DiY LED - Cree CXA3070

Cali weed

Cali weed

Well-Known Member
I was gonna ask the difference between pk1 and pk3 but seems irrelevant after that last post by supra. Is this the right kind? Prolimatech PK-3 Nano Aluminium Thermal?
Also should I use the 1 mil 1/2 inch kapton tape or the 1 mil 1/4 inch, or something completely different. Thanks in advance!
 
Doer

Doer

Well-Known Member
I was reading the "correct" way to use paste is to use a stencil. That way we can control the depth. .5mm or whatever, by the thickness of the stencil material. A good start is the thickness of the TIM on store bought CPU coolers that have the goo in place when we buy it.

Also, the only way I know to make sure we are not trapping bubbles of air is to start the device down on one EDGE only. And slowly lay it down without moving or lifting that edge. The air is pushed out the other sides.

Try the paste with a little square of glass first to see what I mean.
 
SupraSPL

SupraSPL

Well-Known Member
Gotcha, good points. I noticed on the Rosewill CPU coolers their stock paste is runnier at room temp than PK3 and MX4. When I press the COB on the stock paste I get the same effect, paste squeezing out the sides of the COB, so the pressing method is giving us an even thinner layer than TIM printing provides on its own.

Very good point about reducing air bubbles by using an even layer rather than dabs. That is the main reason I have to waste so much paste, maybe I should use a tool to spread it. I will definitely try your suggestion of mounting onto glass so I can see if I am using enough or if I can use less by spreading first.

Tending to the thermal interface is a worthwhile effort but when it comes down to it, as long as there is a TIM based thermal interface, there is not much we can do to improve performance. I was very surprised in my testing to discover that sanding and polishing made no difference whatsoever, PK3 gave no advantage over MX4 etc. What did make a significant repeatable difference was the heatsink itself, but even that was only a percent or so when run hard. It becomes even less important when running at low currents (.25-.75% temp droop for CXA3070@ 25W).

Another way to put it, the thermal interface becomes much more important when the heat flow/surface area is large and the heatsink itself is insufficient. This is great news for DIYers, sanding was kind of a PITA, although I still do give heatsinks a once-over just to make sure they are not warped.
 
Doer

Doer

Well-Known Member
http://www.tim-consultants.com/application_instructions.pdf

Instructions for Use

Once you begin to mix the material, the viscosity will decrease significantly and it will be easy to apply. Once applied, the greases will again become rigid and therefore will not flow; while maintaining adequate thermal coverage between your substrate (i.e. heat sink) and heat producing device (i.e. CPU).

Application:
Spread on a uniform coating thickness between 0.003” to 0.006” (.15mm) across the thermal substrate in an area large enough to cover the heat producing component.

Stencil Printing:
Place the heat sink under the stencil. Place a dollop of thermal grease across one side of the stencil. Run a hard rubber (70 – 90 Shore A durometer) squeegee across the dollop passing across the stencil. Repeat if necessary. Remove the stencil to reveal the printed grease
 
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alesh

alesh

Well-Known Member
Doer said:
http://www.tim-consultants.com/application_instructions.pdf

Instructions for Use

Once you begin to mix the material, the viscosity will decrease significantly and it will be easy to apply. Once applied, the greases will again become rigid and therefore will not flow; while maintaining adequate thermal coverage between your substrate (i.e. heat sink) and heat producing device (i.e. CPU).

Application:
Spread on a uniform coating thickness between 0.003” to 0.006” across the thermal substrate in an area large enough to cover the heat producing component.

Stencil Printing:
Place the heat sink under the stencil. Place a dollop of thermal grease across one side of the stencil. Run a hard rubber (70 – 90 Shore A durometer) squeegee across the dollop passing across the stencil. Repeat if necessary. Remove the stencil to reveal the printed grease
Click to expand...
Assuming 0.0045" thickness, single 30g tube should perfectly cover 129 3070's w/o any losses.
thickness = 0.0045" = 0.01143 cm
area of 3070 = 27.35 mm * 27.35 mm = 7.480225 cm^2
volume per 3070 = 0.01143 cm * 7.480225 cm^2 = 0.08549897175 cm^3
density of PK3 = 2.7 g/cm^3 [link]
mass per 3070 = 2.7 g/cm^3 * 0.08549897175 cm^3 = 0.230847223725g
3070's per 30g tube = 30 g / 0.230847223725g = 129 pcs
 
Doer

Doer

Well-Known Member
I think what I will do is make a stencil card, the size of the sink, and cut 8 x 35mm squares, perfectly aligned, put the goo on the sink and that aligns all the COBs. Align all the COBs, that aligns all the holders and aligns all the screw holes.

