How to: Interior Dome Light LED Conversion (PICs)

[FL.Cracker]

You guys should use a driver to power the led's to avoid over driving them and it will allow you to adjust the intensity. All you need is an LM317T from radioshack wired like this http://www.rog8811.com/laserdriver.htm Never mind the voltage figures they are specific for the application of particular laser diodes. The LM317t is capable of 30v+ and can easily handle regulating led's from a 12v+ input.

You do not need the capacitor and 1N4001 diode (reverse polarity protection) for this application. Simply take your 12v+ connect it to the IN on the chip. Then solder either a resistor, potentiometer or combo of the two between the out and adj. pins to set the amount of current that will be delivered to the led's. Then solder (or wire) the adj. pin to the led's + IN. Finally solder you - (ground) connection to the - IN of your led's.

You will need to wire the led's in parallel (+ to + and - to-) so that your current requirements increase but your forward voltage stays the same. you can use just about as many led's as you want the LM317T is capable of delivering up to 1.5amps and at most the average led only requires 15-25ma.

If your not going to use a potentiometer (25ohm pot should work fine) to adjust the output and your using a fixed resistor to save space or whatever you can calculate the output as follows:
LM317T ref. voltage=1.25v
Formula- ref. v. divided by the resistance = current output

So for one average led (say 20ma) do, 1.25v/60ohms=20.8ma
to drive 1 led @ 20ma use about a 60 ohm resistor.

So to drive say 10 led's @ 20.8ma each you would use a 6 ohm resistor for a total of 208ma.

If you are using a pot then just make sure to have it set to full resistance prior to powering. Then apply power, the output of led's should be very dim, slowly increase current by turning the pot and lowering the resistance until the desired output is achieved.

This really is the proper way to power an led, they are NOT like conventional bulbs and WILL die (or show signs of degrading ie. dimming) if they are over driven. I use these chips to power my very expensive (upward of $200 ea.) laser diodes and I can say that they are VERY reliable.

Give it a try! Let me know what you think.

 

[OneLever]

Thanks for the tip FL.Cracker. I've been using this +5 VDC from Radio Shack to drive my led arrays. I brought up this point in post #10 of this thread as well.

The point was made that this type of regulator was inefficient because all the excess voltage is shunted off as waste heat. However, I never got an explanation as to why waste heat from a voltage regulator should be considered worse than waste heat from a resistor.

Given the 2 V variance (12.4-14.4 V) of the electrical system on our vehicles I decided it was necessary to have a regulator in place. In addition, I use 0.25 A fast acting fuses, and high peak inverse voltage diodes in series with every led array. To catch any shorts that may occur, and to protect from the back EMF of the stock relay coils respectively. Any more wisdom you could share on these matters would be appreciated.

I would also like to thank MustangP51 for giving such a good walk through on this modification so long ago.

 

[FL.Cracker]

Its much better to have an IC getting hot versus a resistor, resistors don't have thermal shut down protection like the LM317t does. It may get quite hot but a resistor will catch fire while the ic will shut off.

It is important to note that you want to control current NOT voltage. I know that on the package the LM317t comes in it says "voltage regulator" but the chip can also be used as a current regulator in the previously mentioned configuration.

The waste heat is generated by the voltage difference between what the LM317t (or whatever ic you choose) sees and the forward voltage of the led's. For example if the forward v. (requred voltage to operate) of the led's is 3.5v and your ic is getting 12-14v minus the 3v drop of the ic itself leaves you with 5.5-7.5v that will be "sinked" (converted to heat) by the ic.

So your left with a few options.
1. Put a small aluminum or copper heat sink on the back of the chip.
2. Run the led's in series-parallel, meaning create a lower voltage difference by running two in series, connected parallel to another set of two in series like this:

this brings the voltage difference down to about 2-4v producing much less heat.
3. Use one LM317t in voltage regulation mode to bring the voltage down, then a second LM317T to control current.

I will try to do a short video soon showing the simplicity of this setup as well as temperature readings @ 12.5v and 14.5v in.

 

[AJizzle]

I know that I'm a little late to the party, but I'm starting this project this week. I just have one question to all that have done this so far, How in the world do you actually connect the cargo light?? I have a 99 exp that used a 211-2 bulb and now a positive and negative wire?! What now??

