The design of an early foglight LED board has begun. mepstein sent me a couple of foglight fixtures to use to design the board. 2 main issues are fitment and heat dissipation. If things work out ok the design should be able to be re-laid out for the later square foglight.

The board will have 8 Cree XP-G3 high power surface mount LEDs with 350ma current each. These will burn about 1W of power with a total power dissipation expected to be less than 10W. Hopefully these will be almost as bright as a headlight.

Each LED will have its own focusing lens. The lenses are Carclo 10192 elliptical 20mm lenses. The light pattern for the 10192 lens is shown below.

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This is the spectral dispersion for the lens.

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The LEDs will be connected in series and driven by a Linear Technologies LT3755 switching converter. It will be the same circuit as applied to the Porsche 356 running lights previously designed.

That running light had 19 LEDs running 275ma each. This one burned about 16W total. The switching converter was placed on a separate PCB as a large heatsink was mounted behind the LEDs.

The 914 foglight fixture is much smaller so only 8 LEDs will be mounted with the switching converter mounted on the backside of a single PCB.

This is what the board looks like right now. It may likely change as the layout proceeds. The heatsink is 2 x 4 inches and will back the LEDs. The rest of the space will be used on the back will be used by the switching converter.

The switching converter could be mounted on the front side but I'm not sure if it would look ok since you'd be able to see the hardware. It would make the assembly much easier to have everything on one side.

I don't understand any of this but it sure looks great. Can't wait to go full LED. Maybe the hood lights next?

I think the Cibie's are used on many other marque's.

Will you be making these for the rectangle style fog lights?

I'd be in for an early set once you get them done and tested.

Once the round board is proved out, yes I plan to migrate to the rectangle style. Also want to do a rectangle style for the 911.

Looks great Spoke.

This is the fixture I'll use to size the board. The reflector and original bulb socket will not be used.

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The wires from the original bulb are quite limited. The ground is a spade and the 12V is simply screwed onto the bulb socket. At least on my '71 these wires are quite short. It might be worthwhile to provide an entire pigtail for the LED board instead of trying to connect to the existing wires.

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I printed the PCB front and bottom sides since I can't print both at the same time.

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Here's the fitment of the PCB to the lens. This would be the clearance to the LED lenses. The depth of the lens leaves about 150mil gap between the PCB and the glass ledge. The PCB has to sit squarely on the ledge.

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This spacer ring was printed to sit between the glass and the PCB to be able to mount the PCB.

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With the spacer attached, now the PCB can sit squarely on the glass.

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Because the spacer and PCB thickness, the original clips which hold the original reflector are too short to hold the PCB in place. The top clip is a new one made from spring wire. It will be able to hold the spacer and PCB in place. This will put the PCB on the trim ring and will make it easy to install the entire assembly.

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I'm totally supporting this. I drive at night 90% of the time, and my fog light reflectors are shot. I got a quote to re-silver at almost $100 each side. A quality LED conversion would give me my fog lights back.

Really excited for this although currently I only have 1 for light some day I will buy another and do this conversion..

Ben- I sent Spoke 3. I have some more somewhere in a box but who knows where I put them. I want to give Spoke a nice set for his car (not the rusty set I sent him) but you are welcome to the odd one.
I think these will be amazing when finished.

If you want the best led headlights out there - in my opinion- its these trucklight 7” headlights. Very popular with the Jeep guys as well as motorcycle riders. There are cheaper options but a lot of times you get what you pay for. They take 10 minutes to install with no mods and are a total game changer. They make driving at night so much easier. They look a little odd but during the day the lights are down anyway. Even though they are very bright, I never get flashed because they have a very good cut off. The high beam is insane. They use less voltage than ordinary lights so are a little easier on our cars older wires and less battery drain.

Good to know! I think I have these on an Amazon wish list already. I just haven't pulled the trigger yet.

