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Old 11th May 2013, 08:09 AM   #1
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Default Fixing transistor on heatsink

Hello everyone!

I'll try to explain my problem clearly.
To fix my printed transistors on the heat sink power circuit I need to insert an aluminum plate 6 mm thick but I find only 3 mm plate.
My question is simple:
If I put two plates of thickness 3 minutes between my transistors and the heat sink, it will be effective equivalent to a single sheet of 6 mm.
I made a little drawing.

Regards!
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Old 11th May 2013, 08:13 AM   #2
Mooly is offline Mooly  United Kingdom
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In practice there probably isn't any issue whatsoever, particularly if you use thermal paste on all surfaces.
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Old 11th May 2013, 08:22 AM   #3
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Mooly thank you for your reply but I use an online translator and the response is inconsistent.
If I understand here is no problem but you have to put the thermal paste between all surfaces.

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Old 11th May 2013, 08:22 AM   #4
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The mating surfaces will need to be flat and shiny and coated with a thin coating of thermal paste.
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Old 11th May 2013, 08:48 AM   #5
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Mooly and KatieandDad, thank you!
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Old 11th May 2013, 09:38 AM   #6
AndrewT is offline AndrewT  Scotland
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you will need a lot of bolts to ensure the gaps between the plates and the sink are small all over the whole plate area.
A grid of bolts @ 30mm vertically and 30mm horizontally?
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Old 11th May 2013, 10:08 AM   #7
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I thought the whole set on the main as indicated by the hole transistors (red points) heatsink.
The aluminum plate is barely wider than the Sanken.

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Old 11th May 2013, 10:17 AM   #8
AJT is offline AJT  Philippines
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imho, you are better off with just a 3mm plate....any reason it had to be 6mm?

with just a 3mm plate you have 1 less thermal junction to worry about...you can always bend the trannie legs a bit....
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Old 11th May 2013, 10:24 AM   #9
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Tony View Post
...you can always bend the trannie legs a bit....
Which is preferable anyway to relieve the stress caused by straight legs.
Translation to avoid project16 the inconvenience of using a translator:
Il est préférable de plier les pattes des transistors pour éviter les contraintes causées par un montage droit

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Old 11th May 2013, 10:36 AM   #10
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Quote:
Originally Posted by Tony View Post
imho, you are better off with just a 3mm plate....any reason it had to be 6mm?

with just a 3mm plate you have 1 less thermal junction to worry about...you can always bend the trannie legs a bit....
This is to avoid bending the legs of the transistors.
But I can (by bending the legs of Sanken) fix directemment on the main heatsink but I have to add an aluminum thickness for BD139 and 140 because the legs are too short.
Why 6 mm:
Is the distance between the base of one and the edge of Sanken PCB.
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