Saturday, January 1, 2011

3$ LED Map Light Replacement

I needed to replace the map light lamp in my car this afternoon and I thought I would go for LED replacement bulbs.  The original incandescent bulb's orange glow looks dingy anyway and the last few times I needed to see by way of the map light it seemed rather dim.  I figured the local auto parts store would be teeming with LED's as it seems all of the futuristic cars nowadays are jamb packed with the things.  This, however, turned out not to be the case.  According to the worker at the parts shop, LED's are "high performance" parts and as such, must be custom ordered.  I was also told that "the internet has them".  Neat. Too bad "the internet" thinks LED replacement bulbs are more valuable than McDonald's orange juice.

Not to be out done, I walked to the dollar store next door to the auto parts shop, where I found these beauties for 1$ each.  A Trisonic 3 LED Push Light; batteries not included.  I bought three, driver/passenger map light and cargo area hence, the $3.  In case you were wondering, the text on the bottom front says "To uplift our character, begin with cultivating peace in mind, body, family, and activity.".




And on the back, the text "Cultivate a big heart-but a small ego", let me know these were the right bit of kit for the job because, that is exactly what I was trying to do.  No, this project wasn't "X to the Z" pimping any rides.  And, my car is neither empirically "faster" nor, objectively, more "furious" because of this upgrade.  Just humble LED's helping electrons change orbitals to emit photons for me to read maps by.


I wanted to verify the light worked as intended and would be bright enough first, before ripping it to pieces.






This is what I found inside.  3 LED's, a switch and a single resistor.




And just what do we have here?  The good people of Trisonic have designed their circuit to have the LED's in parallel.  This works for the design specifications of the product they made but it is not helpful to me so I first desoldered all of the components.  Then, I cut through two of the PCB traces to allow me to solder the LED's back in place in series instead of parallel.


Before


While the LED's were desoldered from the board I wired one of them up to a 9v battery through a 1k0 resistor.  Measuring the voltage across the LED I got a forward voltage Vf=2.8v.  Previously, I had measured the current of all three LED's together to be 130mA before taking this thing apart so, I know each LED can handle at least ~43mA.  To select my current limiting resistor for the series LED's I have ((14vBatt-(2.8*3))/40mA = 140R or standard value 150R for 37mA.  Power dissipation 0.207W so, a 1/4 Watt resistor is fine.

Here, Vbatt = 14v because the car's 12v system operates around 13v with the car running at idle and peaks up to ~14v when the RPM of the alternator increases.  14v is kind of a design for "worst case" scenario with lower battery voltages resulting in LED operation towards safer limits. 

Here you can see the LED's soldered in the new series configuration and current limiting resistor in place.  In series, the LED's are hooked up anode to cathode of each other with a current limiting resistor on one end, the negative side of 12v in my case.


After



Here you can see the LED PCB hot glued into place in the light reflector housing.  You can also see the PCB traces I cut to allow the parallel/series modification.  The +/- 12v (nominal) power leads on the LED board are soldered to the wires that used to deliver battery voltage to the incandescent bulb.  The connector for the original lamp was left in place electrically and solder joints were insulated against short circuits.





A side by side comparison shows the difference in color of the LED's on the left and the incandescent bulb on the right.  The LED's are equally as bright and diffuse quite well so there is no "hot spot" of light.  I will perform the same LED retrofit to the right side of the light housing next.




This was a fun afternoon project and I am pleased with the results.  Average prices for ready made LED replacement bulbs for this style holder seem to be $15 x 3 lights = $45.  The method outlined above came in at ~$3 total. 


12 comments:

Doug said...

Awesome. Wouldn't it be neat if all peripherals ran off of USB ports, so even something like this would be easy to mix and match, instead of having to de-solder and solder. I'm all for steel interiors and just use magnets to mount stuff wherever you want to put it, with USB ports here and there.

Jeff Wooding said...

This just what I was thinking of cause I've been a rental for 2 months a Lincolcn MKS And deciding how I could Mod my lights in my Navigator to LEDS and add AUX input jack of course all to look as factory.

Thanks thats one off my list!

keter-magick said...

The hot glue will melt in a hot car. Just sayin'. ;o)

Very clever, otherwise.

Pete said...

@keter-magick

According to wikipedia High temperature glue guns melt adhesive at 380F.
http://en.wikipedia.org/wiki/Hot-melt_adhesive

According to weather.com car interior temperatures reach temperatures far exceeding ambient. In this case 138F after 90 minutes in 90F outside temp.
http://www.weather.com/newscenter/specialtopics/slideshows/hotcar061909.html?page=5&scheme=image-horiz-plain.css

Although weather.com doesn't state any details on their test procedure I can assume this is approximately correct. I recall reading in the past that interior car temperatures in direct sunlight such as a dash board being just under 200F on a "hot day".

Even so, 200F < 380F.

Aaron said...

Good catch on the hot glue - Use construction adhesive instead.

Steven said...

...Or you could just go to http://www.superbrightleds.com and buy LED bulbs?

Jerry said...

Follow Steven's advice and his link to LED bulbs. No overpriced $15 each deals here. Straightforward stuff and LED replacement bulbs that seem to be little more (some less?) than standard bulbs. No de-solder, re-solder stuff. Just pull the old bulb and put in the new one.

Random Musings said...

another source of led lights
http://www.dealextreme.com/products.dx/category.712

slow shipping but cheap prices

Dennis said...

I used hot glue with a project in my car once. I came back one day to a gooey mess the consistency of cold molasses. I didn't think it would melt either, but unlike a true solid the melting point isn't fixed. It just starts to flow slowly at warmer temps.

Rob said...

any moron can buy his way to a solution (no offense intended to anyone), but Pete used creativity and knowledge to re-use a cheap light into his vehicle. I have a bunch of those tap lights that have worn out their batteries and like Pete's solution. Much more fun than buying it (even if it's cheap).

Pete, can you show a pic of the solder side after wired in series please.

iyeee, the 12voltgod said...

As an old time stereo installer from the hot hot San Joaquin Valley, I can tell you hot glue works fine in a car interior... But you must use the high temperature variety... The standard craft stuff will melt.

Mike Fredricks said...

Some of the smaller automotive exterior accessories make a difference in your car's appearance almost as much as the large ticket items.