This is great, thanks. I posted some lens pictures at:

http://www.914world.com/bbs2/index.php?sho...=233202&hl=

The early and late lenses have different heights, is that what you meant when you said "early?" More importantly, will this affect the LED project??

I LOVE visibility and have ALL of your stuff!!

Paul

Why not mount the power supply remote in an IP65/67 enclosure mounted behind the 914 grille? It would free up some space and maybe reduce temps inside the light assembly.

Thanks for the info. My '71 has the early lens which looks to be a bit deeper. After doing some initial measurements on my early lens, I didn't think I'd need a spacer as needed with the later lens. Either way shouldn't be an issue.

This is what I did for the 356 running lights although the boost converter PCB was mounted inside the housing. I proposed a separate box to put the converter in but the owner didn't want an external box so I mounted on the back of the heatsink.

I'd like to keep it to one PCB for simplicity although a separate module may be needed depending on temperature rise.

OK, the PCBs have been sent to the fab house. Should have bare PCBs in about a week. Only ordered 5 of them since there will be a lot of learning going on with the first units. The PCB solder mask will be white like the other running light for the 356.

The XP-G3 LEDs in white come in different temperatures. I can get 3000K, 4000K, 5000K, 5700K, and 6500K. I know I don't want 3000K as that is basically warm white. I used those on the 356 lights and they were too yellow. I'm leaning toward 5000K right now. Anyone with knowledge of LED color temperatures have a suggestion?

I deal with color temp every day. 3200 is tungsten and 5600 is daylight - generally speaking. 4300 splits the difference with 3200 looking a little warm and 5600 looking a bit blue by comparison. I was thinking that 4000 or 5000 might be nice. 6500 would be really blue.

Why do these need a converter when your other taillight/sidemarker lights don't?

Paul

There's a couple of reasons for using a converter on these lights. First the current is a lot higher for each LED. 350ma per LED for this foglight vs 20ma per LED for brake/turnsignals. Thus the current limiting resistor for brakes doesn't burn that much power. Total power burned by all the current limiting resistors on the brakes is less than 1W and it is evenly distributed across the board.

The brakes/turnsignals have 56 LEDs configured as 16 strings of 4 LEDs in series. 4 red or amber LEDs only need about 2V each or 8V total to turn on. In the foglight there are 8 LEDs total in one series string. White LEDs need about 3+ volts to turn on. Thus the total voltage of the string is over 24V and the need for a dc-dc converter.

With resistors providing current limit on the brakes/turnsignals, there is some brightness difference between battery voltages of 12V to 14V although it is not so noticeable.

For the foglights the light output must be constant for all operating voltages. This converter will turn on when the applied voltage is about 9V and the LED current will remain constant over the entire battery voltage range. This way there will be no flickering or dimming if the battery voltage is high or low.

In the 356 front light there were 19 LEDs in series and the voltage needed to drive that stack was over 50V.

Ideally you would have a converter with no resistors running in constant current mode rather than constant voltage. Or at least that’s how the growers are doing it.

[quote name='Spoke' date='Apr 17 2019, 08:44 PM' post='2706296']
[quote name='orthobiz' post='2706213' date='Apr 17 2019, 02:26 PM']
Why do these need a converter when your other taillight/sidemarker lights don't?

Paul
[/quote]

There's a couple of reasons for using a converter on these lights........

Thanks!

Paul

PDBs going to be green or black in the final version?

I will be in for a set of squares. Last lights on my care that are not LED!

This is pretty awesome and totally something I'm in to buy... I had actually found LED bulbs to replace the stock fog's and well...the light is scattered and kind of looks like crap overall so if you want them for real visibility they're worthless... Keep up the good work Spoke!!

The first boards will be white. I used white for the 356 lights. Here's the first 356 PCB I did as I was mounting the LEDs. These are a PITA since they are surface mount. I would tin the pads then while holding the LED with tweezers, heat the the pad with air and when the solder liquified I'd drop the LED in and wait until the solder re-liquefied then remove the heat. I would do 3 LEDs at a time then test them to make sure they were soldered correctly.

