I'm about to buy 20 of these heatsinks for the 20 cob fixture, or shouldn't I?

Hi there,

I'm about to buy 20 more heatsinks to cool the 20 citizen cobs (1212) running at 50W each.
I have a really cheap option picked out, but I'm not sure if it would do the trickto cool 50W constant so I would appreciate your help!

Option:

• Spire Coolreef II $1.50 per unit

The CoolReef II provides ample cooling for the AMD micro-processors up to 95W
95x95x25mm Silent air-duct fan type
0.357 oC/W


Thanks a lot for your help.

If they're 95 watts and you're only trying to dissipate 50 watts of thermal energy. You've got plenty cooling.

I dare say you could possibly run your cobs harder with 45w of headroom. Even close to the 50w they're rated at.

Strainhunters said:

Hi there,

I'm about to buy 20 more heatsinks to cool the 20 citizen cobs (1212) running at 50W each.
I have a really cheap option picked out, but I'm not sure if it would do the trickto cool 50W constant so I would appreciate your help!

Option:

• Spire Coolreef II $1.50 per unit

The CoolReef II provides ample cooling for the AMD micro-processors up to 95W
95x95x25mm Silent air-duct fan type
0.357 oC/W


Thanks a lot for your help.

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I am also planning to build a 1212 rig and push the chips hard. This is my choice up till now:
http://www.sicomputers.nl/alpine-11-plus.html
Should have a little larger mounting service and more cooling capacity, also bit quieter but also more expensive.

Wotcha, the wattage rating of pc cpu heatsinks has NO direct comparison with an LED equivalent, be careful of basic assumptions. The important number there is the c/w number which gives you the thermal permissivity of the material, have you seen my vero 29 big build thread? it might give you some inspiration before buying.

Nugachino said:

If they're 95 watts and you're only trying to dissipate 50 watts of thermal energy. You've got plenty cooling.

I dare say you could possibly run your cobs harder with 45w of headroom. Even close to the 50w they're rated at.

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Sorry to differ, that is an over simplistic model, a 90w led does not create 90w of heat! indeed, it is a tiny fraction of that or they would only emit infra red light! The numbers for each cob are on the spec sheet but without a degree in thermal management I'm fucked if I can make head or tails of it all, better to experiment and make your own direct 'real world' measurements and work out from there in my humble opinion.

While a cpu cooler may not be designed to run with cob chips. They are designed to dissipate large amounts of heat. Which makes them none the less effective at cooling whatever they're attached to. As long as its within their range. The addition of universal 120mm fans and such makes them upgradeable.

Nugachino said:

While a cpu cooler may not be designed to run with cob chips. They are designed to dissipate large amounts of heat. Which makes them none the less effective at cooling whatever they're attached to. As long as its within their range. The addition of universal 120mm fans and such makes them upgradeable.

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Absolutely agree, was simply commenting on using cpu wattages to guide heatsink choice, not good policy. Could leave you with a set of bad concepts of your subject if you upscale beyond standard cpu h/s capability later.

Hmmm. Some makers can't back up their claims about what their coolers can do. But the likes of coolermaster can. Even with their cheap ones. I'd know. I used to run a phenom 2 on one and that was a pretty toasty chip when OC'd.

Nugachino said:

Hmmm. Some makers can't back up their claims about what their coolers can do. But the likes of coolermaster can. Even with their cheap ones. I'd know. I used to run a phenom 2 on one and that was a pretty toasty chip when OC'd.

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Like you, I looked into cpu coolers as it was a subject I was keenly informed of as a pc builder in the past but...... if your 90w cpu actually emitted 90w of heat, there would be no other functionality, heat is the waste by product of switching in cpu's and due to conversion inefficiency in lighting applications. Neither of these have the remotest direct connection to the led/cpu's rated wattage as that is the 'consumption' figure NOT its thermal output.

Nugachino said:

If they're 95 watts and you're only trying to dissipate 50 watts of thermal energy. You've got plenty cooling.

I dare say you could possibly run your cobs harder with 45w of headroom. Even close to the 50w they're rated at.

