Author Topic: Instrument LED bulbs  (Read 2503 times)

clunker

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Instrument LED bulbs
« on: March 24, 2019, 22:23:57 »
I am changing the bulbs in the instrument cluster, as I have them it for other reasons. There was fairly clear post as to what LED bulbs/color should work posted by 66andBlue in 2013 (reposted here), and now superbrightleds offers BA9s base LED bulbs in various colors, including warm white.

The general warning is that the alternator warning light cannot be swapped for an LED as it specifically requires a 2W (incandescent) bulb for that circuit to work, presumably because the resistance draw of the 2W bulb is needed. I assume that bulbs resistance is  (12v * 12v / 2W =) 72ohms.

In the spirit of no dumb questions -

Given the 1-LED red bulb BA9S-R-90-12VAC from superbrightleds is rated 0.02A at 12v (so 0.24W), we can assume the resistance is (12v / 0.02A =) 600ohms. To get a 72ohm circuit (as per the 2W incandescent) and 2W power draw, I propose adding an 82ohm resistor in parallel with the LED (using 1/72 = 1/600 + 1/82) and the circuit will work as expected. Quite likely I missing something, and of course it assumes it is possible to physically patch in that resistor, but has anyone tried this?
« Last Edit: March 25, 2019, 01:37:14 by clunker »
Charles
1969 US 280SL 4-speed Red/Black
DB9 / 981 S / G300 SWB / CB750 / etc

mmizesko

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Re: Instrument LED bulbs
« Reply #1 on: March 25, 2019, 18:39:21 »
Charles,  Nope, I did not try tpo add a resistor.  Just followed the instructions above.  Very Happy after 6 years.

Mike Mizesko
1970 280SL 291H Dark Olive

Jonny B

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Re: Instrument LED bulbs
« Reply #2 on: March 26, 2019, 00:33:15 »
This is from a good friend of mine, fellow Pagoda owner, and electrical engineer:

Totally agree with the idea. On a practical note:

1) Those green LED's will fry your eyes. If adding resistors, why not experiment with series resistance for the turn signals.
2) Test all this out before installing everything!

I can vouch for the green LEDs, they are like little green laser beams on the dash!
Jonny B
1967 250 SL Auto, DB 568
1970 280 SL Auto, DB 904

clunker

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Re: Instrument LED bulbs
« Reply #3 on: March 30, 2019, 23:49:39 »
So I added the 82ohm resistor and that seemed to work fine with a 1-led red for charging indicator - charge on with ignition on/engine not started, charge light off with engine running. I also checked battery/ alternator charge voltages are just fine.

I did use 1-led's  on the turn signals - the 4-led's were too much!. I also used a 1-led (white) for the center unit illumination, again 4-led seemed too much but ymmv. I am using 4-led x2 on tach and speedo lights and they seem about right. I too had to keep the 2W incandescent bulb on the low fuel slot: the 1-led is just too wide to fit in hole - maybe someone can locate a slim version BA9s one day.

I used a 5W rated 82ohm resistor, but anything over 2W should be fine. I patched it into the cluster plug - soldered in patch wires inside the plug and ran them outside the plug unit and put resistor there, suitable heat shrink sealed.

I also ran patch wires out of the plug for the rheostat short - I refurbished the rheostat but the resistance spring too far gone, and not sure if the LEDs dimmable anyway (did not check).

I attach an amended version of 66andBlue's original diagram reflecting what I have used.
« Last Edit: March 31, 2019, 14:56:44 by clunker »
Charles
1969 US 280SL 4-speed Red/Black
DB9 / 981 S / G300 SWB / CB750 / etc

66andBlue

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Re: Instrument LED bulbs
« Reply #4 on: March 31, 2019, 04:59:45 »
Nicely done - thank you!
Alfred
1964 230SL manual 4-speed 568H signal red
1966 230SL automatic 334G light blue (sold)
1968 280SL automatic (now 904G midnight blue)

TEJOLX47

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Re: Instrument LED bulbs
« Reply #5 on: November 13, 2020, 12:29:43 »
Dear Charles,

Thank you for the very informative posts on the subject.
I have to remove some of my instruments to repair, so I thought I could upgrade normal bulbs to LED.
I have two questions though:
1. Should the lamps be alternate current or direct current; you mention a Bulb BA9S-R-90-12VAC which is for alternate current and I thought (maybe I am wrong) the dashboard uses direct current.
2. Do the LED's produce to much heat when operating for a while; should we be concerned with that?
Many thanks.
Francisco
Francisco

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JamesL

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Re: Instrument LED bulbs
« Reply #6 on: November 13, 2020, 14:57:41 »
DC 12v. Power is off the battery or alternator.

One of the benefits of LED in terms of efficiency is that a much greater portion of the power draw is used to generate light, whereas with older bulbs, most of the energy can end up being used to generate heat (think of what a bulb filament is). For the same “lumens”, less power is needed as less energy is used to create (wasted) heat.
So the answer is that heat is less of an issue with LED than old bulbs
James L
Oct69 RHD 280 in DB906 with cognac leather

clunker

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Re: Instrument LED bulbs
« Reply #7 on: November 13, 2020, 15:34:35 »
Exactly as James said - 90% of incandescent bulb energy goes as heat/10% light, LED 10% heat/90% light, so for same light (lumens) only 11% of power needed and only 1.1% of heat generated (very very broadly speaking of course!). And pretty much all LEDS are DC, those in AC circuits have rectifiers to convert.
Charles
1969 US 280SL 4-speed Red/Black
DB9 / 981 S / G300 SWB / CB750 / etc

TEJOLX47

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Re: Instrument LED bulbs
« Reply #8 on: November 13, 2020, 15:44:01 »
Thank you all!
I am on my way to "futurize" my Classic.
Cheers
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

getsmart

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Re: Instrument LED bulbs
« Reply #9 on: August 03, 2022, 05:01:32 »
Hi all,

Does anyone know if the remaining regular 2w bulb can be replaced with an led (see my question in red in the pic)? I'm not sure if I remember correctly but I might have read that it can be but the problem that most leds don't fit, is that correct?

Rgds, Joe

PS . I just re-read and did see Clunker make a reference to it in reply 3 above - I think I can apply a little dremel grinding , only need a mil off or so for the leds I got
« Last Edit: August 03, 2022, 07:48:36 by getsmart »
Finding the red car
1964 230sl Restoration Project

getsmart

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Re: Instrument LED bulbs
« Reply #10 on: August 05, 2022, 03:56:39 »
ok I can now see one reason the low fuel light can't be updated to led - the housing cannot be easily ground as it is a tube that goes all the way to the front of the gauge to limit light pollution into the rest of the gauge. Looks like it will stay as an incandescent globe for now  ;)


Hi all,

Does anyone know if the remaining regular 2w bulb can be replaced with an led (see my question in red in the pic)? I'm not sure if I remember correctly but I might have read that it can be but the problem that most leds don't fit, is that correct?

Rgds, Joe

PS . I just re-read and did see Clunker make a reference to it in reply 3 above - I think I can apply a little dremel grinding , only need a mil off or so for the leds I got
Finding the red car
1964 230sl Restoration Project