golden dragon leds

Off-topic Chatter
1

http://www.led1.de/shop/product_info.php?currency=USD&pName=sales-osram-dragontape-dt6w2b865-white-6500k-210-lumen-p-1319&products_id=1319

Hi guys i wonder if anyone can help with these lights, i'm after a decent driver for them the one that they suggest costs a fortune. i need one that will work in a cars electrical system.

Thanks

Charles

2

That's where I'd have told you to look. Resistors of the appropriate value will do the trick - they cost tenths of pennies. The trick is working out what value you want. It helps if you already know he forward voltage of the LEDs. You need to work with 14V and control the current to what the LED needs. If the LED needs 350mA you need to hit a 13.8-14V electrical system so it won't kill the LED.

V=IR

So plug in values. We want 350mA - we have 13.8V or thereabouts. So 13.8 = 0.35 x R

Or V/I=R

So divide voltage by current 13.8/.35=39 ohms. Now what power do we want to handle? Say 3 watts

So we need a 39 ohm 3 watt resistor.

Do they make such a thing. That will be right!

So you have to combine resistors according to the standard formulae.

They are accessible by Google-basically connect enough resistors in parallel till you get the value and power handling you want.

3

Assume 3.7V and you won't be far wrong.

4

Thanks for that Don thats a great help, but aren't you supposed to use something like this to control them. I have a voltage regulator set to 9v from another project do i guess i could use that with the correct resistors

http://www.besthongkong.com/index.php?cPath=19_51&osCsid=gssof807mj5o1bpmggfvprlum3

5

For a car system assume 13.8V. You need to keep the current to what the LED can handle. I'm assuming 350mA. May be more than that - need to look up Golden Dragon spec sheets. V (Voltage) = I (current) xR (Resistance)

We know the voltage 13.8V

We know the current - whatever the spec sheet says for the LED. Assuming 350mA

So V (13.8) = I (0,350) x Resistance

Divide by I (Current) and we get V (13.8) / I (0.35) = R

So 13.8/0.35 = 39.43 Ohms resistance

Assume a 3W LED so we need to be able to handle 3W through the resistors. The normal cheap ones are 0.125 (1/8)W

Crudely put we need 24 1/8W resistors to handle the power.

The formula for resistors in parallel is 1/R1 + 1/R2 etc. = 1/total resistance

Time for me to sleep and my logic circuits aren't up to it right now - will conclude this tomorrow. Hopefully someone else will pick up the ball and run with it.

6

In a car you don't need to worry about battery life - to all intents and purposes the current supply is infinite. Most car alternators can produce upwards of 40A at 1500rpm. We really don't need to worry about efficiency which we do with batteries. My car's alternator can produce something like half a kilowatt. Batteries of a sane size and weight can't. We've got a potential of 35A at 14V or 490W to play with. What we need to do is control the current to the LEDs to something that won't burn them out. I'm assuming 350mA - some LEDs can tolerate over an amp. Spec sheets will tell you what the LED can tolerate. The formulae are simple

Volts = Current x Resistance (V=IR)

Power (Watts) = Volts x Amps (P = VI)

The rest is algebra and arithmetic. Efficiency is more or less irrelevant in car systems - you have a few hundred watts to play with. Just make sure the resistors don't get too hot.

7

cheers mate i havn't done this since school. and my brain is burnt out at this time of night

8

Hi Don yes they are 350mA

Don't i need to have some sort of constant voltage my car varies between 13-15v

9

Where in the car is the led going to be.......

10

Number plate lights. for the first idea

11

Cool awesome.......so when your speeding in the dark, all the cops would have to do is look at your plates and send you the ticket....lmao, just joking of course.

12

Yeah something like that, i hoping to dazzel them so i can make a quick get away lol

13

You might as well just install some ssc P7's and just blind them.......

14

now thats an idea

15

Oh man......i should have kept my mouth shut......you would seem to be that type of person that would actually do it as well.

16

WHAT !!! i'm a good lad never had a speeding ticket, well only when i took it drag racing had a pretty gud one then

17

Lol.......now all you want to do is blind the people that tailgate you.....lmao. Take pics when you complete this project.

18

will do might have to adjust the set up if they are too bright, another guy in the club has 3 1 watt stars in each of his

19

Cool take a pic and post it man.....would love to see it.

20

shall do when it done, ill get some of the other guys aswell hes done loads of led mods to his