Festoon 31mm to 400lm conversion - no BS

Here is the deal: some places of our trucks are lighted with really wimpy festoon 31mm bulbs. They are inside the cab as a dome or map lights, and (what is a miserable mistake) in a tailgate of 5th gen 4Runner. Good luck finding anything at night.

So people do LED conversion. But while all bulbs, including ones that are advertised as 9W festoon bulbs, seems to be brighter, really they are not by much. It just a "whiter" color gives the impression of blinding brightness, but as far as the amount of light delivered (meaning flux) they are not much better. So in order to have some reasonable results I had to take matter in my own hands and make my own bulb.

After some research I found festoon 31mm bulb advertised as 9W bulbs, which of course is a marketing BS, but they were very good candidate for conversion. Each bulb contained three LH351B, high power 3W LED chips - hence advertised 9W bulbs . In laboratory they can take up to1A but you would probably require a liquid helium for cooling, so the original bulb used merely 0.15W per LED chip totaling 0.45W (that is 5% of advertised power).



The bulb has very simple circuit: in series: one diode (not even a bridge), 3 LED chips, and one 47ohm resistor. It is also "CAN-BUS safe" what means the bulb comes with resistor connected parallel with the bulb - two 390ohm resistors connected in parallel giving effective resistance of 195 ohm.



When you are looking for these bulbs be aware that there are very similar bulbs also advertised as 9W but containing different LED chips not capable of handling anything more than 60mA. Like this one



The one that contains the "good" LED chips is for example bulb from LUYLED





I am not advertising the company, have no relation to it. Also I don't know if at the time you will read it, they will still have the same bulbs available. This is just an example, so you know what to look for.

Here is the different bulb (not available anymore) - different brand but you can tell it came from the same factory in China. Whatever they are, make sure you will get these LED chips - other chips (flat looking chips) just don't cut.



Measuring the temperature of the LED chips in the bulb at different power I figured out I can keep LED chips within reasonable limits (below 190F) if I run no more than 350mA through it. That is 1W per LED chip total 3W.

But first get rid of these pesky CAN-BUS resistors. They are just dead weight producing pure hit. Most of American trucks don't have "burned bulb detection" so you don't need that "heaters" on the back.



Guess what, now this bulb takes less than half of the original power (50mA instead of 110mA) making exactly the same amount of light, that is about 60lm. Yes, it looks bright because it is "white" and also delivers about twice more light than incandescent 5W festoon 31 (original incandescent bulb gives about 30lm).

Now it's time to increase the light output. First remove (desolder) 47ohm current limiting resistor.



Now there are two options, depending on your needs. For example for map light you may not want much power. You don't want to blind yourself while driving at night. So for that you may use 120mA constant current LED driver AL5809-120P1-7. It comes in the package that fits right in place of removed 47ohm resistor



The good thing of using constant current driver instead of resistor is that the bulb brightness does not depend on the voltage from your battery - it is the same brightness at 12V as it is at 14.4V

Such modified bulb gives about 130lm at 1W taken by all three LED chips. Total current taken is 120mA - the bulb will produce less than 1.5W of heat, so your lamp fixture designed for 5W festoon bulb can easy take it.

For dome lights or for tailgate lights (like my 5th gen 4Runner) I went with more powerful option using 350mA constant current LED driver NSI50350AST3G. It is much bigger so it will not fit in place of 47ohm resistors, but it will fit on the back in place of removed CAN-BUS resistors.

But first the circuit board trace needs to be altered. Simple cut the trace connecting the lower contacts with the bulb right cap as shown on the picture:



Now the constant current driver can be soldered in place of one CAN-BUS resistors, and the second soldering spot is used to solder one end of a jumper wire



That wire goes around to the other side and soldered into one contact from removed 47ohm resistor as shown below



And that's it. Also depending on your bulb version you may want to replace a soft plastic under the caps (they may melt at 190F) with epoxy. At least this is what I did. An the result is astonishing



Each bulb produces about 400lm taking 4.2W from the car - again, the 5W festoon bulb fixture can handle that heat easy. In my 4Runner this is like having 60W household bulb in the trunk. You can find a needle in a haystack (if I carry a hay in my truck).

Lastly here are the diagrams: reverse engineering of the original bulb and modified bulbs by replacing 47ohm resistors with constant current LED drivers.

