DIY LED water cooled, high limit temp switch

So the Cree LEDs I am considering are shown in the tables at 85c, and with a water cooled heat sink scheme I expect temps would more likely run around 20-30c. It's cheaper than heavy passive sinks and active/fan cooled, and using a submersible pump, just about silent. I'd like to put a fail safe temp switch on it to shut the whole thing off in case of any overheating problems. Simple temperature switches can be thermally bonded to the sink, are cheap and can handle the load.

What temp would you choose as a fail safe to avoid frying LED strings if cooling fails (very unlikely)? This would be bonded to the heat sink, so not actual junction temp

Just another thought for something that's fairly cheap and effective and you don't have to deal with water and potential leaks - square aluminum tubing with a pressuriziing fan...take a look at stevesleds.com

jcmjrt said:

Just another thought for something that's fairly cheap and effective and you don't have to deal with water and potential leaks - square aluminum tubing with a pressuriziing fan...take a look at stevesleds.com

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Thanks, You already directed me there on... er... some other forum.

I'll have 5-6 rails and if I run 5-6 fans that's too much cost, or if I build manifolds, it's about the same amount of work to use less fans compared to water cooling. Using water, parts costs are lower, and LEDs will run cooler with higher flux; More operational efficiency/output. My plumbing skills are good, I don't fear leaks.

Water cooling is about as good as it gets. The biggest downside is leaks and if you aren't worried then you'll certainly have a "cool" system in all senses. I'd love to see a pic/ hear about it when you are done.

Bump ^^^

Anyone?

Sorry forgot to reply

I would set your cutoff at 80C (at heatsink), the LEDs will easily take this but it is indicative of catastrophic failure in your cooling, in which case they will only get hotter.

Assuming its XTE's you;re looking at judging from the bin temp?

edit: I would also love to see pics/build journal. watercooling is something i havent really bothered to learn about so im really interested to see the results of someone who knows what theyre doing.

SnotBoogie said:

Sorry forgot to reply

I would set your cutoff at 90C, the LEDs will easily take this but it is indicative of catastrophic failure in your cooling, in which case they will only get hotter.

Assuming its XTE's youre looking at judging from the bin temp?

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Thanks for the reply,

Yes, XTE, however, while 90c would be fine if it was measuring junction temp, we are talking about heat sink temp not junction temp per se. If the heat sink temp was 90, junction temps would be would be a disaster, no?

ninja-edited to say 80C, but if you have such high thermal resistance as to have dramaticdifferences in heatsink/junction temps, there are other problems.

I would expect a junction temp of 100C with a 80C heatsink temp, which is absolutely fine for the short period it would take to shut off.

though, i am giving a pretty optimistic number for some reason...PERSONALLY, i would set it to 50C @ heatsink, because if your cooling fails, your cooling fails right? Its either gonna be at ~30-40C or bust, if you know what i mean?

SnotBoogie said:

ninja-edited to say 80C, but if you have such high thermal resistance as to have dramaticdifferences in heatsink/junction temps, there are other problems.

I would expect a junction temp of 100C with a 80C heatsink temp, which is absolutely fine for the short period it would take to shut off.

though, i am giving a pretty optimistic number for some reason...PERSONALLY, i would set it to 50C @ heatsink, because if your cooling fails, your cooling fails right? Its either gonna be at ~30-40C or bust, if you know what i mean?

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Yes, now we are thinking on the same page. With water cooling, heat sink temp should be running quite low, though depends on the water reservoir volume as well. I may even drop it to 45C. I don't have the engineering smarts to nail this down mathematically, but this seems like a conservative (fail) safe range to shoot for.

this is where my lack of knowledge on watercooling shows (and im a gamer too, fail!)

Sounds good - You'll probably have to do some experiments to test the running temp i guess.

Very cool idea. Although the output of modern blues and whites don't suffer too badly from higher Tj, reds sure do. Another benefit of a very low Tj is very long life of the LEDs without any significant loss of lumens over the years.

There are so many variables it does seem like something that would just have to be tested. Now I have a bunch of questions on my mind How many watts would the pump consume and could you use 1 pump to cool all the heatsinks? Would you need to use some kind of anticorrosive coolant or would water be OK? How big would the reservoir have to be to keep the temp stable? What kind of plumbing would be best and how to interface with the sink?

step-by-step build journal and guide to watercooling yes plz?

SupraSPL said:

Very cool idea. Although the output of modern blues and whites don't suffer too badly from higher Tj, reds sure do. Another benefit of a very low Tj is very long life of the LEDs without any significant loss of lumens over the years.

There are so many variables it does seem like something that would just have to be tested. Now I have a bunch of questions on my mind How many watts would the pump consume and could you use 1 pump to cool all the heatsinks? Would you need to use some kind of anticorrosive coolant or would water be OK? How big would the reservoir have to be to keep the temp stable? What kind of plumbing would be best and how to interface with the sink?

