homemade automotive 921 Luxeon

my car takes 921(18W) type bulbs for reverse lights, I couldn't find anything close, so naturally...




the heatsink is a lug, from a disconnect switch so it's got a hollow (hex key)back, a little pcb board, and a 24ohm risistor.
now for the other side...

Very interesting.........

You may need Luxeon driver....

Good idea...

I used to adapt light in car with luxeon. Car's volt is swing all time and I put LM317 for regulated out put for safe to luxeon.

Id like to see someone put in a Red or Red/Orange LuxIII for brake lights. Regulated on a nice copper HS of course!!!

PhotonFanatic has some Red LuxIII that are "G" flux bin, as good as most red-orange for output!! Only in a deeper more cherry red color...

VERY cool!

I think he'll be safe in this application, because the screw provides enough thermal mass (once attached to the car) to dissipate the heat. Even with his 24 ohm resistor, assuming voltage goes up to 15V, that'll push 488mA to the Luxeon. Remember that we don't start to freak out until the current goes above 1.5 AMPS /ubbthreads/images/graemlins/grin.gif

KevinL, but it's probably not screwed into anything, just the pins pushed into the plastic bulb socket, which is in plastic tail light housing... /ubbthreads/images/graemlins/tongue.gif

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IsaacHayes said:
KevinL, but it's probably not screwed into anything, just the pins pushed into the plastic bulb socket, which is in plastic tail light housing... /ubbthreads/images/graemlins/tongue.gif

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I could be wrong, but I would have to guess that the screw the luxeon is mounted to is steel. Steel is 1/4 of the thermal conductor that pure aluminum is. This shouldn't be too much of a problem as in most cases it wont be on for more than 10 seconds or so. I would avoid idling in reverse for whatever reason (waiting for someone to make a quick run into a store, etc).

Red_Robby:
I would suggest using a lab power supply to drive your LED in its current setup at 15v while monitoring the output with a lux meter or solar cell + multimeter to make sure the output doesn't drop too much after 2 minutes or so (indicating the LED may be overheating). If it drops more than 30%, I would say that LED is getting too hot IMHO.

-Ross

IsaacHayes - something like this?


* I did Take a voltage reading at the socket while the engine was running at 3000-4000RPM, the highest reading was 13.86V
* the lug is high grade aluminum (it's from a 600Amp switch)

* i picked the highest Vf luxeon i had( pulling 176 mA at 4.5 volts)
* I don't use reverse for more then a few minutes at a time anyway...i don't think the luxeon is going to get very hot.

I'd be more concerned with the LM317T overheating, I know....built in thermal protection, but I have rant hem at 1 amp and ended up with toasted LEDs for no aparent reason...

I'm not too worried about the LM317T, it ain't in there...
just a "fireproof" 24 ohm resistor.
for the short runtime this is going to get, i'm ok with the LED getting anywhere from 200mA-700mA, we do it with our lights all the time, and sometimes much worst...
and if it only lasts a month (I'm sure it will be much longer then that), who cares, i'll just throw another lonely lux in there, I've got too many sitting around doing nothing anyway.

Googling for "load dump cars" gives a few hits that
say the voltage can jump to 60V during a load dump
(big load on alternator being disconnected). The ones
I saw didn't say how long they last but the current
pulse through the LED might be enough to pop it.

Putting a capacitor across the LED may help by reducing
the spike to a lower but wider bump in current. (100 uF
would give you a 2.4 ms time constant. So narrower pulse
would be reduced but wider ones than 2.4 would still get
through.) If you can find the length of these load dump
spikes it is easy to pick a cap to filter it out.

Greg

Here's what I made for aux front turn lights (in the roobar) and aux brake lights (in the rear replacement bumper/towbar).

For the turn lights I used a pair of Osram (yellow - which actually are amber). For the brake lights I used a pair of Osram (amber - which are actually red). The Osrams I got from digikey and are only about $3.50 or so each - much cheaper than Luxeons.

I used one of my cc1w (350mA) constant current drivers.

Front (LED) view of the mod. The 'board' is some heavy copper clad PCB scrap. Note the 'slug' is active and must be isolated from the copper - I used a layer of AA epoxy.



Back (driver) view of the mod.



Both the turn and brake lights have the bulb oriented 'sideways' so that works great with the PCB scheme of having the LEDs face sideways.

The final result works great. The turn lights are definitely bright and fast compared to the stock incandescents. Ditto for the brake lights - they are bright and work well and 'light' quickly vs the incandescents.

george.

Oooh! One of my favorite subjects! Eventually I'll show what I've been working on... but for now, I'll just lurk. Continue on, please!

Got some info on this stuff for ya'll, including a demo video:

http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=UBB15&Number=845876

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NewBie said:
Got some info on this stuff for ya'll, including a demo video:

http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=UBB15&Number=845876

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Good stuff. Thanks jar. What makes the video tougher is that the tail lights start on, and brighten while the third light goes from dark to on.

red_robby: was 1 lux not bright enough, so now you built one with 2? [email protected]!! thats high vf!!! Not sure if 2 will be bright enough, well maybe with 700ma going to each one...

You gotta make some Red LuxIII brake bulbs next!! I'm surprised no one has marketed these yet... I guess it's still too new for them...

Cool stuff indeed.

georges80 - that's very cool!, i wish someone would market something like that...

IsaacHayes - that's a different bulb(1157), i took it out of the running/brake light socket to take the picture, that one has been going for almost two years without any problems.
I know there's a market for these bulbs, what's taking so long (maybe cost???)
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