Heatsinks for DIY LED lamps

[zep_lover]

I calculate the perimeter of the 2.08" profile to be 13.09" or 33.25cm. So it is 111.76cm X 33.25cm = 3716cm².

what about the fins? the stats for the profile show that it has a surface area of 84.43 cm 2
sorry about being stuck on this but i thought when you multiply the surface area squared times the length that gives the number needed for calculating how many watts you can run.

 

[Dloomis514]

http://www.heatsinkusa.com/pages/FAQ's.html

To download a document with detailed specifications for all of our available profiles please click here.

https://store-ddfcc.mybigcommerce.com/content/AvailableProfiles2014.pdf

shows the Outer Perimeter to be 12.559 on the top of page 2

what about the fins? the stats for the profile show that it has a surface area of 84.43 cm 2
sorry about being stuck on this but i thought when you multiply the surface area squared times the length that gives the number needed for calculating how many watts you can run.

 

[alesh]

what about the fins? the stats for the profile show that it has a surface area of 84.43 cm 2
sorry about being stuck on this but i thought when you multiply the surface area squared times the length that gives the number needed for calculating how many watts you can run.

Well, surface area is what you're trying to compute. To compute it, multiply outer perimeter by length.
1 in = 2.54 cm
1 in^2 = 6.4516 cm^2

 

[bicit]

While I don't disagree with your claim that 60 watts of heat is 60 watts of heat, i.e. 1 = 1, I do, however, disagree that the heat load is the same between both examples.

If one COB is more efficient then the other, at a cooler temperature, then wouldn't it produce more light and less heat? While the thermal efficiency differences between each method may be miniscule in a larger room, they may indeed be more of a concern in smaller spaces, such as tents or closets where continuous air flow and periodic air exhaust are necessary for temperatures to be ideal.

I agree with you about the actively cooled unit dispersing the warmer air more readily, with the passive allowing heat to buildup around the COB and ultimately the HeatSink.

Light=heat=energy. They are all different forms of the same thing. Only a small amount of the energy released as light get's converted into matter. The rest is ultimately released as heat. 600w of power being displaced in a volume will raise the initial ambient temperature to the same final temperature regardless of what the source of that power displacement is. It's basically calorimetry.

When you add things like extraction fans it makes the matter irreverent.

Use what you will, just know that the ultimate result with respect to ambient temperatures or the total amount of heat energy added to a space is nearly identical. Practical? That's relative to the designer and the user. My potatoes is another persons tomatoes or something like that.

 

[bicit]

shortcuts...
[Alt Gr] + 2 => ²
[Alt Gr] + 3 => ³
[Alt Gr] + m => µ

[CTRL]+[ALT]+ 2 => ²
[CTRL]+[ALT]+ 3 => ³
[CTRL]+[ALT]+ m => µ
...

alt+0181=µ
alt+0178=²
alt+0179=³

This seems needlessly complicated....

 

[guod]

Simulator for paaring Heatsink and Leds.
Vero 29 on a 24" 5.886 profile

in short...
section: LED
Model: just a name
Rthjc, Vf, Current can be found in the Datasheet
exept CREE they dont gives us the Rthjc
eff. - start here with 33% and see was happend if you change it.

single: Wattage of one Led

String: numbers for more then one Led with same current.
note. Tj is given now for mounting all Leds on the same Heatsink.
-------------------------------------

section: Heatsink
Model: just a name
Passiv: can be changed to Forced air cooling
Lenght: just a reminder, no calculation with it.

Rth HS(heatsink) see Datasheet number for a fixed lenght in C/W or K/W
Tim: Thermal Interface
- Grease 0.05 to 0.15. Standard is 0.1
- Glue 0.15 to 0.3

Junktion Temp. (Ta)
as Junktion Temp. change with Room Temp, two Limits given here.
------------------------------------------
section: Heatsink USA – Tool
calculates Rth for different Lenghts of a Profile

Model: just a name
Rth HS(heatsink) see Datasheet.
note C/W/3 is the Rth for a 3" cutting
---------------------------------------------------------------
just play with the Rth in section Headsink and find the lenght in the graph
passiv


forced Air


---------------------------------------------

 

[Abiqua]

What are the drawbacks of using a simple pot like this to slow down your fans.
I just can't bring myself to build an entire circuit based around a LM317. These seem to work in smaller applications, quite well!

