Resistor question

[scifimodeler]

Hi All

How hot or warm do resistors get? I am building a T2 model with some SMD's. The SMD's are rated at. 3.3v, 25ma and I will be running it at 12v. (I have a large box of 12v wall warts). I am using a 340 Ohm resistor. When I touch the resistor it is quite warm. I CAN hold it in between my fingers so it is not extremely hot. Is this a normal thing??

Thanks
John

 

[TiM]

To provide resistance, the energy has to go somewhere - heat.

So unless you're going to melt anything that is pretty usual. A toaster is a bank of resistors 8)

 

[Grendels]

TiM has it right, resistors work by converting current to energy, and that energy is heat.

One way to look at it is that voltage is the energy that drives the circuit.

An LED is a device that converts most of the energy feed to it to light with a little bit of heat.

If you feed it too much energy, it will burn out. So to reduce the energy available, you put a resistor in place that takes out some of that energy and expels it as heat. Then the energy level is low enough so that they LED doesn't burn out.

It is normal that it will heat up, that means it is doing it's job.

The bad part is if you get too many in a model at once.....

But that would have to be an awful lot of them.

 

[scifimodeler]

Awesome... Thanks guys..

 

[Papermodder]

Hi John.
Make sure you are using at least 1/4 watt resister as you are running close to 0.21 watts though it to make sure you will not fry it. A 1/2 watt would be preferred and will run cooler.

Jim