3w led and resistor help

[audioguru]

The datasheet for the LM317 says that the 2 ohm resistor will have 1.25V across it. Ohms Law says that the current in the resistor is 1.25V/2 ohms= 625mA. Then the power dissipated by the resistor is 1.25V x 625mA= 0.78W. A 1W resistor will be pretty hot. A half watt resistor will be too hot and might be destroyed.

The distance from the resistor to the LED must be less than 20,000 miles or whatever amount of wire resistance dims the LEDs.
The resistor should be close to the LM317.

Your circuit probably needs an input capacitror for each LM317.

 

[JMW]

Red and Amber auto lamps are specific colors. The colors are measured in wavelength of the light usually nm. I don't remember where I saw a the breakdown, but you can do a search for it. The white will pose no problem, but the red may, depending on the local police.

 

[gizmo13]

Don't know how to determine what value/type of capacitor I need.
There will be a controller and an interface (this is where the lm317 and the resistors
will be). Approximately 4 feet away from where the led's will be psitioned.
So the size of the relays wont be much of an issue now.
I am still curious about needing a heatsink. These 3w led's already come mounted on a metal type plate.
Still confused on whether I need additional heatsinking.

 

[IntelGent]

Don't know how to determine what value/type of capacitor I need.

This thread might help you......

https://www.electro-tech-online.com/threads/how-to-calculate-the-value-of-a-smoothing-capacitor.106374/

 

[gizmo13]

Haven't really found any carbon filmed versions so should I be using metal film resistors?
What's the difference?

 

[colin55]

Here is the circuit you need:

This circuit provides constant current for high-power LEDs. The battery voltage for a car can range from 11v to nearly 16v, depending on the state-of-charge and the RPM of the engine.
This circuit provides constant current so the LEDs are not over-driven.
**broken link removed**

 

[gizmo13]

I finally got the chance to purchase the parts and wire up 1 leg of this thing and let me tell you
the led's, regulator and metal heat sink all got hot.
So now do I need a higher wattage resistor or what?
For those that don't remember, I am making a night rider light display for my car to run
two 3watt star (luxeom) led's in series to run off 12v.
What's next???????
Help, Please!!!!!!!!!!!1



giz

 

[gizmo13]

Just as an added note, I didn't pay much attention to the last schematic posted. I am going to have to try that one too.
I was referring to the original schematics that I was directed to try using the lm317 circuitry.


giz

 

[gizmo13]

????????
If your not going to be helpful, don't respond at all.
I don't need your smart ass remark and the point is I am trying to learn this stuff.

 

[kinarfi]

????????
If your not going to be helpful, don't respond at all.
I don't need your smart ass remark and the point is I am trying to learn this stuff.

Well put, & I agree, what's the voltage and current of 1 LED? The LEDs do get hot, so they do need a heat sink, I'm thinking your LEDs are 3.2 volts each and your LM317 is set for 600ma and your supply voltage with the engine running is 14.2, so if you subtract the 6.4 for 2 LEDs, your LM317 is left with 8 volts at 600ma and is dissipating 4.8 watts. Put a 5 ohm 5w resistor in series with the LEDs and it will take the heat instead of the LM317.
The other option for less heat is a buck regulator like a LM2576, but I recently tried one of them and it got hot too. Remember, it doesn't matter how you regulate the current for your LEDs 600ma supplied by 14.2 volts is 8.52 watts and you will have to get rid of that much to keep things happy, so you will have heat.
Also, for the 5 ohm 5 w resistor, you may be well off to use 2 10ohms in parallel
Kinarfi

 

[gizmo13]

Thanks. Definitely going to try that.
I am going to experiment with the last "nite rider schematic" posted.
Can someone tell me what the R (I know it is a resistor of sorts) is where
it says :
R= 1R0 for 680 mA
R= 2R2 for 300 mA
I am a bit lost on that part.

Thanks for the "helpful" response.

Giz

 

[kinarfi]

From what I understand, 1R0 is the European method for 1.0 Ohm & 2R2 would be 2.2 ohm

 

[gizmo13]

Excellent!! Thanks!!
Have to pay some bills but can't wait to try these in a couple of weeks when I can buy some more parts.


giz