Hot resisters on LEDs

[Barmybaz]

I have built this light box all works well,
However I'm a bit concerned over the heat the resisters give out (you can't hold your finger on them) surely this can't right.
I have used the LED suppliers characteristics. for different colours,
pumped into a website that works it out for you and found correct resister for each colour and a wiring diagram and followed it to the T,
so I ended up with a + rail a - rail and the circuits strapped between them
The p/s is from a set of Xmas tree lights, quoted at 24v. when rectified I found 26.2 dc none load at 450mA

It must be me !
but What am I doing wrong ?

Bazza

 

[kubeek]

Please post a schematic. More than likely this is a normal behavior, and you just used resistor with too low power rating.

26.2 dc none load at 450mA

So is the 26.2V measured without any load, or at 450mA load current?

 

[Barmybaz]

Thanks for reply,
I have to admit I havn't taken any current measurements,
I guess I should have,
Taking a current rating for each circuit would tell me whats going on,
according to the spec's each circuit takes 20mA , 8 of them.
so I guessed the p/s should be more than enough, the resisters are as suggested,
If the heat is the way it is, that's the way it is
just seems a wast of energy.


During investigation I found on a learning site,
the suggestion, to decrease the heat decrease resistance,

 

[MikeMl]

Post the schematic of how the strings are wired, how many LEDs in each string, and how many strings.

 

[audioguru]

The website that calculated the resistor value maybe did not calculate the amount of heating.
A resistor is designed to get very hot, your hand is not.

Sure it is a waste of energy. To waste less energy then you can buy thousands of LEDs and measure their forward voltage. Connect only the ones that add to close to your power supply voltage.