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led’s in parallel

Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=68408
Printed Date: May 31, 2024 at 9:27 PM


Topic: led’s in parallel

Posted By: jokerzwyld
Subject: led’s in parallel
Date Posted: December 14, 2005 at 9:45 PM

hello

ok i have heard that it is bad to run led's in parallel with one resistor.  i understand this, but the project i am trying kinda needs it.  anyway i am lookin for help with the calculations.  this is for a vehicle.  i used 13.5v for the supply current.  now 6 leds @ 2v 20mA  each in parallel makes 2v 120mA according to the math and what i have read.  so the resistor would be 13.5 - 2 / .120 = R.  is this correct?  if so then i need to figure the power rating.  using the V of the Led in ohms law, then i get .24w,  but if I use V of the vehicle - led it comes out to be 1.38w, and if using the vehicle x .120 i get 1.62.  so which is it? the V*I, V-Vled*I, or Vled*I?  This has been buggin me for a couple days.  any help is appreciated.  and is my origional calculations correct.  ie: 6 led with 2v 20ma, you add the C but not the V because they are all the same and it would come out to be 2 anyway.  and it equals .120mA?

thanx 




Replies:

Posted By: jokerzwyld
Date Posted: December 14, 2005 at 10:10 PM
i forgot the R values i got was 95.8 (100) using the V - Vled / .120mA



Posted By: ff-mike
Date Posted: December 15, 2005 at 2:50 PM
You are correct with the calculations
If you stay with parallel, be aware that after 1 LED goes, the rest are going to die off at a quicker rate.
A series solution would use less current and a smaller resistor (75 ohms), and/but the string would go out if 1 LED failed





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