Wiring for LED's

MSG419

Registered User
I'm doing a little custom work with LED's and was wondering if anyone knows about wiring 10-12 together.

I know they need to be wired in Parallel and was wondering if I need to install a resistor on each LED or will one resistor cover the bunch if installed between the 12V and the positive lead to the LED's?

From what I've read it seems that multiple resistors on the positive line will cause all the LED's to be dimmer. Anyone know if this is correct?

Thanks,
Mark
'95 SC 5spd
 
this will depend on the color of the led and the power requirements of them. most led lights (individual) run on anywhere from 1.2 to 2.2 volts for the most common over the counter light.
If your running a red led with a requirement of 2.2 volts then you will need to put 5 leds in parallel to not use a resistor. you can go 6 safely but will shorten the life.
To make it easier on you and me heres a link that I used to use to put it all together before I finally figured it out http://www.besthongkong.com/information.php?info_id=12 Tha should answer most your question. Also they are great to deal with if you happen to order from them I have order numerous times and have never had a problem, plus you cant hardly beat their prices. If you need help trying to design something let me know Ill help as much as I can.

S
 
i would think you would just need one resistor to knock down the voltage so they don't burn up. And i have a ? how many ohm's does it take to knock off one volt? i need to do some led work too and can't find the info i just asked for. its been to long since i was in high school electrical class.
 
i would think you would just need one resistor to knock down the voltage so they don't burn up. And i have a ? how many ohm's does it take to knock off one volt? i need to do some led work too and can't find the info i just asked for. its been to long since i was in high school electrical class.


yea you are right I forgot to put that in there after reading it again and you busting me :eek:
For 5 red leds you would need a 100 ohm resistor, 1/4 watt should more than cover it.
The above link that I gave should cover what you need to know, I fit doesnt Ive got alot more resources to help.

S
 
If your running a red led with a requirement of 2.2 volts then you will need to put 5 leds in parallel to not use a resistor. you can go 6 safely but will shorten the life.


S

I don't think that statement is correct. your not increasing resistance by wiring in parallel. so you would still have the 12v to each LED. now if you wire it in series that should be true, but if one goes out in series they all go out like chrismas lights.
 
Yea in parallel you would need what, a 560 ohm to each one I believe. In series (end to end) 100ohm will cover it at 12 volts. Eve though most vehicles run at about 13.8 its still ok at this level You may lose a few hours of burn time but you would probably never notice it. Little brighter too. I just got in from a 14 hr day so scuse my errors I mean well and can throw these suckers together in my sleep but its getting lost between my puny brain and my fingers.

S
 
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You wire them in series. LED's are current driven devices, so ideally you have a constant current source for them. If you're a member you can check out this thread where there has been discussion of repairing/replacing the factory led array.
http://www.sccoa.com/forums/showthread.php?t=44550&highlight=led

LED's typically like 20milliamps of current to provide maximum light. Ideally you run them a little below that as heat kills them. Since they are a diode, they eat voltage as you drop across them.

Say a LED with a 2.2volt forward voltage and 20ma current draw.

With a 12v source, you can stick 5 of them in a string in series. 2.2v * 5 = 11v so you'd need a 56ohm resistor in a 1/2 watt package to take the balance. This website can help you calculate this stuff http://led.linear1.org/led.wiz

One problem you find with LED's is that they are not a constant product. I.e. put 5 in a row and light them up and you will likely find a few that are at a different brightness. This is because some will consume the voltage differently. if you drove them with a constant current source this wouldn't be an issue. A discussion of this is in the member forum as we worked to finding a constant current source in an IC package. Most production parts use constant current sources with pulsed square wave that turns the led on and off fast enough that the eye doesn't capture it. You can also change perceived intensity of the led by varying the frequency of the pulse.
 
Thanks for the replies from everyone. I see I have some reading to do.

I've already replaced some of the LED's in the window and lock switches from the horrible green to blue. There's one resistor for two LED's in each switch. I also made an LED 3rd brake light using white LED's but thinking of changing them to red and using about 10 of them. I'd also like to change the gauge cluster lights, but not sure if it'll work.

Mark
'95 SC 5spd
 
I also made an LED 3rd brake light using white LED's but thinking of changing them to red and using about 10 of them.

Mark
'95 SC 5spd

the brake light from a 02-03 yamaha r1 thats a motorcycle fits perfect in the housing you just need to clip like an 1/8 of an inch off each side of the board, thats what i have in mine.

if you wanted something neat you could buy the UFO tailite for the r1 it has different brake patterns you can program into it. I have the UFO one in the bike and just used my stock one in the car. they cost about $160 for the UFO. heres a web site you can look at videos of it. http://www.spyderracing.com/02-03-YZF-R1-UFO-Light-Kit-p/ht-02-03%20yzf-r1.htm Or i can sell you a factory tail light for 80 bucks and you just cut the case open and use the board.

then i used tractor trailer led lights in my corner tail lites for the leds that you can actually see instead of the 3157 led bulbs they sell.
 
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If the Lens is red, RED LED's won't help it as the lens will filter out the Red light. It could end up dimmer. Super whites are the best color to use behind any kind of colored filter.

By driving them direct off the voltage, you cut their life. That's why there are actual IC's available that let you package a group of leds in a low power device. Cell phones all use led's for illumination. Those tv remote controls use LED's. Car dash boards are starting to use leds. They want that stuff to have low power drain and long life. PWM driving of them is what gives them the long life. It's also one of the causes of our deck lights failing, led's just burn out.

Oh and when you're sizing the resistor, keep in mind that a automotive electrical system is usually at 13.5 volts, not 12.
 
I always use 2700 ohm resistors for LED's regardless of what voltage I'm running up to about 24 volts. It doesn't matter whether you use one resistor in the common side or use one per LED, just make sure the wattage rating is sufficient if you have a lot of LED's or use super brights.
 
If the Lens is red, RED LED's won't help it as the lens will filter out the Red light. It could end up dimmer.

I think that a red lens only ALLOWS red light to pass through, however, I'd agree that if anything it would result in a dimmer light. I would say that this is because the red led's ouput wavelength may not match match up to the red taillight lens' filtering wavelengths, so it may block some of the light. I've thought about that alot actually, since red led's are cheaper than white. :D I'd recommend white also.

As far as wiring LED's... just aim for a current a little under what the LEDs are rated for. I personally would feel better about wiring them all in parallel with a resistor on each. Resistors are pennies each and the work is fun to me. But there are a few different ways to wire them. As long a something is impeding the flow of current appropriately (or equivalently, dropping the voltage supplied across any given LED), then they'll be nice and bright, and won't burn out. If you have a variety of resistors and plenty of LEDs, you could even experiment and find what yields the best illumination.

Anyhow...Mike has you one the right track. :)
 
02-03 r1 3rd brake lite
tractor trailer lite in right tail lite
stock left tail lite.
 

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You don't want to put LED's in Parallel, they don't current-share and one could hog it all.

Either wire up one per resistor , or put them in series with a proper resistor.

I'm sorry, I screwed up on the lights to use. For sure you want to use a RED led. The issue with White LED's is most of their power is in the blue spectrum so that'll get filtered out by the RED lens. Paul93sc is who is helping me with my led project in that member forum thread I liked to and I had to review it for the opinion on led color.

I bought something like this one from these guys.
http://www.superbrightleds.com/specs/r3mm3_specs.htm
 
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