Qx2: Mounting and voltage

[LedElk]

Hello, everybody!

I've got a DIY on my hands and there's two things I am still unsure about.

1. How do I mount a 10w LedEngin onto a 3/4" copper pipe?

2. The sum of the led's required voltage (Vf?) on each of my two strings are 47,5 and 48.

My two (cc) drivers can output 9-50V each. Am I pushing it?


Any help will be much appreciated!

 

[hempfield]

Hello and welcome to ICMAG !

1. If the copper pipe is not flat we can't mount it. Why don't you use a regular CPU heatsink ? I have mounted 10x 10W CRE XML leds on an average heatsink and the temperature does not exceed 40 degrees celsius when they are driven at 2500mA. If the copper pipe is flat you can bond it with thermal adhesive compound.
2. A CC driver assure that the current passing the LEDs is constant, which means they adjust the voltage accordingly when the internal resistance of the LEDs is changing (when temperature increase or decrease). The 9-50 limits on the drivers means that it can assure a proper functionality (constant current) in the designated voltage range. If the forward voltage of the load is lower than 9V the driver will probably shut down (under voltage/shor circuit protection) and if is higher than 50V, the current will be lower than the nominal value, or the driver will eventualy shut down (over voltage protection).

Anyway, this is a good reading for thermal management: http://www.ledengin.com/files/products/appnotes/thermgt_LedEngin_emitC1.pdf

 

[LedElk]

Thanks for the welcome and the quick response!

1. The copper pipe is indeed round. I was going for a closed water-circuit driven by an aquarium pump. All the parts of which I had lying around and cost me nothing. A cpu-heatsink might be a better idea, but, first of all, I'd have to get one and second I was really happy with how the water-project came together so nicely with my old pump and all.. (except for the mounting-issue).

I was thinking maybe of making a pipe joint (==x==) where each LED is supposed to go, and mounting the LED on the nut. The nut has six sides and is made of brass. Would brass be a good thermal conductor?

Or maybe I could solder a copper square to the pipe and mount the led on that?

2. So, as long as the LEDs operate at anything under 50v I'm ok?
I was thinking maybe the voltage could fluctuate or something... Anyway, if the worst case scenario is that it doesn't work, I'll probably try it out.

 

[hempfield]

If you use water cooling (which is 30 times more effective than air cooling) you need a big tank of cold water to circulate through the cooper pipe, but remember that heat accumulates on water and should be dissipated eventually into the surrounding air.

But why don't you use a cpu water cooling block which is design for this purpose ?

 

[LedElk]

Well, my growcabinet is square, so my plan was to bend a straight pipe into a square and connect the two ends with a pump and a copper-pipe spiral composed of 6 thin pipes that sits beneath the air-intake (or outside the cabinet entirely) and is thus cooled by the airstream. I can't imagine it would get above an acceptable temperature.

I don't have a cpu water-cooler at hand, but what does it do, exactly?

Got any ideas for making a heatsink out of a bunch of old copper pipes, if I can't mount on them as they are?

 

[hempfield]

Well, my growcabinet is square, so my plan was to bend a straight pipe into a square and connect the two ends with a pump and a copper-pipe spiral composed of 6 thin pipes that sits beneath the air-intake (or outside the cabinet entirely) and is thus cooled by the airstream. I can't imagine it would get above an acceptable temperature.

You can use the external radiator from an old fridge to circulate the water through it, but keep the 'radiator' outside the growing space for better cooling and to keep the inside temperature down.

I don't have a cpu water-cooler at hand, but what does it do, exactly?

http://en.wikipedia.org/wiki/Water_block

Got any ideas for making a heatsink out of a bunch of old copper pipes, if I can't mount on them as they are?

A heatsink has two main roles : to conduct heat away from the heating source and to dissipate that heat into the surrounding medium. Copper is a very good heat conductor, so if the exposed area is large enough it could also dissipate properly.

I don't know if a cooper pipe is the best choice for a heatsink because the walls are too thin, and the thermal resistance is high. In general , the thicker the heatsink, the better.

 

[LedElk]

Good idea with the fridge, but I only have one and there's food in it.

So, I'm mainly trying to use what I have around the house and I should be good if I just could find some way to mount those leds on pipes...

Wait, I do actually have one of these:

It's about the size of a rubik's cube.

How many leds could this thing cool?

It is a cpu heatsink, but could it really handle 10x10w leds?

