Elly LED's in dome light

[Hellbore]

Well, I had 4 of the LED stars that came in the Elly flashlights, didn't know what to do with them.

I checked and for whatever reason, the bulb socket of my dome light only sees 11 volts. There must be something in there that reduces the voltage or something.

So, I removed the dome light module and mounted the 4 stars inside the housing behind the diffuser. I wired them in 2 separate circuits, each with 2 LED's in series with a 10 ohm 1 watt resistor.

The LED resistor calculator I used said I should use a 13 ohm resistor to run the LED's at 350 mAh... Unfortunately, they didn't have 13 ohm, or 3 ohm, or 1 ohm, or anything smaller than 10 ohms at the local Radio Shack. I figured for now I would just use 10 ohms and add 3 ohms later or something like that.

So from what I figure, i'm running the LED's at 450 mAh, which is probably too high... right?

Anyway, it's crazy bright, really lights up the cabin better than the stock light! The light is more blue than I would like but what can ya do. Anyway...

Then in the back there is a tiny cargo light, I replaced that guy with a Luxeon 1 + 20 ohm resistor. Again it is brighter than the original bulb. The original bulb was a piece of crap.

So anyway, I'm really happy with how it looks, but the LED's get hot to the touch. That wasn't a surprise, but what DID surprise me was that the two 10-ohm resistors I have wired to the 2 pairs of LED's get REALLY hot! Those resistors get hot enough to burn my fingers.

Is that normal? Did I need to use larger resistors or something? Or is it OK for them to get hot like that as long as I don't let them touch and melt other things?

Any advice?

I could get one of those Tasklight driver boards and stick it in there if things don't seem to be working out the way things are.

At any rate, it's plenty bright, WOW it really lights up my car... A lot more than the original bulb did!

 

[carbine15]

it shouldn't get that hot. YOu need higher watt rated resistors or double up or quadrupple up with 4 x 80 ohm in parallel for more heat discipation capacity.

 

[Hellbore]

Well they are 1 watt rated resistors, I thought that was enough, what kind of resistors should I use?

 

[Norm]

Wire all 4 in series and you won't need to drop so much volatage across your resistor.
Norm

 

[Hellbore]

Wire all 4 in series and you won't need to drop so much volatage across your resistor.
Norm

Well... if I do that, there's a bit of a problem.

I believe the Vf of these LED is about 3.3 volts. 3.3 * 4 = 13.2 volts. The light fixture only supplies about 11 volts when the engine isn't running. Isn't that a problem? The LED resistance calculator said the total supply voltage needs to be higher than the combined Vf of the series LED's.

I think even with the engine running I only got about 13 volts at the fixture. Even though my battery reads 12.5 volts at the battery. The fixture seems to have some internal something or other going on in the switch.

 

[carbine15]

I think you need a 4 watt resistor since each LED is capable of pulling one watt. I'm probably wrong about this. so disregard. I think automotive aplications usually pull anywhere from 5 to 20 amps.. at 12-14 volts that's a hell of a lot of watts. At least 60.

 

[Hellbore]

Well my problem is, when a resistor is rated for a certain wattage, I don't know what that is referring to, so I dunno, I think I need to do some reading.

 

[2xTrinity]

Well my problem is, when a resistor is rated for a certain wattage, I don't know what that is referring to, so I dunno, I think I need to do some reading.

The amount of wattage being consumed in the resistor is equal to the current squared times the resistance. You are driving .450 amps through a reistance of 10 ohms. (0.45^2)*10 is equal to about 2 watts, or double what those resistors are rated for.

I believe the Vf of these LED is about 3.3 volts. 3.3 * 4 = 13.2 volts. The light fixture only supplies about 11 volts when the engine isn't running. Isn't that a problem? The LED resistance calculator said the total supply voltage needs to be higher than the combined Vf of the series LED's.

I think you'd be better off running just three of your LEDs in one string rather than two strings of two.

 

[Hellbore]

The amount of wattage being consumed in the resistor is equal to the current squared times the resistance. You are driving .450 amps through a reistance of 10 ohms. (0.45^2)*10 is equal to about 2 watts, or double what those resistors are rated for.


I think you'd be better off running just three of your LEDs in one string rather than two strings of two.

But that wouldn't be as bright, right?

Thanks for the help. I'm going to get some 2 watt resistors... That sucks that I'm throwing away 4 watts in the form of heat, out the resistors

I bet this is one reason people by far prefer a driver board over resistors...

 

[Meduza]

yep i think you are much better out running them three in series with two 10ohm resistors in paralell, that would work out to about 250ma per led and should let the heat be quite manageble too even if not as bright as your current setup, if it not is bright enough you can allways put another 10ohm resistor in paralell and through that increase the current.

 

[2xTrinity]

yep i think you are much better out running them three in series with two 10ohm resistors in paralell, that would work out to about 250ma per led and should let the heat be quite manageble too even if not as bright as your current setup, if it not is bright enough you can allways put another 10ohm resistor in paralell and through that increase the current.

Agreed, this is a good way to do it. You can at least get the setup running with your current parts, and if you need more power, just buy a third resistor, wire it in parallel, and that will drop the resistance a bit more. You'll also consume far less power in the resistors with the setup described above -- under half a watt as opposed to 4 watts.

Anyway, I've been thinking of doing this exact thing myself. I'm upgrading a few of my old Luxeon flashlights to Cree, and thinking about using those in my car. I could use the Elly LEDs as well for that. What does your current rig look like when it's on, do you have any photos?

 

[mchlwise]

Where's the "this thread is worthless without pics" smiley?