This can be wired with one of the those cheap voltage gauges too. This one is a 1k ohm 1 amp. Linear Pot.

I have been running [2x] 12v fans for a over a year with no problems. It gets negligibly hot if at all even when dimmed down to around 5v.The ramping isn't too bad down to 5-6v's, although if left in a dimmed state, it probably needs a capacitor to help with voltage if it ever bottoms out. A 500ohm pot would be nice, but I wasn't able to track them down and haven't looked since.

Thoughts?

 

[guod]

1k ohm 1 amp. Linear Pot...never..... maybe 1kOhm 1Watt acording the size
1k is also way to high... i think more at 0.1k which is 100 Ohm

 

[getsoutalive]

Lots of good info here, can't believe that I missed it til now. Been a fan of passive cooling as well. Thought I would turn you guys onto the heatsink that I have been fooling with as no one else has mentioned it here yet.

http://www.wakefield-vette.com/products/productlist/productresults/tabid/341/CategoryID/173/ProductID/521/Default.aspx

These have served well with 60W of 3070, 3050, Vero18 and Vero 29. At 1.4a the sinks will get slightly warm with no air movement at all, but if your canopy fan can provide the slightest breeze to them, they are dead solid. We have taken the power up to 100w without issue, but feel more comfortable in the 60W range.

There is a document on Cree's site about thermal solutions for its 3050 series and they were pleased with the performance of this hunk of Al up to 2.1a. We have in fact cut one of these in half and have been satisfied with the performance of even just half this thing at 1.4a.

Have not yet tested these Taiwanese made units, but they are next on the list. http://www.led-heatsink.com/seepricesandbuy.php?subcate=980.

Do passive units cost more? Yes, a little bit. But they don't have to be insanely large and with fewer parts to fail and nothing that is moving, the reduced complexity and reliability is worth the couple of extra bucks, IMO.

Now for a commercial unit, things are different because of the need to make multi-chip units and these star shaped sinks don't lend themselves to being enclosed in a box.

IMO, tho, the individual chips on a star pendant offers the grower the ability to keep the chips as close as possible to the plants, even if they don't have the most even canopy around.

 

[SupraSPL]

The point I may have not underlined or that may be too obvious for some, including yourself, was that if you grow in a larger room in comparison to a tent within a closet, the larger room is going to better handle (@Greengenes707 , hehe) larger amounts of heat than the inside of the tent, given ambient temperatures are around the same.

@SupraSPL
While it may not be necessary in your large room, measuring the ambient temperature rise with each method may be worth noting, especially in a grow tent.

That is a good point. I did the test in a large room to eliminate that variable because we all have different ventilation/circulation airflow. I suspect bicit and Dloomis are on to something, the amount of heat in the system is the same whether passive or active. Once the temp heatsink stabilizes, it is eliminating heat into the ambient air at the same rate whether active or passive cooled. It may seem like having a relatively hot item in a small tent would be bad news for canopy temps, but the ventilation fan will be pulling fresh air in at the same rate either way so there should be no difference. That said, it be nice if I could set up a test that could demonstrate that.

The reason HPS is so notorious for high canopy temps is because it is dissipating a large amount of power but also, it has a strong infrared output that is literally beaming heat to the canopy in addition to the heat from conduction, convection and photon conversion. Also, aluminum is great at reflecting infrared radiation so it focuses the heat (and light) into the canopy like a flashlight.

CMH as well:

 

[SupraSPL]

exactly what I have been thinking. Its a logistical nightmare in any decent sized grow to run a whole roof of aluminum. It gets in the way of everything including my noggin. All the successfull large 100% passive designs I have seen end up using the grow room ventilation to cool the lights.

It is true, I do occasionally bang into the heatsinks when working in the grow tent. Actually I just scraped/smashed my head on the 2X3 supporting the heatsinks while taking these measurements . But I believe that would be a problem whether I was using passive or active. And you are correct, passive cooled sinks will benefit quite a lot from the grow room circulation fan and slightly from the ventilation fan. As we have seen from the test, juts a slight bit of air movement is very effective at reducing the heatsink temp. Now that we have some reference heatsink temps, we can compare those directly to what we observe in any grow.

