Newbe with some LED questions (yet another tail light thread)

[majorboost]

Hello everyone! First post here, please don't crucify me

Great forum! Tons of great electrical minds on this site !

I have done the whole search thing, and have spent about five hours reading to try and make an educated decision on my project. I have a 1971 Dodge Challenger Show car / Drag race car that I am bringing into the modern lighting scene. I am not worried about DOT approved, but I am concerned about high visibility (I don't need someone smacking into the back of my big dollar car because they didn't see that I was stopping ). At first I was going to go with 5MM bulbs before my new found knowledge, but after finding this site I now know I will be going with 5mm Piranha's (thanks again!).



Here is the run down of what I know........................

I am building custom tail light lenses made out of 3/16 thick smoked black plexiglass (so light will be more difficult to pass through them than normal red tinted lenses). The lenses will be 24" wide x 2 1/8" tall. That breaks down to 204 LEDs in each lens (3 rows vertical of 68 LEDs horizontal) according to my following arrangement. The LEDs will be double spaced, meaning there will be a blank the size of a super flux next to and on top of each super flux for better cooling. The LEDs will function as both tail lights, stop lights, and turn signals (the stop lights and turn signals are one in the same). My battery voltage is at a constant 14.0 volts due to a high quality racing voltage regulator.


Now the questions..................................................

Which Super flux LEDs do you think would make a better choice for my application? All have different viewing angles, and different MCD ratings.

http://cgi.ebay.com/New-100X-Superflux-Red-5mm-R-H-LEDLamp-13-000mcd-F-S_W0QQitemZ7623975978QQihZ016QQcategoryZ66954QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262
140* viewing angle, 11,000-13,000 MCD (I don't know about the reality of that)
or
http://www.besthongkong.com/product_info.php?cPath=75_18&products_id=157
70* viewing angle, 1000-1500 MCD
or
http://www.besthongkong.com/product_info.php?cPath=19_36&products_id=438
100* viewing angle, 2500-3000 MCD
All are right around the same forward voltage, But the last is a 80ma LED.

Resistor ratings?
I have found a bunch of schematics on how to wire LEDs to run as tail lights (dim) and brake lights (bright). Everything I found shows pretty much splitting the required impedance as 50/50% or 70/30% (full 100% needed impedance when the tails are on, but only partial resistance when the brakes are on). Correct me if I am wrong but..................... Wouldn't you rather have the full required resistor as your brake lights the add impedance on top of it for your tail lights? The reason I ask is the 50/50 or 70/30 splits that I see make me think too much voltage would be sent to the LEDs when in "brake" mode and would shorten the life of the LEDs.

Finally last question (for now) Diode?
I feel there should be a diode in between the tail and brake light resistors to keep any voltage "back feeding" from occurring (all the drawn schematics I found on this site made no mention of a diode). Again correct me if I am wrong. But if I am correct, what Diode should I run? I will be at a constant 14.0 volts situation, and accoring to the calculator I will be drawing around 680 mA for each complete tail light assembly.

Thank you everyone in advance for your help!!

[cadstarsucks]

why not just 12 HBs at 80Lm each?

I think the first on is at least an order of magnitude off (40Lm is not possible from one of those)

the second seems right at 1Lm each...

The third claims 10Lm and the calculator says 5.6.... dunno, maybe they are right since the calculator is not good at wide angles.

do not use an color over the LEDs-you will just decrease the light you get from them.  It is not the split but the max that effects the LED life.  I would use current sources to drive them, resistors are either very lossy or very damaging to the LEDs when the rail voltage is high.

[majorboost]

why not just 12 HBs at 80Lm each?

I think the first on is at least an order of magnitude off (40Lm is not possible from one of those)

the second seems right at 1Lm each...

The third claims 10Lm and the calculator says 5.6.... dunno, maybe they are right since the calculator is not good at wide angles.

do not use an color over the LEDs-you will just decrease the light you get from them.  It is not the split but the max that effects the LED life.  I would use current sources to drive them, resistors are either very lossy or very damaging to the LEDs when the rail voltage is high.

Thank you for the response!

I am assuming you are thinking of something to the following effects? Are you suggesting running a driver rather than resistors to get away from the carbon burn resistors can be associated with?

