k-2 for tail lights

[a1953mdl]

I read and have re-read the majorboost thread and the other tail light threads, but not sure of the answer to this question.
Probably cause it's too simply.

Any way.... I am wanting to use LEDs in the tail lights of a 59 VW bug.
It has been converted to 12v. The tail lights are fairly small. I am thinking one K2 in each side would be a lot better than what I have.
When I use the calculator, it says to use a 18 ohm 8.8 watt resistor. I can't find a 18 ohm 8.8 watt resistor.
If I use the buck puck will I still need to use a resistor in line for the brake light and a second one in line for the tail light.
I was thinking something in the range of 30 ohm for the tail light and a 6 ohm for the brake light. Should give me 18 total.

My question is where do you find the high ohm resistors. Google didn't help or I don't know what to search for.
When I look for a resistor, do I want a ceramic or what.
In this simple scenario, is a buck puck even needed?

A single K2 is much brighter than a stock incandescent bulb, so I am okay with a single K2, correct? I was planning on recessing it back in the reflector where the stock bulb would go. It would set the LED approx 1+ inches from the lens. I would make a plate to mount the K2 and secure it to the steel reflector and use that for the heat sink, good enough?

I could get some pics if that would help.
Thanks for your help and patience with us newbies.

Lee

[cadstarsucks]

oh yuck!!!!  there are a number of ways to do it, but no the buck puck does not require the external resistor. 

High ohm?  those are actually pretty typical power resistors.   problem with power resistors is that they do not compensate for the power rail varying, the buck puck does.

Dan

[a1953mdl]

Cadstarssuck writes:  High ohm?  those are actually pretty typical power resistors.

Sorry, I meant high wattage. Seems like 1 watt was the highest most carried.

So I could just run the buck puck with no resistors and it would control the brightness of the K2? Both for the tail light and brake light.

Thanks
Lee

[cadstarsucks]

50Wers are even pretty common... digikey carries hoards of them... that said, you should be using the buck puck anyhow since the lack of regulation in a car electrical system will leave you either running dim and variable or blow out the LEDs

[a1953mdl]

Thanks, digikey certainly did have the resistors.
I now understand the need for the buck puck. Stable Power  The buck puck uses some power also, so what voltage do i need to use in the calculator? The car puts out between 14.4 to 12.8 or so.
If I use the 30 ohm for tail lights and the 6 ohm for the brake, for a combined resistance of 18, what wattage would each resistor need to be if used with the buck puck? Still 8.8 watt each or ??
I am sure these are very basic questions, but I surely appreciate the help.
Lee

[justDIY]

Thanks, digikey certainly did have the resistors.
I now understand the need for the buck puck. Stable Power  The buck puck uses some power also, so what voltage do i need to use in the calculator? The car puts out between 14.4 to 12.8 or so.
If I use the 30 ohm for tail lights and the 6 ohm for the brake, for a combined resistance of 18, what wattage would each resistor need to be if used with the buck puck? Still 8.8 watt each or ??
I am sure these are very basic questions, but I surely appreciate the help.
Lee

you don't use any resistors with the buck puck - that is why it costs so much, it does everything for you.

There's another thread in this forum which isn't very old - someone else did almost the exact same thing you're doing.  I recommend giving that thread a read as to how the brake / taillight problem was solved.

edit: here's the similar thread:
http://forums.linear1.org/index.php/topic,1576.0.html

[a1953mdl]

I had read and re-read the majorboost thread several times before I posted this thread. Sometimes i just have a hard time catching the minor details or applying the information to my situation.
Thanks for clarifying the buck pucks role in this application. I had read the information on the buck puck, but wasn't positive if I needed the resistor or not.  It all runs together in my mind.
That thread really does help a lot. It was where i learned of K2s and the buck puck.
You guys really do help us newbies out alot.
 Thanks
Lee

[justDIY]

to summarize the other thread, a pwm generator, which could be a simple 555 timer circuit, was used to keep the buck puck on "dim" unless the brake light switch required the lights at full brightness.  turning on the brakes would disengage the pwm generator, allowing the puck to operate at full brightness.

[a1953mdl]

Thanks for the link. The first item was this
http://www.dprg.org/tutorials/2005-11a/index.html
That was very helpful in understanding what the buck puck does.
Lee