LED COB Heat sink check

G

galgo

New Member
Hey all,

I'm putting together a DIY LED COB lighting build, and I just want a sense check on my passive heat sink plans. I followed ledgardener.com's advice on calculating requirements, however the heat sink he used looks to be over £20 each - so my 4 lights will need £90 worth of cooling! That seems a little excessive and I don't want to be throwing money away.

Build Plan:
I'll be using 4 x Cree CXB3590 [CXB35900N0BDB40E] which should be a 'DB' bin, and I will be running these at 1.4 amps, giving 50 Watts / light. Assuming 50% efficiency that means I have 25 heat watts to deal with.


Heat Watts : 25 degrees C
Interface Resist 0.5 degrees C
Max Case Temp : 85 degrees C
Ambient Temp : 25 degrees C
Case - Ambient : 85-25 = 60 C
RC-a : 60 / 25 = 2.4
RC-b : 2.4-0.5 = 1.9

So as I understand it, I can use any heat sink with a thermal resistance lower than this figure right? So I can use for example this one (below) which is only £3.91 each? if so - that's a massive saving, but obvs I don't want to melt £140 quids worth of COBs so would really appreciate a sense check.

Many thanks in advance!

Heatsink:
Universal Rectangular Alu, 1.65K/W, 75 x 88 x 35mm

RS PRO Heatsink, Universal Rectangular Alu, 1.65K/W, 75 x 88 x 35mm, Screw Mount | RS

uk.rs-online.com uk.rs-online.com
 
galgo said:
Hey all,

I'm putting together a DIY LED COB lighting build, and I just want a sense check on my passive heat sink plans. I followed ledgardener.com's advice on calculating requirements, however the heat sink he used looks to be over £20 each - so my 4 lights will need £90 worth of cooling! That seems a little excessive and I don't want to be throwing money away.

Build Plan:
I'll be using 4 x Cree CXB3590 [CXB35900N0BDB40E] which should be a 'DB' bin, and I will be running these at 1.4 amps, giving 50 Watts / light. Assuming 50% efficiency that means I have 25 heat watts to deal with.


Heat Watts : 25 degrees C
Interface Resist 0.5 degrees C
Max Case Temp : 85 degrees C
Ambient Temp : 25 degrees C
Case - Ambient : 85-25 = 60 C
RC-a : 60 / 25 = 2.4
RC-b : 2.4-0.5 = 1.9

So as I understand it, I can use any heat sink with a thermal resistance lower than this figure right? So I can use for example this one (below) which is only £3.91 each? if so - that's a massive saving, but obvs I don't want to melt £140 quids worth of COBs so would really appreciate a sense check.

Many thanks in advance!

Heatsink:
Universal Rectangular Alu, 1.65K/W, 75 x 88 x 35mm

RS PRO Heatsink, Universal Rectangular Alu, 1.65K/W, 75 x 88 x 35mm, Screw Mount | RS

uk.rs-online.com uk.rs-online.com
Click to expand...
3.5"wide? I dunno... Doesn't seem like enough to me .
 
To me, the sinks mentioned don't look like good choices for COBs.

diyleduk.com

Luminus Gen 4 DIY Led Cob Kits

A selection of Luminus Cob gen 4 led kits. Featuring the new, high efficiency Luminus gen4 CXM22 cobs, Meanwell drivers and blue anodised pin heatsinks. Completely passive and dimmable down to just 10% via the handy dimming knob. At under £1 per watt, the luminus CXM22 cob kits are a great choice.
diyleduk.com

Heat Sinks – CobKits.com

cobkits.com cobkits.com
 
1212ham said:
To me, the sinks mentioned don't look like good choices for COBs.

diyleduk.com

Luminus Gen 4 DIY Led Cob Kits

A selection of Luminus Cob gen 4 led kits. Featuring the new, high efficiency Luminus gen4 CXM22 cobs, Meanwell drivers and blue anodised pin heatsinks. Completely passive and dimmable down to just 10% via the handy dimming knob. At under £1 per watt, the luminus CXM22 cob kits are a great choice.
diyleduk.com

Heat Sinks – CobKits.com

cobkits.com cobkits.com
Click to expand...
Agreed. That's why the one I linked was the only one I'd feel kinda safe with. Finned across the whole top. the base is VERY THICK too which makes a massive difference.
 
Ok all thanks - how do you decide on which heat sink to use? Is there a general rule of thumb you can apply?
 
First thing I would try if in UK is email diyleduk.com

Though he doesn't have them on the website I think he used to sell pin heat sinks, so he may just have some left over for sale.

After that you could try primelight.uk, they sell citizen cobs and have a range of heatsinks.

I might be inclined to move away from COBs unless you already have them, just because we don't have much in the way of cheap heatsinks over here.

I had to buy my 163mm pin heatsinks from china several years back. As an example it costs around £35 for a 133mm pin heatsink in UK, the exact same thing is $9.50 from kingbrite on Alibaba.
 
Moflow said:

Extruded heatsinks in bars

Extruded heatsinks in bars | Page 1 of 2
www.poweralia.com www.poweralia.com

Yea, @coreywebster is right, not much options here.
@diyled usually has something or could point you in the right direction.
Cobkits heatsinks would be a nice fit.
Or the good old fashioned Arctic Alpine GT pc heatsinks with fans.
Cxbs aren't the best option or particularly cheap.
Click to expand...
I think cutter sells the whole 4 COB setup with holders sinks and all for like $150 now
 
Airwalker16 said:
I think cutter sells the whole 4 COB setup with holders sinks and all for like $150 now
Click to expand...
Thats not bad price. Ive never used them. They're too far away..... lol
I bought a 1m length of monstrous heatsink for the Growgreen boards from Poweralia. It was @Rocket Soul put me on to them. I cut it up to fit the boards. I needed a passive heatsink to withstand 200 watts. Weighed a fecken ton! Lol
Those were the days before I came to the conclusion that an even, light spread across the canopy with thousands of diodes running very softly was the way forward for I.
 
Moflow said:

Extruded heatsinks in bars

Extruded heatsinks in bars | Page 1 of 2
www.poweralia.com www.poweralia.com

Yea, @coreywebster is right, not much options here.
@diyled usually has something or could point you in the right direction.
Cobkits heatsinks would be a nice fit.
Or the good old fashioned Arctic Alpine GT pc heatsinks with fans.
Cxbs aren't the best option or particularly cheap.
Click to expand...
Those are some sweet profiles.
 
Hey all thanks so much for your advice, I've never looked at alibaba or poweralia before so they're both great resources to know about.

Most of the Poweralia boards don't seem to have a thermal resistance value, though I can probably guess at it by comparing to others I've seen that do.

Cutter is based in Australia so with the shipping that becomes a bit expensive unfortunately, but I am using him as a guide for the build.
 
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