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Correct resistor for 12v LED

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don(at)dmack.net
Guest

Posted: Mon Feb 12, 2007 12:01 pm Post subject: Correct resistor for 12v LED

I have several 12v, 12ma LED’s from Radio Shack (part 276-272)in my panel.

According to the calculators (15V max Supply, 12V LED, 12ma), I need a

27.0kohms, 1/8w resistor. Two questions: 



1) led.linear1.org reports "The wizard thinks your forward voltage spec is

suspiciously high, but will proceed with the calculations.". The input

voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

correct that it just does not recognize 12v LEDs?



2) Where do I find 1/8w resistors?



Don Mack | don(at)dmack.net | dmack.net

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john(at)ballofshame.com
Guest

Posted: Mon Feb 12, 2007 12:19 pm Post subject: Correct resistor for 12v LED

Well.... you probably put in 12V for the "forward" voltage.  12V should be

the "source" voltage.  Your forward voltage is the voltage across the LED

when it's turned on.  This voltage will never get much above 2V, or so

(increasing the voltage will simply increase the current and eventually

blow it up, though).  It varies a bit depending on the color of the LED. 

You should be able to look it up somewhere online what your particular

color needs.



Hope this helps.



-John

www.ballofshame.com



 	  Quote: 	
		   



 I have several 12v, 12ma LED’s from Radio Shack (part 276-272)in my panel.

 According to the calculators (15V max Supply, 12V LED, 12ma), I need a

 27.0kohms, 1/8w resistor. Two questions:



 1) led.linear1.org reports "The wizard thinks your forward voltage spec is

 suspiciously high, but will proceed with the calculations.". The input

 voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

 correct that it just does not recognize 12v LEDs?



 2) Where do I find 1/8w resistors?



 Don Mack | don(at)dmack.net | dmack.net

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john(at)ballofshame.com
Guest

Posted: Mon Feb 12, 2007 12:23 pm Post subject: Correct resistor for 12v LED

Ok...so I played with the calculator a bit (cool).  How's this for

convenient.  Click on the question mark next to "forward voltage" and it

will pop up a list of color vs. voltage.



1/8W resitors?  Just use a 1/4W.



-John

www.ballofshame.com



 	  Quote: 	
		   



 I have several 12v, 12ma LED’s from Radio Shack (part 276-272)in my panel.

 According to the calculators (15V max Supply, 12V LED, 12ma), I need a

 27.0kohms, 1/8w resistor. Two questions:



 1) led.linear1.org reports "The wizard thinks your forward voltage spec is

 suspiciously high, but will proceed with the calculations.". The input

 voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

 correct that it just does not recognize 12v LEDs?



 2) Where do I find 1/8w resistors?



 Don Mack | don(at)dmack.net | dmack.net

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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bob(at)bob-white.com
Guest

Posted: Mon Feb 12, 2007 12:25 pm Post subject: Correct resistor for 12v LED

Hi Don,



If it's a 12V LED, the resistors are built in.  Just connect them to

your 12 V source.  Going to 15V or so shouldn't hurt them but you

could add a small resistor to make up the difference.  Figure 3v at the

12 ma rating would be a 250 ohm resistor in series.  Most LED's have

an actual forward voltage of around 2V.



Bob W.

On Mon, 12 Feb 2007 13:59:15 -0600

"Don Mack" <don(at)dmack.net> wrote:



 	  Quote: 	
		   

 

 I have several 12v, 12ma LED’s from Radio Shack (part 276-272)in my panel.

 According to the calculators (15V max Supply, 12V LED, 12ma), I need a

 27.0kohms, 1/8w resistor. Two questions: 

 

 1) led.linear1.org reports "The wizard thinks your forward voltage spec is

 suspiciously high, but will proceed with the calculations.". The input

 voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

 correct that it just does not recognize 12v LEDs?

 

 2) Where do I find 1/8w resistors?

