# Can carbon film resistors be used as heating element?

I am doing a project which needs a heating element to produce heat in a 10cm cube when temperature drops below 0C.

I have a 5V DC source that can only provide 100mA or even less. Thus the maximum power is P=IV=0.5W. If I put one or two 0.5W 50Ohm carbon film resistor in the circuit(P=I^2R=0.1^2*50=0.5W), can it be heated up and increase the temperature to 10C?

Is it a good idea to use carbon film resistor as heating element in this case? If not, what kind of heating element should I try?

• unless the cube is glass, you shouldn't need the much power. but yes, resistors get predictably hot within rating. it might be slimmer or more logistical to use a resistance wire. Oct 24 '17 at 5:15
• Basically what a resistor does is convert electrical energy into heat. As long as you do not exceed the maximum dissipation of the resistor and don't allow it to get too hot (allow the heat to flow away from the resistor) then yes you can use a resistor as a heating element. Oct 24 '17 at 5:24
• Why don't you first work out how much power is needed to achieve your goals in the worst case environment you need to deal with (including radiation, conduction, and convection losses.) Asking if a carbon film resistor works as a heating element, and wondering about a lower power DC supply, will come later once you know what you have to contend with. Just a thought to consider.
– jonk
Oct 24 '17 at 7:16

A resistor makes a perfectly good heating element for air. All electrical heaters are 100% efficient, whatever they're made of. If you want to heat a solid thing though, it can be a bit difficult to physically couple a tubular resistor nicely to the surface.

If you put half a watt of electrical power into a carbon film resistor rated at 0.5W, then it will get hot, and will stay below a temperature that's safe for it, and will deliver 0.5W into any enclosure that it's in.

Whether 0.5W is enough to raise your enclosure by 10C is another matter. As it's 10cm on a side, that's quite a lot of surface area, and would need to be fairly well insulated to get that temperature rise with that little power.

one or two 0.5W 50Ohm carbon film ...

one 50ohm resistor is just fine for 0.5W from 5v. Two would need to have a different value, two 50ohm resistors in either series or parallel would not give you 0.5W with your limited current 5v supply.

0.5W resistor?

I would tend to use a resistor with a larger power rating, or use several 0.5W ones, so they will run cooler. Although the surface temperature rise will be safe for it, it may not be comfortable for you. Most engineers tend to 'derate' components to put in a margin of safety anyway.

Carbon film? I tend to avoid them and go for metal film or metal oxide instead, but I think that's just irrational prejudice. As they are sold, by reputable companies, and to a specification, they should be OK. They had a well-deserved bad rap in the old days for noise, but the manufacturing has improved today.

• " and will stay below a temperature that's safe for it" - Only in free air at a reasonable ambient temperature. Embed it in a good insulator and you can get into all sorts of trouble. Oct 24 '17 at 15:53