DIY LED Dome Light (updated 9-15-09)

My little Honda Del Sol was in need of a brighter dome light. I went from regular bulb to a manufactured LED replacement to finally one high brightness one that I can even read with.

Step 1 Bit of Caution

These LEDs do get HOT. Normal opening and closing the doors do not allow the LEDs to get very hot. Just do not do what I did and leave the car door open for several hours. The hot glue and epoxy melted into the lense of the dome light and the LEDs got heat damaged. They still are bright, but not as strong as they where.

Comments

[opliko]

I would like to add that most modern cars use 13.4 volts, not 12, so make your own calculations accordingly. That is of course from a fresh battery. I find it easier to over estimate the cars' power than under, it makes it a little safer and your light will last longer!

[indivara]

I tried replacing the dome light in my car (also a Honda) with LEDs, but instead of making it myself, I bought a ready-made one (3 x 3 grid, same as yours). Unfortunately, it refused to light up in the winter, probably couldn't stand the low temperature.

You should probably consider including the schematic diagram, will make it easier to understand the wiring. The one below, I created using the freeware version of Eagle (use it if you like...)
http://www.cadsoft.de/index.htm

How did you calculate the resistor values? What is the forward voltage drop of the LEDs you've recommended? The seller on ebay doesn't say.
Since you've used a 22 ohm resistor with three 100mA LEDs in series, that would make 2.2V across the resistor, leaving 9.8V (12 - 2.2) across all 3 LEDs, making it around 3.25V (9.8 / 3) for each LED.

How good was the heat dissipation once you hot-glued all the components? Wasn't there any overheating of the LEDs?

[Rob K]

Thanks for the advice. I will put the schematic up.

The 22 ohm value I got from http://led.linear1.org/led.wiz using 3 LEDs at 3.4fV,100mA at 12v. Using 3.6fV the resister value was at 12 ohms. For some reason I had a few left over 22 ohm resisters from another project. I used them for this project.

As for the the LEDs over heating. I had used a 14vDC wall wart. This made the hot glue over the pins start to melt and get squishy almost instantly within 2-3 seconds. Using the right voltage 12v and the cars 12v makes the LEDs warm but not too warm to cause a problem. The regular filament bulb was warmer then the LEDs.

[indivara]

Cool site! Even gives the schematic!

[JakeTobak]

You might want to do the testing before you put on the hot glue.

[blakkat]

You're right Jake Tobak. Nice instructable.