LED bulbs for turn signals using the OEM flasher

[Mike Self]

Electronics are nearly as much of a mystery to my old brain as a carburetor is to the average 13 year old.  

 

I've been told that my red center turn signal bulbs in my '69's tail lights are hard to see in daylight (probably why BMW changed 'em to amber), despite my brightening the reflectors with silver mylar.  

 

I'd like to install some LED bulbs, but know that their very low amperage draw will cause problems with the flasher relay and cause the lights to blink way too fast.  And yes, I know I could install a new, all solid state flasher relay, but I like the sound and cadence of the factory one. Anyway, I've finally figured out the turn signal and emergency flasher wiring scheme and am loathe to change that!

 

Can one of you electronics gurus tell me what value resistor (or whatever electronics bit) I should wire in series with the bulb to provide sufficient load to the flasher relay so it will work properly?  Or is there another way to do this without changing the flasher relay?

 

TIA

mike

[visionaut]

Mike - they make drop-in LED bulbs now in many standard bases (like 1156/1157/BA15S/etc.) that need no extra electronics and work with the existing relay. (maybe the load resistor is inside such LED bulbs).

 

What's the bulb style you want to swap for LED?  All the brake light and running bulbs in my rear tails are LEDs now and I'm not using any extra added load resistors with my relays.  ( I haven’t changed backup or turn signals yet, less need). They're both brighter, longer lasting and cooler (thermal temp-wise).  I think they're cooler too!

 

Tom
 

ps: I got my LEDS from superbrightleds.com. - you can shop by make/model/year.  Page for 1976 BMW 2002

Edited March 23, 2020 by visionaut
Clarification & link added

[dlacey]

If you specify the exact LED lamp you plan to fit, then the resistance/power can be calculated.

But make sure it physically fits! The rear lamp central indicator socket does not quite comply with standards...there's a problem with clearance just above the base. But if your LED lamp physically fits and we know it's spec then the resistor is easy to calculate.

[TobyB]

Sure, it complies with a standard- it's just not the standard 1156!  It's a different German D- standard, of which zere are veddy many!

 

At the risk of making this easy, just look at the wattage BMW specified.  I THINK it's 21w (not the 'standard' 26 of an 1156)

but it might be 15.  I forget things.

 

watts = volts * amps

and

amps = volts / resistance,

so when you solve for resistance, you get 

14/21 ohms, or about .7 ohms.

In theory, you should subtract the wattage of the LED lamp you're using,

but in practice they don't use enough to matter.

 

https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html

 

has a calculator, if I've messed this up.  

 

But I'd bet a torn accelerator pump diaphragm that a 1 ohm 20 watt resistor per lamp would trip the light on your dash.

 

 

(mine never flashed fast, they just refused to light the dash light, as there's a current sensor in the flasher that

trips the indicator light.  If you wanted to go all nuts, you could re- wind the coil in the current sensor to make it more

sensitive, and then it might work with LED lights.  But that would be... a project!)

 

One flaw with using resistors to 'simulate' a lamp is that a lamp draws less current the brighter it burns.

So if you meter a light bulb, it measures a much- lower resistance than the math says it will.  But as it heats,

its resistance increases, making it a very stable load. 

The sensor relay in the flasher uses that initial current spike to pull in the dash light contact- so while the 

turn signal circuit draws an average of 42 watts, the relay in the flasher's using the 8+ amp spike

at the start of each flash to do its 'click'.  

 

t

[Vicleonardo1]

Three things: 

1. Another advantage of LED lights is responsiveness. They are closer to "instant on" when activated. You would be surprised at 60 mph the difference in the number of feet it can gain in a safety cushion when the person behind you reacts to your brake lights. 

2. It may just be easier to use LEDs for the brake lights, backup lights  and running lights and keep the standard bulbs for your turn signals. I am not sure what advantage LEDs offer over regular bulbs for turn signals  due to their limited use.  (unless you are like my uncle Ralph that could never manage to switch off his right blinker). And you wouldn't have to muss with relays etc. You may be able to find brighter standard bulbs online. 

