# 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

What causes a resistor too much heat?

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

Mar 31, 2012
18,088
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3. ### WBahn Moderator

Mar 31, 2012
18,088
4,917

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
12,642
3,457
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
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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
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No, actually less power

9. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
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
4,791
976
You should always size a resistors wattage at 2 to 3 times the actual dissipation..

11. ### Lundwall_Paul Active 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 Well-Known Member

Oct 26, 2011
616
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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
1,240
531
Get a resistor rated for higher wattage.