can any wiring gu rus help me determine what size resistors im going to need for 10 leds with the following stats. I realize not all of that is required info. But I included it anyway.

Source Material:InGaN !
Emitting Colour:0.5W 8MM WIDE VIEW RED 0.5W LED
Luminous Intensity-MCD: Typ: 95,000 mcd
...Reverse Voltage:5.0 V
DC Forward Voltage: Typical:
DC Forward Current:100mA

 

so far ive had one friend tell me

i need a 100 ohm resistor per led

and another say i need a 22 ohm resistor per 2 leds....

but neither have mentioned a wattage for the resistor....

 

So if the manufacturer is right and you need 5V across each LEDs MAX to get good brightness and light, you need to burn up ~4.5 extra volts at 100mA to drive them reliably. Your R/R puts out approximately 14.5 when running. So using ohm's law, V=I*R, 4.5V=0.1A*R =>R=45ohm. So 2 22ohm resistors should work The power dissipated by the resistor is going to be quite a bit unfortunately. Joule heating (power use of resistors) is given by P=I^2*R =.1A^2*22=0.22W. You'll need .25W resistors, but I'd go up to 0.5W because you might have trouble getting air out.

Better safe then sorry. It's too bad that you can't use 3 4V LEDs or something, cause nearly 1/3rd the power to drive each 2 led strip is dissipated in the Resistor.

 

So if the manufacturer is right and you need 5V across each LEDs MAX to get good brightness and light, you need to burn up ~4.5 extra volts at 100mA to drive them reliably.

Your R/R puts out approximately 14.5 when running. So using ohm's law,

V=I*R, 4.5V=0.1A*R =>R=45ohm.

So 2 22ohm resistors should work The power dissipated by the resistor is going to be quite a bit unfortunately. Joule heating (power use of resistors) is given by

P=I^2*R =.1A^2*22=0.22W.

You'll need .25W resistors, but I'd go up to 0.5W because you might have trouble getting air out.

Better safe then sorry. It's too bad that you can't use 3 4V LEDs or something, cause nearly 1/3rd the power to drive each 2 led strip is dissipated in the Resistor.

 

I guess i should better clarify....

im making a running light/brake/signal led board.... so i need the running light resistor to make the leds somewhat dimmer, while the brake resistor to make them brighter....

i will probably use the same brake light resistor on the turn signals

 

which would also mean im not running a constant power... running lights run around 9v where your brake is more between 11-12 <----- i may be off there slightly

 

1/4 W would be fine.

 

On a stock bike, both should run at 14.4V if they're good old incandesant bulbs. Your leads should not eat up more than a couple hundred milivolts at most and should be close to nil if you use relays. The running lights just run more current and then put out more power. If you want to fake that, then you'll have to decrease the current thru the LED. Without knowing more about the luminescence/current relationship and the IV curve of the LED, I couldn't give you a value. The ammount of light a led puts out with increasing voltage is not linear, and since I usually don't drive them at anything besides the spec voltage, you'd have to get a more detailed data sheet and make some judgement calls.

 

if it's running at full power, you'll have .22W going through each tiny resistor. That's a lot! I've fried 1/4W resistors with less power. I like to use a resistor of at least double the power rating the resistor will dissipate in operation.

 

How many LED strips were you planning on running total? If i'm seeing your diagram right, it looks like you have 5? Then you will have much more current thru the resistors if you tie them into 1, and you will have a larger voltage drop across the resistor, dimming all the LEDs. You should have individual resistors for each resistor. If you run the resistors in paralell with all these banks, the current thru the resistor will jump up and your LEDs might not even turn on. Also, you will dissapate a lot of power in the resistor, and it might burn up unless you up the power rating.

I hope I'm not being a dick, but it would be easier for others to understand your diagrams if you used standard circuit component symbols. I've included some that you've used below. Here's a link to more: Standards - Electronic components

LED (Anode is positive side, or side where current flows into device)

Momentary Switch (IE Brake switch)


Battery (the positive side is the one with the longer line, on the top here)

Resistor