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Wired 2 different coloured SMD (white & orange) but when connected to a 3v coin battery or AA battery, orange is working but not the white SMD. There is a 1/4 resistor connected too. Why is it so. Help please.
 

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Wired 2 different coloured SMD (white & orange) but when connected to a 3v coin battery or AA battery, orange is working but not the white SMD. There is a 1/4 resistor connected too. Why is it so. Help please.
I presume you are testing them individually and not in series. If so, flip the connections and try again. If it still doesn't light, then it could be fried. Use another one.
 

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It works when tested individually but when I put the 2 SMDs together, orange works but not the white SMD. I tried on 2 yellow SMDs and it works, so I am not sure why what is the problem.
 

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white and blue leds require 3.5v each. 3v is enough for the orange led, but not it and the white led. It ought to fire up the white led by itself.

Edit: if these are the only two LEDs you are lighting up, then 5v should be enough. IIRC, normal LEDs need 1.5v, so that plus the white LED, 3.5v, should be 5v.
 

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Thanks. I will try with 5v. May i know what is IIRC? I am trying to link up 2 yellow, 1 orange and 1 white. Is 9v battery too powerful?
 

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Thanks. I will try with 5v. May i know what is IIRC? I am trying to link up 2 yellow, 1 orange and 1 white. Is 9v battery too powerful?
IIRC = If I Recall Correctly

Both yellows and the orange should pull 1.5v each, for 4.5v, and the white 3.5v. Again, kind of pulling it out of deep memory. 9 volts should work, since you are pulling 8v on the LEDs. I would still put in a resistor, otherwise the LEDs would be brighter than normal and shorter lived. I think you can also find an electronics circuit calculator on the internet that can help you figure out the resistance you need. I remember VxA=W, but there is also an equation for Ohm's Law that I don't recall off the bat.

Edit: Just saw Indy5000's post. That link goes into Ohm's Law, which will help you figure some of this out. The resistor you mentioned? What is its value?
 

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Not sure where some of the forward voltage (Vf) values are coming from that are stated in the above posts but here is a chart that shows the typical Vf for the common colors of leds used in the electronics industry:
https://img.rcgroups.com/http://www.hacksmods.com/wp-content/uploads/2012/08/smd_led.png?h=GEVscILYEE-nEELMhIkuIA

Also, Here is a really good tool for calculating the value of resistors for dropping a battery(source) voltage and a given led voltage and current. This wizard also has a feature that helps to design the series and or parallel circuit needed for a group of leds:
LED series parallel array wizard

While you are on that site also check out the LED basics tab for a wealth of information;
LED center » LED basics
 

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I looked up the voltages for white and blue leds on Google. The rest, I assumed.
 
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