. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    No, actually less power :)
     
  9. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    B.T.W How much is too much heat? Some power resistors are designed to run hot if necessary - or rather to safely dissipate a certain amount of power, depending upon the various physical conditions and requirements of their operating environment.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
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    You should always size a resistors wattage at 2 to 3 times the actual dissipation..
     
  11. Lundwall_Paul

    Member

    Oct 18, 2011
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    Is this a new design or something that has been working?
     
  12. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    too much heat sir, you cannot touch it by your fingers, and if the unit still running, the said resistor smoke.
    the unit is kavo k-control.
     
  13. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    thanks a lot guys for your genuine help and ideas.
     
  14. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    Nobody can really give a definite answer as to why your resistor (s) are getting hot without your schematics and photos maybe of your appliance and my Crystal ball is away for a polish and service
     
    Lundwall_Paul likes this.
  15. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    526
    Get a resistor rated for higher wattage.
     
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