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My concern is that from my perspective there is a difference between the constant heat generated by a cob vs the heat generated by a cpu (which these are made for).
Since a CPU

freemanjack said:

Like you, I looked into cpu coolers as it was a subject I was keenly informed of as a pc builder in the past but...... if your 90w cpu actually emitted 90w of heat, there would be no other functionality, heat is the waste by product of switching in cpu's and due to conversion inefficiency in lighting applications. Neither of these have the remotest direct connection to the led/cpu's rated wattage as that is the 'consumption' figure NOT its thermal output.

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do you think it's possible to run these cob's at 1400/50w each on a heatsink as I mentioned?

it's not like I can't spend a bit more on them, but DAMN $1.50 is a STEAL!

is the surface area big enough on the sink to cover the whole chip? pretty cheap for sure

Strainhunters said:

My concern is that from my perspective there is a difference between the constant heat generated by a cob vs the heat generated by a cpu (which these are made for).
Since a CPU


do you think it's possible to run these cob's at 1400/50w each on a heatsink as I mentioned?

it's not like I can't spend a bit more on them, but DAMN $1.50 is a STEAL!

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Have you seen any of my builds yet? as I suggested these things are all but impossible to calculate, so better to take a known good system and alter as few variables as you can meaningfully calculate. In our experiments here the thermal gradient is more or less linear in c/w so if your h/s is at 50c @ 50w then it is 30c above room temp and will be approximately 80c @ 100w. My concerns with buying 20 units of anything before testing them would be the cost of return postage, I tend to go by the old adage; slowly, slowly, catchy monkey!

Just by way of explaining myself more clearly, the problem as I see it is this; most heatsink material is spec'd at a c/w figure which can be either total c/w OR c/w per kilo or G of h/s, then to add to that we have the 'theoretical maximum' conversion of electrons into photons @ <800lm/w, so current conversion rates of 150lm/w (ish) give some indication of heat proportion of total wattage consumption, still a remarkably low figure but I suggest we will top out at around 3-350lm/w in the very near future for visible white spectrum due to the phosphorus conversion from deep blue to full spectrum (3 and 5 step mcadam process). then you add active cooling with fans and you enter the pandoras box of constant pressure/constant flow rate and effective airflow calculations, good luck making head or tails of all that fuckaries, better to suck it and see, then adjust as measured. Perhaps thats the old engineer in me talking but it has got me this far without resorting to extended advanced math of any sort.

That largely depends on how many watts of heat that cob outputs at 100% load. I highly doubt a 50w led would output more than 50w of heat. Otherwise where is the light coming from.

That's like a stock clocked i7. Whatever they say the wattage of that chip is. Is usually a representation of that chip clocked up to maximum factory setting. And as such. Under a properly rated cooler. Will not need anything bigger. Unless you intend to push past that maximum factory setting.

The same goes for the cob. If it's rated at 50w @ 1.4amps. Then technically it shouldn't need 100w cooler on it. The only time you would need to go add a massive cooler. Is if you intend to push that chip to 1.6amps and up. That's where you'll start to see more heat than that chip is normally rated for.

Nugachino said:

That largely depends on how many watts of heat that cob outputs at 100% load. I highly doubt a 50w led would output more than 50w of heat. Otherwise where is the light coming from.

That's like a stock clocked i7. Whatever they say the wattage of that chip is. Is usually a representation of that chip clocked up to maximum factory setting. And as such. Under a properly rated cooler. Will not need anything bigger. Unless you intend to push past that maximum factory setting.

The same goes for the cob. If it's rated at 50w @ 1.4amps. Then technically it shouldn't need 100w cooler on it. The only time you would need to go add a massive cooler. Is if you intend to push that chip to 1.6amps and up. That's where you'll start to see more heat than that chip is normally rated for.

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Sorry to keep correcting you, but heat watts and consumption watts are two separate metrics, they are connected but the efficiency and power input are the primary variables being discussed here and it is over simplistic to say that because a cpu cooler is rated for cpu's of 100w DOES NOT mean it is capable of dissipating 100 heat watts that is all I am trying to impress on you here. the h/s material will have what is called a 'thermal permissivity' in c/w meaning it will rise 1 deg c for 'x' watts in this case the heatsink with fan is rated at 0.3c/w which means it will heat by 1c every 3w of HEAT not cpu power or led rated wattage. This does not mean i'm stating that these coolers will be ineffective for this application, merely that it cannot be simply derived or calculated from the available data.
edit; the op's question was 'should I buy 20 units of this item' my answer is no, buy one and test if you want any degree of certainty and want to avoid costs of returns shipping fees.

