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Heatsink USA Extruded aluminum heatsinks, specializing in small custom cut orders

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Old 21st January 2009, 01:42 PM   #11
vonfilm is offline vonfilm  United States
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I will be following this thread as well. I plan on building several F series amplifiers this year.

If the heat sink is large enough, say 16" x 12", are vertical fins really that important?
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Old 21st January 2009, 01:44 PM   #12
labjr is offline labjr  United States
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Quote:
Originally posted by vonfilm
I will be following this thread as well. I plan on building several F series amplifiers this year.

If the heat sink is large enough, say 16" x 12", are vertical fins really that important?
Yes. Simple physics. For good convection the fins need to be vertical so the heat can rise. Otherwise it gets trapped and can not dissipate.
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Old 21st January 2009, 02:04 PM   #13
vonfilm is offline vonfilm  United States
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If these 12" wide heat sinks were oriented with the fins vertically, how tall would it need to be to be used for 1 channel of an F series amp?
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Old 21st January 2009, 02:18 PM   #14
labjr is offline labjr  United States
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Quote:
Originally posted by vonfilm
If these 12" wide heat sinks were oriented with the fins vertically, how tall would it need to be to be used for 1 channel of an F series amp?
I'm guessing 6" minimum to about 8".

Nelson's article states one 6" x 8" chunk with 2" fins per output device. That means one piece 12" x 8" per channel. He may have made a rough estimate for that.

Also, I emailed Russ about the heatsinks and he may make the fins longer at about 2.5" so he can make the extrusion about 11" wide. Saves on production cost if the die is more narrow.

I wouldn't even mind if he did 3" fins using a 10" wide extrusion Calculates out about the same. The amp could be a little more cube-shaped and compact.
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Old 21st January 2009, 02:42 PM   #15
AndrewT is offline AndrewT  Scotland
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long fins need to be thicker or for economy tapered.
The root thickness ~ fin height/10.
50mm fins need >=5mm thickness at the root tapering to about 2mm at the tip.
75mm fins need >=7.5mm thickness at the root tapering to about 2mm at the tip.

Similarly. the distance from the furthest corner to an adjacent device must be controlled by the thickness of the backplate. Again this 10:1 ratio applies.
12inches wide and 8inches tall with two devices located 40% up from the bottom and 6inches apart will result in a device to corner distance of ~129mm. This requires a backplate thickness >=13mm.
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Old 21st January 2009, 03:05 PM   #16
labjr is offline labjr  United States
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Quote:
Originally posted by AndrewT
long fins need to be thicker or for economy tapered.
The root thickness ~ fin height/10.
50mm fins need >=5mm thickness at the root tapering to about 2mm at the tip.
75mm fins need >=7.5mm thickness at the root tapering to about 2mm at the tip.

Similarly. the distance from the furthest corner to an adjacent device must be controlled by the thickness of the backplate. Again this 10:1 ratio applies.
12inches wide and 8inches tall with two devices located 40% up from the bottom and 6inches apart will result in a device to corner distance of ~129mm. This requires a backplate thickness >=13mm.
You obviously know much more than many of us do about heatsink design. Perhaps you can assist Russ in designing an extrusion die for an efficient heatsink. It would cut down on wasted production cost and be useful for more projects here on DIY. Thus he would be able to sell at a higher volume and pass on the lower cost to everyone.

One problem I see with the F5 board is that the 2 output devices are only about 4 inches apart. Not sure if this makes a difference or not. Seems they should be farther apart. Maybe a compact heatsink with longer fins helps out here?
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Old 21st January 2009, 03:58 PM   #17
AndrewT is offline AndrewT  Scotland
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hi,
closer spacing of the devices results in a bigger device to edge/corner distance.
Choice; accept that the heatsink will need to be de-rated for poorer efficiency than the rated Rth s-a
or
find a heatsink better suited.

In this case we can either change the backplate thickness to fit the new and bigger device to corner distance
or
move the devices
or
simply run hotter.
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Old 21st January 2009, 05:16 PM   #18
pooge is offline pooge  United States
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Quote:
Originally posted by labjr

Would be nice if it was anodized black. Then again maybe you can have it anodized locally after you drill all the holes etc.
I checked on doing this locally. Turns out it cost more than buying already anodized heat sinks that are bigger than I need. They also would not anodize anything I had in a larger batch including other people's stuff. They said that different type parts in the same batch could potentially interfere with the process, so they would not combine parts to save money. Don't know how important this is, or even whether it is true, but the bottom line was that it was far from economical to have them anodized locally.
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Old 21st January 2009, 05:28 PM   #19
labjr is offline labjr  United States
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Quote:
Originally posted by pooge


I checked on doing this locally. Turns out it cost more than buying already anodized heat sinks that are bigger than I need. They also would not anodize anything I had in a larger batch including other people's stuff. They said that different type parts in the same batch could potentially interfere with the process, so they would not combine parts to save money. Don't know how important this is, or even whether it is true, but the bottom line was that it was far from economical to have them anodized locally.
How about powder coating? Does this change the thermal properties? I have friends who work in metal production and can easily have stuff powder coated. Anodizing is not so easy to have done, because it's not as popular as it used to be.
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Old 21st January 2009, 05:37 PM   #20
tms0425 is offline tms0425  United States
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Quote:
Originally posted by labjr


How about powder coating? Does this change the thermal properties? I have friends who work in metal production and can easily have stuff powder coated. Anodizing is not so easy to have done, because it's not as popular as it used to be.
This is from the Conrad site regarding their powder coating:

"Coating Material
Textured black polyester powder coating has been chosen as the standard finish on all coated Conrad heatsinks and provides:

* a quality, durable and attractive finish capable of withstanding elevated temperatures,
* increased thermal dissipation in the order of 5% to 8% (depending on the heatsink) under natural convection."
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