Heatsinks for DIY LED lamps

I think this is right. Not sure why the inch square to cm square is 6.45 but appeared to be the number used by supraspl

Cost: $4.37
Number of Fins: 31
cm or in?: in
Fin Height: 1.0"
Riser Height: 0.375"
Width: 8.0"
Length (fin length):
Perimeter: 78.75"
Surface area per inch square: 78.75"
Surface area per cm square:507.94
cm square / $: 116.23

Voidling said:

I think this is right. Not sure why the inch square to cm square is 6.45 but appeared to be the number used by supraspl

Cost: $4.37
Number of Fins: 31
cm or in?: in
Fin Height: 1.0"
Riser Height: 0.375"
Width: 8.0"
Length (fin length):
Perimeter: 78.75"
Surface area per inch square: 78.75"
Surface area per cm square:507.94
cm square / $: 116.23

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Bonjour
116.23 $.for what lenght?...40 inches?
CU

That means you get 116.23 square cm for each dollar. I think it's per inch of length.

Voidling said:

Part of it would be to look at the c/w/3 lower the better. Second would be to put the dimensions of the new profile in the format supra has for the others.

How long is your 4.6" heat sink for two 3590 at 1050mA?

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Each cob is mounted on its own 7" of 4.6" profile, and i think the fans i got were about 3w 35cfm, if i remember right, lights are off right now. The heatsinks never really even get warm, i was thinking about getting one of those pinpointer thermomters, would that accurately read junction temperature? Or is my thinking completely off?

Voidling said:

I think this is right. Not sure why the inch square to cm square is 6.45 but appeared to be the number used by supraspl

Cost: $4.37
Number of Fins: 31
cm or in?: in
Fin Height: 1.0"
Riser Height: 0.375"
Width: 8.0"
Length (fin length):
Perimeter: 78.75"
Surface area per inch square: 78.75"
Surface area per cm square:507.94
cm square / $: 116.23

Click to expand...

Thats the info i was needing, surface area per inch or cm, this heatsink packs more surface area into a smaller package than the 4.6 or any other heatsink for that matter. Now would that be better for passive cooling? If it is not impossible, i may go passive cooling on these cobs if that can be done @1050ma. I am thinking 4 to 5" of the 8" profile but i have no idea the math you guys use to figure out how much heatsink you need for a certain application.

I would recommend waiting until supra checks my numbers just in case I screwed up.

From my understanding:

For active you want at least 40 square cm per watt and for passive 120 square cm per watt. But from what I remember seeing the other night they are only counting heat watts.

Hypothetically you have 100w running and the cop is 30% efficient then 70% goes to heat. So 70% of 100 is 70w of heat to cool.

For active cooling you need 40 square cm per 70w. So 40 x 70 is 2,800 square cm needed. The profile is 507.4 sq cm per inch, so 2,800 / 507.4 is 5.52 inches.

For passive at 120 square cm
120 square cm x 70w = 8,400
8400/507.4 = 16.6"

I was reading a post the other night about accurate readings on heat but don't remember where it was. An infrared can give you a rough idea I think

So looks like you are running 80.85 watts at 36.7% efficiency.
100 - 36.7 = 63.3% goes to heat
80.85 x .633 = 41.9679 watts of heat

Active cooling
40 x 41.9679 = 1,678.716
1,678.716 / 507.4 = 3.3084666929 inches

Passive cooling
120 x 41.9679 = 5,036.148
5,036.148 / 507.4 = 9.9254000788 inches

Though with this heatsink I don't know if the find are too close together for much passive cooling. If my numbers are right you could get a 10 inch length and test passive for single cob. If that doesn't work for passive put a fan and two more cobs on it. Or cut into 3 with fans on each

Ok so maybe not the best choice. I just read thru most of this thread, that helped. I am thinking maybe the 5.375 profile with active cooling. 2800/345=8.11" for active cooling. Im thinking two 18" sinks with 2 3590s @1050 each and one fan per sink.

Where did the 2800 come from?

Active cooling
40 x 42 = 1680
1680 / 345 = 4.87 inches per cob
4.87 x 2 = 9.74 inches for two

Passive cooling
120 x 42 = 5040
5040/ 345 = 14.6 inches per cob

Could have 2 per 10 or 4 per 20 just need to put good fans on.

Opinions on using a 1/4" plate with CPU heatsinks on top of it? I'll have some air circulation up there but not going for full on active cooling. Probably a 120mm fan per bar running at 7v?
Today I picked up 25 surplus cpu heatsinks, two 140mm fans and two 18v 65w laptop power supplies from a surplus place all for $20 cash, no receipt requested.
I need to cool Vero 29's run at 1050mA.
One option is to just use 4 heatsinks for the Vero's.
or...
My space is 2'x4' so I was thinking of making two bars out of 1/4" x 4" x 24" aluminum plate (will cost me $23 for a 48" piece, could use more) then put every heatsink I can on top of each bar, the two Vero per bar, one blurple "30w" (~20w?) cob per bar and a few colored LED's to adjust the spectrum for whatever may be growing on. Loss of thermal transfer efficiency between the 1/4" plate and heatsinks, I know. Can drill and tap the bar stock and heatsinks to give stronger attachment and find some thermal grease (going to need a cheaper option because silver cpu compound would break the bank for that many heatsinks.
Thoughts on using 1/4" aluminum plate? Yes, it would take smoothing.

disengaged said:

