5050 SMT LED Help Please

Hello everyone. This is my first post here.

I received some 5050 surface mount LED's in both white and red. The product information says that the whites work at 2.9V to 3.6V and the reds work at 2.2V to 2.4V.

I am having problems with the red. The intended voltage is 12V. The whites are in series of four to bring the voltage down to 3V each. The reds are in series of five to bring the voltage down to 2.4V. The whites work fine. The do not work at all. Can someone help me out here?

Thanks,
Kev

boredom.is.me said:

Hello everyone. This is my first post here.

I received some 5050 surface mount LED's in both white and red. The product information says that the whites work at 2.9V to 3.6V and the reds work at 2.2V to 2.4V.

I am having problems with the red. The intended voltage is 12V. The whites are in series of four to bring the voltage down to 3V each. The reds are in series of five to bring the voltage down to 2.4V. The whites work fine. The do not work at all. Can someone help me out here?

Thanks,
Kev

Click to expand...

Kev, this is not a lot to go on.

You may have wired the reds wrong, the forward voltage of the reds may be too high and did not turn on (though would expect they would be at least dim), or if you did not incorporate a current limiting element, then you may have just blown them up.

Semiman

SemiMan said:

Kev, this is not a lot to go on.

You may have wired the reds wrong, the forward voltage of the reds may be too high and did not turn on (though would expect they would be at least dim), or if you did not incorporate a current limiting element, then you may have just blown them up.

Semiman

Click to expand...

I hope I am not breaking the picture rule with this. Sorry for the size.

This is what I have right now. The white is on the top. The red is on the bottom. I measured the actual voltage source today and it is 12.49V. The white worked fine on my test voltage which was 12V to 12.6V. There was no type of current limiter.

http://static.rcgroups.net/forums/attachments/1/8/0/5/7/9/a5721707-240-wiring.jpg?d=1366669482



These are the specs for the red.

Following the V=IR rule, I would need a resistance of 210 ohm. Would it be ok to have the entire set of 5 on a single resistor?

Well over two weeks to comply with my request to resize your image, image now converted to a link - Norm

LEDs are very different to filament bulbs ! Increase the voltage by 10% and the current can increase 100%

To run White LEDs off 12 volts, the normal practice is to put 3 LEDs in series and then a resistor, which keeps the current more constant with a bit of change in supply voltage . . . . OR change in LED voltage as they warm up !

check each led before making a string, sometimes they come defective, not often, but it happens. if you had too much voltage you would defiantly see and hear them burn, if nothing happens, than circuit is broken, either due to defective led, or led soldered backwards accidentally.

Thanks guys,

I was checking each string individually, but giving them the current of all three strings. I wanted to keep it as simple as possible by having everything connected with as few resistors as possible. I gave up on that for reliability.

I had a moment of common sense. Here is where I'm at. The orange blocks are stand ins for resistors. Now it's just finding the right one. By the way, the setup has a constant positive and is controlled by the grounds. The reds are all on one ground and the white on on their own ground.



I also managed to find this:
http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

V = 12.5V
Voltage drop across white = 3v
Voltage drop across red = 2v

I should have a 27 Ohm resistor on each white string, and a 150 Ohm resistor on each red string.

The white in the picture above are backwards. They should be the rotated 180.

They sell these 5050 on flexible strips that are cuttable and you can just feed them 12v, maybe thats a better solution?