Advice: DO NOT put LED lights into your dash? - PeachParts Mercedes-Benz Forum

jbach36 · #1 01-18-2019, 02:14 AM

Aye carumba!

I thought I'd do my car a nice favor and put in LED lights, maybe not in the speedometer because I know those are really hard to get to, but at least on the shifter and climate control area.

This has been a mess.

First was finding the RIGHT bulbs. Someone posted after I bought mine from SuperBrightLED's about the Sylvania types (which are waaaaaay more expensive anyways). But I finally got the right bulbs. I got the cool whites (slightly blueish tint), put one in and it is indeed brighter by maybe 30% than the standard type.

Problem #1 is getting the old bulbs OUT of the climate control area. Years ago I used a straw to get the old ones out but this time that didn't work. So I got maybe a 1/4" rubber hose and FINALLY got ONE out. I worked and worked on the 2nd one for at least 1/2 hour and still can't get it out.

Problem #2 is that I think the window switches by the shifter and the switches above the climate controls have their bulbs built into the switches, and those are the old yellow kind. So I'll end up with some areas of cool white bulbs, and other areas of old yellow light bulbs which will be weird.

Does anyone know a way out of this? Are there any ways to make the switches cool white light? I doubt anyone would even sell cool white switches.

Thanks,

1991 300d

jay_bob · #2 01-18-2019, 07:10 AM

The window control switches and the row of rocker switches above the climate control are all lit by LEDs. You would have to disassemble the switches and replace them with modern white LEDs.

You’ll need to check the data sheet for the LEDs and see what the If max (maximum forward current) specification is. Then look at the resistor inside the switch and see if that will result in an apppropriate current for the new LEDs.

LEDs are effectively a dead short and are dependent on the series resistor to limit the current to a safe value.

It is easy to calculate, the formula is basic Ohms law or I = V/R.
14 (system voltage under operation) / (the resistor value) = forward current of the LED.

If your calculation results in a current more than about 80% of the data sheet value then you’ll need to pick a different resistor to get a current in range. You want to shoot for 60-70% of rated current to get some decent brightness while not burning the device out.

I thought about the dimming system on the W124 and the switch lights are all on the N40 illumination control repeater. I highly suspect that the output of the N40 is a PWM dc voltage. This is perfect for dimming LEDs so this may work out very nicely on the switch lights. PWM is constant voltage, variable on/off ratio, a square wave that varies from full “off” to full “on”. Usually the square wave is turned on and off several hundred times a second. 50% would be equal off and on times.

Under PWM the LED only has one brightness level set by the resistor. But the LED is not on 100% of the time when you turn the dimmer down. Due to the behavior of the human eye, the rapid flashing of the LED is seen by your eyes as a dimmed light. This is exactly how the new vehicles with LED tail lights work. The tail light is a low “on time” waveform and brake is 100% on, coming from the same set of LEDs.

The rheostat drives the main cluster bulbs. This is a variable voltage device. LEDs, being a constant current device, don’t react well to dropping the voltage to dim them. Basically the LED will maintain brightness until the voltage drops low enough that the LED can’t conduct (parameter Vf min - minimum forward voltage). Below this value the LED will turn off and will not light at all.

tjts1 · #3 01-18-2019, 09:29 AM

I just did LED tail lights and signals. They work nicely.

jbach36 · #4 01-18-2019, 11:11 AM

Quote:

Originally Posted by tjts1

I just did LED tail lights and signals. They work nicely.

You said you changed your tail and signal bulbs but to what real benefit? Those are all on the outside and you'll never see them. I guess they might give a bit of a brighter light of course but everyone can see the original type bulbs anyways. On the inside of the car the original dash bulbs are too dim.

What type bulbs did you use for those outside lights and where did you get them?

jbach36 · #5 01-18-2019, 11:12 AM

Quote:

Originally Posted by jay_bob

The window control switches and the row of rocker switches above the climate control are all lit by LEDs. You would have to disassemble the switches and replace them with modern white LEDs.

You’ll need to check the data sheet for the LEDs and see what the If max (maximum forward current) specification is. Then look at the resistor inside the switch and see if that will result in an apppropriate current for the new LEDs.

