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Bi-color LED

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knoober

Member
Joined
Mar 18, 2015
I have a small project that is browing in size the more I look into it. Here are the essentials.

I have this fan controller and dislike the color the LED lights. Blue is fine, but the red has gotta go. I thought to simply swap the red bulb for a white LED, but it was not that simple. There are not 2 LED in there. ONly 1 that shines in 2 colors depending on the position of the switch. No big deal right? Get a blue/white bi-color LED and be done right? Perhaps.

Here is where things have gotten complicated. Apparently all colors of LED require a different voltage, normally about 1.3-1.6V (quoting from memory, I hope it is near correct), while the white needs (again from memory) 3.6-ish V. What I have seen when looking for bi-color replacements is that many are the colors that share similar voltage (red/green blue/red etc). I worry that there may be some sort of voltage issue that will arise from swapping a red/blue for a blue white. The specs are similar but I am not sure if they are similar enough.

Blue/white

A red/blue. Not neccesarily the one that is already installed

Thanks in advance guys
 

NiHaoMike

dBa Member
Joined
Mar 1, 2013
Cut the wire for the red half of the LED and you'll only be left with the blue half. Then you can get a white LED (much cheaper than white and some other color), connect it from where the red one was connected to the common (middle) pin, and point it to shine in the same general direction. The LEDs are generally powered using resistors and the voltage drop is unlikely to make much of a difference.
 
OP
knoober

knoober

Member
Joined
Mar 18, 2015
Cut the wire for the red half of the LED and you'll only be left with the blue half. Then you can get a white LED (much cheaper than white and some other color), connect it from where the red one was connected to the common (middle) pin, and point it to shine in the same general direction. The LEDs are generally powered using resistors and the voltage drop is unlikely to make much of a difference.
I already have a few white LED from when I started this month's ago. Before I knew about the voltage difference for white, I had a similar plan. I haven't cut any leads because I can get the white to lite when I touch the leads from the replacement led to the original led. There are 3 leads of course, and I jumpered them all (1/2 1/3 2/3) and still couldn't light a known working bulb (fresh bought and tested on a 9V battery)

Here are things that I think may be going wrong.

A) I burnt the bulb on the 9v battery. I was just testing to see if it worked, but didn't have a resistor to add to the circuit

B) touching the leads with my hands is I terrifying the circuit just enough

C) I'm just doing it wrong :)

D) I will need to change the resistor to get proper voltage before the light will work. I am leaning in this direction because of the nearly double voltage required for white.

If you happen to have a white LED and could confirm that It will run on less that 3.x V I would appreciate knowing before I start cutting. Thanks again
 
OP
knoober

knoober

Member
Joined
Mar 18, 2015
You need a resistor. For testing with a 9V battery, a 1K works nicely.

I learned this lesson the hard way. Luckily I have a couple of spares so it didnt hurt me to lost a test piece.

Further reading has brought be to this formula: (Input Voltage - LED Voltage)/target amps

so plugging the numbers in gives: 12V(molex from the psu) - 3.6V(for a white LED)/.02 (20mA) =420 So I had planned to use a 420 ohm (or whatever is closest I dont think 420 is a standard size). I am not sure what voltage to plug in for the bi-color LED that I linked above.

I would just clip one lead like you said, but I am not sure that will work, because of the test I did to jumper to white LED across the existing leads. Unless there wasnt enough juice left for the White LED to light while the original LED was lit?
 
OP
knoober

knoober

Member
Joined
Mar 18, 2015
Clipping one lead on the bi-color LED worked :) the reason I couldn't light an led from it without Clipping the wire was because there wasn't enough voltage to run both the existing led and the one I was trying to test. Thanks for the info as I now have blue and while leds instead of blue and red :D