 

 Don Mack | don(at)dmack.net | dmack.net

 

 

 

 

 

 

 


	




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mprather(at)spro.net
Guest

Posted: Mon Feb 12, 2007 12:51 pm Post subject: Correct resistor for 12v LED

I don't think there are _any_ LED's designed to use 12v supply directly to

the diode (someone might prove me wrong).  However, many electronics

houses are selling LED illuminated lamp fixtures that include biasing

resistors built into the package.  The part number you listed appears to

be one of these.  It doesn't need any additional biasing to make it work

in a 12V environment.  In other words, the forward voltage spec the

calculator expects is for a bare LED.



You can get away with a 1/4th watt or 1/2 watt if those are easier to find

(they will be).  The only problem with using the larger rating is that

they will be physically larger (bulkier).

Regards,



Matt-



 	  Quote: 	
		   



 I have several 12v, 12ma LED’s from Radio Shack (part 276-272)in my panel.

 According to the calculators (15V max Supply, 12V LED, 12ma), I need a

 27.0kohms, 1/8w resistor. Two questions:



 1) led.linear1.org reports "The wizard thinks your forward voltage spec is

 suspiciously high, but will proceed with the calculations.". The input

 voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

 correct that it just does not recognize 12v LEDs?



 2) Where do I find 1/8w resistors?



 Don Mack | don(at)dmack.net | dmack.net

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Peter Laurence

Joined: 10 Jan 2006
Posts: 50

Posted: Thu Feb 15, 2007 9:37 am Post subject: Correct resistor for 12v LED

Don,



If I read this correctly, The max amps of the LED is 20MA. If this is being 

used in your airplane, then it's going to see approx. 13V. This would 

require a 13/.020 -- somewere around 650 ohm resistor.



Peter





 	  Quote: 	
		   



 I have several 12v, 12ma LED's from Radio Shack (part 276-272)in my panel.

 According to the calculators (15V max Supply, 12V LED, 12ma), I need a

 27.0kohms, 1/8w resistor. Two questions:



 1) led.linear1.org reports "The wizard thinks your forward voltage spec is

 suspiciously high, but will proceed with the calculations.". The input

 voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

 correct that it just does not recognize 12v LEDs?



 2) Where do I find 1/8w resistors?



 Don Mack | don(at)dmack.net | dmack.net

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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nuckollsr(at)cox.net
Guest

Posted: Thu Feb 15, 2007 9:50 am Post subject: Correct resistor for 12v LED

Check this part out at:



http://www.radioshack.com/product/index.jsp?productId 62570&cp



It's not very explicit in the listing but examination of the

photos shows a resistor already installed. Further, on one

page, they call this a "12v" LED.



This product can be hooked directly to your electrical system with

NO external resistor needed.



Bob . . .



At 12:34 PM 2/15/2007 -0500, you wrote:



 	  Quote: 	
		  

<Dr.Laurence(at)mbdi.org>



Don,



If I read this correctly, The max amps of the LED is 20MA. If this is 

being used in your airplane, then it's going to see approx. 13V. This 

would require a 13/.020 -- somewere around 650 ohm resistor.



Peter





>

>

>I have several 12v, 12ma LED's from Radio Shack (part 276-272)in my panel.

>According to the calculators (15V max Supply, 12V LED, 12ma), I need a

>27.0kohms, 1/8w resistor. Two questions:

>

>1) led.linear1.org reports "The wizard thinks your forward voltage spec is

>suspiciously high, but will proceed with the calculations.". The input

>voltage is listed as 12-16V, 12-20ma, so I ASSuME that the calculation is

>correct that it just does not recognize 12v LEDs?

>

>2) Where do I find 1/8w resistors?

>

>Don Mack | don(at)dmack.net | dmack.net



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sales(at)6440autoparts.co
Guest

Posted: Thu Feb 15, 2007 1:32 pm Post subject: Correct resistor for 12v LED

They look like they would make a very clean looking and easy install. 

Also looks like they have them in green and red.



Randy



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