mounting high power LEDs

[aliyesami]

I see a lot of posts telling how to make DIY LED panels but they all are using LEDs mounted on a star . I was wondering if you can make a pcb and layout your leds there and then mount the whole PCB on a heat sink ?
This way you can put LEDs closer like Radion PRO does.

 

[chuckey]

I think the surface temperature of a star is too high for a LED to survive.
PCBs are not good conductors of heat, also they tend not to be flat, i.e. The heat sink would have to have pockets or holes in it to clear the solder connections.
Frank

 

[aliyesami]

so the leds mounted on stars and stars assembled as closely as possible is a good distance for building an LED panel for aquariums ?

 

[godfreyl]

stars

What sort of stars are you talking about?

aquariums

Do you want to put the LEDs underwater or what?

 

[betwixt]

I can see this leading to...

1. Is it possible to remove an LED from a supernova without getting burned?
2. Does gravity on white drawf stars mean you don't need solder?
3. What kind of flux should I use on a red giant?
4. Does an LED emit light at all if it falls into a black hole?

and maybe.... can you submerge a star in water without it boiling? (need a lot of water to test that theory...)

Brian.

 

[aliyesami]

humor is good for life
but on serious note I think I have a valid question or not?

 

[alexan_e]

What sort of stars are you talking about?

A star is an aluminum base for the led and is very common

 

[aliyesami]

A star is an aluminum base for the led and is very common

View attachment 99597

View attachment 99598

so has anyone mounted the leds on the pcb or is it not feasible or possible ?

 

[alexan_e]

You can do whatever you want as long as you can provide sufficient cooling to the led.
A star base can be easily mounted on a heatsink but if you mount the led on a PCB directly how do you intend to cool it?

 

[aliyesami]

I was planning to thermal glue the pcb to a heat sink and also use small fans , wont the heat dissipate that way ?

 

[chuckey]

It would be very inefficient way as the PCB is essentially flat and the only way would be to mount the fan so the air flow is at 45° to the flat surface of the board, hoping the air flow picks up some heat. If you point the fan at the PCB, you will get a pressure build up at the board surface and the moving airflow will flow around this high pressure area. If you aim the fan at the end of the board you will cool that end of the board, but unless the air in constrained it will be diverting away from the PCB, leaving the other edge of the PCB without much cooling. I suspect your star shaped heat sink is so air can flow though the holes between it and a round enclosure.
What you after is free air flow- which is always vertical, so work out in what axis your PCBs are going to be mounted and make plans to get the radiating surface vertical, the people who make the "star" shaped mountings would not do it unless mounting the LEDs on a cheap PCB would not work. One trick is to spray the PCB with matt black paint (both sides) as it greatly aids infra-red radiation. I seem to remember a Mullard publication in the 1960s claimed that a matt heat sink is nine time more effective then a shiney ali one. I have looked on the web for the book but I can't find it.
Frank

 

[schmitt trigger]

I once attempted to use a double sided FR4 board to drive 18 Star LEDs at 650mA. The board was something like 20 by 10 cm, and used thermal vias.

For the commercial application which had to demonstrate good lumen maintenance for at least 10,000 hours, and that operating on a 40C environment, it simply was not possible.
But you could get away with it, specially if you use water cooling, and you are willing to degrade the devices a little faster.

And no, do not space the devices as closely as possible.
There is a good paper on Luxeon's site: AB20-4.PDF

 

[aliyesami]

I once attempted to use a double sided FR4 board to drive 18 Star LEDs at 650mA. The board was something like 20 by 10 cm, and used thermal vias.

For the commercial application which had to demonstrate good lumen maintenance for at least 10,000 hours, and that operating on a 40C environment, it simply was not possible.
But you could get away with it, specially if you use water cooling, and you are willing to degrade the devices a little faster.

And no, do not space the devices as closely as possible.
There is a good paper on Luxeon's site: AB20-4.PDF

hi !
you suggesting not to space the devices as closely as possible but yet the two most popular LED panels namely Radion and Kessil both have very tightly packed leds so how does it work in their setup?

 

[schmitt trigger]

Are Radion and Kessil located on a FR4 board or a metal substrate?
How is its thermal management, from junction to ambient?
What forward current are they being operated?
What sort of electrical insulation is used from the heatsink?
etc, etc etc.

Believe me, both of those panel suppliers must have done extensive analysis and testing to achieve high power densities.

My suggestion to add sufficient board surface area is only a simple rule-of-thumb for un-optimized thermal management.