HB LED star
http://www.besthongkong.com/product_info.php?cPath=19_23&products_id=197

and

HB LED driver
http://www.besthongkong.com/product_info.php?manufacturers_id=&products_id=447

I have never worked with the heat sunk star HB LEDs, I'm not quite sure how they mount/solder to a PCB. Judging by the size of them (just over 3/4") I would still be able to go 3 rows tall, and at least 10 across, for a total of 30 on each side. But that in theory brings me to 42 amps of working current for both sides! I could run one relay for each side for full power handling.

Using LED drivers of this nature, how would I go about making a dim light for tail lights, and bright for stops then? I know you seem to be against them, but would a resistor before the driver for tails, then full 12 volt supply after the resistor for brake lights do the trick here?

As for color, I know you shouldn't use it over LEDs due to cutting down the light. But I am looking for a certain look, and am willing to add LEDs to make up for the brightness lost by having a color barrier.

Thanks again for the suggestions!
Eric

[justDIY]

I recommend starting a bit smaller than 30 hb leds.   A typical taillight app might support 2-4, depending on how good you are at thermal management.  The prolight led is old technology.  You'll get a lot of heat and a little bit of light from it, compared to something like the zLed or Luxeon Rebel.

consider this led ... it puts out 50 lumens at one watt and 100 lumens at three watts:

http://luxeonstar.com/item.php?id=5161&link_str=&link_catg=&partno=LXML-PH01-0050

consider this driver ... it supports dimming either electronically or by a manual dimmer control, a rheostat connected to two of its pins.  This would be able to operate  2 leds in series under all conditions or 3 leds in series under optimum conditions.

http://www.luxeonstar.com/item.php?id=862&link_str=240::241::1396&partno=3021-D-E-700

[cadstarsucks]

I am assuming you are thinking of something to the following effects? Are you suggesting running a driver rather than resistors to get away from the carbon burn resistors can be associated with?

HB LED star
http://www.besthongkong.com/product_info.php?cPath=19_23&products_id=197

and

HB LED driver
http://www.besthongkong.com/product_info.php?manufacturers_id=&products_id=447

I have never worked with the heat sunk star HB LEDs, I'm not quite sure how they mount/solder to a PCB. Judging by the size of them (just over 3/4") I would still be able to go 3 rows tall, and at least 10 across, for a total of 30 on each side. But that in theory brings me to 42 amps of working current for both sides! I could run one relay for each side for full power handling.

Using LED drivers of this nature, how would I go about making a dim light for tail lights, and bright for stops then? I know you seem to be against them, but would a resistor before the driver for tails, then full 12 volt supply after the resistor for brake lights do the trick here?

As for color, I know you shouldn't use it over LEDs due to cutting down the light. But I am looking for a certain look, and am willing to add LEDs to make up for the brightness lost by having a color barrier.

Thanks again for the suggestions!
Eric

Yes, but besthongkong's are crumby by today's standards.  I was actually thinking of 12 total, you want to alert the driver behind you, not blind him.   Pointing 60 100Lm LEDs at him is like 6 headlamps shining in his face!

12 good LEDs at 700mA each is 1200Lm already.  A car headlight is about 1000Lm.  12 of those besthongkong LEDs will be 600Lm still potentially blinding and only 8.5A total.

They would be PWMed for dimming and max for braking, though you would want to set the "max" down to a safe level.

[majorboost]

I recommend starting a bit smaller than 30 hb leds.   A typical taillight app might support 2-4, depending on how good you are at thermal management.  The prolight led is old technology.  You'll get a lot of heat and a little bit of light from it, compared to something like the zLed or Luxeon Rebel.

consider this led ... it puts out 50 lumens at one watt and 100 lumens at three watts:

http://luxeonstar.com/item.php?id=5161&link_str=&link_catg=&partno=LXML-PH01-0050

consider this driver ... it supports dimming either electronically or by a manual dimmer control, a rheostat connected to two of its pins.  This would be able to operate  2 leds in series under all conditions or 3 leds in series under optimum conditions.

http://www.luxeonstar.com/item.php?id=862&link_str=240::241::1396&partno=3021-D-E-700

That looks like the ticket right there. Due to the space that I have (24" wide and 2 1/8" tall), I should be able to run a total of 6 (like cadstarsucks suggested in the first place) in each light housing with no chance of overheating them.

The only problem I have with running the newer HB LEDs is I have no idea how they mount (I'm used to pins that stick through a PCB), or how to heat sink them properly. I have only played with the 5mm and the Pirahna style lights before. I am more of a PCM programmer than a PCM builder when it comes down to cars.

