LED Foglight Project Options

[Spoke]

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?

[FlacaProductions]

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.

[orthobiz]

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

Paul

[Spoke]

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.

[Morrie]

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.

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.

[orthobiz]

[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

[914forme]

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

[Mblizzard]

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

[eric9144]

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!! (IMG:style_emoticons/default/beerchug.gif)

[Spoke]

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

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.




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

[76-914]

(IMG:style_emoticons/default/popcorn[1].gif)

[ValcoOscar]

Same here... (IMG:style_emoticons/default/popcorn[1].gif) (IMG:style_emoticons/default/popcorn[1].gif) (IMG:style_emoticons/default/popcorn[1].gif)

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

Oscar

[DRPHIL914]

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

[Spoke]

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.

(IMG:style_emoticons/default/agree.gif)

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.

[Spoke]

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

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.

[ClayPerrine]

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

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.




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

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.

[Spoke]

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.

[Al Meredith]

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

[windforfun]

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.

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

[Spoke]

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

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.