I doubt if I would bother to tap, in any case. I think I will use a type 23, (fine thread) self tapper.

I can even cut the bottom taper off after I start it, if it bottoms too early.

And it is nice to know you can get 120 squares more or less from a 30g tube. (considering some waste and the fact the 3590s are bigger)

Good math!
 
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nogod_

nogod_

Well-Known Member
I dont think card is what youre after if youre shooting for .15mm. I was thinking about stencils a while back and

The two methods I came up with were custom silkscreen (more for someone doing things on the scale of happy76)
and a custom cut vinyl sticker sheet that you could run down the middle of the heatsink. If you were savvy you could even print your hole guides on the sticker and it could serve as your drilling template and TIM stencil in one.

edit: another method that just occurred to me is to score through one of those really wide rolls of painters tape. Then you have many many stencils. Use a 3" plastic spackle spatula and your in business.

Doer said:
I think what I will do is make a stencil card, the size of the sink, and cut 8 x 35mm squares, perfectly aligned, put the goo on the sink and that aligns all the COBs. Align all the COBs, that aligns all the holders and aligns all the screw holes.

I doubt if I would bother to tap, in any case. I think I will use a type 23, (fine thread) self tapper.

I can even cut the bottom taper off after I start it, if it bottoms too early.

And it is nice to know you can get 120 squares more or less from a 30g tube. (considering some waste and the fact the 3590s are bigger)

Good math!
Click to expand...
 
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Doer

Doer

Well-Known Member
Yeah! It looks like you can get it at about .15mm thick for Scotch Brand. Good idea. A self sticking, thin stencil mask.
 
pirg420

pirg420

Well-Known Member
Does anyone have a link to the efficiency charts for the latest and available cxB 3070's? Ive searched mutliple threads but can only find the 3590 stuff.

thank you
 
nvhak49

nvhak49

Well-Known Member
Does anyone think it's better to mix up the spectrum or keep it all the same? I'm wanting to make a 400w panel on one big heat sink Id like to run them at 700mA or 1050 but most likely 700, I have 4 CXA 3000k AB Bin and I was thinking of buying four more I just didn't know if it should get a different color, I'll probably get some CXBs if they're available.
 
nomofatum

nomofatum

Well-Known Member
nvhak49 said:
Does anyone think it's better to mix up the spectrum or keep it all the same? I'm wanting to make a 400w panel on one big heat sink Id like to run them at 700mA or 1050 but most likely 700, I have 4 CXA 3000k AB Bin and I was thinking of buying four more I just didn't know if it should get a different color, I'll probably get some CXBs if they're available.
Click to expand...
Mix for sure if you are going for quality. 75% 2700k-3500k, 25% 6500k, also adding UVB (5w of UVB 10% bulbs per sqft) will be well worth it.
 
L

LeanMcsheen

Active Member
I used a stencil for my TIM on my current build. For the stencil I used a thin piece of acetate... Although tape would probably be a bit better
 
bizfactory

bizfactory

Well-Known Member
Something I hadn't thought about until now...with CXB3070s @ 1400mA, how far away will I need to keep my plants? I don't have TONS of vertical space...hopefully I didn't just build a light I can't even use because it's too powerful lol...

18 inches enough!?
 
Scotch089

Scotch089

Well-Known Member
18" is probably perfect depending on how many you're using. Heat won't be an issue at that height and With 8 cxas plus some reds and cooler whites at 700mA at 18" I am getting ~860ppfd on my apogee meter. So if you had 4 at 1400 at 18" I think that'd be about as close as you'd want during most of flower, I doubt there'd be negative issues if you had to get closer. But you wouldn't NEED to get closer.
 
bizfactory

bizfactory

Well-Known Member
Scotch089 said:
18" is probably perfect depending on how many you're using. Heat won't be an issue at that height and With 8 cxas plus some reds and cooler whites at 700mA at 18" I am getting ~860ppfd on my apogee meter. So if you had 4 at 1400 at 18" I think that'd be about as close as you'd want during most of flower, I doubt there'd be negative issues if you had to get closer. But you wouldn't NEED to get closer.
Click to expand...
Nice! Thanks for the quick answer. I think I can maintain at least 18" as long as I don't let my plants get out of control and mount the light pretty high in the tent.
 
beppe75

beppe75

Well-Known Member
bizfactory said:
Nice! Thanks for the quick answer. I think I can maintain at least 18" as long as I don't let my plants get out of control and mount the light pretty high in the tent.
Click to expand...
Biz... how Many W total does your 4 CXB3070s @ 1400mA output?
how big is your tent? and what about efficiency...
i'm thinking to go with this setup of yours for my grow.
 
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