The driver confuses me too (I'm sorry for my ignorance) I understand the wiring for full brightness, but I would need the dim feature triggered by a single wire not a rheostat. The driver instructions also say to use the number of LEDs that will equal 2 volts under drive voltage for drop across the driver it's self. In my mind that would mean I should use 4 LEDs per driver due to running a perfect 14 volt supply. Again please excuse my ignorance if I am incorrect.

I have much to learn about the newer LEDs and drivers. It looks like I will be completely revamping my project. At least this way it is guaranteed I am happy with the results though.

If you have some time to explain these modern LEDs and drivers to a simple minded guy, I would appreciate it.

[majorboost]

[/quote]
Yes, but besthongkong's are crumby by today's standards.  I was actually thinking of 12 total, you want to alert the driver behind you, not blind him.   Pointing 60 100Lm LEDs at him is like 6 headlamps shining in his face!

12 good LEDs at 700mA each is 1200Lm already.  A car headlight is about 1000Lm.  12 of those besthongkong LEDs will be 600Lm still potentially blinding and only 8.5A total.

They would be PWMed for dimming and max for braking, though you would want to set the "max" down to a safe level.
[/quote]

Got ya!

Thank you for putting that into prospective for me! That is tearms I can understand! I did not know that a car headlamp was around 1000Lm. That will now allow me to make a better educated guess on how bright certain LED clusters MAY be.

Thank you again!!!

[cadstarsucks]

Thank you for putting that into prospective for me! That is tearms I can understand! I did not know that a car headlamp was around 1000Lm. That will now allow me to make a better educated guess on how bright certain LED clusters MAY be.

Thank you again!!!

Not a problem....another little frame of reference is that the incandescent bulbs in the tail lights are about 10Lm/W and you can take probably 75% of that away for the red filter, leaving you with 2.5Lm/W.   Now when you compare that to these LEDs that are putting out 50Lm/W you can get an idea of how much light you are getting.

[majorboost]

[/quote]
Not a problem....another little frame of reference is that the incandescent bulbs in the tail lights are about 10Lm/W and you can take probably 75% of that away for the red filter, leaving you with 2.5Lm/W.   Now when you compare that to these LEDs that are putting out 50Lm/W you can get an idea of how much light you are getting.
[/quote]

That is some killer info right there! I now have a better idea on what to expect performance wise out of what I am building. I don't need to be as nervous thinking "will they see me stopping", Now I just need to worry "am I going to blind someone" LOL.

Also the link that JUSTDIY gave me for the HB LEDs gives no beam angle. They describe it as "Radiation Pattern     Lambertian" What does that mean angle of viability wise?

Thanks again guys! I am glad I have your knowledge to soak up!

[justDIY]

the rebel has a bug eye (fish eye?) lens on it, supporting a viewing angle of approx 140 degrees.   the page I linked to contains more links to the technical specifications, as well as a thermal design guide.

you want a heavy chunk of aluminum or copper to attach these leds to, to keep them cool - if you can machine something to replace the stock plastic/steel taillight reflector with something in aluminum, with areas to attach the leds, you'll be a real good shape.  failing that, try to find some surplus "socket 771 xeon" heatsinks.   They're a big slab of copper/aluminum with a very flat base and generous fins - they would easily have enough room to hold your six leds.  however, I have ~10 watts of leds on one, and it gets hot to the touch relying on natural convection alone.

you're correct with your voltage calculation ... you need at least 14v to run 12v worth of leds at full power.  The buckpuck actually has less than 2v of overhead, the ones I've worked with deliver nearly full current with approx 1v of headroom.

one approach to driving the six leds Dan suggested would be a 3 x 2 array (2 parallel strings of 3 leds) and using the 1000ma driver.   This will drive the leds at about 2 watts each, and let you use one driver to run each group of six. 

for the dimming part - set your "dim" brightness level using a pot or fixed resistor, and then open the resistor circuit with a relay on your brake light switch, which will kick the buck puck into full output mode.