No its ok. If I'm wrong I'm wrong. I'm used to working with hot computer parts and have done so for for about 10 or so years.

I'm not great with mathematics. But, couldn't see how 50 watts could convert into more than that thermally.

I am a tinkerer though. And don't mind jerry rigging one thing to another... with varying degrees of success.

I will say though. If our friend does choose to go the cpu cooler route. Do not underestimate the benefit of good TIM grease. Arctic silver hasn't ever left me with a cooked chunk of silicon when paired with an appropriate cooler.

Nugachino said:

No its ok. If I'm wrong I'm wrong. I'm used to working with hot computer parts and have done so for for about 10 or so years.

I'm not great with mathematics. But, couldn't see how 50 watts could convert into more than that thermally.

I am a tinkerer though. And don't mind jerry rigging one thing to another... with varying degrees of success.

I will say though. If our friend does choose to go the cpu cooler route. Do not underestimate the benefit of good TIM grease. Arctic silver hasn't ever left me with a cooked chunk of silicon when paired with an appropriate cooler.

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you are quite right in thinking 50w of consumption cannot convert into greater than that wattage in heat output, indeed quite the opposite if anything other than heat is the 'output' of the device, heat is the inefficiency in this case NOT the work done. This 'heat inefficiency' is the problem as both it and thermal permissivity of a cooler are very variable and tricky to calculate. As to thermal paste, for led's I use a gold based paste as the potential differences in expansion rates leave me wanting a grease that will not dry out quickly. its an industrial product and dirt cheap; HY610 thermal grease.

freemanjack said:

Sorry to keep correcting you, but heat watts and consumption watts are two separate metrics, they are connected but the efficiency and power input are the primary variables being discussed here and it is over simplistic to say that because a cpu cooler is rated for cpu's of 100w DOES NOT mean it is capable of dissipating 100 heat watts that is all I am trying to impress on you here. the h/s material will have what is called a 'thermal permissivity' in c/w meaning it will rise 1 deg c for 'x' watts in this case the heatsink with fan is rated at 0.3c/w which means it will heat by 1c every 3w of HEAT not cpu power or led rated wattage. This does not mean i'm stating that these coolers will be ineffective for this application, merely that it cannot be simply derived or calculated from the available data.
edit; the op's question was 'should I buy 20 units of this item' my answer is no, buy one and test if you want any degree of certainty and want to avoid costs of returns shipping fees.

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thanks for your replies, I'm learning a lot from them.

The problem is however that I can not buy 1 at that price from this company.
I can buy a minimum of 40 @ $1.5 each (overstock). Besides, I can't return them.
To make it even harder: I can only get this insane bargain today because the guy I know in this company will be gone for 4 weeks starting tomorrow. He will buy these on his own name from his job, thats why the price is low.

Strainhunters said:

thanks for your replies, I'm learning a lot from them.

The problem is however that I can not buy 1 at that price from this company.
I can buy a minimum of 40 @ $1.5 each (overstock). Besides, I can't return them.
To make it even harder: I can only get this insane bargain today because the guy I know in this company will be gone for 4 weeks starting tomorrow. He will buy these on his own name from his job, thats why the price is low.

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Ok, just took a look at the specs on the cpu coolers, while i'm sure they are a bargain and you may find some use for them someplace, as to cooling 50w cob's?? they look too small from our experience, I would want probably double the amount of cooling they will provide but I would only be hazzarding an 'educated guess' based on our experience here (sadly none of it with cpu coolers and led's)

freemanjack said:

Ok, just took a look at the specs on the cpu coolers, while i'm sure they are a bargain and you may find some use for them someplace, as to cooling 50w cob's?? they look too small from our experience, I would want probably double the amount of cooling they will provide but I would only be hazzarding an 'educated guess' based on our experience here (sadly none of it with cpu coolers and led's)

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Strike that last statement^^ just remembered, I did a 'spider cob' conversion that used just those type of components and it is more than happy effectively cooling 40w cob's. I doubt the extra 10w would severely hinder it.