Thank you very much for all your help.
Thank you very much for all your help.
Ok... I've been going over this in my head for over an hour and doing countless calculations and something just wont click... let me give variable values for a real-life problem i had.
Battery V=6
LED fV=2.95 (Amber LuxIII)
LED Target ma=1400 or 1.4A
Soooo...
R=V/I
R=6/1.4
R=4.3...?
According to the resistor chart on this website there should be a 2.2 Ohm 5w resistor in there... so i went back and recalculated...
R=V/I
R=2.95/1.4
R=2.1...?
Well close... but i felt i was missing something... so i tried that calculation with a blue Lux V...
FV=6.84
Target ma=700 or .7A
R=V/I
R=6.84/0.7
R=9.7...?!
I know that's waaaaay off... what did i miss? Maybe beating my head up against a brick wall multiple times might help... a coma wouldn't be too bad right? I hear morphine comes in vanilla now.
Join the Dark Side... We have cookies =)
V should equal the Source Voltage (battery voltage) minus the Voltage Drop across the LED (Vf), divided by the target current. Try it that way.
And guys, it's spelled resistor!
Last edited by Jedi-Loreen; 05-06-2010 at 03:55 AM.
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As a few matters of note (since this topic is being re-addressed)...
1. Don't forget that your multi-meter has its own resistance, so... if you use it to check/meter your resistor (or battery pack voltage, etc.)... there is a bit of a margin of error.
2. Speaking of margin of error... if some online calculator (correctly calculated of course!) tells you that you need 2.5 ohms of resistance... and yet you can only find a 2ohm or 3ohm resistor... that's probably just fine. Minor differences such as 0.5ohms or less... really won't matter.
That being said--yeah--if you're off by 5 ohms... that's bad, heheh.
3. If you take into consideration "over-driving" (when calculating a resistor for an LED)... well--that is another reason why you could possibly use a 1ohm resistor when it called for 2 ohms of resistance. Not to say I recommend that unless you really know what the heck you're doing.
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I think J Lo means Vf is the voltage drop across the LED.
The formula is as so.
The resistor value, R is given by:
R = (VS - Vf) / I
VS = supply voltage
Vf = LED forward voltage (usually 2V, for red but 4V for blue and white LEDs)
I = LED current (e.g. 10mA = 0.01A, or 1400ma = 1.4A)
Resistor calculators on the web will give you a value on the safe side. If you want to over drive go a little lower.
The best way I have found to set up an LED is measure current with a clamp, dial it in with a pot, then remove the pot & measure the resistance. This will take into account variables in the final installation parts.
Heh, oops.
That's what can happen when I edit my posts before submitting.
In order to see the Light,
you must sometimes risk the Dark.
TCSS MODERATOR
BLUE 8 Ready to ROCK and ROLL!
what is the differance between a 5W resistor and a 1/4W resistor? (and please dont say 4 3/4W)...lol.
ok fine I'll bite... Yes size is one difference.. (a BIG difference as well between the 2 your comparing lol)Originally Posted by hebert466
but its basically it's in the amount of resistance givin by the material that it's composed of.. the more material the higher resistance.. the higher rating givin to the resistor (yeah its not exactly rocket science).. well ok it is but its the very very first line in the book.. after that it gets very technical (technically speaking)
"Yes Lord Vader, and I too have a gift... for you.."
"There is no good or evil, no black or white.. There is only.. Perspective"
Well the difference in Wattage is how much power can flow through it before the resistor will fry. You can always use a larger wattage resistor (space permitting of course) than is recommended, but using a lower wattage resistor will result in smoke and tears.
Resistance is a whole other story.
We all have to start somewhere. The journey is all the more impressive by our humble beginnings.
http://led.linear1.org/1led.wiz for the lazy man's resistor calculator!
http://forums.thecustomsabershop.com...e-to-Ohm-s-Law for getting resistor values the right way!
Ok people. A better answer is wattage is a power measurement. For resistors this is how much heat it can dissipate. The more power it has to control the more heat it must dissipate. If the resistor has a lower rating than necessary it will overheat and burn up. Inside a saber where the heat can be trapped it is best to use a resistor a little bigger than a calculated value.
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