Heatsinking Questions - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th October 2004, 06:29 PM   #1
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
Default Heatsinking Questions

For my future DIY amp project, i am considering several case layouts and i have some questions about heatsinking.

I will be building a pair of large mono blocks. probably a Holtan or higher powered Borbely etc. something in the 200, or 400-800w range.

My power supplies will be in a seperate case below the main amp chassis. so that leaves me with plenty of room to play with amp designs in the top case! I have some very large Heatinks that i will be placing on either side of the case as is found on most large amps. But, because i am building monoblocks, this would palce the transistors some distance away from a driver board in the center.

So my thought was, why not put a thick Almuminum plate horizontally across the outside heatsinks with the transistors and driver boards in the middle?

This would allow me to play with various designs at will.

Now my question becomes. How to effectivly tie the two outside heatsinks together?

My guess is that a thick aluminum plate at least 10mm thick across the bottom with silcon paste on the ends where it contacts the outsink sinks would be enough thermal mass to wick away a bunch of heat.

But, should the bottom plate be thicker? say 13+mm???

And should the bottom plate simply be flat? what if i were to curve the bottom of it so that it was thinner in the middle and thicker on the ends? would that help wick away the heat more effectivley?

And from a heat point of view, would it be better if the transistors were closer together in the middle or seperated some distance apart on the bottom???

Please take a look at the 4 examples i have posted and tell me if anyone of these makes more sense from a thermal point of view over the others?


Im sure this is all Overkill in design. But that is the name of my Audio Business. Overkill audio inc. ( www.overkillaudioinc.com ).



I look forward to your thoughts and comments!


Zero
Attached Images
File Type: jpg example 1 d copy.jpg (76.0 KB, 308 views)
  Reply With Quote
Old 19th October 2004, 07:22 PM   #2
diyAudio Member
 
Swedish Chef's Avatar
 
Join Date: Jun 2004
Location: Stockholm
#3 is "best" but it is far from "good". The interface between the alu plate and heatsink will have WAY to high thermal resistance. You need to bolt them together with lots of pressure so the use of an L-type (or U-type in this case) profile is pretty much the only way to go if you're going down this path. While it might be tempting to use the alu plate for the reasons you stated it is a terrible solution from a thermal point of view.

There seems to be much confusion regarding heatsinks and thermal resistance (see this post for example Ultra High Current Mosfets from Hitachi)

Once steady-state conditions are reached, it's just a matter of Ohm's law and the definition of volume resistivety.
Oh, well and convection and black-body radiation as well...

See the ESP pages for an introduction.

/Magnus
__________________
"Knowing what to do but not why is no use in a changing world" - The Art of Sound Reproduction
  Reply With Quote
Old 19th October 2004, 07:37 PM   #3
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
I say also, avoid heat transporting elements. Try to locate your power transistors as close as possible to the big heatsink. If you plan a 800 watt Holton, forget about this arrangement Have you seen his heatsinks?

Why can't you do like PMA (and others) does? Place the whole pcb directly on the big heatsink.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 19th October 2004, 07:57 PM   #4
pro is offline pro  Italy
diyAudio Member
 
pro's Avatar
 
Join Date: Feb 2004
Location: Milano
Why don't you join the two heat-seenk togeather, and use them like.....Cover?
Ciao.
__________________
Michele
  Reply With Quote
Old 19th October 2004, 08:02 PM   #5
diyAudio Member
 
Swedish Chef's Avatar
 
Join Date: Jun 2004
Location: Stockholm
Quote:
Why can't you do like PMA (and others) does? Place the whole pcb directly on the big heatsink.
I would second that. It really is a great way of mounting the PCB:s. And suddenly you have plenty of space inside the amp box!
Pretty much all of the really high power electronics (motor control etc) I have seen use this approach.

/Magnus
__________________
"Knowing what to do but not why is no use in a changing world" - The Art of Sound Reproduction
  Reply With Quote
Old 19th October 2004, 08:04 PM   #6
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
Quote:
Why can't you do like PMA (and others) does? Place the whole pcb directly on the big heatsink....
Ideally thats what i would normally do, BUT, Remember these are mono blocks so there will be 2 heatsinks per chassis. I need to find a way to use both heatsinks.

