Luxeon Dome light

[mccavazos]

I was looking at the pitiful yellow tint of the dome light in my truck, and I got an Idea. I have seen several dome light mod kits for cars, but they all seem overly complicated. Could I take a downboy probably 917 or 1000, and heat sink the Star and driver to a piece of aluminum and hook it directly into the car power lines for the bulb? I think that a down bow is rated at 16V maximum. My dome light is never on for very long.

 

[red_robby]

a cheaper route wouls be a resistor, you don't really need the regulation of a downboy...
i've got the same in my dome light, been there for over a year with no problems. just make sure you get the proper power rated resistor, not just the ohm value.

 

[mccavazos]

What value resistor are you using? I can get power resistors quite easily.

 

[VidPro]

put 3 in, and the resister
nothing better for reistance than a resister that puts out Light
i use 4x luxIIIs in my car, that way they can cope with a myriad of voltages and still work. and when the battery is almost dead, they dont draw much power.

but the same idea would work (better) to use 2 or 3 then resistance adding in to balance the possible voltages it will be hit with.

if you want 100% the SAME exact output though, your going to want a driver.
because what were replacing is often 5-15-30watts depending on the dome light, its important to have 3-5-9 watts of lux, to be at LEAST as bright with power savings, and long life too.

i calculate the cost of a driver, divide by the costs of the led, and end up with more leds , instead of a driver. but that is just me, and more often a driver would be better, but i also calculate the LIFE of it, if its underdriven, so its ALL relative as usual.

 

[modamag]

Here's another solution.

2-3 LuxI (or LuxIII) in series connected to a current source LM317 with a 3.3 Ohms sense resistor for a cool 380mA drive. Here's the schematic

3x LuxIII ... $24.00
1x LM317 ... $1.25
1x 3.3 Ohms 2W resistor ... $0.14
Total cost ... $25.39

 

[reefphilic]

I've built one with 2X5W white and 1X5W RB using LM317 as a current regulator. With a switch to select either 5W white, 10W white or 5W RB.

I would recommend the LM317 route instead of just a resistor. Automotive electrical systems are subjected to voltage spikes and load dumps etc. that can damage LEDs. The previous dome light and third brake light that I've diy using 5mm LEDs start diming/burnt after using for only a few months. So are many LED third brake lights I've seen on the road.

A LM317 solution will give constant brightness unlike resistored solution which will start "flashing" when you turn on the turn signal/hazard lights.

 

[IsaacHayes]

I built one a while back. It has 1 Royal Blue 3W emitter, and one 1W White star. I used a LM317 AA'ed onto an aluminum plate, along with the star and emitter. I built a switch for 2 levels of output, low and high. The thinking was on low I could have the Royal Blue on while I drive to cast a nice glow, but alas, it was still too bright at ~200ma. Full power they both get ~890ma, so the 1W is quite overdriven. The white looks brighter than the stock light was, and whiter of course. It's a Q2K. The royal blue is super bright, and a real attention getter. What's cool is just 1 RB lux3 is way brighter than any Car Neons I've had, and it is hidden in the dome light!!!

Yes the plate gets scorching hot, and yes probably really hot for the luxeons, but they'll last plenty. My domelight will shut off after 15mins even if left on so no worries about the battery. The ciruit is inefficent, but cheap! And it keeps constant brightness since it regulates.

What's weird is I can detect a slight strobe when the car is not running, like 70hz or so. But turn on the car and it is steady light... WHY IS THIS? It's not really noticible, but weird!!!

Click here for my post. I don't have pictures of the actual unit that was finished, since the floppy that had the pics on it was dropped or corrupted somehow /ubbthreads/images/graemlins/frown.gif

red_robby: only 1 lux and 1 resistor? what value?
I've found 5mm led's resistored down on car voltage to be dim enough for indicator lights don't change with voltage changes in the car. Unless my blinkers don't make my voltage dip, which I know is the case because I have a volt meter and it's rock solid now.