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Nice pun.

All good questions. Lacking any engineering background, i agree, needs to be built and tested.

The pump I have and used for my shoulder cooling cuff is 19w, 225gph. I am quite sure I could get by just fine with much less wattage and flow.

Corrosion with aluminum: glycols (antifreezes) have corrosion inhibitors. Whereas I would avoid ethylene glycol (automotive antifreeze)which is toxic, Propylene glycol is non toxic, and I have extra propylene glycol for antifreeze in my radiant house heating system (Which i built).
Reference article: http://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Safeguarding-Aluminum-From-Water-Corrosion

Plumbing, all same metal type to avoid any possible dissimilar metal corrosion, probably 1.25" square aluminum rails in parallel, 1/4" NPT aluminum pipe nipples and automotive heater hoses.

Functionally I'd prefer distribution manifolds, but could possibly get away with serpentine flow.

I have spent ages trying to figure out the pun and still dont get it...


edit: I get it. Kill me.

Any updates? I wanted to use cpvc pipe. Saw an article about how thermoplastic is a better cooler than aluminum.

my thoughts would be all the added weight of a liquid cooled object attached to something i might want to raise and lower. concerned also about even heat displacement via your manifold... I dunno seems like allot of work to me...you could look into grabbing a cold fusion device a cold fusion device like doc has for the DeLorean

Hey Brian, I would really like to see you build this, I just put together my custom panel, I used the air flow over the heat sinks to also provide negative pressure in my grow chamber. You might want to have a look at the first few pages of my thread (link in the sig) maybe it will give you a few ideas?

Anyway could you tell me a little more are how you want to build in the temperature cut off system? You should anodize the aluminum yourself to protect it, its pretty easy, I have done it many times and you can color it to.

Also how will you be driving the LEDs, you have to make note that using water cooling you might get lower then normal operating temperatures, I don't think this is to much of a problem except you might need to run voltages a lot higher, the LED's I have stabilize just under 39 volts when they warm up at full power, when the system is cool, I am running over 40 volts to get the same amount of current. If your driver is on the edge of what it can produce normally, voltage wise then you might run into a problem.

Some simple tests ahead of you, I would very much like to see some pics!

Water cooling is fine, you just need to do it properly.

The temperature of the heatsink should only deviate from the water temperature by very little. This means that you should choose a turn-off temperature only a bit above that. I would think that you are able to keep the heatsink below 30ºC, for which I would turn all of it off if it reaches 45ºC. Any temperature above that will mean that your system has failed.


Have you thought on how you are going to cool the water?

http://m.ebay.com/itm/121188166667?nav=SEARCH&sbk=1
Would this driver work for LED panels? Need like 40v and 360w off this drive.


http://www.ledinside.com/interview/2013/9/replacing_aluminum_with_thermoplastic_in_heat_sinks_cuts_cost_by_20_30
Thermoplastic heat sinks


Cpvc pipe can get up to 150°F/65°c. Its alot cheaper than buying a $30 heatsink and paying $50 to ship it. Well for a poor guy like me.
To cool the water id like to make a radiator looking system, pipes on an aluminum sheet pump mounted on a corner. First the lines run along the surface of the aluminum. Then at the opposite corner of where you started you should end up with no where to go but above the already laid pipe. You run the first 2nd level of pipe all along the "back side" (opposite side of where pump is mounted). When you get half way you go up several inches and add a "T" with one side open facing up and the other sides facing forward and one facing down. There u will start to make another radiator "wall" so the fans can cool the water in the lines

jackbukc said:

http://m.ebay.com/itm/121188166667?nav=SEARCH&sbk=1
Would this driver work for LED panels? Need like 40v and 360w off this drive.


http://www.ledinside.com/interview/2013/9/replacing_aluminum_with_thermoplastic_in_heat_sinks_cuts_cost_by_20_30
Thermoplastic heat sinks


Cpvc pipe can get up to 150°F/65°c. Its alot cheaper than buying a $30 heatsink and paying $50 to ship it. Well for a poor guy like me.
To cool the water id like to make a radiator looking system, pipes on an aluminum sheet pump mounted on a corner. First the lines run along the surface of the aluminum. Then at the opposite corner of where you started you should end up with no where to go but above the already laid pipe. You run the first 2nd level of pipe all along the "back side" (opposite side of where pump is mounted). When you get half way you go up several inches and add a "T" with one side open facing up and the other sides facing forward and one facing down. There u will start to make another radiator "wall" so the fans can cool the water in the lines

Click to expand...

That power supply wont work properly by itself. It is only constant voltage, not constant current, you would still need to and a driving circuit, 40V is high, what leds are you using, also what cuntry are you in, the minimum AC input voltage on that PSU is 176V, wont work in the USA.

I would not buy into plastic heat sinks, you are not the one benefiting, the manufacturer is. I cant really visualize your cooling system, heatsinks can be bought very very cheap,say $10-$15 if you know where to look.