If you’re looking to connect different colored LED lights on a single strip, you’re going to run into series/parallel SMD LED wiring issues.

In short, the power supply must be equal to or more than the sum of the voltage requirements, per LED and its resistor. When you want to mix colors and wire them in parallel, then you need to add resistors to each LED, which levels the amount of power required to light the LEDs.

It’s important to remember that colored LEDs have different voltages and therefore require more or less of a power source and also that when you wire in parallel, you have to split the positive and negative lines into multiple wires.

 

 


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craigp

Joined: Jul 05 2012
Posts: 3
Post Thu Jul 05, 2012 5:18 pm

I have purchased a number of different colored SMD LEDs. The idea is to wire them together to have them on a single strand alternating colors for decorative lighting . I have tried both wiring configurations. On any given attempt only 1 LED in the chain will light. Seems to be the one at the end (Red Blue Green etc.). I have tried different power 3-9V and resistors. Again same results. The LED types in most cases have differing forward voltages. I’m not sure if that matters.

Can only the same color / type leds be in a single chain?

Any insight is welcome.

Thank you

craigp

Joined: Jul 05 2012
Posts: 3
Post Thu Jul 05, 2012 5:25 pm

I think I may have found my answer.

Connecting different colored LEDs
The power supply must be equal to or more than the sum of the voltage requirements for each LED and its resistor. If you want to mix colors and wire your LEDs in parallel, then you need to add the right resistor to each LED (not one for the entire circuit). This levels the amount of power required to illuminate each LED.

Aken

Joined: Feb 12 2003
Posts: 10885
Post Thu Jul 05, 2012 5:29 pm

Correct. Mixing colors that do not require the same voltage requires using resistors to verify you don’t overpower the lower voltage colors.

For your problem, it sounds more like a wiring issue than anything. Verify that you have connected them properly. A crude/basic example:

User posted image

craigp

Joined: Jul 05 2012
Posts: 3
Post Thu Jul 05, 2012 6:00 pm

Yes,

I also tested the LEDs one by one to ensure it wasnt a bad solder joint.

The next quest is the following:

Red 1.2 v
Green 2.2 v
Blue 3.2 v

Do I need different resistors to bring the voltage down depending on the power need of the specific color? (ie 1k for the Red and 2k for the Blue)
(These number are not exact)

Nice animation by the was Aken.

corvettecrazy

Joined: Dec 17 2003
Posts: 4357
Location: moved (twice)
Post Thu Jul 05, 2012 7:15 pm

craigp wrote:
Yes,

I also tested the LEDs one by one to ensure it wasnt a bad solder joint.

The next quest is the following:

Red 1.2 v
Green 2.2 v
Blue 3.2 v

Do I need different resistors to bring the voltage down depending on the power need of the specific color? (ie 1k for the Red and 2k for the Blue)
(These number are not exact)

Nice animation by the was Aken.

Not sure where you got the vf of the green LED or maybe you typed it incorrectly but it is wrong. It should be around 3.2v. Also, I would be shocked if red was 1.2. It is probably 1.7-2.2v

AnthonyMartello

Joined: Sep 06 2012
Posts: 2
Post Thu Sep 13, 2012 10:24 pm

Hello community,

You can connect the SMD LED in parallel method. Parallel means that instead of wiring LED to LED, eachLED or small group of LEDs gets its own ‘line’ from the power source. You can combine this idea to make parallel wiring of LEDs in series to get past the forward voltage issue. In that case, you could use two resistors for two LEDs per parallel line, but the wiring is just a little different. You could also use three LEDs on one parallel line and a singleLED on a separate line. Parallel lines give you the same voltage as a single line did, but it does add to the total current drawn through your circuit. Wiring in parallel just means you have to split the positive lines and negative lines into multiple wires.

Best Regards,
Anthony Martello icon_smile.gif

Aken

Joined: Feb 12 2003
Posts: 10885
Post Thu Sep 13, 2012 11:19 pm

Aaaaaaand there’s what we suspected. Please keep your advertising links off the message board.
lesliemorris85

Joined: Dec 12 2012
Posts: 13
Location: Dallas, Texas
Post Thu Feb 07, 2013 8:35 pm

Yeah those values are a bit low. Red is in the 600nm range of wavelength so their vf should be around 1.8-2.2v at 20ma.