For example, I just did a check of my heatsink temps and they are about 27C, noticeably lower than the results from test #2 (33C) which used similar power dissipation to what I am using in practice (~58W) on the same 10.08" heatsinks (~95cm²/W). Incoming air is 20C but the ambient temp is 23C. The reason for the lower heatsink temp is mostly due to the benefit of the circulation fan (a 55W ceiling fan overhead, but sucking air up rather than blowing down unfortunately). That circulation fan needs to be used no matter which kind of lighting I choose, so it is nice to derive that additional benefit from it, but it is not necessary to the design of the lamp.

One of the benefits of these tests is to show that, at least for CXAs, if your thermal interface is solid and your heatsink temps are below 35C, you are not losing much light to temp droop. I expect it to be the same for the Veros and will test that out as well.

 

[AquariusPanta]

Light=heat=energy. They are all different forms of the same thing. Only a small amount of the energy released as light get's converted into matter. The rest is ultimately released as heat. 600w of power being displaced in a volume will raise the initial ambient temperature to the same final temperature regardless of what the source of that power displacement is. It's basically calorimetry.

When you add things like extraction fans it makes the matter irreverent.

Use what you will, just know that the ultimate result with respect to ambient temperatures or the total amount of heat energy added to a space is nearly identical. Practical? That's relative to the designer and the user. My potatoes is another persons tomatoes or something like that.

Right, a hot cup of coffee won't become hotter in a cold room but depending on the volume of the room, the room itself may become slightly warmer over time. The real question is, will the room outside the room become any hotter as a result. Just food for thought.

Heat is defined as the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference. Temperature difference is the driving force for heat transfer. The larger the temperature difference, the higher is the rate of heat transfer.

 

[bicit]

Heat and thermal energy are a bit different. I've been lazy with my terminology and I guess maybe that has led to a bit of confusion?

The amount of thermal energy transferred into a given volume by and actively cooled light and a passively cooled lights is identical assuming both systems are doing the same amount of work(power draw in kw/h).

It's not even a question. A coffee cup placed into a room will add thermal energy into the system will cause a temperature rise, even if it's a tiny amount until they've reached a state of equilibrium . The thermal energy will also be transferred to the room will also be emitted into the 'surrounding environment'.

 

[Greengenes707]

Once again the discrepancies between perfectly insulated theory and actual real world use. But it is because of every thing that exist in a real world situation.
Bicit is correct...heat is heat and is it literally can't go anywhere and the systems are the same wattage...the same heat output will occur.
But in the situations most grow in/under...there are other ambients and temps pulling heat out of the room, like AP just touched on. Specially in a tent situation...basically non-insulated. The concept of equilibrium comes to mind...
In an active situation, EQ(equilibrium) should be achieved sooner than a passive system.
Ex. passive...
heatsink 45c...ambient tent 30c...ambient outside tent...20c
Ex. active
heatsink 35c ambient tent 30c...ambient outside tent...20c

The heat will flow to the colder areas till EQ is established. The active should be closer to equilibrium faster because of the rate it is dispersed, then it will flow out the tent to the true outside ambient.

***As a note, I am coming from a somewhat commercial grow point of view...most bang for the buck...while still making a system that knocks the the socks off hps. And defiantly driving at least 1a...call it medium current(I think SDS had a real term for it). When someone comes and says I need to cover 20'x20' with cxa's...is someone really going to recommend passive???...probably not.
If I was in a 3x3 or smaller area just for my self and wanted to make a stealth as fuck super light that I only need to build once, and cost not being an issue cause it's just for me and I don't need to be "sold" on led's...passive all the way. But on a larger scale I personally think that passive is too much material to be practical physically and cost wise.

 

[getsoutalive]

***As a note, I am coming from a somewhat commercial grow point of view...most bang for the buck...while still making a system that knocks the the socks off hps. And defiantly driving at least 1a...call it medium current(I think SDS had a real term for it). When someone comes and says I need to cover 20'x20' with cxa's...is someone really going to recommend passive???...probably not.....

Well, why not?

The number of chips required being equal, what makes active more suited to larger areas? In fact, I might argue the opposite.

