# 0402 LEDs



## UPBigBoy (Jan 2, 2012)

Can 2 0402 LEDs be run off 1 470OHM resistor wired in parallel or would series work better? This is on a HO scale DCC system.

Thanks in advance

Jim


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## oldSmokey (Jul 31, 2011)

Hi UPBigBoy,

The resistor has to go in series with the led, as for the 470OHM resistor, it depends on what the voltage is, here is a link for a led calculator, it will also show you the circuit once you enter your data.


http://led.linear1.org/1led.wiz


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## T-Man (May 16, 2008)

Preferring to use Ohms Law I played with the calculator.

Normally is use 20ma or .2 amps for calculating so I back tracked 4.7k ohms. A good LED uses 3 volts like a white so pulling 2.5 ma it is good for 110 volts. A little high for a 12 to 24 volt system. You need the voltage to start, and the specs for the LEDs.


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## xrunner (Jul 29, 2011)

T-Man said:


> Normally is use 20ma or .2 amps for calculating ...


20 mA is .020 A - not .2 A. hwell:


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## T-Man (May 16, 2008)

That's true.:smokin:

Glad I used the calcuator this time.hwell:


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## waltr (Aug 15, 2011)

It is not recommended to run two LEDs in parallel with one current limiting resistor.
If the source voltage is high enough then you can run the two LEDs in series with one resistor else each LED needs its own resistor.


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## gunrunnerjohn (Nov 10, 2010)

I'd run them in series if you have the voltage. Why waste the power in the resistor? Also, I rarely run LED's at the full 20ma, even for O-scale headlights. I normally run headlights at 10-12ma, and markers are frequently down in the 5ma range. If you run everything at full current, IMO they're way too bright and look kinda' silly.


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## NIMT (Jan 6, 2011)

0402's WOW those suckers are tiny!!!! I stay with the 0602, 0805, and 1206's!
I run all my LED on a parallel setup with one resistor per LED. 
I have monkeyed with the figuring out the right value to the right LED and found that a 1Kohm resistor works 99.9% of the time! (The other .1% nothing works). A 470ohm will run most LED's at around max most of the time.


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## UPBigBoy (Jan 2, 2012)

NIMT said:


> 0402's WOW those suckers are tiny!!!! I stay with the 0602, 0805, and 1206's!
> I run all my LED on a parallel setup with one resistor per LED.
> I have monkeyed with the figuring out the right value to the right LED and found that a 1Kohm resistor works 99.9% of the time! (The other .1% nothing works). A 470ohm will run most LED's at around max most of the time.


Yep they are small - you don't want to drop one as it's just about impossible to find.

What do you guys think is the best wire (magnetic wire of course) - 30G or 26G?


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## gunrunnerjohn (Nov 10, 2010)

I use #30 wire wrap wire for most of my LED installations. More than sufficient current handling capability and nice and small to take up minimal space.


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## NIMT (Jan 6, 2011)

For my 0603's I use 34awg and that's almost too big. I have used .10 magnetic wire with great success it's small but still strong enough to hold up.
If you don't have any give me a shout I have several rolls of it and I could shoot you up some in a hurry!


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## gunrunnerjohn (Nov 10, 2010)

I don't trust the insulation on magnet wire, which is why I use the wirewrap wire.


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## NIMT (Jan 6, 2011)

A 0402 in it's entirety is almost as big as a 30 awg wire without any insulation, So that makes for a near to impossible connection!


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## gunrunnerjohn (Nov 10, 2010)

Well, not quite that bad, but they're pretty small.  I have not had any use for an LED that small in my "tiny" O-scale world, and I'm thankful for that.


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## Lighthouse LEDs (Aug 5, 2012)

The 0402's are intensely small, and last I checked they qualified for the world's smallest leds


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