Working with LEDs for my dome and have a question
Thread Starter
Joined: May 2004
Posts: 1,372
From: Hoagieville, PA
Working with LEDs for my dome and have a question
Tried searching for the answer but can't find it. I'm working on LEDs for my dome light and I have a 2000 Max. I have put together 16 LEDs (each 5mm, 55,000 mcd, 20 mA) on a circuit board with one resistor. I have tried a 22 ohm resistor with 1/4 watt and 5 % tolerance but it tends to heat up.
I used this site: http://metku.net/index.html?sect=vie...x_eng#parallel
Does anyone know what type of resistor I should use for my setup? I think I might need a 2-4 watt resistor but I can't find one? I checked Radio Shack and they don't have it. Anyone know where I can find one or if my set-up is wrong.
Thanks!
I used this site: http://metku.net/index.html?sect=vie...x_eng#parallel
Does anyone know what type of resistor I should use for my setup? I think I might need a 2-4 watt resistor but I can't find one? I checked Radio Shack and they don't have it. Anyone know where I can find one or if my set-up is wrong.
Thanks!
hey.. its cool to see anothr fellow org member take on da same mod i do 
it wznt mi idea but its juss cool.. so anyways.. i used dis website here : http://www.kpsec.freeuk.com/components/led.htm to calculate wat resistor i needed.. i used only 2 5mm, 10,000, 20mA wit 2.3 volts ea. from Radioshack n i 4got wat resistor, but i wired it in a series. The website also stated that i should use the next highest number resistor if they didn hav the exact 1.. so i did.. and wen i leave the the dome light to "door", the LED's stay on and dont go off evn wen i close the door, but goes off if i switch it off.. wierd huh? LOL i think i mightv used the wrong resistor too but i rarely use the dome light.. only as a mood light wen im in da back seat *wink wink* lol but this didnt happen to any other of my LED mods to the window switches or heated seats switches.. google around and you might find some answers.. my local radioshack are a bunch of retards.. i, an 18y.o. unemployed knows more than they do.. ttyl.. i wish you luck man
it wznt mi idea but its juss cool.. so anyways.. i used dis website here : http://www.kpsec.freeuk.com/components/led.htm to calculate wat resistor i needed.. i used only 2 5mm, 10,000, 20mA wit 2.3 volts ea. from Radioshack n i 4got wat resistor, but i wired it in a series. The website also stated that i should use the next highest number resistor if they didn hav the exact 1.. so i did.. and wen i leave the the dome light to "door", the LED's stay on and dont go off evn wen i close the door, but goes off if i switch it off.. wierd huh? LOL i think i mightv used the wrong resistor too but i rarely use the dome light.. only as a mood light wen im in da back seat *wink wink* lol but this didnt happen to any other of my LED mods to the window switches or heated seats switches.. google around and you might find some answers.. my local radioshack are a bunch of retards.. i, an 18y.o. unemployed knows more than they do.. ttyl.. i wish you luck man
i juss thought up of an idea when i was in bed already so i hopped back onto my laptop to tell you before i forget.. i had read sumwhere on the internet before about LEDs that.. say if you have a total of 12volts power from the dome light.. you can just solder up a bunch of LEDs in a series as long as thier total voltage is equal to 12 volts then you wont need a resistor.. you only need a resistor because LEDs operate on thier low volt specs.. any higher the LED will burn out.. the resistor is needed to "resist" greater power to burn out the LEDs BUT if you have a series of LEDs that thier total volts is greater than power source.. the power source (12volts in the dome light) that is divided into ea. LED will be less than thier max volt spec. so no resistor needed. If i were to use the same LEDs i have in my dome now.. i would need 6 LEDs.. 6X2.3v=12.18 and if my power source is 12v and i have 6 LEDs.. then 12v/6=2v per LED.. so if ea. of my LEDs can operate at a max 2.3v and i only hav 2v to ea. LED.. then *tada* no popped LEDs.. but the only downside is that they may lose a little intensity to them.. but realy slightly.. lik.. .3v slightly and its not like your going to notice lol i hope i didnt explain it too much lol juss an idea i read off the internet.. dont flame me plz if it dont work lol its always worth a try though.. ttyl
It really all depends on HOW you set up the LEDs.
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
true true Dark-V.. i 4got of that.. i should know this since im still in H.S. and Physics is still fresh in my mind lol im surprised mi LEDs still lasted then lol thanks for that tip for me too.. THANKS! n good luck Maximized
Senior Member
Joined: Dec 2005
Posts: 1,124
From: Leicester, Ma
Thread Starter
Joined: May 2004
Posts: 1,372
From: Hoagieville, PA
Originally Posted by Dark-V
It really all depends on HOW you set up the LEDs.
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
Awesome man thanks. The LEDs i'm using is white and I have them in four lines of 4. I think I tried the 1k resistor and it still heated up thats why I thought it was the watts.
Supporting Maxima.org Member
Joined: Nov 2001
Posts: 653
From: SoCal
Originally Posted by Dark-V
It really all depends on HOW you set up the LEDs.
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
If they are white LEDs, usually take around 3.4v drop.
Your dome light, contrary to what it says on it, puts out multiple voltages.
~12.5 when the car is off (while on battery power) and ~14 when the car is on (while running via the alternator). Now, if you set everything up via the 12V, then when your car is on, will overpower your LEDs, and burn out.
When I set up my dome/map/plate/trunk etc etc LEDs, I ALWAYS use 14v as my starting voltage.
Now, if you are using white or blue LEDs, I use 3.4v drop as a good average. Red, amber, and yellow LEDs use typically 2v.
If you want, you can put LEDs in series, but calculate for the voltage drop.
Start with 14v, then subtract the LEDs in that line. 14 - 3.4 - 3.4 - 3.4 - 3.4 = 0.4
The 0.4v left over is the voltage you need to use to calculate the resistor.
so... using Ohms law, R = V/I where R= resistance, V= voltage and I=current.
The current is each "line" of LEDs. So it would be 0.002 amps (20mA) so, 0.4/0.002 = 200ohm resistor.
So if you had 2 lines of LEDs it would be 0.004amps (40mA) due to the double "lines" of LEDs.
With using such a low voltage, even with all 16 white LEDs (four lines of four LEDs or 0.008amps (80mA)) would only be 0.0032 watts. WAY less than you'll EVER need to worry about.
Hope that helps!! Good luck!
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