 

[blankskater1]

I dont know if anyone has said or done this yet, but the SMD 194 bulb fits in the middle dome light on the left and right sides. (The sides run by the switches). And the look great in there. Just a heads up so you can have a full LED dome light system.

And thanks for posting this, it turned out great. No problems at all!

 

[FIND]

Yeah, we all know about the plug and play LEDs. The point of doing it this way is that plug and play LEDs are junk.

 

[blankskater1]

Yeah, we all know about the plug and play LEDs. The point of doing it this way is that plug and play LEDs are junk.

I agree, I made my own for both fronts (left and right), the middle and the rear dome lights.

But this doesnt show how to do the middle left and right, so I used some extra SMD 194s from the cluster to fit in those spots and they look great.

Was just letting people know they fit because I wanted all my lights to be LED.

 

[MustangP51]

I agree, I made my own for both fronts (left and right), the middle and the rear dome lights.

But this doesnt show how to do the middle left and right, so I used some extra SMD 194s from the cluster to fit in those spots and they look great.

Was just letting people know they fit because I wanted all my lights to be LED.

I agree it looks great when they are all LEDs, but I got tired of the b**ching about the light being bad for putting on makeup in the car...... so the visor mirror lights and spot lights were changed back to incandescent bulbs. Dome lights reamin LEDs.

Just something you may want to know, that never in a million years dawned on me when originally did the project.

 

[blankskater1]

I agree it looks great when they are all LEDs, but I got tired of the b**ching about the light being bad for putting on makeup in the car...... so the visor mirror lights and spot lights were changed back to incandescent bulbs. Dome lights reamin LEDs.

Just something you may want to know, that never in a million years dawned on me when originally did the project.

I think the spot lights are brighter as LED...I didnt even think about the visor lights.

But these are great write ups man. Thanks again!

 

[blankskater1]

This is what I did.

 

[MustangP51]

I think the spot lights are brighter as LED...I didnt even think about the visor lights.

But these are great write ups man. Thanks again!

The LEDs were brighter, but apparently it just wasn't the right color, somehow the difference between 4100k and 4300k is too drastic of a difference to her.

 

[combatmedic10]

Not sure if the poster is still part of the group but how do you wire these in, you dont show a great pic of them actually wired in, would like to know how it is done.

 

[MustangP51]

Not sure if the poster is still part of the group but how do you wire these in, you dont show a great pic of them actually wired in, would like to know how it is done.

Front: Soldered into wiring harness
Mid: I made a connector that replicates the 194 bulb base to slide into the bulb socket in the overhead console

forgive the crudeness

the cargo area also just plugs into the socket in the back with the Male crimp connectors.

 

[EXPLODRR]

red led 194s

from superbrightled.com
and more micro dot led reds to put in various locations inside.

 

[willzilla]

^ Thanks for the write-up... I just did my front map light/overhead console with red LED's... Though I was lazy and just bought 2 10 LED discs already with everything in place and installed those and soldered them up. Little less work but cost about $8 each 10 LED disc

Did a partial write-up in my build thread.

Going to do the mid console and hatch next using your guide as a basis! Thanks!

 

[littlebro294]

If possible, I'm not sure if someone has already done a thread doing step by step, but i have tried to stay away from wiring. I like this idea a lot better than my direct plug in LED's and would like to give this a shot but I'm not sure exactly on how to solder, what bulbs to look for and how these actually plug in. If there is a thread, can anyone direct me to it so i can learn a little bit about this before I try this project?

 

[MustangP51]

If possible, I'm not sure if someone has already done a thread doing step by step, but i have tried to stay away from wiring. I like this idea a lot better than my direct plug in LED's and would like to give this a shot but I'm not sure exactly on how to solder, what bulbs to look for and how these actually plug in. If there is a thread, can anyone direct me to it so i can learn a little bit about this before I try this project?

Best thing to do is go by a cheap 20 to 40 watt soldering iron, a spool of solder, and practice soldering some scrap wire together. I'm sure there are dozens of tutorials on soldering on google/youtube.

 

[willzilla]

I made a write up on this a while back... May be of some help

http://www.explorerforum.com/forums/showthread.php?t=387684