 

[luvdemshrooms]

Brass pipe fittings are available with flat sides. A handful of those along with either pipe nipples (seems like it might be tough to get the alignment right) or barbed hose fittings (easy to get the alignment right). I could link to some but am unsure of the rules regarding linking.

A possible advantage of the nipples would be that an inspired individual could actually aim the LED's where he or she might want them.

Seems like it'd be "easy" to do for a dedicated assembler.

 

[luvdemshrooms]

Or... square aluminum tubing.

 

[LedElk]

Ok, so you think brass might be good enough material to mount the leds straight on?

I was thinking of tilting the leds inward towards the canopy, as they would be mounted on a "pipe-frame" running along the walls of the cabinet.

Damn, I hope this isn't one of those times where things get way too complicated...

One important thing is that this water-circuit is very low-pressure, so I'll just be using solder and glue to assemble it. Leakage won't be a problem.

 

[luvdemshrooms]

This can be as simple... or as complicated... as you make it.

Seems simple to me.

 

[hempfield]

Check this post for a 10x10W on a 200x100x25mm heatsink : https://www.icmag.com/ic/showthread.php?p=5620318#post5620318

If the heatsink is design to disipate 100W it can be used without any problems to cool 10x10W LEDs, but it depends also on the LEDs type. An XM-L2 efficiency is almost 40%, which means that only 6W are dissipated as heat when the LEDs are driven at maximum current (which is 3000mA - but not recommended).

If the heatsink temperature is bellow 45degrees Celsius, everything it's ok.

 

[jcmjrt]

Since you are trying to work with what ya' brung...I'd think that braised on flat mounting areas would be fine as long as you get good contact over some broad area. If it's just a tack weld holding on a something-with-flat-mounting-area (whatever you decide that to be) then that's the limit for your effective heat conduction...that small tack area. If you can get a good broad contact with something then it would probably be hard to get a better heat conductor than copper and water. I probably wouldn't do it just because it's more complicated than it needs to be and anything with water will eventually leak...but d*mn, it could be very effective at heat management if you get that flat mounted area with good contact.
I have some diy lights which are mounted on square aluminum tubing (with one small fan) and they run nice and cool

 

[LedElk]

Hello, again and thanks for all the replies!

I've thought about scrapping this whole water-project and going for the heatsink&fan type of deal, but then again I'd have to buy all that stuff and plan all over again and all... Might as well try to get to the bottom of this pipe-dream.

OR, is there any way to combine a bunch of copper tubes and the heat sink I posted earlier?

I've got 9x10w leds to 'sink. I could hammer a pipe flat, but I don't know if "flat" in normal circumstance is considered "flat" when mounting a 10w led...

My main problem with figuring out this for myself is that I have no idea how hot these leds get and how effective a given heatsink would be.

If I had aluminum tubes I would go with that at this point.

 

[rives]

Flat means flat. Even irregularly applied thermal compound can impede heat transfer. Hex shaped brass fittings should work just fine - you can get the orientation where you want by setting them on a flat surface prior to soldering, so they will all be forced into the same plane. The minor differences in conductivity of brass vs copper vs aluminum should be easily compensated for by the higher efficiency of liquid cooling.

 

[LedElk]

Thanks, brass fittings it is.

Some experimentation with solder and whatnot will be had in the next few days, just so I know what it'll take to seal the joints. Thanks for all the good ideas and advice, I'll try to post pics of the rig when It's done!

Still plenty of things to work out, but only minor details from now on.

 

[luvdemshrooms]

If I had aluminum tubes I would go with that at this point.

Type aluminum tubes square in at Amazon.

The flat brass fittings I was thinking of are threaded.

At the same site type in square pipe couplers for an example, though they have a very limited selection.

 

[LedElk]

I guess the aluminum tubes is the easiest/most effective way to do this, but I think I've got this watercooling down.

BAM!!

This is probably what you've been talking about and I think it'll do the trick. It also fits the pipe so I can just screw it right on the pipe ends and glue/solder 'em tight. The surface angle should also be easy to adjust before mounting.

I have to confess, I've never mounted leds or done much soldering before, so I'm probably on the deep end on this one... Luckily, I am a good swimmer.

I'll let you all know how this goes.

 

[LedElk]

There is one more thing I'd like to know. How far from the canopy would a 9x10w fixture be placed? I need to know that to figure out the angle of the leds.

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[luvdemshrooms]

Not quite. Like this:

Lots of flat surface area. Available in many forms.