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Old 1st August 2001, 07:39 AM   #11
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Old 1st August 2001, 02:59 PM   #12
peted is offline peted  United Kingdom
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Quote:
Originally posted by Lisandro_P
[BTW, could you brief me on how you painted yours and how it performs? Thanks.
Haven't tried auto paint - maybe it's too thick? Either way you'd have to use =matt= black. I used black-board black - water based - used watered down a little, rub the Al with wire wool - it's too shiny for the paint to take otherwise, then degrease (I used washing up detergent in the sink) and paint with 2 coats. I found it best when watered down a little. Objective is a =thin= matt black layer - it looks OK and meets those objectives, though anodising is better. I tried some Al black from a gunsmith - it doesn't work so well, and is horrendously expensive and chemically unfriendly too!

Performance: each of the half circle sinks in the photos achieved 0.17C/W (free convection), and 0.11C/W with a slow (silent) fan. The thick Al plates are 300mm wide, the rest of the plates are dimensioned to be a 320mm diam circle. All the Al plates/fins are 250mm high. I wrote a little C prog to calculate areas and cutting data based on the formula for a circle. I guess the same could be written in Excel. Want the C source code?

Given the lack of design data I could find, I determined the figure for a single vertical sheet (free and forced) by experimentation, and worked from there. Turned out to be reasonably accurate, but have to say there was an amount of faith involved! Dunno how many devices are in JLH - I used the v.thick Al plate to carry the MOSFETs because only 2 in a Zen stage - very concentrated heat compared to being able to spread many around a sink. My MOSFETs run at 128 (gain)and 112 (cc source) watts. Get yourself one of these 3 terminal temp chips to use as a temp probe (with some thermal grease) - use with battery and a voltmeter. BTW the outer plates =do= run almost as warm as the others so the heat transfer spacers do their job well. Mine are 180mm long(ie 35mm free either end), 25mm wide, 9mm thick.

Also bear in mind temp derating for the device, junc <> case (0.5C/W for me), and case <> sink (0.2C/W for me) values. always worth going for as much extra h/s as you can.

Al Vs Stainless? Al wins hands down - remember how they put Copper inserts in the bottom of those expensive stainless saucepans to stop local burning? Also a tad easier to work!!

Cheers

Pete

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Old 2nd August 2001, 02:41 AM   #13
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Quote:
Originally posted by peted
Haven't tried auto paint - maybe it's too thick? Either way you'd have to use =matt= black. I used black-board black - water based - used watered down a little, rub the Al with wire wool - it's too shiny for the paint to take otherwise, then degrease (I used washing up detergent in the sink) and paint with 2 coats. I found it best when watered down a little. Objective is a =thin= matt black layer - it looks OK and meets those objectives, though anodising is better. I tried some Al black from a gunsmith - it doesn't work so well, and is horrendously expensive and chemically unfriendly too![/B]
That was pretty much what i had in mind... the paint i'm refering to is that kind of "industrial" black matte paint used on cabinets, floors, equipment, etc. If that's no good, i'll go your way.

Quote:
Performance: each of the half circle sinks in the photos achieved 0.17C/W (free convection), and 0.11C/W with a slow (silent) fan. The thick Al plates are 300mm wide, the rest of the plates are dimensioned to be a 320mm diam circle. All the Al plates/fins are 250mm high. I wrote a little C prog to calculate areas and cutting data based on the formula for a circle. I guess the same could be written in Excel. Want the C source code?
... Dunno how many devices are in JLH - I used the v.thick Al plate to carry the MOSFETs because only 2 in a Zen stage - very concentrated heat compared to being able to spread many around a sink. My MOSFETs run at 128 (gain)and 112 (cc source) watts. Get yourself one of these 3 terminal temp chips to use as a temp probe (with some thermal grease) - use with battery and a voltmeter. BTW the outer plates =do= run almost as warm as the others so the heat transfer spacers do their job well. Mine are 180mm long(ie 35mm free either end), 25mm wide, 9mm thick.
I'd like that program, send the source to Lisandro@Hotmail.com . Now, i've been working with Rod Elliot's Excel sheet, and i plan to go with 20 15x17cm plates, separated in the middle by a 2cm wide bar (5mm thick). Just as you did, two of these plates will be thick to allow heat to flow faster off the semiconductors. Ideally, this should set me in the vecinity of 0.1C/W. The original JLH'96 uses two power BJT's per channel, but i'm putting two more in parallel so they run cooler and power derrating does not become a problem.

Quote:
Al Vs Stainless? Al wins hands down - remember how they put Copper inserts in the bottom of those expensive stainless saucepans to stop local burning? Also a tad easier to work!!
Yah, i did some research yesterday and it's completely true. I don't know where i readed once that steel was a much better heat conductor... oh well Thanks for the feedback!
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