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ohm’s law

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=100642
Printed Date: July 07, 2025 at 11:04 PM


Topic: ohm’s law

Posted By: seeker1
Subject: ohm’s law
Date Posted: January 01, 2008 at 11:04 AM

I need some help w ohm's law. I understand the basics. and can figure out simple stuff. But what I'm trying to do has some extra variables I'm having trouble with. I sure there pretty simple if you know what your doing. But I don't. Basically I have 4 circuits of LED's I'm putting in my daughter's 96 Mustang. I got them from https://www.oznium.com/led-flex-strips & https://www.besthongkong.com/index.php?cPath=21_71. The OZNIUM site says's no resistors are need for install, but I'm not buying it. I have to much work in this project to blow it for the lack of a .29 cent resistor. From what I can figure out a 100 ohm resistor is what I need, what I'm having a problem with is the wattage req. I'm using blue LED's, which I believe have about a 3.3 forward voltage rating. All sets are wired in parallel as follows.

1st set - 5 strings 48cm(19") ea, 48 led's in ea string setup in sets of 3 = 16 x 3 leds ea w/320 mA for ea string & 3.3 forward voltage on ea LED. 

2nd set- 4 strings 24cm(9.5") ea, 24 led's in ea string setup in sets of 3 = 8 x 3 leds ea w/160 mA for ea string & 3.3 forward voltage on ea LED. 

3nd set - 4 strings 12cm(4.7") ea, 12 led's in ea string setup in sets of 3 = 4 x 3 leds ea w/80 mA for ea string & 3.3 forward voltage on ea LED. 

4th set - 2 strings 6cm(2.4") ea, 6 led's in ea string setup in sets of 3 = 2 x 3 leds ea w/40 mA for ea string & 3.3 forward voltage on ea LED. 

Any help in how to break this down and figure it out would be greatly appreciated, both in this project and any other crazy idea I might come up with.

Seeker



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Only the strong survive.
Eat the weak.



Replies:

Posted By: techman93
Date Posted: January 01, 2008 at 12:47 PM
https://led.linear1.org/led.wiz
This may help you with doing calculations and to see if you follow the math so you may be able to understand how it works out to the voltage and needing or not needing resistors.

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The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.
Do it right the first time... or I might have to fix it for ya


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