 

Awesome! Love the tech! Ill be filling this one away for a future tinkering project.

 

I think you and @crashnburn80 will become good friends.

 

OK, looks great, where do i buy

 

You can pick up the LED drivers from Mouser.com. There about $0.60 each. The exact bulb with those LEDs I've been unable to find. This is the closest thing and same brand. https://www.amazon.com/gp/product/B01DNM13IE/ref=ox_sc_act_title_1?smid=A1DMDMQXPSM323&psc=1

 

I got my drivers of Digikey, These bulbs on Amazon contain Samsung 2323 chips (flat ones) - they can't handle that power. They are only 150mA absolute max current, 60mA nominal.

http://www.samsung.com/global/busin...ighting/201310/LM231A_data_sheet_rev005-0.pdf

Last year I got these:

LUYED 2 X Super Bright Cree-XBD 3-EX Chipsets 1.25"es DE3175 DE3021 DE3022 3175 LED Bulbs Used For Dome light,Xenon White

https://www.amazon.com/gp/product/B01B1CKCB2/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1 but they are not available anymore. Bummer.

 

Those so-called CANbus resistors are probably not for detecting burned out bulbs but rather that the controller knows they are on and kick in the battery drain protection to turn them off to avoid a dead battery. I guess ~195 ohms did the trick (a festoon bulb is nominally about 3W) but they had to use parallel 390 ohm in a 1210 package (good to 1/2 watt) to avoid burning them up.

BTW, cool hack.

 

hmmm

 

Then the bulb I listed would require this driver. https://www.mouser.com/ProductDetai...E420DPIasPkhv16Jt02dfQxRqGhxod5FIC/Ht7iDTJA==

 

This will do and probably will be better than resistor. Just don't expect 400lm performance . At 60mA you will end up at 70lm which is what most "super" bulbs do.

I don't think the manufacturer thought that far. I was not aware of the "battery drain detection" in our trucks. But I have 1995 Tacoma with doesn't even have a dimming circuit. I thought all "timed turn off" is just based on "time" not the "current drain". But I might be wrong - not the first time

Anyway I was not able to locate a reliable source of 31mm bulbs with Cree-XBD chips. Bummer. These chips are now quite popular in other types of bulbs. They are really good chips with huge potential as long as a correct heat sink is provided.

 

Now here is a hardcore solution for anyone who can operate soldering iron on small SMD elements:

Digikey part numbers:
1.5A max LED chip 1510-1816-1-ND (https://www.digikey.com/product-det...inc/SPHWH2L3D30ED4VPK3/1510-1816-1-ND/6569462) - 145lm at 350mA for less than 10 dollars per 10pcs
350 mA LED driver NSI50350AST3GOSCT-ND (https://www.digikey.com/product-det...or/NSI50350AST3G/NSI50350AST3GOSCT-ND/3152828)

And swap LED chips and driver on the bulb @mechanicjon showed.

 

Not sure when the protection was added, but I know a 2001 I had did it and my 2008, too. If you leave the dome light on it will turn itself off eventually to prevent draining the battery. I don't know for sure how it works but I assume it's measuring current to know the light is on but it's not the door switch or the alarm doing it. But even if it's a simple RC circuit would still need current to flow for the cap to charge and discharge. Normally the LED will be so much less than a filament bulb that instead of a few second taper it might be 30 seconds or minutes or who knows. Your modifications probably will negate any need for such a thing, though.

 

All is in a magic black box called "Master Body ECU". How it works nobody knows besides few guys in Toyota . But now it is all computer. Not only that - it talks to other computers in a car (via CAN BUS) and based on their responses it does what it does. I was surprised that the tailgate lock has its own ECU in my 2012 4Runner. The whole computer just to operate a tailgate. This computer is also operating lights in a tailgate.

 

What's your opinion on these new COB LED's https://www.amazon.com/LEDIN-Power-...=1511392333&sr=1-18&keywords=cob+31mm+festoon

Enough time and patience a black box is hackable.

 

In general COB LED is quite cool technology and COB panels became quite popular. The main problem is that it is next to impossible to get a true values from seller. COB LED has efficiency about 150lm/W but these 6W in description looks very fishy to me. Not from that size. And no Amazon prime can make it difficult to return when all this spec is BS.