Opinions on using a 1/4" plate with CPU heatsinks on top of it? I'll have some air circulation up there but not going for full on active cooling. Probably a 120mm fan per bar running at 7v?
Today I picked up 25 surplus cpu heatsinks, two 140mm fans and two 18v 65w laptop power supplies from a surplus place all for $20 cash, no receipt requested.
I need to cool Vero 29's run at 1050mA.
One option is to just use 4 heatsinks for the Vero's.
or...
My space is 2'x4' so I was thinking of making two bars out of 1/4" x 4" x 24" aluminum plate (will cost me $23 for a 48" piece, could use more) then put every heatsink I can on top of each bar, the two Vero per bar, one blurple "30w" (~20w?) cob per bar and a few colored LED's to adjust the spectrum for whatever may be growing on. Loss of thermal transfer efficiency between the 1/4" plate and heatsinks, I know. Can drill and tap the bar stock and heatsinks to give stronger attachment and find some thermal grease (going to need a cheaper option because silver cpu compound would break the bank for that many heatsinks.
Thoughts on using 1/4" aluminum plate? Yes, it would take smoothing.

Click to expand...

It can work. it won't be as efficient at removing the heat as a single piece of aluminum. But I have been surprised at how much heat actually moves across a dry joint between heatsinks and the angle aluminum I use to frame\hang the lights.

I'm using thermal silicon glue in the joints. Not as good as arctic silver, but a lot cheaper and easier to use on a 4' long heatsink joined to 4' long angle aluminum. The pieces could also be soldered together.

I guess i am getting myself confused on what efficiency i am running at on my current light and the one i am about to build since my "old" light has the 77v version on the 5000k cxa3590 driven @1050ma so its about 75w or so per cob @ about 49% efficent(these numbers are wrong and were based off cxb chart) and the newer light with 36v cobs will be driven @1050ma 35w per cob @ 61% efficient will be dissipating about half the wattage? So talking spacing on the heatsinks, i am very happy with the spacing on my "old" light ~16" between the two cobs, should i be looking more at 12" between cobs? Numbers above are from a chart supra posted i just found in his most recent thread. 2800 was from your post above that was about my old light, i see my mistake.

Heres his chart for the cxb3590s, i may select a different driver for 36v and order a couple 72v and drive them harder. I guess step one in building a diy light is choosing how efficent you want your light to be. I kind of just winged it building this last light, and is why i ended up ordering 77v cxa3590s. Anyways that light works just fine, just not as efficent as i would like to build my next lights. Maybe a dimming driver would be a good choice.

Instead of going with one of the high end drivers with dimming , I'm going to try supra's 3 way switch type thing. I won't have any middle ground if I use identical drivers, but he used two drivers at different amperage and had 3 known amounts; A, B, A+B.

I probably lose efficiency that way but oh well.

Voidling said:

Instead of going with one of the high end drivers with dimming , I'm going to try supra's 3 way switch type thing. I won't have any middle ground if I use identical drivers, but he used two drivers at different amperage and had 3 known amounts; A, B, A+B.

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haven't heard of that method, any idea where @SupraSPL posted about it ?

Heh, search two drivers one cob. That's supra's humor for you.

BobCajun said:

A person could make a lot of money by buying a bunch of the floodlight bodies and a bunch of cobs and assembling them. Have you seen the prices for retail LED floodlights? How much would it cost for a body and two 100w cobs? Less than $100. If you look in places like Home Depot they don't even carry high wattage floodlights and the highest ones they do carry are usually sold out. I see big opportunity in LED floodlights. Where I live there is nowhere that I can just walk into and buy high wattage LED floodlights or high bays. I've never had so much trouble finding such a seemingly common item. I would have literally no competition anywhere near where I live. Importing stuff from China is a pain in the ass though isn't it? I never tried.

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Nah. At least not in Europe. Certification process is a pain and you can sell anything without at least CE and RoHs. For private stuff it's great. But not really commercially interesting. Plus: let's face it: floodlight bodies ARE ugly...

Update: I got the following deal: 40$ for a tracking light with cxb3070 (3590 would not fit). Passive lamp, 50W and PFC active driver. Shipment is around 150$ for 10pcs including tracks. The lamps leave tomorrow and will take a week to arrive. I calculated another 60$ import taxes. More on this upon arrival.

Anyone interested: on ali track light or down light housings, aluminium including lens and reflector are 10-18$ / pc, depending on max wattage. Also, you can find good drivers (50W pfc active, low ripple noise, CE certification) for 6$ pc. Meanwell is SO overpriced...

Be careful tought: there is no magic; if the price is too low, ask twice about the exact specs of the parts used. Many so-called-experts out there have no clue about COBs tuning.

On a sidenote, if enough persons are interested in it, I'm thinking about organizing a container to rotterdam or hamburg with 1000-2000 pcs. Track light or downlight possible. Complete lamp including driver and reflector. That way, we could broker 50W cxb3590 for 40-50$ / pc including shipment. Anyone in it ?

qwerkus said:

Anyone interested: on ali track light or down light housings, aluminium including lens and reflector are 10-18$ / pc, depending on max wattage. Also, you can find good drivers (50W pfc active, low ripple noise, CE certification) for 6$ pc. Meanwell is SO overpriced...

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I'm wondering if you'll be saying this once you peek inside the case of the driver...or after a year of use.
Yes, some small MW drivers are pretty expensive but ie HLG-185H-C or ELG-150-C series have the top quality parts, functions and protections with a competitive pricing.