Will a Luxeon fry my Car's Dome light circuitry??

Will a Luxeon fry my Car\'s Dome light circuitry??

I want to modify a spare domelight cover for my car that will plug into the original bulb holder and contain 2 luxeons. A Royal Blue and a normal White. It will have a switch on the outside of the cover for White/Blue/ & Off since my car will always turn it on when you open the doors no matter what.

The thing is, my dome light is run by a circuitry controled box, that dims light until it goes out much like a theatre when you close the door. (it doesn't go out instantly with the door switch). I know incandecents eat a lot of juice but I don't know what Watt the dome light is... Will it handle a 1W luxeon with a resistor?
I will be using a resistor instead of a voltage regulator becuase I want to keep the dimming effect and a regulator would keep it bright for too long. The resistor will probably keep it glowing/dimming for a longer time too as I belive it uses a capacitor to slowly dim out the lights...

So do I have to worry or is the interior lights of a car a lot more draw than a 1W luxeon? /ubbthreads/images/graemlins/confused.gif Also should I go with a HD or a LD? (no optics)

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

You should make sure that you have a good heat sink and that the resistor will allow you to drop the 12V that your circuitry is supplying. Verify your forward voltage of your Luxeons so you can properly adjust the resistance for optimal brightness.

If you have seriously deep pockets and a desire for sincere amounts of light, you will use three Luxeon in series. Dropping the remaining voltage will be much less of a problem, and the resulting light will perfectly explain the sunglasses you are wearing.

If your Kung Fu is strong, you will build in a potentiometer so you can dial up your brightness.

One last thing, there is no such thing as a heat sink that is too large.

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

You should check the current your original dome light draws, and figure the wattage from that.

Wattage = current x voltage.

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

It's been a while since I took eletronics class. What are the ways to measure vF and current draw using a multi meter?
I feel dumb asking /ubbthreads/images/graemlins/ohgeez.gif

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

Check this guy out.

http://www.geocities.com/george_tlc/led.html

Replacing all of his Land Cruiser Lights with LED's

Selling kits too.

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

[ QUOTE ]
IsaacHayes said:
What are the ways to measure vF and current draw using a multi meter?

[/ QUOTE ]

Well, you would only measure Vf on a diode.
But you would measure the voltage drop on a bulb, by putting the meter in parallel with the bulb, with the meter in V DC mode. (unless of course, you're measuring AC)
You would measure current by putting the meter in series with the bulb, with the meter in Amps mode. (and make sure those leads are in the right sockets on the meter.) Of course, you have to open the circuit somewhere to put the meter in series with the bulb.

How to drive a DMM

[ QUOTE ]
IsaacHayes said:
It's been a while since I took eletronics class. What are the ways to measure vF and current draw using a multi meter?
I feel dumb asking /ubbthreads/images/graemlins/ohgeez.gif

[/ QUOTE ]

Pony pucky about asking 'dumb' questions. All honest questions are equally valid, sometimes the answers can be a bit wide of the mark.....

To measure current we need to put the meter in series (so the current has to actually flow through the meter). This is easily done in most cases. Typical DMMs have a high DC Amp range, we want 10 Amps or so, which almost always involves moving the positive lead to a different hole in the meter face (usually right next to the correct switch position). Pull one side of the (cartridge style) bulb up and while pressing one end into it's clip, stab the free contact on the other end of the bulb with one meter lead. Then stab the open socket contact with the other lead. Now (if the door's open), the current can flow again, this time through the meter (and getting measured in the process). Screw or bayonet base bulbs are a bit trickier. Pull the bulb. Stab one lead into the bottom of the socket, you can insulate it from the walls of the socket with a strip of paper wrapped around the tip of the meter lead if you're not all that steady. This is important as a "short circuit" between the hot side of the socket and the wall by the probe tip would pass a very large current (Hopefully only an annoying, very hard to reach, expensive fuse will pay the ultimate price should you slip). Now brace the bulb body against ground (the car frame, perhaps the outside of the socket?) with your little finger and stab the contact on the end. Again, the current flows through the meter leads and body to complete the circuit.