I could mount the NPN's on one and the PNP's on another, but then there is a large distance between the 2 heatsinks where i would have to run leads from the output boards to the driver board. and i was hoping to keep those leads as short as possible to avoid oscillations and this seems to make the most sense....

and i dont want to use fans! So a heat tunnel like Holtan used is out of the question. (i am most likley building a class AB 200, or 400 watt amp).

With this arraingement i could mount the driver board on top of the output board and have no internal wiring at all except power!

I could make the bottom plate as thick as need be if that would help. i mean i could make it 20mm thick or more if thats the way to go! Or i could make the bottom contour in any desired shape or pattern.

My outside heatsinks are about 6" high by 9" long with 3" fins and a 3/8" thick plate at a guess (there on there way here now) they are similar in design to what is on the Classe 400 amplifiers.
Big thick meaty heatsinks!


I know this is not the most ideal situation. but, from a flexibility standpoint this is best.

Any suggestions on how to optimize such a design???. I will read the ESP paper on this as you suggested.



Zero
  Reply With Quote
Old 19th October 2004, 08:09 PM   #7
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
Quote:
Why don't you join the two heat-seenk togeather, and use them like.....Cover?
Because the plan is to leave to top open so i can swap out driver boards and experiment. with the heatsinks on top there would be a lot of hassle involved to swap out boards.


Quote:
And suddenly you have plenty of space inside the amp box!
With the power supply located in a separate chassis below the amp chassis, there will be nothing in the top box except the amp boards!

The power supplies are being built to facilitate any number of amp designs or power ratings. I have multi tap transformers that can be reconfigured for any amp from 100W to 1000 watts.

The whole thing is being set up as sort of a test bed for amp building.
  Reply With Quote
Old 19th October 2004, 10:06 PM   #8
diyAudio Member
 
Join Date: Oct 2004
Go for copper young man. Aluminium is cheap to extrude and all.
But when it comes to serious heat moving copper is king.
And stop for a little while and think. Think of the little volume of metal sitting there right under the transistor chip, it is as small
as 5x5mm. In this volume you will get a pretty serious temperature gradient. This is a term from vector analysis and can be easier understood in this matter as a flow for instance of water. If you use copper the gradient will be half that of aluminium. You will save maybe 30 degres C on chip temperature,
at these hefty powerlevels. You must have a scrapyard nearby, most of the time one can find copper bars from giant electric installations there. Take for instance something like 100x6mm
in lengths of 250mm. These can take at least 200W dissipation without overheating. And if you are really smart put all positive transistors on one and the negative on the other. Heureka no need for isolating mica washer or the like. Then you will notice somthing strange, the transistors are almost the same temperature as the the whole heatsink and this is not a normal situation. I have built PA amps putting out 2x500W with only one sheet of copper 420x350x3 mm and only a little 90mm fan never any heat problems in years.
  Reply With Quote
Old 20th October 2004, 12:35 AM   #9
diyAudio Member
 
Join Date: Jun 2004
Location: Knoxville
Copper is great and all, but it does corrode. It needs to be plated or coated in some way. Especially if you live in an area close to a coal power plant and all of the SO2. (sulfer dioxide)
  Reply With Quote
Old 20th October 2004, 06:10 AM   #10
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
The heatsinks i have are aluminum, but i could make the bottom plate all copper!

this bottom plate will be about 14" long and 10" wide and about 2" thick on the ends before it attaches to the heatsinks on each side. so were talking some pretty good mass.

Im not sure what i could coat the copper with to prevent oxidation.... I deal with a lot of recycling facilities so im sure i can find some large chunks of copper!


Zero
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
heatsinking Ted205 Chip Amps 24 30th August 2008 08:50 AM
Heatsinking issues pjpoes Chip Amps 12 18th September 2005 05:14 PM
Class A heatsinking, or heatsinking in general! NUTTTR Solid State 27 22nd January 2005 01:48 PM
LM4780 Heatsinking jackinnj Chip Amps 3 5th January 2005 06:00 PM
Heatsinking has now become less dense! cunningham Solid State 5 9th November 2004 07:09 AM


New To Site? Need Help?

All times are GMT. The time now is 03:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2