# Heatsink Design Question

@dbrn32 When calculating heatsink area, does one allow for the total wattage of the COB, or only the heat portion of that wattage?

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You only need to dissipate the heat. That being said, it depends on which method youâ€™re using.

Bridgelux has an application note that covers it pretty well. Itâ€™s still a lot of engineering lingo, but I was able make sense of most of what they were trying to say.

The variables are tremendous given climate and ambient thermal mass heat transfer, wattage use is not a determining factor, ambient hot or cold is, for instance, night time operations have less ambient heat than day time operations, thatâ€™s just one factor in many.
1000 watt light (photons) doesnâ€™t need 1000 watts also devoted to cooling, especially with geothermal heat pumps.

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@dbrn32 I am still pondering a DIY pin heatsink. Will try to post excel calcs and a sketchup drawing. I have a souce for aluminum plate and rod (shop cut-offs) and almost unlimited time (in the short term, I am 79 years old). I recall a post or ? that 17 sq in/watt is needed for passive cooling and much less for active.
Thanx for the quick response.

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Ya Iâ€™ve seen a couple numbers thrown around. Like 17-20, per heat watt. I can measure a 140mm pin sink for you if youâ€™d like?

After doing a little calculating on excel, Iâ€™ve come to the conclusion that DIY pin heatsinks are just too much labor. Back to the drawing board. Maybe active or passive liquid cooling?

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What are you looking to use the heatsinks for?

@dbrn32 Just exploring avenues to reduce the cost of heatsinking. My son, also known as Mcgyver, suggested gluing LEDs to the bottom of a copper pot!

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What are you trying to do though?
Give us a layout and maybe we can think of something from a different angle?

You mean who we usually call macg here? If thatâ€™s the case, how big of a light are you looking to do?

He was being a little â€śoff the wallâ€ť, but it did get me thinking about liquid cooling.
How about soldering/thermal epoxing soft copper tubing to an aluminum plate/bar?
I have enough West System epoxy around here to build a battleship (well, maybe a dinghy). Iâ€™d like to mix some up with aluminum powder for thermal epoxy to do some testing.

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It would be really helpful if you laid out what your trying to do for what use here, I feel a bit blind.
But weâ€™re tryingâ€¦

But if itâ€™s top secret and you canâ€™t tell us I would suggest you go look at computer cooling systems to get a better idea.
It used to be a big hobby for me.
You can pull heat sinks off lots of stuff but computers have some of the most efficient ones on their CPUâ€™s and GPUâ€™S, at least it will give you an idea.
Look at the heat tube designs.

Flying blind here

If you have time and materials Iâ€™m not sure what it would hurt to try.

@dbrn @nicky
Thanks so much for the responses. I still have a 24 x 18 aluminum plate, and considering packing ten BXEB-560 strips on it for a 30"x30" tent. Driving the bridgelux strips at 1050ma would give me close to 200 watts. I know it will need some active cooling.

My first plant is close to harvest, looks like the yield will be larger than I ever hoped for.
My â€śtentâ€ť is built of PVC pipe, cardboard, tinfoil, and a ton of masking tape. Initial lighting was 4 large CFLs on a parabolic reflector, pulling 125 watts at the wall. Not much to look at, but it seems to work. My daughter bought me an amazon type LED grow light for Christmas, and that seems to have saved the day for flowering.

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That should work.