100W LEDs are tough to cool. With good VGA coolers you can maintain 30W LEDs. For a 100W LED you almost have to use 4, and place in the middle.

Pay me some money, I make you a prototype. I've done it with no more nails, and smaller LEDs, working for some months.

The power supply isnt easy too.

I used for instance a laptop brick, 2x large 20W LEDs in series on 2 VGA coolers, and a 12v/35v booster module hacked to 60 volts. At this voltage you have quite a few volts margin between LEDs turning on, and LEDs current reaching nominal current. Always remained cool, and was quite bright.

Blue LEDs are quite iffy, they overheat and just zap more easily, while the red one's are more tolerant.
Cree LEDs are prone for just one chip failing, fixed by connecting a cluster of single LEDs.

2012 I had quite a lot of this stuff around, but its all gone now, also dont have much space now.

Just the VGA coolers wont do if you use some hundred Watts (I had upto 500).
You need a large fan for convection too, or it all heats up within a few minutes.

And it mainly depends on the substrate (I just had VGA coolers and pentium heatsinks), as well the total area.

Never did any maths, never used expensive materials or complicate circuits or just even screws.

As I say, using 4 good VGA coolers for one 100W LED is a start. You can drive them with 15 volts or more so they spin faster

By all means you should monitor the temperature with small I2C sensors.

Yet a laptop brick is a bit thin for a 100W LED. You have conversion loss for stepping up voltage.
But, you can drive them with less than 100W, recommended anyway for longer life.

So each 100W module as such is not difficult to make (for me), and the compents are cheap and easy to obtain. Just takes the knuckles to use No more Nails on 4 VGA coolers and mount the 100W LED + hack the dc/dc booster (it needs better FET + Diode too, as the original FET will blow at or even below 80 volts, and a better output cap too, but it's all doable.

The good thing is, if you approach 100W, the laptop brick current limit will kick in. If you put 20 laptop bricks in a box they will heat up a lot and will need some kind of simple sinks on them + fans too. Even the cables will heat up if you bundle them.

 

Most of us don't have 4 foot by 8 foot sheets of aluminum!

It's more available than you'd think. Any local machine shop should have a supplier they can order from. Not cheap though - 2 of them for 8x8 would work well , I think, but would be more expensive than necessary. Could be a quick solution though.

 

without fast spinning fans it will get messy + expensive you'd need special components, which you cant easily buy ready made, and a lot of tools as well + a workshop + experience with processing metal.

Just copper pipes is not effective, you need a fin structure and pressure on the coolant, so you get a larger surface. And a heat exchanger somewhere.

With individual fans on the coolers + larger fans for convection you rely on airflow to transport the heat, for 2kW isnt that easy, but think, is equal to just 4 large Halogen floodlights (they produce mostly heat).

Only problem is your LEDs are not allowed to get as hot as a Halogen floodlight, if the cooler is 80C hot measured, the chip will be near dead (its much hotter inside the chip).

Ideally, coolers should only get warm so you can still touch them (speaking from a lot of experience + burned chips, without any math).

I tried with IRF MOSFETs some time, at 105 C measured, it shorted out (much hotter inside).

 

I need to fit all 20 modules in a 8 x 8 foot square ...

Heat transfer is a three dimensional problem. What's your 3rd dimension? Is this thing insulated - in a ceiling or wall for instance - or exposed to ambient? Can the heat be removed from the enclosure with moving air?

Heat transfer projects without these specifications and constraints are just wheel-spinning exercises.

 

Heat transfer is a three dimensional problem. What's your 3rd dimension? Is this thing insulated - in a ceiling or wall for instance - or exposed to ambient? Can the heat be removed from the enclosure with moving air?

Heat transfer projects without these specifications and constraints are just wheel-spinning exercises.

This is what I pointed out, at 2kW you need to take care the convection. Hot air will flow upwards, and if there is no space or no opening, it will creep on the roof, and somehow will use the roof surface.

If that's wood or plastic or something, bad, if it is concrete, can be suitable.

It's like you can mount a 250W floodlight on the roof indoors if the material is brick/motar/concrete all trough, but if there is any wood or the like, you cant do it. So they have stickers on them "Dont use indoors under any circumstances", but if you know whats happening, you can just ignore that.

If you knock on the walls and it sounds hollow, bad, they will have very little capacity to transport heat. If you have a solid brick wall or even concrete, that can act as heatsink.

 

Flat plates make horrible heatsinks.. They lack the surface area that a proper finned/pin heatsink has.. And natural convection cooling is all about surface area..

Actually a lot of commercial process systems rely on simple flat panel type heat dissipation/exchange for primary cooling often times unloading far more that 2000 watts of heat off of a 8 foot square surface area without excessively high heat levels.

Most of us don't have 4 foot by 8 foot sheets of aluminum!

No but most anyone can walk into their local metals supply dealer and get them.

 

Most of us don't have 4 foot by 8 foot sheets of aluminum!

Most of us don't need 2000W of LEDs either..

 

Actually a lot of commercial process systems rely on simple flat panel type heat dissipation/exchange for primary cooling often times unloading far more that 2000 watts of heat off of a 8 foot square surface area without excessively high heat levels.

Whatever systems you are talking about probably already have the sheet there for other mechanical purposes

My point is just that a flat plate is NOT a good/efficient heatsink..
That and I'd rather manage 20 x $8-10 heatsinks
Than a $300-400+ heavy sheet of aluminum and the crane/rigging crew I'd need to lift it to the ceiling..

 

You need about 900 square inches of surface area per LED to hold a 60C rise in temperature. The 8X8 foot plate just barely makes it and costs several $100. Probably wouldn't fan cool well either. It's all about surface area & as #12 always reminds me it has to be thick enough to conduct to the edges.

 

Any way you cut it you need to get rid of 2000 watts. I would rethink water. If your a do it yourselfer you might be able to solder some copper plate to some copper pipe (several rows) and use like a transmission radiator and a fan to get the heat away. The cost of the heat sinks will break the bank otherwise. I've helped a couple of people do this with big electronic loads.

Is that true?
Leds must be more efficient than zero? All the power is waste heat?

I'm surprised. A quick google shows 75% wasted. I thought they were much better.

 

I expected them to be even worse, something like 1% being light output and the rest being heat, seems the efficiency has gone way up in the past years. But still you can safely count that a 2000W LED will produce almost all of that as heat, and that is not taking the current regulation and PSU into account.

 

One of the guys on one of the other forums I go on tested some LED fixtures with some fancy equipment and I can't find the post now but I believe it was around 17% of the energy in going out as light with LEDs...

 

Please be aware that all the power that goes into the LEDs will eventually become heat. Maybe 17% of it becomes light, but the light quickly turns into heat. For the micro-environment of the individual LEDs, it might be 83%, but for the gross envelope of the space, it's all heat. Just keep in mind that all the heat has to leave the building in one way or another.

 

I just looked at the specs he posted for the power - 33v X 3.5 amps, but that does raise the question of where you are going to find a 36 volt 70 amp power supply. Or are you going to run them in series from a mains supply?

 

24v is pretty standard and there are also 48v supplies but 36v is pretty offtrack.

you'd have to use 24v bricks probably because they are cheapr + step up.

No you cant get 36v 70A off the shelf unless you pay a premium price.

 

berry hasn't been back for 3 days. We've probably beat this horse as far as necessary if that's the last we'll hear from him.