Shipping to up here sucks balls
I got tons of different kinds of aluminum as i work with it.
But i didnt have anything that looked like heat sink .
Just didnt know how big a difference the heat sink vs 1 big u channel with a smaller one inside like fins?
There is no big difference between a heatsink and a DIY heatsink. Calculate the surface area, you need ~110cm² per heatwatt for passive cooling(40cm² for active cooling). If you have a 50% efficient COB/strip running at 50w, it creates 25w of pure heat. To cool that passively multiply 25w by 110cm². A heatsink with 2750cm² can be used. For strips the needed area could be smaller(~90-100cm²), because strips radiate almost half of the heat fromtwise.
I did exactly what you described to cool my CRI90 COB's.
At first you compute all perpendicular and horizontal lengths together (Pic 1),
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then multiply it by the length (Pic 2).
This heat sink of an 25x 35x 25x 2mm and an 20x 15x 20x 2mm channel with a length of 350mm offers approximately (246 x 350mm) 861cm² cooling surface.
Dividing this through 110cm² you get 7.82w of heat, which can be passively removed with it.
Say we, we use a 50% efficient COB (7,82:50x100=15,64w), then the surface of this DIY-heatsink is enough to passively cool a 16w COB without airflow.
Say we, we use a 60% efficient COB( 7,82:40x100=19,55w), then the surface is enough to cool a 20w COB.
Say we, we want to calculate it for active cooling(40cm²/heat watt). Surface area 861cm² : 40cm²/w = 21,5w heat.
With the same 60% efficient COB it would be enough to cool ~54w actively.(21,5:40x100=53,75w).
I just glued the little one in with the same thermal tape I'll use for the strips and it works very well!