700B/ Series II heat sinks

[WOPL Sniffer]

Well, as you guys know, I have been looking for a set of heat sinks for an amp and THEY ARE IMPOSSIBLE to locate. So, Necessity being the mother of invention, I decided to make my own. They need a little tweaking but looks like the idea WILL WORK. It is a butt-load of labor but I believe (Thermal testing will tell ) they will wick heat away just like the originals without the costs Lee incurred while doing a set in copper, which by the way look way awesome comparing them to these economical aluminum ones. I'd love to do a set in copper, but the cost to do 4 sinks for one amp ran at $400 just for the copper parts. Hey, maybe I'll strip the SAE and use those!!! (NOT).

I still have the option to laser scan and have them CNC'd like the handles but the cash is not there....

 

[grapplesaw]

Nice Perry. Maybe some thermal grease between the plates before tightening. The original extrusion or something simalar must be available through the window industry. I have a friend in it and will ask where to look for this. The problem is they want to run a lot of material for single order.

 

[laatsch55]

Amen Perry, they are a but load of work
I did 4 sets in copper in total. Are you going to anodize them when you're done? How thick is the plate?

 

[WOPL Sniffer]

Nice Perry. Maybe some thermal grease between the plates before tightening. The original extrusion or something simalar must be available through the window industry. I have a friend in it and will ask where to look for this. The problem is they want to run a lot of material for single order.

Look close,
Thermal grease is in the crack.....

 

[WOPL Sniffer]

Amen Perry, they are a but load of work
I did 4 sets in copper in total. Are you going to anodize them when you're done? How thick is the plate?

The plate is 1/8"
Anodizing is expensive, im going to see how it conducts heat as is, i have a laser thermometer and will do some experimenting with it down the road.

 

[laatsch55]

Emisstivity increases greatly with black anodizing. Almost necessary with aluminum. The only reason I got away without anodizing the copper one a, is because they were copper. It will be interesting to see how the bare aluminum does.

 

[WOPL Sniffer]

Interesting, maybe ill check with the anodizer again, it's been a while.

 

[grapplesaw]

Emisstivity increases greatly with black anodizing. Almost necessary with aluminum. The only reason I got away without anodizing the copper one a, is because they were copper. It will be interesting to see how the bare aluminum does.

Try this on.
Because of a relationship between absorptivity and emissivity described by Kirchoff's Law of thermal radiation. In short: The reason why black is more emissive is because it absorbs more radiation in thermal equilibrium and thus must also radiate more to maintain that equilibrium.
Why heatsinks aren't black is because plain aluminium is still quite emissive in infra-red (where it matters) and because black paint may have lower thermal conductivity than bare metal, reducing the primary method of cooling, convection, as plain radiation is a far less important method of cooling.


there's two things to consider:

1. Emissivity is always relevant for radiative heat transfer. Emissivity describes how a certain material interacts with EM radiation across all wavelengths, not just in the visible region. Think of it as a graph of emissivity vs. wavelength. If you have an object that isn't hot enough to glow visibly, you are still interested in the emissivity graph at wavelengths greater than 700 nm. Since emissivity refers to the whole graph, it's a little weird to say that emissivity doesn't matter when the object isn't visibly glowing (i.e. < 700 K). However, you can say that emissivity in the visible region isn't relevant.
   
2. Radiative heat transfer is not always relevant. For this specific application, convective heat transfer is much more important, so radiative heat transfer (and therefore emissivity) isn't really relevant. However, radiative heat transfer is strongly dependent on temperature (~T[SUP]4[/SUP] vs. ~T for convection). So if an object is hot enough to glow visibly, it's likely that thermal radiation is a significant contributor to the overall heat transfer.

To try and summarize: Does emissivity only become relevant if the object is so hot it's giving off visible light?

• No, because emissivity covers all wavelengths, not just visible. So an object's IR-range thermal radiation depends on its emissivity in the IR range.
  
• Yes, because radiative heat transfer isn't a significant contributor to overall heat transfer at lower temperature

 

[grapplesaw]

anodising is far and away the best coating for aluminium.

 

[krellmk]

Nice work Perry

 

[laatsch55]

Perry, I did a total of 4 sets of coppers, 2 for the 400's and 2 for a 700. Blaze ES's 400 has a set, Stephen's 400 and Ed has the two 700 sets...

 

[WOPL Sniffer]

Dang it, I need a set....

 

[Geegz]

Hey Perry, what size C channel (OD width and ID width) did you use for this? Is the ID crowding the transistor vs the stock heat sink? I have a thought on a 1 piece aluminum heat sink but the only extrusion I can find has a 2" OD at the base, plenty of room for the transistors but might hinder some of the backplane mounting hardware.

 

[WOPL Sniffer]

1.75"

The consensus is: No worky worky...... The junction from the channel and the fins won't transfer the heat. The project is being abandoned.

 

[Geegz]

So a 1 piece fin is needed, correct?

 

[laatsch55]

That is it...

 

[Northwinds]

Damn, if you had a metal break you could just bend your own aluminum/copper flat stock. Or maybe fab a hydraulic setup

 

[grapplesaw]

I have measured and 2"x 6" X 1/16" rectangular aluminum tubing should work. Just cut off one end at stock length or leave them long at full 6". I am going to build a set. The high heat sensors will have to be mounted prior to assembly with counter sink screws from the back side. I am using six of these in my monster mono build in 1/4" wall. Say tuned. It's a little down (3or4) on my list. Need a full comp 400 first. Then finish referb of my original 700 series one then after that. In the mean time I am ordering the heat sink stock

edit: will need to use 4-40 screws for the counter sink holes as it will not work with 6-32 in the 1/16" stock chassi . 6-32 screws should be ok in Joe's new chassis as i think it is .188 wall

 

[Northwinds]

I love threads like this, it's amazing the ingenuity this board has to make things work better

 

[laatsch55]

I have measured and 2"x 6" X 1/16" rectangular aluminum tubing should work. Just cut off one end at stock length or leave them long at full 6". I am going to build a set. The high heat sensors will have to be mounted prior to assembly with counter sink screws from the back side. I am using six of these in my monster mono build in 1/4" wall. Say tuned. It's a little down (3or4) on my list. Need a full comp 400 first. Then finish referb of my original 700 series one then after that. In the mean time I am ordering the heat sink stock

edit: will need to use 4-40 screws for the counter sink holes as it will not work with 6-32 in the 1/16" stock chassi . 6-32 screws should be ok in Joe's new chassis as i think it is .188 wall

How are you going to layout and drill the output holes Glen??