For these boards I'll use solder paste and an infrared reflow oven to put the LEDs down. Then the board will be flipped and the converter components will be mounted using solder paste and hot air.

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These are the Carclo 10192 elliptical lenses; one for each LED.

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Same here...

I see several sets of SPOKE LED Fog Lights on my cars in the near future.

Oscar

thanks for taking this on! I asked about this a year ago when I backdated my bumpers and sourced a nice set of OEM NOS early round fogs. I had put the H1 LED bulbs in my late square fogs and they worked fine but this is a much better way to go. I don't want to clog this documentation thread with requests so I will be looking forward to a new thread for purchase of these once you are ready !

I agree about the comments on color, you don't want to go too blue so probably staying closer to the 4000-5000k max would be best - why not a "spectrum" not just one but rather 2or 3 different ones all on the same board , how would that work?

Phil

This is a boost converter running constant current of 350ma. There are a couple of control loops. One for the FET/Inductor current, one for the LED current and a 3rd constant voltage output in case of open LEDs to protect the components from over voltage.

Not sure what a light would look like with mixed temperature LEDs.

I just ordered 5000K LEDs enough to do 4 boards. We'll see what they look like when put together. Also ordered the heatsinks and all other components. Digikey was out of the Carclo 10192 lenses so I'll order them through Arrow.

I used to do component level repair on computer motherboards. We would desolder the offending surface mount chip, tin the contacts on the replacement chip, and use a drop of super glue to hold it in place. After that, less than a minute in the hot air machine and it would be soldered.

That was 26 years ago. Maybe technology on how to install surface mount chips has changed.

To reduce component and assembly cost, I'm looking for modules to do the 12V-to-constant-current conversion. I found this one from LEDsupply up in Vermont. It looks like it has all the features (12V input) and 350mA output. The package is only 0.83x0.83x0.43 inch. The one downside is the maximum operating temperature is 85C. It might be high enough temperature. Won't know until I build up a board.

PCBs are out of the fab and in shipping. Also ordered all other components. Should be able to do some assembly next week or the week after.

would it make sense to have two levels, one for running / daytime and one for night time use. the heat for daytime running would be decreased . AL

This is known as Plank's Law or Wien's Displacement Law. FYI. I guess you can tell that I'm partially retired now.

It is possible to do that. Also most LED drivers have an input to dim or decrease the current. By putting a negative temperature coefficient resistor on the input, the current can be decreased by an increase in temperature.

Just a thought but if you're using a LED chip with an optic and then putting behind a standard thick fluted lens the output is going to be severely reduced. I would guess roughly 30%.

Have you put the standard lens on top of your prototype to see what happens?

Not sure how the glass lens will attenuate the light from the LEDs. Once I get the first PCBs populated I'll be able to do some testing on it. The vertical diffusers of the glass lens will tend to broaden the width of the beam. The LED lenses also broaden the beam so maybe I'll have to use more of a spot type of LED lens instead of the 10192 lens and let the glass do the horizontal spreading.

Have the PCBs in hand. Will assemble the first boards on Monday.

Here's the PCB under the glass. It will be interesting to see how the fluted glass will diffuse the beams. The LED lens already provides some lateral diffusion.

The Boostpucks by LEDynamics also arrived. I'll probably power the first prototype with these as it will shorten the time to first light-up.

Looking good! Cant wait to see them in action!

Things like this happen when you set the temperature profile wrong on the infrared oven.


@mepstein I have your foglight board. Not sure why it doesn't light up but I'm working on that.

That looks more like when I try to do electrical work.

With the correct settings, the oven worked fine.

BTW Mark, this one is mine.

All lit up with LED lenses. Won't be able to compare light output until night. Also want to compare with original bulbs.

Printed a jig to drill the heat sink for tapping. Will be using 6-32 x 3/8 stainless cap screws.