LED resistor help

[BluFlameGTP]

I'm going to attempt Abrasive's lighted cupholder mod, but use the color changing LEDs.

I know i can wire it up just fine, the only thing i'm having trouble with is figuring out which resistor i need, since each color needs different power voltage.

I've used the resistor calculators and stuff, but still can't figure it out.

Here's the link to the specs page
Auto Color Changing LED specs

Thanks a lot for the help guys.

[Scimmia]

From what I can see, this isn't a standard LED that you can just use a current limiting resistor on. It's got electronics in it that control the voltage to the LED itself, you need to supply it with a constant 4.5V.

[Toofastgs]

Each color LED is built different something to do with a gap of the material on the chip in the led the decides the color

[BluFlameGTP]

So all i would need to do is to wire it into to say... the constant 12v cigarette lighter plug (using a switch) and that should be all it needs? NO resistors right?

[Scimmia]

So all i would need to do is to wire it into to say... the constant 12v cigarette lighter plug (using a switch) and that should be all it needs? NO resistors right?

you need to supply it with a constant 4.5V.

12V will fry that thing.

Datasheet: http://www.superbrightleds.com/pdfs/RL5-RGB-ACC.pdf

[BluFlameGTP]

alright... so i need a resistor that will bring it down to 4.5V.

Does anyone know off the top of their head what size resistor would do that?

[Scimmia]

No. Forget all about resistors, they aren't going to help you in this case. A resistor is reactive, and this thing could draw varying amounts of current. Your best bet is to use a voltage regulator like an LM317. Although a zener diode with a resistor could work, the LM317 is a much better option.

[BluFlameGTP]

Alright, i get it. I've never used anything like the LM317, and am kinda confused on how i'd wire it up.

I'm trying to read up on it right now.

[BluFlameGTP]

Alright, i'm stumped. I have no idea. If no one can help, maybe ill just take the easy way and just follow the sticky....

[Scimmia]

1 LM317 + .1 uf cap (ceramic) + 25 uf cap (electrolytic, value not really that critical) + 240 ohm resistor + 620 ohm resistor = 4.48V power supply.

A 10 uf tant cap on the adj rail could be good, but I doubt it would make much difference in this application. Heck, you could probably eliminate the caps all together and be fine.

[BackInBlack]

See my web site.

[Scimmia]

See my web site.

I took a look at your site, I don't see anything that will help. Link?

[bsumpter05]

i would say a 510 ohm resistor +/- 5%, if it's auto changing that means auto changing, you shouldn't have to change the input voltage.

brandon

[Abrasive]

I would just save yourself the trouble and buy the LW-RGB Wired RGB LED's from Superbright. They have the resistor built in so you wouldn't even have to worry about it. This was my original plan when I was thinking of using the color changing ones. I was just going to take off the screw on nut part on the top and stick the threaded housing of the LED through the holes in the cupholder so they were flush with the bottom.

Third item from the bottom of the page....
Super Bright LEDs - Car Accents

Specs on them....
http://www.superbrightleds.com/specs/LW-RGB.htm

[BluFlameGTP]

Thanks a lot guys, i really appreciate the kind of help that's given here. Thanks to everyone that pitched in advice.

I think i'm going to go with the LEDs that Abrasive just informed me of. I looked through that exact page and never saw those, thanks for the link.

Do you think the LED has enough "extra" on the top that i could just sand it down flush with the threads?

[bsumpter05]

if you cut it from the bottom you might be able to bevel the hole so you don't have to sand it down, not sure how thick it is though, just a thought

[BluFlameGTP]

That's also a thought that ran through my head. I just want as much surface area from the LED showing as possible so that it doesn't focus the light too bad...