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Old 28th October 2003, 05:47 PM   #1
Magura is offline Magura  Denmark
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Default Heat dissipation

Ive been thinking a lot about how to give the components of a SOZ the lowest possible running temperature.

Ive machined a round cabinet of aluminium (20mm wall thickness 180mm high 450mm diameter) and mounted the heatsinks on the outer diameter all the way around (around 35kg of heatsinks, all machined to fit).

The point of this is to be able to run all components at the same temperature by simply mounting them closer or further from the center of the box at the bottom side (exept the mosfets that will be mounted on the upper side alone to make sure they are plenty cooled).

I thought of the option to mount the components on a block of copper and then mount the copper on the aluminium, to take advantage of the excellent heat transfer properties of copper at the relatively small surface i have between the component and the copper...and then make the copper block lets say 4 times the footprint of the component and mount it in the box....


anybody knows if the loss of heat transfer between the respective surfaces is too big to make this work??

Magura
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Old 29th October 2003, 12:07 AM   #2
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If you're a machinist, then you already know how to
make a really flat surface and put it under pressure
against another. A little thermal grease won't hurt, either.

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Old 29th October 2003, 03:43 PM   #3
Magura is offline Magura  Denmark
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What i really wanted to know was if it pays off...is it a good idea.
The making of such is no big deal.

Im a toolmaker in diecasting and have acces to any machine i could ask for.

Magura
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Old 29th October 2003, 05:41 PM   #4
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The SOZ was specifically designed to appeal to guys who
aren't afraid of big hardware but are a little shy about
circuit complexity. Interestingly this appears to comprise
a large segment of the DIY community.

So big hardware for SOZ is highly recommended.
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Old 29th October 2003, 08:17 PM   #5
moe29 is offline moe29  United States
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Plus it's cool to see so few parts doing so much!

I remember reading that you can run the high power resistors a
lot closer to their ratings without having to worry about it, as
opposed to the FETs.
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Old 29th October 2003, 10:40 PM   #6
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A couple of comments.

1. I am very jealous of your machining tool access.

2. Using copper as a heat spreader plate works very well. I have done this in the past while designing a 400MHz to 860MHz Class A push pull amp using a LDMOS device that had two mosfets in the same package. Bias dissapation was around 10 watts and the package just wasn't big enough to get the heat out of in our space requirements without going to a 1/4" thick copper spreader plate first.

A later version of the design did go straight to aluminum, but I had forced air cooling working for me there.

Use thermal compound (sometimes called heatsink grease) and make sure both devices are as flat as possible.

Scott


Quote:
Originally posted by Magura
What i really wanted to know was if it pays off...is it a good idea.
The making of such is no big deal.

Im a toolmaker in diecasting and have acces to any machine i could ask for.

Magura
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Old 30th October 2003, 03:13 AM   #7
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Zalman makes some killer copper mushroom shaped finned
assemblies. You'll see them in ZV6, if that's what it ends up
being called.
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Old 30th October 2003, 10:19 AM   #8
Magura is offline Magura  Denmark
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Quote:
Originally posted by ScottRHinson
A couple of comments.



2. Using copper as a heat spreader plate works very well. I have done this in the past while designing a 400MHz to 860MHz Class A push pull amp using a LDMOS device that had two mosfets in the same package. Bias dissapation was around 10 watts and the package just wasn't big enough to get the heat out of in our space requirements without going to a 1/4" thick copper spreader plate first.


what ratio did you have between the size of footprint (resistor-copper> copper-aluminium) ?

Magura
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Old 30th October 2003, 12:39 PM   #9
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Quote:
Originally posted by Magura



what ratio did you have between the size of footprint (resistor-copper> copper-aluminium) ?

Magura
The transistor package had a total surface area of .186 sqaure inches. I kind of went overkill on the copper spreader. It was 2"x4", .5" thick. For short times of debugging it was enough of a heatsink by itself. What kind of output devices are you using, how many and how much power will they be dissipating?

Scott
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Old 30th October 2003, 01:58 PM   #10
Magura is offline Magura  Denmark
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Its meant mainly for the resistors of a SOZ...they dissipate 250W

Magura
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