italicizedsponge

iTrader: (3)

So i finally bought an assload of 5mm red and white leds so i can do full blown led tail lights on my car over the winter.

My question is, if i wire in parallel and i do 50 leds with 1 resistor, will that work ok or is it better to have like 1 resistor per 10 leds and have 5 total resistors. i have a resistor calculator program but im not sure if its a good idea. once the project gets going ill post up pics. i bought 200 red leds for the main tail/brake lights and 100 white leds for the turn signals/reverse lights.

LS1-450

iTrader: (33)

It depends on the Amp load restriction. We need to know the fuse rating, LED resistance per LED & the size of the resistor you want to use. If the program says that the parallel circuit is correct using one resistor/one hunder LEDs relative to the restiction of the circuit load, then you are OK in terms of circuit protection. However, if the LEDs require enough resistance as to not overload prior to circuit protection & the program says that the resistor is correct for the 100 LED parallel circuit & the overall circuit protection , then you are OK, assuming that there is little to no LED resistance.

We really need the details to say for sure.

dragonrage

Use like a 5W resistor of the appropriate size and you'll be fine.

italicizedsponge

iTrader: (3)

these are the specs

Emitted Colour : Red
Size: 5mm
Lens Color : Water Clear
Forward Voltage (V) : 2.0~2.4
Forward Current (mA):20
View Angle: About 25 degree.
Static Sense:Yes
Luminous Intensity: 15000mcd

italicizedsponge

iTrader: (3)

i posted all the specs they give for the LEDs. in the program i put 14V source 2.2V voltage drop and 20mA desired current and 50 leds and it came out with 11.8Ohm resistor value. that sound right?

screamin96ss

iTrader: (4)

Try out this site for calculating what resistors to use.


http://led.linear1.org/led.wiz


Also, for more knowledge on LEDs check out this site.


http://www.hidplanet.com/forums/

I'm actually in the process of making prototypes for all the different tail lights and 3rd brake lights for all our 4th gens. After I get the prototypes done the way I want then I am going to become a sponsor and start offering my services to do full LED conversions. I'm also going to be doing interiors.

vjo90rs8

iTrader: (9)

Vf=2.2V
Vbat=14V
Vr(esistor)=11.8V
# of LEDs = 50
Iled=20mA

Vr = Iled * # of LEDs * R
11.8V = 0.020A * 50LEDs * R
R=11.8 ohms (you are correct)

Power = I^2*R = (0.020A*50)^2*11.8ohms = 11.8W

11.8W is a lot of power, you might be able to find 2-3 5W resistors and wire them in parallel but then you need to recalculate your resistor values.

OR.....

to take advantage of your 14.4V battery you could wire 10 strings of LEDs in parallel with each string containing 5 LEDs.

Vf=2.2V*5LEDs = 11V
Vbat=14.4V
Vr=3.4V
Iled=20mA
# of LED strings=10

3.4V = 0.020A * 10strings * R
R=17ohms (1 resistor is not recommended, use one per string)

P=(0.020*10)^2*R = 0.68W (a huge reduction in power) you'll be able to use a few cheap 1/4W resistors in parallel or 2 1/2 watt resistors.

OR to be safe you could run 4 LEDs in each string but 5 should be fine. You just might get a big drop in LED current when you shut off your car because Vr will only be about 1V with 12V on the battery (unless all your LEDs are at 2.4V, then with 5 LEDs per string you would have a Vf=12V and have no current, which might not be good for hazard lights, then youll only get 6mA/LED but you might not care. You could play around with the numbers but the more you put in series, the less current/energy you waste on the resistor. Even if you use 2-3 in each string and 18-25 strings in parallel you would benefit.

LS1-450

iTrader: (33)

Sorry, I didn't get back to this thread before today. Looks like what you need has been posted. Good-luck & let us know how it works out with pics.

dragonrage

In reality, you shouldn't actually put them all in parallel. They should be in series-parallel.

LS1-450

iTrader: (33)

Isn't that what vjo90rs8 has demonstrated in his post? That's how I interpreted it anyway. Maybe I missed something.

dragonrage

Yes, but his #s are somewhat arbitrary.

vjo90rs8

iTrader: (9)

I would just not worry about trying to minimize the number of resistors, you should keep at least 1 resistor per series string of LEDs (whether it be 3, 4, or 5 in series). If you have one resistor feeding into 50 LEDs then you will not necessarily get 20mA per LED. You need the resistors to help ensure that each string matches the next as closely as possible.

italicizedsponge

iTrader: (3)

thanks for the replies everyone, ill decide on exactly what im going to do once i tear the lights about and start going at it. the leds should be in a week id say so ill post up pics of the project once it gets underway. my goal is to have them look in the same ballpark as the 04 cadillac dts where the running light is a bar on the outside edge of the tail light and the hole tail light is the brake light. the only difference will be that the turn signal will be a separate light since i have ls1 tail lights.

Brian2006

iTrader: (42)

Little bit of advice, use 10mm at +50,000mcd. I really think you will be disapointed with 15,000mcd 5mm in your tail lights