3. Hot Rodders have found that using Gloss white paint in the housing significantly brightens ups the bulbs vs shiny reflective paint or coatings. You may wish to try that. 

 

 

 Wash your hands. 

 

Cheers! 

Edited March 23, 2020 by Vicleonardo1

[2002#3]

An Aside:  I, too, have found gloss white paint to be so superior to both mylar and shiny silver/chrome paint as reflectors inside tail light housings that I have not needed to go the new-bulb route.  Thank you to whomever suggested it initially.

 

Now, back to our topic...bulbs.

 

 

[Mike A]

Bought mine from Superbrightleds.com....they have every bulb you would want. But if you decide to replace the instrument bulbs, leave the generator bulb in the cluster...the tach won't work without it.

[Vicleonardo1]

1 hour ago, 2002#3 said:

An Aside:  I, too, have found gloss white paint to be so superior to both mylar and shiny silver/chrome paint as reflectors inside tail light housings that I have not needed to go the new-bulb route.  Thank you to whomever suggested it initially.

 

Now, back to our topic...bulbs.

 

 

I'll take credit. Posted it here a long time ago from a hot rod website. They even tested the difference for brightness using light meters etc. 

Hot Rodders Rock! They are a very good resource for vintage mods, builds, paint, rust, restoration etc. Always have been helpful even though our rides aren't 'merican.... very good brethren to have. 

 

You would be surprised on how much info they have to help the 02 community. Hit your friendly neighborhood  local Hot Rod show someday (when they start up again) and you will be surprised on what the builders, sellers and vendors have to offer. 

 

Cheers! 

 

Keep safe, Wash your hands. 

[Vicleonardo1]

Mike A and Visionaut. 

No hyper flash issues with the blinker bulbs? Or did you have to add load resistors? 

[2002#3]

Vicleo,

You, huh?  THANKS so much for the tips, both glossy white and the hot rod route to '02 happiness.

[Mike A]

2 hours ago, Vicleonardo1 said:

Mike A and Visionaut. 

No hyper flash issues with the blinker bulbs? Or did you have to add load resistors? 

No resistors used .no hyper flash issues ..and .the reverse lights are amazing 

Edited March 23, 2020 by Mike A

[layers]

Hi Mike--

I encourage you to retrofit to LED bulbs; I did that 8-10 years ago and I'm pleased with the results.  I also replaced the turn signal flasher relay with a solidstate relay that works fine but it does sound different (from the OEM and many replacements I needed in my late '73).

A few points for you to consider:

• I bought my bulbs from SuperbrightLED but they no longer have identical bulbs to the ones I used; expect to have some trial and error in selecting exactly the ones you like.
• You incorrectly state you are considering using resistors IN SERIES with your LED bulbs.  The load resistors go in PARALLEL with the LED bulbs to increase the flasher load current without dimming the LED bulbs.  The primary use of the resistors is to keep the failed bulb sensor on newer cars from trying to tell you the lower-current LED bulb has failed.  Some bulbs have the parallel resistor(s) installed in the base and are called "CAN Bus".
• You do not need more than about 100 lumens for a stop or turn bulb, especially if you choose the proper color (red or amber).  But if most of the light bounces around between the bulb and reflector before exiting through the lens then more lumens may be needed.
• Be sure to choose the proper color LED bulb for your application since using a "white" bulb is very inefficient and the color will be different from an incandescent bulb with a colored lens in almost any case.  For a turn signal bulb, the LED provides mostly monochromatic light and therefore if you want a red turn signal simply choose a red LED (but the lens will always look whatever color the lens is).  I recommend an amber turn signal as it is somewhat more visible than red but the color is up to you.
• When I installed my LED bulbs I visually compared the angular light distribution in both the horizontal and vertical directions. It is entirely possible that light from the LEDs could be concentrated in a narrow beam that is a lot less visible from the various angles another driver be looking from-- that's why SAE-NHTSA specifications call for photometric measurements at a series of angles left-right and up-down from the lamp center (H-V).  A visual comparison of your new LED bulbs in one tail lamp compared to your other tail lamp with your existing incandescent bulbs should at least give you some confidence that you are not operating in stealth mode.

Have some fun increasing your night-time visibility!

Larry