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From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: Question about linear derating factor for MOSFETs
Date: Thu, 14 Nov 2002 04:05:11 -0000
Organization: Your Organization
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References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
In article <email@example.com>,
>I wish I had the volume to make a custom extrusion worthwhile...3 feet
>a year probably isn't high enough. :-)
>last week, I priced out some Thermalloy extrusions I was considering.
>They ranged from $600 to $1900 for 6 feet!! Melcor
>(http://www.melcor.com) had some nice bonded fin heat sinks at what
>thought was great prices. They're made for their thermoelectric
>coolers but will work fine for a lot of things and they have fan
>mounts too (purchsed separately). These are the ones I've been using
>in my calculations.
This type of heatsink is optimized for serious forced convection, and isn't
very good for natural convection (the fins are for too close for that). So I
assume you are using forced air.
As far as the aluminum extrusion costs are concerned, extruders can handle a
5:1 aspect ratio (fin height to fin gap) with standard extrusion processes,
before things have to get fancy (and expensive). A typical die that can fit
in a 5" diameter circle, for example, should cost less than $1000. After
that, minimum runs are usually 1100 pounds (500 kg) of aluminum, at $2.50 or
so per pound. Some extruders will do half that at a little higher cost per
pound. (this assumes the usual 6063T5 allow that is nice and "gooey" when
heated and thus is the favoured extrusion alloy).
Considering that the average medium size heatsink will end up costing only a
buck or two, it doesn't take a lot of volume to recover the die costs.
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