Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 1st July 2002, 10:45 PM   #1
Apogee is offline Apogee  United States
diyAudio Member
 
Apogee's Avatar
 
Join Date: Feb 2002
Location: Tacoma, WA
Question Heatsink question

Yes, I know this topic has been beaten to death, but I wasn't able to find an answer to this question....

Yes, H.H - I did search...

Take just about any standard flatback heatsink. Now imagine taking 3 of them and laying them next to each other like this:

E
E
E

If I take a piece of 1/4" aluminum flat plate and cut it to the correct dimension and then bolt the heatsinks to it (using grease), does this raise or lower the thermal efficiency? I'm wondering if I can buy smaller extrusion and ultimately achieve the same thermal efficiency as using a larger one...

This is what I'm envisioning (the vertical lines would actually be one continuous piece of metal):

|E
|E
|E

I ask this question because I've seen many TO3 style amps that have been designed using a "carrier" to mount the TO3's which is then bolted to the heatsinks... It seems to me that this would significantly raise the junction temps but it doesn't seem to be a problem... The carriers often look like this (only the heatsink is actually one large extrusion):

.E
[E
.E

How would one go about calculating the thermal sinking of the combination of the two pieces of metal? Just add their dissipations together and subtract the joint loss? Or, is it not so simple?

Any help would be appreciated!

Thanks,
__________________
"If I had my life to live over again, I would have made a rule to read some poetry and listen to some music at least once a week." - Charles Darwin
  Reply With Quote
Old 1st July 2002, 11:22 PM   #2
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I do this sort of thing all the time, just look at Threshold
and X products.

Calculations? We don't need no stinkin calculations! We just
make them really big!
  Reply With Quote
Old 1st July 2002, 11:25 PM   #3
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
I once tried to make a large heat sink out of many small ones. It was for Zen amp. But since there were only 2 transistors attached to the sink the heat distribution wasn't even and some spots were much warmer than the others even after many hours of operation (I used thermal grase).
I liked the looks anyway.
I plan to build Aleph 5 on that and with 6 transistors per side it should work really fine. I usually don't do calculations as well. It either runs hot or not at all.
Attached Images
File Type: jpg heat.jpg (45.2 KB, 2368 views)
  Reply With Quote
Old 1st July 2002, 11:26 PM   #4
Banned
 
Join Date: Apr 2002
Location: Germany, Clausthal
very sympatic way of engineering!

i love this philosophy, thats the way i could handle and understand building your amps.
  Reply With Quote
Old 1st July 2002, 11:45 PM   #5
Jean is offline Jean  United States
diyAudio Member
 
Jean's Avatar
 
Join Date: Mar 2002
Location: Sacramento, CA
Send a message via AIM to Jean
Is there a good source for just various thickness aluminum in sheets ?
  Reply With Quote
Old 2nd July 2002, 12:08 AM   #6
PedroPO is offline PedroPO  Portugal
diyAudio Member
 
PedroPO's Avatar
 
Join Date: Jan 2002
Location: Lisbon,Portugal
Send a message via ICQ to PedroPO
Default Heatsink Calculation

Last time I tried to calculate a heatsink, I put my amp at 100șC...''

I guess you can allways try to bolt a single power resistor (with aluminium housing), apply a voltage until the heatsink get the temperature you want (say 50șC), then read the tension and P=R^2/R. You get the maximum power dissipation of the heatsink before you drill all the dissipators to put the transistors and / or resistors.

Pedro Oliveira
PS: I agree with Nelson Pass: Bigger is better at least in heatsinks.
__________________
Pedro Oliveira
  Reply With Quote
Old 2nd July 2002, 12:35 AM   #7
herm is offline herm  United States
diyAudio Member
 
Join Date: Mar 2002
Location: Pasadena, CA USA
Jean;

www.onlinemetals.com
  Reply With Quote
Old 2nd July 2002, 12:53 AM   #8
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
Bigger is better with heat sinks and bias current

If you want to use multiple heatsinks, you are best to mount the transistors on each individual heatsink and then use strap or angle pieces to mechanically join each heat sink around the edges. Just keep the number of devices per heatsink equal.
  Reply With Quote
Old 2nd July 2002, 02:06 AM   #9
Paper mache horn fabricator
diyAudio Member
 
carpenter's Avatar
 
Join Date: Mar 2002
Location: Oregon City, Oregon
Thumbs up nice link, herm

I checked out some of the sheet goods and related prices. They compete well with prices at my local metal yard. A 3'x4'x1/16" piece of aluminum cost roughly $2.55/pound. New aluminum is $3.00/pound here in Portland, Oregon. Excellent lead! It's still way cheaper to buy in bulk and make your own cuts, though. They don't give their labor away.


John Inlow
  Reply With Quote
Old 2nd July 2002, 03:59 AM   #10
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Quote:
Originally posted by Nelson Pass
Calculations? We don't need no stinkin calculations! We just
make them really big!
Harley Davidsons are designed using a similar philosophy I think.

If you have the choice between a tall skinny heatsink and a short broad one with a same area, the short broad one will win every time. Only the first couple of inches seems to do anything much, after that the rising air has been warmed enough as it rises through the fins that it cannot cool any further fins higher up.

I love fans! I did a little test with a h/s 110mm x 95 with 11 fins 25 mm deep and 1.5mm thick, both on it's lonesome and with a 12v fan covering most of its finned side and a 25w metal clad resistor attached to the flat side with thermal paste. Here are the figures:

Heatsink vertical both sides exposed
24.25 watts
44.40 deg C rise
1.83 deg C per w

Heatsink vertical with 2.8 watt Sunon fan @ 5v
24.25 watts
10.20 deg C rise
0.42 deg C per w 4.36 times improvement

Heatsink vertical with 2.8 watt Sunon fan @ 12v
24.25 watts
7.70 deg C rise
0.32 deg C per w 5.77 times improvement

Heatsink vertical with 2.8 watt Sunon fan @ 15v
24.25 watts
7.50 deg C rise
0.31 deg C per w

Heatsink vertical with 2.8 watt Sunon fan @ 20v (12v fan, mind you!)
24.25 watts
7.50 deg C rise
0.31 deg C per w

At 5v the fan is inaudible.

GP.
  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
Another heatsink question! k.junold Solid State 7 24th July 2004 04:31 PM
heatsink question? xdissent Solid State 13 18th June 2004 02:44 AM
Heatsink question kheldar Chip Amps 8 30th January 2004 02:50 PM
heatsink question tpenguin Solid State 3 23rd December 2003 09:47 PM
yet another heatsink question BrianGT Pass Labs 3 19th September 2002 07:55 PM


New To Site? Need Help?

All times are GMT. The time now is 07:35 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