same heatsink, different datasheets - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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 5th July 2009, 11:36 AM   #1
jazz is offline jazz  Netherlands
diyAudio Member
 
Join Date: Dec 2001
Location: leiden, physically that is...
Question same heatsink, different datasheets

Hi,

I'm a bit puzzled by different heat resistance ratings for virtually identical heatsinks from Seifert and Fischer.

The sk-130 from Fischer and the kl-240 from Seifert differ only in the thickness of the baseplate as far as I can tell from the datasheets. Yet Fischer gives a heat resistance rating which is about double that of Seifert (~,5 K/W versus ~,25 K/W for 100mm heigth).

Which am I to trust?

regards,
Joris

Link:
http://www.fischerelektronik.de/index.php?id=114
http://www.digtion-medien.de/seifert...punkte/pdfs/46[0].pdf

Edit: can't seem to get the links working directly, sorry
__________________
oh, what a beautifull day
I wanna go out and play!
  Reply With Quote
Old 5th July 2009, 12:11 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
you must look out the information sheets from both manufacturers where they define the test conditions used to rate their heatsinks.

The biggest difference is made by choosing a different DeltaT s-a.
But this, with other conditions, could account for this apparent 2:1 discrepancy.

BTW,
I could not link to the digtion site.
__________________
regards Andrew T.
  Reply With Quote
Old 5th July 2009, 12:52 PM   #3
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: Behind you
HTML entities let you link to files with stupid characters in their names.

Anyway, I thought it was the other way around and manufacturers chose a particular power to apply to the heatsink and then measured delta-T, rather than choosing delta-T.

Another factor that can make a huge difference is the area they apply the heat to. If they simulate a tiny TO-220 package, the thermal resistance will be higher than if they use a larger area like a TO-264.
__________________
https://mrevil.asvachin.eu/
  Reply With Quote
Old 5th July 2009, 01:20 PM   #4
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
You have luck, because this is exactly the heatsink profile I used extensively for my Class A power amps, such as here :

http://www.diyaudio.com/forums/showt...t=#post1744005

I used Seifert, but it is exactly the same as Fischer. The Seifert thermal data are attached.

http://www.seifert-electronic.de/en/index.php

(you need to do some surfing to get to the right page for KL240)
Attached Images
File Type: jpg seifert kl240 resistance.jpg (49.2 KB, 176 views)
  Reply With Quote
Old 5th July 2009, 01:22 PM   #5
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
The fischer :

http://www.fischerelektronik.de/index.php?id=114

(just type sk130 and search)
Attached Images
File Type: jpg sk130.jpg (6.6 KB, 171 views)
  Reply With Quote
Old 5th July 2009, 01:25 PM   #6
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
The difference can easily be explained by different assumptions such as dT (heatsink temperature above atmospheric).
Neither figure is close to reality if you are trying to operate at say 55C.

A third supplier who produced the same profile was kind enough to do a full blown simulation for my application (length 550mm, free convection, black anodised, vertical), and you can see how things depend.


Patrick
Attached Images
File Type: jpg heatsink.jpg (33.6 KB, 184 views)
  Reply With Quote
Old 5th July 2009, 01:33 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by Mr Evil
Another factor that can make a huge difference is the area they apply the heat to. If they simulate a tiny TO-220 package, the thermal resistance will be higher than if they use a larger area like a TO-264.
indeed.
Most manufacturers will try to show their product with the best figures. They achieve this by taking the whole backplate surface up to the test temperature (isothermal) and then finding what power the sink can dissipate.
It would be very unusual for big heatsink to use published data based on a single device that left the remaining surface exposed to ambient.

Simulators can do this modeling for you if you want to see how badly the sink can dissipate when it has a few hotspots where the device/s are located.
__________________
regards Andrew T.
  Reply With Quote
Old 5th July 2009, 02:41 PM   #8
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
All manufacturers assume that the flat side has uniform heat flow. This is of course not reality. It is up to the user to provide further heat spreading devices in case such a large area heatsink is used with few heat generating spots. But this is easily done.


Patrick
  Reply With Quote
Old 6th July 2009, 07:37 AM   #9
jazz is offline jazz  Netherlands
diyAudio Member
 
Join Date: Dec 2001
Location: leiden, physically that is...
Hi,

Thanks for the answers and the working link.

I searched a bit more for additional data on measurements and ratings but I could only find a statement on the K/W rating for Seifert.

They state that the rating is for black anodised, free standing with the fins vertical in static air conditions. The ratings given should be good for practical situations they say. This is the same condition I intend to have and I suppose it means I should be able to use them.

I intend to dissipate 100-130 W per heatsink and allow for a 30deg.C temperature rise. I will also use a copper heat spreader of 20/8/1cm (w/h/d) located at one end of the heatsink. Each Fet will dissipate about 20W. The backplate of the heatsink will not be in free air but the case will probably make up for that.

I'll just have to hope it works out ok. The data from Fischer have me doubting quite a bit though.

regards,
Joris
__________________
oh, what a beautifull day
I wanna go out and play!
  Reply With Quote
Old 8th July 2009, 02:50 AM   #10
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
In my experience, the values provided by Fischer is on the optimistic side if you want to work with a 30C temperature difference. And you would almost certainly NOT be able to reach the values stated by Seifert.

Even with a height of 550mm instead of 100mm, the heatsink I used can only dissipate 220W with a temperature rise of 40C, or 0.17K/W (proven by measurements). I know that height above 150mm does not bring a lot, but to hope to get 0.23K/W with a height of 100mm is IMHO a bit unrealistic.

But prove me wrong, by all means.


Patrick


PS A fan running at below nominal voltage will work wonders and can hardly be heard even at close distance. Try one of these :

http://www.noctua.at/main.php?show=p...s_id=26&lng=en

Even blowing on the flat surface (where the transistors are mounted) will help quite a bit.
  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
Looking for datasheets satelitis Tubes / Valves 1 18th May 2007 09:37 AM
Sony Datasheets Bernhard Digital Source 0 16th May 2007 11:30 AM
Help me I need MAB8441PT164 DataSheets Babylon_audio Digital Source 5 13th November 2005 07:13 PM
tube datasheets and amp sch trancy Tubes / Valves 1 10th April 2004 05:03 PM
Sovtek datasheets... JoeBob Tubes / Valves 5 27th July 2002 09:34 PM


New To Site? Need Help?

All times are GMT. The time now is 06:18 PM.


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