LEDs are effectively a dead short and are dependent on the series resistor to limit the current to a safe value.

It is easy to calculate, the formula is basic Ohms law or I = V/R.
14 (system voltage under operation) / (the resistor value) = forward current of the LED.

If your calculation results in a current more than about 80% of the data sheet value then you’ll need to pick a different resistor to get a current in range. You want to shoot for 60-70% of rated current to get some decent brightness while not burning the device out.

I thought about the dimming system on the W124 and the switch lights are all on the N40 illumination control repeater. I highly suspect that the output of the N40 is a PWM dc voltage. This is perfect for dimming LEDs so this may work out very nicely on the switch lights. PWM is constant voltage, variable on/off ratio, a square wave that varies from full “off” to full “on”. Usually the square wave is turned on and off several hundred times a second. 50% would be equal off and on times.

Under PWM the LED only has one brightness level set by the resistor. But the LED is not on 100% of the time when you turn the dimmer down. Due to the behavior of the human eye, the rapid flashing of the LED is seen by your eyes as a dimmed light. This is exactly how the new vehicles with LED tail lights work. The tail light is a low “on time” waveform and brake is 100% on, coming from the same set of LEDs.

The rheostat drives the main cluster bulbs. This is a variable voltage device. LEDs, being a constant current device, don’t react well to dropping the voltage to dim them. Basically the LED will maintain brightness until the voltage drops low enough that the LED can’t conduct (parameter Vf min - minimum forward voltage). Below this value the LED will turn off and will not light at all.

Jay, maybe it's not as hard as it sounds to change out all those bulbs, but that sounds like a major production. Plus who would sell those type bulbs?

Maximan1 · #6 01-18-2019, 11:23 AM

Quote:

Originally Posted by jbach36

You said you changed your tail and signal bulbs but to what real benefit? Those are all on the outside and you'll never see them. I guess they might give a bit of a brighter light of course but everyone can see the original type bulbs anyways. On the inside of the car the original dash bulbs are too dim.

What type bulbs did you use for those outside lights and where did you get them?

I'm not the original poster, but I install LED tails and turn signals on all my cars because

A) They are brighter, come on immediately, and are easier to notice.

And B) I know I won't get pulled over for a tail/brake/turn signal/license plate light out.

LEDs are a cheap option to make sure I'm seen.

jay_bob · #7 01-18-2019, 12:17 PM

Quote:

Originally Posted by jbach36

Jay, maybe it's not as hard as it sounds to change out all those bulbs, but that sounds like a major production. Plus who would sell those type bulbs?

Mouser Electronics or Digi-Key

These are online electronics distributors

Pretty much the only option now that there is no radio shack anymore.

I would harvest a set of switches from the JY and modify those. That way you don’t ruin your existing switches if you don’t like the results.

tjts1 · #8 01-18-2019, 02:30 PM

Quote:

Originally Posted by jbach36

You said you changed your tail and signal bulbs but to what real benefit? Those are all on the outside and you'll never see them. I guess they might give a bit of a brighter light of course but everyone can see the original type bulbs anyways. On the inside of the car the original dash bulbs are too dim.

What type bulbs did you use for those outside lights and where did you get them?

I don't need to see them, I want everyone else to see them. Take a look at a W124 next to any modern car at night. The W124 tail lights are dim and small by comparison. LED bulbs reach full brightnessucg faster than incandescent bulbs. When I slam the brakes the driver behind me knows it earlier. Also LEDs make less heat so they don't melt the center brake light housing.

Dubyagee · #9 01-18-2019, 02:38 PM

I agree with TJts. Im converting mine to LED. May go panel mount and fill the whole lens.

jbach36 · #10 01-18-2019, 11:47 PM

Quote:

Originally Posted by tjts1

I don't need to see them, I want everyone else to see them. Take a look at a W124 next to any modern car at night. The W124 tail lights are dim and small by comparison. LED bulbs reach full brightnessucg faster than incandescent bulbs. When I slam the brakes the driver behind me knows it earlier. Also LEDs make less heat so they don't melt the center brake light housing.

Where did you get your bulbs from and what bulb numbers are they? If I change them out, I'll try to avoid all the problems I've gone through trying to get the right bulbs to change out the climate control lights.