Re: Heatsink cooling

On Wed, 04 Jan 2006 21:41:53 GMT, Ignoramus18299
<ignoramus18299@xxxxxxxxxxxxxxxxxxxx> wrote:

>Let's say that I have a source of about 800-1000 watts (two dual IGBTs
>inverting 200 amps). They should run relatively cool, to stay safe say
>under 80 C. I have a heatsink that is about 6x13 inches and weighs
>perhaps 12 lbs. I am cooling it with a fan mounted right next to the
>ribs, pushing air along them, the fan is about 20 watts. Ambient temp
>could be quite hot, say 40 C (inside welding machine). Would you say
>that this amount of cooling should be enough? I will have a overheat
>switch mounted on the sink, so, hopefully, worst case would be a
>inconvenience of having to stop welding, but I would like to have some
>idea of adequacy of this setup.
>
>i

I did a big ugly 800-watt CAMAC power supply, with a heatsink about
that size. A single 120 CFM fan was ducted (custom vacuum-formed
plastic thing) to blow all its air through the fins, not *near* or
*around* the fins as fans are wont to do.

I got a tad over 0.04 K/W, but that was with the heat load fairly
uniformly distributed over the heatsink baseplate. Concentrated heat
loads would be worse because of lateral (spreading) thermal
resistance.

If you don't duct the air, impingement is almost as good: orient the
plane of the fan parallel to the sink and blast the air directly into
the fins at short range. Tweak distance maybe.

Your numbers sound tough to do, but not impossible.

John

.

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