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LED Voltage

post #1 of 9
5/6/12 at 10:33am
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I have 2 white LED strips in my case for some subtile accent lighting. The strips are rated at 12v and I have them connected directly to the PSU via a molex. At 12v, however, these things are rather bright. A little too bright for my liking. I was hoping to lower the voltage going to the LED's themselves to dim them a little. I know it would be as simple as soldering a resister to the power wire but I'm not sure what size resistor I would need.

I am hoping to lower the voltage from 12v to about 7(ish)v. What size resistor would I need to do this? I have tried searching but was not able to find any type of calculator or helpful information on the topic. Can anyone help me out?
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post #2 of 9
5/6/12 at 10:49am
I would suggest maybe a 1K resistor in series with the led. That is a guess on what resistor you would need. As that would depend on you. Just buy a wide coverage pack of the resistors and try them one at a time until you find one you like. Thanks

Example:If the LED is drawing 10 mA, that will drop its supply voltage by about 1 volt. If it's still too bright, try 2 in series, or three. Test this on BOTH of you bright LED's and find the right value. If necessary, go back to the store and buy the right ones - say, a 3.3 K instead of three 1K's in series. As for power rating, a 10 mA current through a 1K resistor is only 0.1 watts; if it's 20 mA, that's still only 0.4 watts. So a ½ watt resistor is very likely suitable.


Or you could use a color correction gel wrap as found here maybe. http://www.amazon.com/Cowboystudio-Color-Correction-Gels-12in/dp/B0036BGJ2I/ref=pd_sim_sbs_t_8

They do make some led pot adjusters. But I haven't seen any in a long time. You could build one also. Just depends on your skills and knowledge though.
Edited by KILLER_K - 5/6/12 at 10:52am
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post #3 of 9
5/6/12 at 10:52am
Quote:
Originally Posted by mwl5apv View Post

I have 2 white LED strips in my case for some subtile accent lighting. The strips are rated at 12v and I have them connected directly to the PSU via a molex. At 12v, however, these things are rather bright. A little too bright for my liking. I was hoping to lower the voltage going to the LED's themselves to dim them a little. I know it would be as simple as soldering a resister to the power wire but I'm not sure what size resistor I would need.
I am hoping to lower the voltage from 12v to about 7(ish)v. What size resistor would I need to do this? I have tried searching but was not able to find any type of calculator or helpful information on the topic. Can anyone help me out?

I would suggest doing the molex mod to reduce the voltage. You can get to right around 7 volts doing that.


for 12 volts connect red from led to yellow from molex and black from led to black next to the yellow from the molex

for 7 volts connect the red from the led to the yellow from the molex and the black from the led to the red from the molex

for 5 volts connect the red from the led to the red from the molex and the black from the led to the black next to the red on the molex
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post #4 of 9
5/6/12 at 4:05pm
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Quote:
Originally Posted by jared872 View Post

I would suggest doing the molex mod to reduce the voltage. You can get to right around 7 volts doing that.
for 12 volts connect red from led to yellow from molex and black from led to black next to the yellow from the molex
for 7 volts connect the red from the led to the yellow from the molex and the black from the led to the red from the molex
for 5 volts connect the red from the led to the red from the molex and the black from the led to the black next to the red on the molex

I don't know how that could have slipped my mind! I completely forgot that the molex has the 12 and 5 volt wires. Thanks bud!
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post #5 of 9
5/7/12 at 2:40pm
Quote:
Originally Posted by mwl5apv View Post

I don't know how that could have slipped my mind! I completely forgot that the molex has the 12 and 5 volt wires. Thanks bud!

No problem!
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post #6 of 9
5/8/12 at 6:17pm
I purchased several led strip for my car, I plan on installing them as 2 DRLs in the front of the car and 2 strips as Interior lighting...Flexible LED Strip Lights I plan on connecting them to one of my park(position) lights.. Would I have issues when doing this, i'll make a diagram... Outdoor LED Lighting Once again I'm doing them in parallel that way if one goes out, they dont all go out...

Position lights
… interior LED strip
..spliced.............. |..................... |
............................|.........… interior LED strip
........................... |--One DRL
........................... |
........................One DRL:)
Edited by LanHarjochee - 5/8/12 at 6:20pm
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post #7 of 9
5/8/12 at 9:32pm
Thread Starter 
Quote:
Originally Posted by LanHarjochee View Post

I purchased several led strip for my car, I plan on installing them as 2 DRLs in the front of the car and 2 strips as Interior lighting...Flexible LED Strip Lights I plan on connecting them to one of my park(position) lights.. Would I have issues when doing this, i'll make a diagram... Outdoor LED Lighting Once again I'm doing them in parallel that way if one goes out, they dont all go out...
Position lights
… interior LED strip
..spliced.............. |..................... |
............................|.........… interior LED strip
........................... |--One DRL
........................... |
........................One DRL:)

the DRL LED's on the outside you can go ahead and wire into your ambers. that way when your ambers are on the LED's are on. But make sure you choose a color that is legal in your area. Splice the power of the LED into the power of the ambers and ground them to any existing ground under the hood.

The lights inside however....I personally have done A LOT of electical work on cars. from custom lighting to sound systems, etc. Interior lighting more often than not is illegal. So I would suggest running the power directly from your battery, through a 5 or less(depending on the amperage rating of the LED's) fuse and into a switch mounted somewhere inside your car. That way you have control over when their on and off. But that is all personal preference of course and is dependant on the final product you are looking for. Running the power from under the hood and inside the car is as simple as finding an existing grommet and feeding it through to the interior of the car. If you have any questions on anything feel free to shoot me a pm and ill do what i can to assist you.
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post #8 of 9
6/12/12 at 7:28pm
in fact man,if you don't want the White LED strips so bright,you can connect a LED strip dimmer,so that you can adjust the brightness of LED strips.
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post #9 of 9
6/13/12 at 7:46am
You just need to buy some resistors or LED strip dimmers, you would try http://www.vozop.com/index.php/led-controller.html

I vouch for this site as I have done business in the past, it is professional and good quality thumb.gif
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