[majorboost]

the rebel has a bug eye (fish eye?) lens on it, supporting a viewing angle of approx 140 degrees.   the page I linked to contains more links to the technical specifications, as well as a thermal design guide.

you want a heavy chunk of aluminum or copper to attach these leds to, to keep them cool - if you can machine something to replace the stock plastic/steel taillight reflector with something in aluminum, with areas to attach the leds, you'll be a real good shape.  failing that, try to find some surplus "socket 771 xeon" heatsinks.   They're a big slab of copper/aluminum with a very flat base and generous fins - they would easily have enough room to hold your six leds.  however, I have ~10 watts of leds on one, and it gets hot to the touch relying on natural convection alone.

you're correct with your voltage calculation ... you need at least 14v to run 12v worth of leds at full power.  The buckpuck actually has less than 2v of overhead, the ones I've worked with deliver nearly full current with approx 1v of headroom.

one approach to driving the six leds Dan suggested would be a 3 x 2 array (2 parallel strings of 3 leds) and using the 1000ma driver.   This will drive the leds at about 2 watts each, and let you use one driver to run each group of six. 

for the dimming part - set your "dim" brightness level using a pot or fixed resistor, and then open the resistor circuit with a relay on your brake light switch, which will kick the buck puck into full output mode.

Perfect, I think I am catching on to these suckers now.

I will be building custom housings for the tail light lenses out of .063 thickness aluminum so I assume I can use the complete housing as a heat sink (that should make for nice surface area for heat dissipation) . I would also assume then that I would just drill holes into the aluminum where the anode and cathode connections are and solder wires strait to them? How would I mount the LEDs to the aluminum, screws and thermal grease (if that is the case I don't see any factory holes in the LEDs for screws, where is it safe to drill through), or should I use thermal epoxy?


2 parallel strings would look something to this nature? 

                    >---------->----------->
        pos-----                                 ----------- neg
                    >---------->----------->

Just want to be 100% sure so I don't fry my project to oblivion.


For the relay action I should be able to use two single pole double throw relays piggy back style then. The first relay would be triggered when either the tail lights, or the brake lights were turned on to send power to the second relay in it's triggered state. In it's rest state, it would be open circuit. Then the second relay in it's rest state would be the tails with resisted voltage, in its triggered state (brake lights illuminated) it would be full 14 volts.

Does all of this sound right so far?

[cadstarsucks]

Perfect, I think I am catching on to these suckers now.

I will be building custom housings for the tail light lenses out of .063 thickness aluminum so I assume I can use the complete housing as a heat sink (that should make for nice surface area for heat dissipation) . I would also assume then that I would just drill holes into the aluminum where the anode and cathode connections are and solder wires strait to them? How would I mount the LEDs to the aluminum, screws and thermal grease (if that is the case I don't see any factory holes in the LEDs for screws, where is it safe to drill through), or should I use thermal epoxy?


2 parallel strings would look something to this nature? 

                    >---------->----------->
        pos-----                                 ----------- neg
                    >---------->----------->

Just want to be 100% sure so I don't fry my project to oblivion.


For the relay action I should be able to use two single pole double throw relays piggy back style then. The first relay would be triggered when either the tail lights, or the brake lights were turned on to send power to the second relay in it's triggered state. In it's rest state, it would be open circuit. Then the second relay in it's rest state would be the tails with resisted voltage, in its triggered state (brake lights illuminated) it would be full 14 volts.

Does all of this sound right so far?

Yep...I was actually thinking of 3 strings with 2 in series so it would get away from the battery voltage... I never think of the buck pucks since I design the stuff all day anyhow and tend to have more resources then your general hobbyist.  If I wanted to be fancy I could get raw rebels and make a PCB by etching a laser printer image and go next door and solder the things down with the infrared reflow ovens!  I might be getting a design job soon that will be using them! 

The notches around the edge of the stars are for screws.  There are a number of ways to do it, but what ever you do you need to regulate the current through the LEDs and dim them further for your "running lights"

Dan

[justDIY]

For the relay action I should be able to use two single pole double throw relays piggy back style then. The first relay would be triggered when either the tail lights, or the brake lights were turned on to send power to the second relay in it's triggered state. In it's rest state, it would be open circuit. Then the second relay in it's rest state would be the tails with resisted voltage, in its triggered state (brake lights illuminated) it would be full 14 volts.

Does all of this sound right so far?

if you're using a buckpuck, your relay or relays should be isolated from the car's electrical system, other than being switched by the existing brake light wiring.   the buck supplies 5v on one of its pins, and feeding that 5v into the dim pin causes the puck to turn off.   using a resistor to drop that voltage to something between 0v and 5v causes the puck to vary its output proportionally (more or less), with 0v being full-on and 5v being full off.

Dan suggests "pwm" which turns the puck on and off rapidly, resulting in a dimming effect thanks to our slow eyes.   The puck supports pwm dimming and you'll need a simple circuit to generate the pwm dimming signal.  You'll also need some way of determining when it gets applied.