3070 3kAB @ 1a is really not putting out much heat at all. I have cut one of the large passive sinks that I linked above in half and it is currently cooling a 3050 3k @ 1.4a. Now, it was a PITA to cut, but it leads me to believe that the $13 sink from Taiwan that I also linked above should be more than up to the task of cooling this chip @1a. If you subtract the need for a power supply and lead wire for each fan, the price is a wash.

The real trick is hanging all of these chips.

 

[SupraSPL]

Very good points. Maybe at some point down the road as COB efficiency increases we could see a passive cooled commercial lamp that doesn't sacrifice too much efficiency. It is reassuring to see how well the output of the CXA stands up to heat and how effective a slight air movement can be for active cooling. This changes the way I imagine the perfect grow lamp. Maybe using a smaller heatsink profile like the 3.5" with a modestly powered 80/92mm fan. That would give us a very good spread and would be even lighter than the 5.88" setups. Or for maximum bang for the buck, using the Vero29 on a CPU cooler, running at 2.4A with a reflector.

 

[PurpleBuz]

Well, why not?

The number of chips required being equal, what makes active more suited to larger areas? In fact, I might argue the opposite.

3070 3kAB @ 1a is really not putting out much heat at all. I have cut one of the large passive sinks that I linked above in half and it is currently cooling a 3050 3k @ 1.4a. Now, it was a PITA to cut, but it leads me to believe that the $13 sink from Taiwan that I also linked above should be more than up to the task of cooling this chip @1a. If you subtract the need for a power supply and lead wire for each fan, the price is a wash.

The real trick is hanging all of these chips.

But the number of chips would not be equal

 

[getsoutalive]

But the number of chips would not be equal

Why would you use a different number of chips to make an active unit vs a passive unit? His example was 3070 chips at 1a. There are a number of choices for passive sink at that level. So why would you change the number of chips?

 

[Greengenes707]

Why would you use a different number of chips to make an active unit vs a passive unit? His example was 3070 chips at 1a. There are a number of choices for passive sink at that level. So why would you change the number of chips?

We are on different pages...but I see what page your on...

Let me explain it this way...
700w light is the end goal...
Assuming same # of cobs and we will use the heatsinkUSA profiles for ease to relate to for most...
700w passively: means ~85inches of 10.8" profile...84.15lbs...costing $557.6
700w actively: means ~81inches of 5.8 profile...20.25lbs($140.94)...plus the 3 [email protected] and 3$ power supply...costing $170.94

Now factor in the ability to drive harder and add cooling to decrease the cobs necessary
Passively: could take 18(~1.05a) cobs costing $720(@40ea)...totaling $1277.6 for the cobs and heatsink(s)
Actively: could take 13 cobs costing $520(@40ea)...totaling $690.94 for the cobs and cooling systems(heatsink(s), fans, power)
If you drive the passive design actually soft(<1a) and you get even more upfront cost.

Also...if you guys think that wiring fans is hard to do or any kind of real work...you guys are lazy. Look what we are talking about and doing in our gardens...don't give me that fans are complicated stuff.

If we go even farther into this DIY heatsinks...not just cobs...
Red monos have a shitty temp droop problem and will be effected by higher operating temps worse. With reds I would do the best I could to have a lowest Tj/Tc to keep them up to par with the cobs or blues.

Now, if I was a person just building one light for my one little flowering spot...then ya I could justify that kind of cost per light and tell myself the gain in efficiency is worth it...
But what about that fact I need 2, maybe 3 of these 700w lights...or what about the guy who needs 25+ of them. Cost becomes an issue to remaining practical and saving in the long run.
I run apache's too...I know about trying to get back expensive price tags...no reason for diy to fall into that too.

 

[getsoutalive]

If you wish to run the 3070 @ 1a, you could most likely, though I have yet to hear anyone who has, run that passively on this $13 sink, @ 1.4 lbs each. Using your number at 18 chips that brings the cost to $240 and the weight down to 25.2 lbs.

If you wish to drive harder, this $27 heatsink, will work just fine at 2+a with a 3070 3k AB. 12 of those will get you into the 1k driven range. Still only $324 of metal and I believe that they weigh on the order of 4 lbs each.

The numbers are not as bad as you make them appear. Obviously, if you can wire up a cob, you can wire and power a fan. But with nothing more than a driver and chip that could fail in a passive setup, you are adding additional possible points of failure and a moving part that will fry your device if/when it fails.