Anyone ever try the LCD bulbs? - PeachParts Mercedes-Benz Forum

the tenor man · #1 10-27-2006, 10:47 AM

Fellow Diesellors,

My 1987 300D Turbo cluster lights are so dim, I can barely see the gauges at night. I've tried cleaning and replacing the bulbs. The old 260E's lights were really bright. Anyone out there ever try replacing the bulbs with a couple of LCDs. I know that they don't get very hot so melting of the plastic would not be an issue....

The Tenor Man

Kynetx · #2 10-27-2006, 10:53 AM

You mean LEDs? It's possible, but a little more complex. You'd need a simple circuit to do current limiting. If you want to be able to dim them, that's a bit more complex. Take a look at this:
http://www.dansdata.com/caselight.htm
It's a basic primer on rigging up LEDs. The 5mm variety are more than ample for the purpose of lighting a dashboard. He also has a writeup on using Luxeon Stars, but that would kill your night vision.

Johnhef · #3 10-27-2006, 11:11 AM

I went this route before. 4 LED's per bulb and they didnt last. one side "burned out" completly and the other lost two of them and the remaining two only flickered. They were in for about two months before I went back to regular bulbs.

Find a newer 124 to get the cluster housing from and swap that out. Mine was melted so I just bought one from another member, but post an ad in the parts section, I had many people email me with them for sale.

Kynetx · #4 10-27-2006, 12:05 PM

I'm betting you didn't use a current-limiting resistor. If you did, you could get something like 100,000 hours of use out of an LED.

Johnhef · #5 10-27-2006, 12:50 PM

these were direct plug in bulb shaped LED's. i.e. remove bulb, plug in bulb of LED's. I even asked first before I bought them if they would work with what I was going to use them for and of course the answer was yes.

leathermang · #6 10-27-2006, 12:58 PM

Something other than the fact that they were LED's was wrong... the connection at the base, ground... something.. because most of the new cars are using them... and the traffic lights at intersections have them also....they are very long life and now are available in very bright and multi colors...

TVRTASMIN · #7 10-27-2006, 02:21 PM

If you have a bulb failure warning light, then using LED bulbs will bring it on unless you fit resistors into the relavant wiring.

Kynetx · #8 10-27-2006, 04:40 PM

Quote:

Originally Posted by Johnhef

these were direct plug in bulb shaped LED's. i.e. remove bulb, plug in bulb of LED's. I even asked first before I bought them if they would work with what I was going to use them for and of course the answer was yes.

LEDs aren't a direct plug-in for incandescent bulbs. As they heat up the internal resistance drops and the get warmer. Basically you have a positive-feedback loop and you get "thermal runaway". Semiconductors can't tolerate much heat so they eventually fail. You have to put a resistor in series with the LED to limit current flow so the don't run away on you. With something like a watch battery powered keychain light there isn't enough current available in the battery to take it beyond its limits. 1 watt into an LED is way too much power.
Follow the guidelines and the math outlined in the link I put in the second post and you can't go wrong. This has got me thinking. I'd love to replace all my dashboard lighting with LEDs. Even the climate control stuff.

leathermang · #9 10-27-2006, 06:08 PM

" You have to put a resistor in series with the LED to limit current flow so the don't run away on you"--Kynetex

UNLESS they have them built in... for example :

www.globalsources.com/manufacturers/Diode-LED.html

www.superbrightleds.com/led_info.htm

www.aeroelectric.com/articles/leds3.pdf

Parrot of Doom · #10 10-27-2006, 08:28 PM

Quote:

Originally Posted by leathermang

" You have to put a resistor in series with the LED to limit current flow so the don't run away on you"--Kynetex

Thats not quite accurate. Devices do not supply current - they draw it. I have 2x H6N LED bulb replacements on the sidelights of my W210:

LED sidelights

I have the bulb warning message, I simply need to wire a suitable resistor in parallel to each bulb.

Its fairly easy to calculate, normally the bulbs are 6W - the LEDs are much less, 1.2W IIRC. The voltage across each bulb is 12V. So the normal bulbs would draw 0.5 amps. The LED bulbs draw about 0.1 amps. A decent wirewound resistor that can withstand about 5W of power is all thats required. Unfortunately I'm about to eat a plate of sausages so I'll leave the parallel resistance calculations to someone else!

Kynetx · #11 10-27-2006, 11:14 PM

Quote:

Originally Posted by Parrot of Doom

Thats not quite accurate. Devices do not supply current - they draw it.

I never said they did. I work with DC power plants for a living so I have a pretty good grasp of DC theory.

If you put a resistor in parallel with the load you're only going to be creating heat and doing nothing else.

Mercury · #12 10-27-2006, 11:52 PM

Quote:

Originally Posted by the tenor man

Fellow Diesellors,

My 1987 300D Turbo cluster lights are so dim, I can barely see the gauges at night. I've tried cleaning and replacing the bulbs.

Since the original question looks like it was asking about LED's in the instument cluster, I think I can help. I bought one for my 84. Left one as incandesent. There is a slight light intensity increase in the LED, but the real difference is the color. LED's are the blue-white, incans are yellow. Don't really know which I like better as far as color, but the LED's are a little brighter. Another post gave the link to superbrightleds, they have a drop in replacement for everything in the car. I also got a festoon bulb for the back seat and the trunk. These made a HUGE light difference, and do not pull down the battery like the oe bulbs.

The t1 bulbs are also a drop in for other dash lighting.

Kynetx · #13 10-28-2006, 03:23 PM

That's an awesome site. Thanks for posting it.

Parrot of Doom · #14 10-29-2006, 06:56 PM

Quote:

Originally Posted by Kynetx

I never said they did. I work with DC power plants for a living so I have a pretty good grasp of DC theory.

If you put a resistor in parallel with the load you're only going to be creating heat and doing nothing else.

My apologies, I misread your quote. If you wire a resistor in series though (to eliminate the bulb out warning), you'd also be reducing the voltage on the lamp, and hence the brightness?

Much better to stick a 5W resistor in parallel of the correct resistance for the LED bulb - the bulb gets the 12V it needs, and enough current, and the resistor draws enough current for the car's computer not to get confused. A bit of heat is wasted yes, but its only going to be similar to what is emitted from a normal H6N bulb?

Kynetx · #15 10-29-2006, 09:26 PM

Quote:

Originally Posted by Parrot of Doom

My apologies, I misread your quote. If you wire a resistor in series though (to eliminate the bulb out warning), you'd also be reducing the voltage on the lamp, and hence the brightness?

Much better to stick a 5W resistor in parallel of the correct resistance for the LED bulb - the bulb gets the 12V it needs, and enough current, and the resistor draws enough current for the car's computer not to get confused. A bit of heat is wasted yes, but its only going to be similar to what is emitted from a normal H6N bulb?

Oh, ok. I see. Sorry about my smarmy tone. I guess in the more modern ones you'd have to come up with a way to trick the sensor.

As far as the series resistor goes, you have to pick the correct value. Too little resistance and you can kill the LED. Too much it it's dim.