Relays can get a bit tricky too.  Lets say your brake lights are on, and so is a turn indicator... typically it's not a problem with a hot wire bulb, since you either have two bulbs, or one bulb with two filaments.  with the leds, you'll have to work out some logic to make sure the braking and flashers still work as intended.

You could of course, rip out the car's analog brake light circuit and control the tailights digitally.  a simple microcontroller and a few fet switches could provide the pwm signal needed to dim the lights, as well as flashing them for turning / hazard or even strobing them for showing off in the parking lot.

[majorboost]

[/quote]
Yep...I was actually thinking of 3 strings with 2 in series so it would get away from the battery voltage... I never think of the buck pucks since I design the stuff all day anyhow and tend to have more resources then your general hobbyist.  If I wanted to be fancy I could get raw rebels and make a PCB by etching a laser printer image and go next door and solder the things down with the infrared reflow ovens!  I might be getting a design job soon that will be using them! 

The notches around the edge of the stars are for screws.  There are a number of ways to do it, but what ever you do you need to regulate the current through the LEDs and dim them further for your "running lights"

Dan
[/quote]

Yeah, I don't know if I would be able to tackle my own drivers too. I think as it is I am starting to get a little over my head in this project LOL. I definately don't have the resources you do. All of my resources are for mechanical and pre-made electrical automotive parts. I use off the shelf electrical parts for the most part when I want to build something custom. My only resource for this stuff is right here on this forum. I can build simple boards with the right instruction, but a good chunk of this site is well over my head. I will be using the off the shelf Buck Pucks, I like the way they are packaged and everything.

I will be using the luxeon Rebel LEDs that JUSTDIY gave me this link to
http://www.luxeonstar.com/luxeon-rebel-led-redorange-50-lumens-350ma-p-153.php?id=5161&zenid=12rh7d6ujv5262gamncavrvnq7

Although I may go with the pure reds that put out 80Lm

Do I still need the stars for these, or can I go strait to the aluminum housing as the heat sink?

[majorboost]

if you're using a buckpuck, your relay or relays should be isolated from the car's electrical system, other than being switched by the existing brake light wiring.   the buck supplies 5v on one of its pins, and feeding that 5v into the dim pin causes the puck to turn off.   using a resistor to drop that voltage to something between 0v and 5v causes the puck to vary its output proportionally (more or less), with 0v being full-on and 5v being full off.

Dan suggests "pwm" which turns the puck on and off rapidly, resulting in a dimming effect thanks to our slow eyes.   The puck supports pwm dimming and you'll need a simple circuit to generate the pwm dimming signal.  You'll also need some way of determining when it gets applied.

Relays can get a bit tricky too.  Lets say your brake lights are on, and so is a turn indicator... typically it's not a problem with a hot wire bulb, since you either have two bulbs, or one bulb with two filaments.  with the leds, you'll have to work out some logic to make sure the braking and flashers still work as intended.

You could of course, rip out the car's analog brake light circuit and control the tailights digitally.  a simple microcontroller and a few fet switches could provide the pwm signal needed to dim the lights, as well as flashing them for turning / hazard or even strobing them for showing off in the parking lot.
[/quote]

I understand now. I am using the Buck Pucks own 5 volt reference with a resistor on top of it to dim the lights. I am simply attempting to bring the 5 volt reference to around 2-4volts to find the best cut light for tail lights. I am just using vehicle brake supply voltage to trigger the relay for the Buck Puck. Got it!

My brakes and turn signals are on the same circuit, that passes through the turn signal switch. I will need to run two relays per tail light. Relay #1 will be energized by the tail lights + the brake / turn signal switch. When energized the relay will send full 14 volts to the puck. I will need a diode on the tail light wire pointing towards the relay so when the brake or the turn signals are energized the rest of the lights don't illuminate. Relay #2 will be for the puck it's self on the 5 volt side with resistor. When relay #2 is in rest state (single pole double throw) it will supply the reference to the puck telling it to dim the lights. When relay #2 is energized (by the brake switch, or the flashing turn indicator) It will go to open circuit causing 0 volts at the puck reference return and allowing full brightness.

In theory the relay should put enough load on the system to still flash with the signals. If not, I'll worry about that hurdle when I come to it. I could try an electronic flasher first, if that doesn't work, I may have to eliminate the factory set up and go all out custom. Again I'll worry about that later. If you see a new thread entitled "custom built tail lights, now the turn signals won't work" you know it's me LOL.