Help with automotive project....

ocelot27 · Mar 20, 2009

Hi,

I'm going to work on a headlight system for a Lotus Exige (the car currently has H1 and H7 lamps). I was thinking 3 P7's for the low beam and 4 P7's for the high beams - this would put me in the realm of HID automotive lamps in terms of light output.

I plan to cluster the P7's on 40x40mm heat sinks for each light assembly.

The issue is driving (not the car). I can't find a driver that will do 20A (enough to drive 7 P7's). I have found LED driver chips that will do 20A but not any completed boards using these chips. Is there anyone here who does one off custom board design/fab or is there a production 20A driver board that could be powered from 12vdc?

Why you ask? Well... it will be fun and, yes I know they could fail and they won't be legal etc etc

Any help is greatly appreciated...
-john.

Superdave · Mar 21, 2009

remember, operating voltage of a car is typically between 13.6 and 14.4V while running. Sometimes even into the 15V range.

ocelot27 · Mar 21, 2009

Superdave said:
remember, operating voltage of a car is typically between 13.6 and 14.4V while running. Sometimes even into the 15V range.

Yeah, I know... luckily, most of the buck driver chips have wide input voltage ranges - need a board that will do 5 P7's for each side of the car. I was thinking 3 running for low and then adding another two for high - that would put the low in the 2100-2800 lumen and the high in the 3500-4500 lumen range...
-john.

LukeA · Mar 21, 2009

This is a very inappropriate and illegal project to attempt. It's also one that you are almost wholly unqualified to begin, as you don't seem to understand the dangers involved.

saabluster · Mar 22, 2009

LukeA said:
This is a very inappropriate and illegal project to attempt. It's also one that you are almost wholly unqualified to begin, as you don't seem to understand the dangers involved.

You are making some assumptions there Luke. It very well could be for "off road" such as on a race track. DOT has no say so there. Considering the type of car I'd say that was very likely. Also do you really understand his qualifications?

jasonck08 · Mar 22, 2009

ambientmind · Mar 22, 2009

John, I dont know of any drivers that will power that many P7s off of that voltage, if you find one let us know! My only concern is the heatsink. 40x40mm isnt much to dissipate ~60 watts of heat. A single P7 will make even a maglite hot, nevermind 5 of them. Maybe some sort of forced cooling is in order? :thinking: Also, optics will be a concern. Output is one thing, but its hard to beat HID in terms of throw and beam shape for a vehicle. It would be very difficult to match that with the P7 given the available optics. In any case, good luck!

LukeA · Mar 22, 2009

saabluster said:
You are making some assumptions there Luke. It very well could be for "off road" such as on a race track. DOT has no say so there. Considering the type of car I'd say that was very likely. Also do you really understand his qualifications?

ocelot27 said:
they won't be legal etc etc

The OP begins to address the issue of legality. That issue of legality applies on public roads, so yes I do understand.

ocelot27 · Mar 22, 2009

LukeA said:
This is a very inappropriate and illegal project to attempt. It's also one that you are almost wholly unqualified to begin, as you don't seem to understand the dangers involved.

I know I'm new here but I've a lot of experience with forums and it seems they all have their ups and downs. You my friend would be a down.

I canme here seeking help and get this - great forum.

Please explain what my qualifications are - where I went to college what degree I have, where I got my post graduate degree, where I did my post-doctoral training, how many year experience I have etc etc.

Also explain how it's "dangerous."

Thanks for your help.
-john

ocelot27 · Mar 22, 2009

ambientmind said:
John, I dont know of any drivers that will power that many P7s off of that voltage, if you find one let us know! My only concern is the heatsink. 40x40mm isnt much to dissipate ~60 watts of heat. A single P7 will make even a maglite hot, nevermind 5 of them. Maybe some sort of forced cooling is in order? :thinking: Also, optics will be a concern. Output is one thing, but its hard to beat HID in terms of throw and beam shape for a vehicle. It would be very difficult to match that with the P7 given the available optics. In any case, good luck!

I was thinking of not running them at full output as it won't be necessary to meet the amount of light needed. I've read the thermal management papers and heat sinking will be tough design challenge but it's doable - I'll use Peltiers if I have too.

My EE skills are a little rusty.... I found that National Semiconductor actually has a web site that will design boards for you - for some chips they will make the board - and it's cheap! So, I think I will end up contacting them. I'm surprised Mr. Skywalker didn't mention that in his generously tactful and helpful post?
-john

ocelot27 · Mar 22, 2009

LukeA said:
The OP begins to address the issue of legality. That issue of legality applies on public roads, so yes I do understand.

Maybe I should remind you of some other issues of Legality - such as the illegal trade in radioactive materials that occurs right here on this forum. The legality of the project isn't your concern - you're not helping - please be nice and find someone else to pick on.
-john.

ocelot27 · Mar 22, 2009

ambientmind said:
John, I dont know of any drivers that will power that many P7s off of that voltage, if you find one let us know! My only concern is the heatsink. 40x40mm isnt much to dissipate ~60 watts of heat. A single P7 will make even a maglite hot, nevermind 5 of them. Maybe some sort of forced cooling is in order? :thinking: Also, optics will be a concern. Output is one thing, but its hard to beat HID in terms of throw and beam shape for a vehicle. It would be very difficult to match that with the P7 given the available optics. In any case, good luck!

National Semi makes a bunch. Linear makes a 10A but that is the highest. I Shark Buck appears to use a Linear product. You can design whatever board you want here:

http://www.national.com/analog/webench

If they support the chip you've chosen they will even build the prototype board for you to eval. If not you just take the schematic to your favorite PCB fab house.

As far as optics - the low beam is easy since it's basically a flood lamp with a horizontal cutoff - the car already has the low beam "lenses" I was hoping to use those somehow - experimentally. The high is going to need some optics for longer throw.

-john

ocelot27 · Mar 22, 2009

Oh, one last thing Luke - I found this:

https://www.candlepowerforums.com/threads/192918

Very interesting!
-john

ecotack · Mar 22, 2009

Replacing 'E' marked 55/60 watt bulbs in cars with HID or even 100/80 watt is supposedly illegal, but lots of people do it. As long as the beam pattern passes an MOT (or equivalent) then there isn't a problem, well until you crash and the insurance company finds out. I have HIDs on my Honda Blackbird, to help reduce the SMIDSY incidents. It passed the yearly MOT no problem. Getting the beam pattern correct for LEDs is going to be the difficult bit.

For your driver make sure it has the voltage range expected from a car (12-15VDC) and use several drivers keeping the LEDs wired in such a way that if one LED or driver fails the others keep going.

TaskLEDs CCHIPO driver looks useful.

I have a TVR Chimaera and have started on some small spots using DXs P60 sized module sets.

ocelot27 · Mar 22, 2009

Looks like the CCHIPO is only 1A...

Benson · Mar 22, 2009

ocelot27 said:
Hi,

I'm going to work on a headlight system for a Lotus Exige (the car currently has H1 and H7 lamps). I was thinking 3 P7's for the low beam and 4 P7's for the high beams - this would put me in the realm of HID automotive lamps in terms of light output.

I plan to cluster the P7's on 40x40mm heat sinks for each light assembly.

The issue is driving (not the car). I can't find a driver that will do 20A (enough to drive 7 P7's). I have found LED driver chips that will do 20A but not any completed boards using these chips. Is there anyone here who does one off custom board design/fab or is there a production 20A driver board that could be powered from 12vdc?

I think you might be approaching several aspects of the design poorly. First, it seems you want to use one driver for both low and high beams. But that means when you want low beams, you'll have to switch off the high-beam LEDs and cut back the current supplied -- if you keep them all connected, they just run dimmer, and if you just disconnect the highs, the lows take the full 20A and :poof:

. So I'd think you want two separate drivers, one for low and one for high.

Second, if you want to drive 3 or 4 LEDs at 3A each, you shouldn't connect them in parallel and feed it 9A or 12A, unless you're somehow sure the LEDs are quite well matched. The lowest-Vf emitter will hog current, which will make it heat faster, which may result in thermal runaway and :poof:

, but at best will "only" cause significant brightness variations. You either need to run the LEDs in series chains, use a separate driver per LED, or both (i.e., several series chains with one driver per chain).

(I've thought some about rigging my own LED headlights, and it looks like a fun project, but since I don't have a car to put them on, kinda pointless for me... Good luck and have fun with yours!)

ocelot27 · Mar 22, 2009

Benson said:
I think you might be approaching several aspects of the design poorly. First, it seems you want to use one driver for both low and high beams. But that means when you want low beams, you'll have to switch off the high-beam LEDs and cut back the current supplied -- if you keep them all connected, they just run dimmer, and if you just disconnect the highs, the lows take the full 20A and . So I'd think you want two separate drivers, one for low and one for high.

Second, if you want to drive 3 or 4 LEDs at 3A each, you shouldn't connect them in parallel and feed it 9A or 12A, unless you're somehow sure the LEDs are quite well matched. The lowest-Vf emitter will hog current, which will make it heat faster, which may result in thermal runaway and , but at best will "only" cause significant brightness variations. You either need to run the LEDs in series chains, use a separate driver per LED, or both (i.e., several series chains with one driver per chain).

(I've thought some about rigging my own LED headlights, and it looks like a fun project, but since I don't have a car to put them on, kinda pointless for me... Good luck and have fun with yours!)

Thanks! I've kinda came to that conclusion last night by playing with the tools on National Semi's site. There will need to be 4 drivers and the LED's will be in series.
-john

Al Combs · Mar 22, 2009

+1 to Benson's they must be in series. The exception is something like the P7 itself. Being made on the same die, the 4 LED's really are identical. Of course that doesn't hold true for multiple P7's.

If you're already looking at TaskLED, have you seen the hipCC? It's a buck regulator, so you can only have 3 per regulator. That would mean if you want 4 LED's per high beam, you need a 3rd regulator there, or 5 all together. They're not too expensive and very efficient. Figuring 3 P7's @ 13.5 volts is roughly 96% efficient based on the graph.

As far as the heat goes, I don't know if there is enough room but a heat pipe CPU cooler could easily handle the power.

Al Combs · Mar 22, 2009

I almost forgot, :welcome:

ocelot27 · Mar 22, 2009

Al Combs said:
+1 to Benson's they must be in series. The exception is something like the P7 itself. Being made on the same die, the 4 LED's really are identical. Of course that doesn't hold true for multiple P7's.

If you're already looking at TaskLED, have you seen the hipCC? It's a buck regulator, so you can only have 3 per regulator. That would mean if you want 4 LED's per high beam, you need a 3rd regulator there, or 5 all together. They're not too expensive and very efficient. Figuring 3 P7's @ 13.5 volts is roughly 96% efficient based on the graph.

As far as the heat goes, I don't know if there is enough room but a heat pipe CPU cooler could easily handle the power.

I think that 3 low and adding 2 for a total of 5 for high is a good place to be and that board will work - I will need 4 of them though...

I have thought a lot on the cooling and the space behind the headlight assemblies is limited - I really to take the tires off again and get in there to have a good look to see how much space there is for heat sink(s).

I used two heat pipe style heat sinks for a Peltier cooler I made -- worked very well...

Thanks a lot for the help
-john

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