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Old 29th September 2009, 02:12 AM   #1
GeeVee is offline GeeVee  Australia
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Default heatsink thermal transfer

Hi all

I was recently fortunate enough to come into posession of a good quantity of large heatsinks, but they need to have the old anodising stripped, and re-anodised.

At present, the heatsinks do not have any coating on the semiconductor mating surface.(the back)

Unfortunately when they are re-anodised the back mating surface will also be coloured.

What I do not know, is if the transistors are mounted onto an anodised surface, will it have a detrimental effect on the heat transfer?

I have searched threads here, but I cant quite find the answer I am looking for.

I did however find a good thread on the best place to mount the transistors though.

Any help here will be appreciated.
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Old 29th September 2009, 02:36 AM   #2
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by GeeVee View Post
Hi all

What I do not know, is if the transistors are mounted onto an anodised surface, will it have a detrimental effect on the heat transfer?

I have searched threads here, but I cant quite find the answer I am looking for.
If you worry about that theres only one answer, have the mounting surface plane grinded

I have tried to do it by hand, which didnt work too good
But I discouvered that underneath the black anodising there was a rather thick grey layer, of what I dont know
But I really dont think thats very optimal

Anyway, isnt optimal heat transfer only very important in exstreme cases
But I wouldnt know

But I would like to try a piece of soft silver plate between device and heatsink

btw, maybe the best you could do is avoid the anodising, and instead have it sandblasted, or glassblasted
That should theoretically make the cooling surface bigger
But ofcourse not on the mounting surface

Last edited by tinitus; 29th September 2009 at 02:51 AM.
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Old 29th September 2009, 02:51 AM   #3
eyoung is offline eyoung  United States
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Hola Y'all,

A good old auto machine shop that does cylinder head resurface can mill your heat sink...


Regards, El
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Old 29th September 2009, 07:40 AM   #4
wwenze is offline wwenze  Singapore
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Just cover the part that you don't want anodized, or don't dip that part into the electrolyte.

Oh, add: I've seen a few amplifiers with the power transistors attached to the anodized parts, but I figured that isn't a problem, because the layer of insulating plastic will add more to the thermal resistance than the anodized surface, which at least is made of metal.

Last edited by wwenze; 29th September 2009 at 07:55 AM.
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Old 29th September 2009, 01:10 PM   #5
GeeVee is offline GeeVee  Australia
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Hi fellas

Thank you all for your replys. very much appreciated.

The heatsinks at the moment have a very smooth / flat back, which would not reqiure any work to be done to them.


The heatsinks are to be used for my Aleph 1.2 amp project, which is nearing completion.

Its due to the extreme heat that these amps generate, that has caused me concern.

Might be best to just have the backs machined, just enough to have the anodising removed, and get me back to the bare aluminium.

Once again, thanks for the advice

Regards

George.
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