:shrug:

 

[Hellbore]

You guys are so smart! Thanks for the advice!

I re-did my install the way you guys suggested, 3 LED's in series with the 2 parallel 10 ohm resistors for about 5 ohms.

However, I made a change... I had 2 Cree XR-E emitters that I didn't know what to do with, and I have an SSC P4 emitter on its way to put in my MagLED module...

So, I removed the Luxeon III from my MagLed, and used it with 2 Cree emitters for my dome light, then I used the 3 Cree LED's in series with the same resistor setup, for my rear cargo bay light!

It's freakin awesome, these Cree put out beautiful light! The light color is amazing, WAY WAY better than with the chinese LED's.

BUT the other cool thing is, the chinese LED's are putting out much better light now too! It was extremely blue light before, but now it's pretty good. I think that I was overdriving them far too much and that was causing the color to shift. Does that sound right? Anyway, now they are getting close to the amperage they were getting in the Elly lights they came from. Look MUCH better, plus, now my cargo area has some light. I would rather have the dimmer Chinese ones back there and the good Crees and Lux in the main dome light

I will post pics in like 5 minutes, I'm taking some pics to show you.

To reiterate, I did as you guys suggested, but same thing on both the dome light and the cargo light: 3 LED's in series with 2 parallel 10 ohm 1 watt resistors as the current limiter.

Pics in a minute...

Edit: I also just noticed, after the light has been on a few minutes, the Cree and Luxeon III LED's aren't even hot to the touch! They are barely warm. I think this is a MUCH better sign for their lifespan! The way I originally set it up, the Chinese LED's got so hot after a minute or so that they would burn my fingers! Also, I wasn't going to admit this, but one of them burned out already :O Now, with the new setup, the Cree and Luxeon LED's barely get warm, and the Chinese LED's in the back cargo bay get a little warm but no more so than in my flashlights, definitely not burn-your-finger heat like before.

 

[2xTrinity]

BUT the other cool thing is, the chinese LED's are putting out much better light now too! It was extremely blue light before, but now it's pretty good. I think that I was overdriving them far too much and that was causing the color to shift. Does that sound right? Anyway, now they are getting close to the amperage they were getting in the Elly lights they came from. Look MUCH better, plus, now my cargo area has some light. I would rather have the dimmer Chinese ones back there and the good Crees and Lux in the main dome light

I noticed the same thing myself in that the one Elly of mine that was dimmer than the others was also "whiter". I think they didn't use enough phosphor so what happens is once you drive the Chinese LEDs past a certain point, you just get more and more blue as the phosphor is already giving off its max output.

 

[Hellbore]

OK here are the pics!

This is the rear cargo area light. You can see I used a sort of unconventional mounting arrangement, but I couldn't think of any better way. Hopefully heat won't be a problem. So far it doesn't seem to get very hot.

This is the dome light without the diffusser lens on it. For the heat sink I used a sheet of brass that I happened to have lying around. I realize this is probably not ideal, you'll probably tell me copper or aluminum is better or something, but this is what I had and I couldn't wait any longer to do the mod So far it seems to dissipate the heat fine though, after the LED's have been on a few minutes, if I touch them they don't feel hot, and the metal sheet gets warm. So, I think it's working fine as a heatsink, let me know if this looks like a problem though. The thermal epoxy I used is Arctic Alumina. Also, I think the brass reflects at least some of the light, and might possibly make the tone a little bit because of its color? You might notice I also glued on a strip of brass at an angle down by the buttons, in hopes of reflecting light that goes that direction, so it wouldn't get wasted inside the guts of the light switch.

This is a picture of the fixture mounted and turned on. Couldn't get a good picture, I guess there's too much difference in brightness or whatever that's why the surrounding area is black. You can see the funky golden look the light has. It's my bling bling light LOL.

This is a picture from the passenger seat looking back at the rear seat which is full of junk. This digital camera is kinda old so it needs a LOT of light otherwise the shutter speed is slow, so a couple of these pics came out blurry if I didn't hold the camera steady enough. It is definitely brighter than with the stock bayonet (right?) base light bulb I had.

Another blurry pic, yay. You can see the sweet golden glow of the dome light. You can also see my stupid neighbor's house, bathed in the beautiful sickly yellow/orange of a sodium vapor street lamp. Yuck huh. My light has much nicer color.

This is a shot of the rear cargo bay light. Look at those Chinese LED's shine! Whoo-ee! They are still blue compared to the Cree and Lux but WAY whiter now than before, I was pushing the poor things at about 450 mA before now they are getting more like 225, they seem to like that a LOT better.

Just a crappy closeup of the back of my seat and the rubber cargo mat to give you an idea of the amount of light / color / quality of the rear cargo area light. Not as impressive as the dome light turned out but still very useable light and significantly brighter than the tiny bulb that was originally there.

I do wish now that I had taken pictures of the lights with their original bulbs, so you could see how much brighter everything is now.

Anyway, what do you guys think of it?

 

[lightbug]

:goodjob: well done!

 

[Hellbore]

I was also thinking that in the future I could get a TaskLED driver to drive these guys. It says it will drive up to 3 LED's in series at 350 mA. That would be perfect for the Cree / Luxeon dome light, maybe a little too much for the Elly LED's.

 

[Newuser01]

Come over and do my car now!

Nice.

 

[Hellbore]

Come over and do my car now!

OK, but you gotta spring for the beers! :drunk: And the emitters! :candle:

Hey, I figure if I'm really an LED nut, I should have LED's in the machines I use the most on a day-to-day basis... My PC already has LED's, so that leaves my car

 

[mchlwise]

:wow: :kewlpics: