2x 20W LED - advice needed for cooling and building

[AndersAR]

Hello, my first post here. I was told to try and get some advice here after posting my build-thread on a bicycle-forum.

I've started building my own 2x20W LED bicycle light, for the purpose of singeltrack riding.

So far, I've built a carbonfiber housing with 2 "barrels" close to each other, with an approx. diameter of 45mm of each barrel.
The LED modules are Edison Opto 20W (bright white, 5000-10000 K)
Battery is Powerizer 5200 mAh 12V LiFe-PO4.
Driver was included from the seller, 1A rated output at 12-14V if I remember correctly.

However, after some building time, wireing and measuring, I've come to a hault. I'm having trouble getting satisfied with the cooling of the modules.
I've tried 2 different aluminium heatsinks, but I'm not happy so far.
I'm a civil engineer by profession, hence, I want to be as conservative as possible when it comes to cooling. My target was staying ~10 C below max rated temp when "standing still" with my bike - meaning there would be virtually NO air traveling across the heatsink, besides the flow generated by the difference in temperature.

So, anyone with some advice/help for me, in regards to:
-Keeping the temperature down
-Fitting all together without too much exposure to "foreign elements" like water & snow
-Lenses with a spreading angel of about 15 degrees.

The max temp rating is about 60 C, and I reach this temperature in about 2-3 minutes of testing.
The likelyhood of standing still for so long during the cold & dark periods of the winter is small, but I want to make sure everything works flawless before bringing my rigg outdoors.

Pictures of the building process and components so far;

Building the housing for the light

Almost done, just need some final cutting, grinding and clearcoat.

3 of the 4 20W LED I purchased for the project

My testbed, an Intel Core 2 Due boxed heatsink with the LED and driver module

Powerizer 5200 mAh 12V LiFePO4 batterypack connected, had to put the light under my couch to protect my eyes

The old and the new heatsink, both intended for computer purposes, the new blue one is a north/southbridge chipset heatsink.
Both cut to fit inside the housing, that's why the corners are cut off.

Best regards,
Andy

 

[dom]

Hi Andy:welcome:

Unfortunately -your heatsinks will be useless inside the housing as all you will have is an oven cooking your LEDs .

You need to have the heatsink outside to take advantage of airflow. I don't think carbon fiber is the best stuff to use for dissipating heat either.

Have a look at some of the bike light builds people have made -will give you a better idea of what you need to do.
http://candlepowerforums.com/vb/showthread.php?t=169531
http://forums.mtbr.com/forumdisplay.php?f=124http://forums.mtbr.com/forumdisplay.php?f=124

Not sure what reflector/optic you could use for those LEDs either.

Cheers
Dom

 

[AndersAR]

Yes, I quickly realized I had to do something about that. Carbon is well known for not dissipating heat, so we might call that a design-error on my part, but I thought that it would make a strong and cool-looking shell around it.
Fortunatly, I anticipated trouble and made the shell a lot longer than necessary.

Thanks for the tip, I'll look into it

 

[DM51]

Welcome to CPF, AndersAR. That looks an interesting project.

In case you are wondering what happened to your 2nd post there, it was awaiting validation as you are a new member. That was the reason for the delay before it appeared.

This is a new procedure which was initiated only yesterday.

 

[odessit]

What about creating a water-proof capsule for the electronics only and placing it inside the carbon "tubes"?
The tubes can have air circulating slots and house the heatsink with a small fan.

 

[AndersAR]

I've tried that, that was the original plan actually...But they develop so much heat, I don't think I can get a fan to cool them sufficiently..Like Dom said, it becomes more or less like an oven inside. I wasn't too keen on adding holes for ventilation, but that might be my only option if I'm going to get this to work out.
I tried with an old 40mm fan behind, that did help for a while, but not enough.

A heatpipe is a possible sollution, I might try that later today if I can find all the components in my "hardware box" - a box filled with virtually all components ever removed from my computers... :S

DM51; I noticed, I've used vBulletin elsewhere, so I started wondering but quickly realized that it was a server-side thing and not something wrong with my connection.

 

[KowShak]

How many lumens do those Edison Opto 20W LEDs put out? Do they put out more lumens than a P7 or MC-E driven at 12W (ish) ?

 

[AndersAR]

At 1.1A or 1.2A (max if i remember correctly) the put out 1000 lumens each.
The driver is rated to 1.0A only, so I guess we could say at least 900+ lumens each.

 

[KowShak]

Is this the LED you're using?

http://www.edison-opto.com.tw/products_detail.asp?category=1&cno=14

Looking at their data for that LED, efficiency is between 40 lumens/watt and 55 lumens/watt (assuming my calculations are correct) and they put out only 900 lumens. SSC P7s would be in the 60-85 lumens/watt range, so it would seem that they're not quite as efficent as a P7, but you'd need 3 average P7s (or 2 top bin P7s) to create the same amount of light!

I've heard people say in the past that carbon fibre is quite a good conductor of heat, the carbon fibre itself is quite good but it tends to be insulated by the resin. Maybe you could lay down your fibres in a special sort of pattern to maximise heat transfer rather than the usual concern of making it strong and light!

 

[AndersAR]

Yes that's the one I assume.
....there should be plenty of light available when I get it done, that's for sure

Carbon is a terrible heat conductor actually. That is one of the reasons you are able to walk on burning coal or so I've heard/read somewhere.

Its a bit of work to get the carbonpart done, so I won't do it again for this project, but I did go out and look for an aluminium box today, in case I find one that fits my project...

But keep it coming, suggestions are always nice...We all learn new things every day...

 

[snarfer]

Actually carbon is not necessarily such a bad heat conductor. You could use pitch-based...

some people even make heatsinks out of it and claim they can beat the performance of copper.

If this was my light I would have the driver monitor the temperature and dim as needed in order to keep the LEDs from overheating. Most likely you will not have any problems when you're actually riding, due to the increased airflow, at least as long as that heatsink is mounted in such a way that it is completely exposed to the outside air. So it is just a matter of addressing the thermal issues when stopped or riding slowly.

Something I don't understand though is your driver setup. Are you saying that you have two drivers each running at 12-14v 1A? According to the datasheet the Edipower 20W emitters are rated at 16 volts, and something like 1.3 A for full 20W output.

EDIT:

Oh I see now. You have drivers that don't dim. Probably some type of boost driver. Maybe you could get rid of the two drivers and run the LEDs in series off of one dimmable driver instead. Then design a circuit that would dim the LEDs based on temperature feedback.

As for your optical question I will be very impressed if you find any way of confining those LEDs to a 15 degree beam. Maybe your best bet is to try to find a reflector or make one yourself. In order to control that sort of beam you need some rather large optics, due to the large size of the light emitting area. Perhaps you could modify something designed for incandescent lamps.

Looks like a very cool project though.

 

[AndersAR]

Looks like an interesting project, thanks for the link. I've always regarded carbon as an insulator rather than conductor

I got the tip about letting the driver monitor temperature earlier, and I might go for that possibility.... Any drivers you would recommend for driving in series / parallell ?
Thanks,
andy

 

[snarfer]

Yes actually carbon fiber is one of the best heat conductors there is, but only along the fibers, and only in certain molecular configuration. It is used for cooling in aerospace applications. And in nuclear reactors too.

There aren't that many drivers out there that can handle that kind of load. There is a list here.

I don't really think driving them in parallel would be such a great idea due to possibility of unevenly distributed load, especially at that kind of power level.

You could use the CCHIPO driver v1.2, but it is kind of bulky.

If you are extremely handy with electronics you could construct this solution, but you'd need a slightly higher output voltage. Probably all you'd need to change would be the capacitors, mosfets and inductor. And of course you'd have to do your own layout and figure out how to mount parts on both sides of the circuit board. Hmm maybe not so easy after all.

I developed my own drivers for these sorts of high power applications. But sadly they're not ready yet. Maybe next month.

 

[AndersAR]

Alright, back on track with this thread!
I've been working on my light the last few days, and finally got a new housing and some "temporary" reflectors installed!
Pictures follow below:

This is my "proposed flowchart for connecting the CCHIPO board, does it look reasonable?




Running a little test to see how long it takes to heat up without air circulating...After 5-10 minutes it got pretty hot, so I say it's good enough.


The new aluminium casing


The reflectors I used were ordinary spotlights, which I simply cut at the back to let the light from my LED pass through. I'm not happy so with that sollution, but it works. On the package it said 12 degrees of light, but that depends mostly on where the lightbulb is placed, right?
It didn't seem like 12 degrees to me at least..


Here is the LEDs assembled. I used the plates I cut out of the front cover to build them a little higher, closer to the back of the reflector.


The front of my bike with the light attached.


Testing


Please give me your comments so I can improve both the design and the technical aspects of my light!
Thanks,
Andy

 

[snarfer]

Your proposed layout for the CCHIPO driver left out the potentiometer (i.e. dimming control). Technically you could go without, but it would probably be nice to have, given the power draw of this light.

 

[AndersAR]

Yes, as I understood from the manual I could use it without an external potmeter. I'll have a look at it when i start to get things put together again, atm I will just use my original drives...

It's been a while (several years actually) since last time I used a potentiometer. Could anyone give me a hint (an old thread or something) as to how I calculate what size I need?

 

[snarfer]

I hooked up a 50k pot to a CCHIPO and it worked fine. It would also possible to make a circuit with temp sense resistor and a transistor in series with the pot in order to automatically dim the light when it gets too hot. Not sure what the exact specs on that circuit would be but I know I've seen something like that done before.

 

[AndersAR]

Alright, thanks for the tip, I'll look into it !
This site is truly a great resource for DIY'ers