A simpler way might be to just take the bulb and meter under the hood and use the battery. One lead on the positive, one side of the bulb on ground, other meter lead on the free side of the bulb. I bet about an Amp? That is say twice as bright as a nightlight?

Anyway, Vf, as another poster said, is measured across the LED (when it's on). The leads go in the 'normal' holes, we want 10 or so DC Volts selected, one probe on each side of the LED (or any other part we want to know the voltage drop across). Since voltage is electrical pressure (as opposed to current, which is a flow rate, like current in a river) we need to sample each side to determine the difference in electrical pressure (voltage) present

Therefore, the rule:

Current meters in series (circuit is broken, current goes through),
Volt meters in parallel (measured across a part of a working circuit).

In each case, polarity is assumed to not be important as we're using an auto polarity DMM, otherwise the red lead goes to the more positive side..


Cheers.

Doug Owen

Re: How to drive a DMM

Yeah I realized how easy to measure current draw of the stock bulb was after I posted. The only real thing I was fuzzy on was finding out vF on unmarked Luxeons. I belive my multi meter has a postive side as It can tell polarity. Anyways I remeber what prongs to put where, thats good. /ubbthreads/images/graemlins/smile.gif I took an electronics class in High school and finished everything 2 weeks before everyone else and did homework the rest of the time. It was too easy. But alas I forgot a lot of stuff.

What do you recomend to test the vF of a LS? Run 3 batteries in series (not car batteries!) and measure their voltage, then put the LS and a 10ohm resitor and measure the voltage drop over the LS and then use ohm's law?

Oh and one more question. Will as single 1W white Luxeon be as bright as the singe dome light bulb? It's one that is held in with 2 wire loops if that makes any difference. I have no idea on the wattage (yet).

Re: Will a Luxeon fry my Car\'s Dome light circuitry??

If you want to use a driver, George's boards are fantastic. Check out what I did: My Rav Dome (I have since added MUCH more heat-sink.)

A single emitter has replaced the 9W bulb that was there. I have more light at approximately 1/9th the wattage. I REALLY like this setup. I have now replaced several domelights in the cars I own.

Re: How to drive a DMM

[ QUOTE ]
IsaacHayes said:

What do you recommend to test the vF of a LS? Run 3 batteries in series (not car batteries!) and measure their voltage, then put the LS and a 10ohm resitor and measure the voltage drop over the LS and then use ohm's law?


[/ QUOTE ]

First off, you only need to be 'close enough for jazz' on Vf, within say a few tenths of a Volt, 10% or so. You can safely assume 'about the average' listed in the specs for the series, 3.42 Volts according to the maker (a generally good guy to trust, at least at first).

If you really want to measure it, you need to set up the actual working current. Assuming you want full power (and who doesn't?), let's go for 350 mA and assume say 15 Volts as a 'worst case' voltage in the car. 15 less 3.4 leaves 11.6 Volts 'across the resistor'. Dividing this by .35 Amps gives us 33 ohms (ten would be over an Amp, probably letting the 'magic smoke' out of the Luxeon). This resistor will have to dissipate 11.6 Volts times .35 Amps, or 4 Watts or so. Actual values a bit higher will improve margins. You can easily clip lead the resistor and LED directly across the car battery to test it. A few seconds run time won't heat the LED too much (assuming it's the Star version), more than long enough to actually measure Vf directly across the device when lit.

After you verify that the current dome light current (I love that pun....) is at least .35 Amps, you can probably just 'plug and play' with say 35 or 40 ohms at five
Watts.

Cheers.

Doug Owen

Re: How to drive a DMM

Darell: I don't want to use drivers or regulators due to the way my dome light fades out would cause it to just stay bright too long after it shuts off.

9W eh? Hmm I could possibly get away with 2 5W'ers if I wanted to hehe. I think it's just a capacitor on a timer that does the dome light fade. It doesn't fade right away, you hear a slight click then it fades out. God 10W of LS light would be bright!!

Doug, thanks for the pointers.