hotbox05

that looks really great but also made yer car pretty damned illegal and if u get pulled for anything else u better be a perfect little angel unless you like lots of expensive tickets. and no they arent 10.00 fix it's unless you go to court and showed them you fixed it. lol been there done that .

Limey

OK so I'm checking out the LEd calculator widget at http://metku.net/index.html?sect=vie...calc/index_eng

Using 14v
Volt Drop 2v
Milliamps 80
# of LEDs 18

(above data from http://www.lsdiodes.com/THC3/5mmred.htm - did I read it right?)

Anyway the calculator tells me I can't do series as I don't have enough supply volts (we can't have that can we).

So i need to do parallel.

So it tells me I need

6.94ohms limiting resitor.
nearest higher rated resistor 8.2ohm
calculatd resistor wattage 14w
resistor with a power rating of 24

Now I picked up 20 22ohm carbon film resistors from lsdiodes - did I do wrong? Will I need to visit the shack?...


hmmm so I just changed the number of LED's to 9 and the ohm'age went up to 15o.

is that a possible solution, just wire them in 6 LED blocks (two ends and a mddle) that calculates to 22ohm on the nose.

Any input greatly appreciated.

Limey

"that looks really great but also made yer car pretty damned illegal"

why is removing the 3rd brake light illegal, there are still 2 others like everyone else has?

taek

i don't think its illegal. i asked my shop

-taek

hotbox05

it IS lillegal check california vehicle code.
it is also federal law that all vehicles newer than 90 some odd (95 i think) year are required to have a third brake light.

Limey

Wow, I didn't know that :O

Tael you should put one of those window 3rd brakes behind the tint you wouldn't see it, until you braked, that would be pretty cool.

daggerSLADE

this looks great (been waitin to see somethin done w/ this) .. anyone ever thought about making the brakelight progressive? have the middle light up and then spread out to the sides? (knight rider anyone?) ... Scott17 did this for his blinker on his friend's xB .. looks sick .. ya just need to add an IC or somethin .. hehe .. and program it ..

Limey

I'll post a full write up when I'm done, took the 3rd brake off this morning, more of a _____ than i thought, required me to totally strip the trunk trim and then you have to un bolt not only the brake light but also the panel under that that houses the license lights.

Cars in the shop getting a tint, time to drill some holes. That's the next part of the story, as the bolts get in the way if you equally space the LEDS in line with the stock ones.

anyone got any thoughts on if you could bake the 3rd brake light to get inside it ?

daggerSLADE

the guy who first posted said dont bake it .. the adhesive melts at a higher temperature then the actual plastic does .. read the first post on this thread

Limey

Oh yeah....dowp. Anywho, drilled my holes, just made a trip to the hardware store - time for some soldering.

engifineer

Cars have been required to have 3rd brake lights by law for a number of years now. Of course your shop said its legal. You believe what they tell you and they make money off of it.

engifineer

you can do it without programmable ICs, but it is cleaner with a PIC or Microcontroller. I actually have thought of this, but am spending time on some gauge projects right now, which do include an additional control circuit, so that is my focus for now.

Limey

Well that was a nightmare afternoon.

Won't go into huge details, except for the fact that I hate soldering, and my resistors all melted once introdcued to a 12v charge.

Ho Hum, tahnkfully it was wired for testing, So I was able to untwist two wires and go back to stock.

I'll revist it another day.

engifineer

I just looked up the specs on the THC3 Red LEDs. They drop 2.4V and should be run between 80 and 100mA. So, if you run them in parallel (which you must if you run 10 on a 14.4V circuit) you will want to use a 150 Ohm 1W resistor. The way to figure this for those that want to know is as follows. Think of the led as a constant voltage drop (they can vary slightly but will drop their rated value as long as the Vs is sufficient)

Vr = Vs - Vl (Vr = resistor voltage drop), (Vs = Source), (Vl = LED drop)
P = I^2 * R (P = power), (I = current), (R = resistance)
Ir = Vr/R (I = current through resistor)

From these and the above info:
Vr= 14.4 - 2.4 = 12V
.09 = 12/R --> R = 133.333 Closest common value that is safe = 150Ohm

To re-figure actual current through the LED with the resistor value:
12/150 = .08 or 80mA

To figure for power:
P = (.08 ) ^2 * 150 = .96W

Something else you guys may consider is the view angle of those LEDs. Those have only a 25 degree view angle. As a point of reference the ones that light your gauges have a view angle of 170 degrees. Higher output LEDs are usually more focused, which gives them the output. However, if you can find some with a wider view angle and high output you will notice less cutoff between the LEDs in the finished design.

Limey

Yeah, the ones in there are the square 4 legged ones.

I think I'll order a new back light from ken and when it arrives try to cut one the old one and actually wire something inside like teh stock lights.

Very insightful post there enginfeer thank you for sharing.

etli

Hi guys

Glad to see my stuff is finally generating some interest. I ran the 10 LED's in 2 separate branches.... In each branch, the lights (5) were wired in series.

So I have one "branch" with a 1/2 Watt 22 ohm resistor powering just 5 LEDs

and same thing on the other "branch".


Oh, and another thing. The third brake light only comes "ON" when you press the brake pedal. I don't think that there's always "power" going to the light itself because there's only two wires going into the brake light itself. So I assume that if you want the 3rd light to be on when lights are turned "on" but the car isn' t breaking, you would need to run an extra wire or two through the body. Otherwise, the light only comes on when you press the brake pedal. And presumably, you wouldn't always have the "knight-rider" effect unless you were actively pressing the brake pedal.


Regarding viewing angle - yeah I looked for LED's with more viewing angle but I figure, the LED's are housed kind of deep inside the brake light housing. The crystal pattern on the light does a pretty good job of diffusing the light anyways. I dunno if having wider viewing angles would help that much.


Regarding water-proofing. Just buy some silicone sealant from Home Depot. The stuff usually comes in a tube like tooth paste - you don't need an actual "caulking gun" container full. Just a little dab on the the exposed wiring after you solder everything together.

Regarding using all 18 LED's. DAMN BOY, YOU CRAZY?!!! just kidding. But just a warning, it's going to be VERY difficult to get your fingers in there to do all that wiring unless you've got other soldering tricks. You'll need to be really careful about shorting something out. I like to physcially wrap my wires around each other so I don't have to hold them and solder at the same time but maybe you have a better way to do it.

Limey

"but maybe you have a better way to do it."

Nope mine looked like ___ when it was finished. I hate soldering.

New idea, I'm probably going to get a new 3rd light from Ken, then when that arrives, I'm going to got o work taking the back off this one I've butchered, and add s-flux leds from the inside of the housing, that way I can keep all my wiring inside and have it soldered striaght into the main supply.

These will be the next batch of LED's I get http://www.lsdiodes.com/s-flux/

etli

Hope you're getting the 10000 mcd red S-fluxes and not the 5000 mcd. Because those will not light up as bright as the stock lights.

Rivulent

Any findings on a large viewing angle w/ high output? I'm interested in doing this, but as usual, with my own twist. Don't want to give it away though . I want to find out more a bit more info before I tackle this one.


How do the lights match up in real life? The only thing I see is that, as engifeener said, the viewing angle seems to be noticeably narrow on the new lights..

Limey

Haven't touched mine since the last screw up, need to re-solder all the leds, without the diodes, 7 per side.

I'm not getting the s-flux, I looked at getting a replacement 3rd light housing that I could cut the back off and do a proper job internal wiring the s-flux ones, but the new housings are $80. Not a high priority right now.