 

[IsaacHayes]

You could get a 1.5 ohm wirewould resistor 3-5w and my circuit to get ~ 890ma to the luxeons. Wire more than one in series and you'll have a more efficient setup that wastes lss power as heat.

I'd say 1.5ohm wired to the LM 317 (one brightness level) and 2 LuxIII White's would be plenty bright!!!

 

[modamag]

Isaac, U luver U.
I like that mood lighting. /ubbthreads/images/graemlins/happy14.gif

 

[IsaacHayes]

Heheh. Girls do comment on the blue light. They really like it /ubbthreads/images/graemlins/smile.gif

 

[evan9162]

Issac,

The strobing is probably from the '317 oscillating. Add an input capactitor (like 10uF) right at the '317 terminals, and you will probably see the strobing go away.

 

[IsaacHayes]

evan, it doesn't bother me enough to filter it with a cap. But I was just amazed that I could see it. So does it not regulate linearly but pulsed or something? I don't get why it oscillates. If so I'm surprised it's at a frequnecy low enough for me to see. Then again I can tell a monitor running 75hz vs 85hz, and 60hz gives me a headache! I can hear and see frequencies much higher that most normal people.

 

[red_robby]

[ QUOTE ]
mccavazos said:
What value resistor are you using? I can get power resistors quite easily.

[/ QUOTE ]
i don't remember the exact value, probably 25-28 ohms
one LS was more then enough light for me...
if i need more light then that then i go for my EDC /ubbthreads/images/graemlins/grin.gif

 

[evan9162]

[ QUOTE ]
IsaacHayes said:
evan, it doesn't bother me enough to filter it with a cap. But I was just amazed that I could see it. So does it not regulate linearly but pulsed or something? I don't get why it oscillates. If so I'm surprised it's at a frequnecy low enough for me to see. Then again I can tell a monitor running 75hz vs 85hz, and 60hz gives me a headache! I can hear and see frequencies much higher that most normal people.

[/ QUOTE ]

Issac,

It does regulate linearly, but given certian conditions, the circuit will become unstable, and will begin to oscillate. I've seen it more often with some of the LDO cousins to the '317 (like the 1585/1587), where you absolutely must have an input cap or the circuit oscillates.

Oscillation can be dangerous - I had an LM350 go on me, it ended up pushing a full 3A through a luxeon for me, even though it was set up to limit current to 1A. Doug Owen said that it could have been oscillation that caused it, since I didn't have any input caps on my current supply, and there often wasn't a load either - He's seen oscillation destroy LM317/338/350 regulators, to where the fail wide-open (like my '350 did). So adding some input capacitance might be a good idea for that case as well.

One more thing you might consider to make your dome light bulletproof would be to put a 1N4002 diode in series with the circuit, to prevent negative spikes from hurting your setup. Newbie has seen -40V spikes in car electrical systems, especially during load dumps after starting.

Auto power systems are a very hostile environment.

 

[mccavazos]

[ QUOTE ]
red_robby said:
[ QUOTE ]
mccavazos said:
What value resistor are you using? I can get power resistors quite easily.

[/ QUOTE ]
i don't remember the exact value, probably 25-28 ohms
one LS was more then enough light for me...
if i need more light then that then i go for my EDC /ubbthreads/images/graemlins/grin.gif

[/ QUOTE ]

I have an SX1K sitting around, thats what I was thinking about using. I belive that I will go with the regulator. Thanks everyone.

 

[IsaacHayes]

Evan, thanks good info. Yes car 12v systems have lots of noise, not just from the alternator in the system. Makes you wonder how high end stereo's and the cars ECU stay alive!

 

[UncleFester]

[ QUOTE ]
mccavazos said:
I was looking at the pitiful yellow tint of the dome light in my truck, and I got an Idea. I have seen several dome light mod kits for cars, but they all seem overly complicated. Could I take a downboy probably 917 or 1000, and heat sink the Star and driver to a piece of aluminum and hook it directly into the car power lines for the bulb? I think that a down bow is rated at 16V maximum. My dome light is never on for very long.

[/ QUOTE ]

Check this out if you're interested in a Luxeon dome light.