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Old 27th April 2005, 02:41 AM   #1
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Default advice on chassis as heatsink

I am not trying to start another flame war on this topic, just looking for advice if this is a reasonable thing to try.

I am building a BrianGT 3875 kit into a mostly wood box. While the sides are wood, the bottom is a 0.09" thick 12"x12" piece of T-5052 aluminum. (To give an idea of the thickness, it is slightly thicker than the plate on a TO-220 heatsink where a chip is connected to it. -- about 2.29mm) Would it be a reasonable thing to just bolt the chips to the bottom of the chassis, or will I need something more substantial to dissipate heat? The transformer has dual 18V secondaries if that is important.

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Old 27th April 2005, 03:20 AM   #2
Stocker is offline Stocker  United States
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If it is not enough, is there room to mount some small heatsinks nearby? Perhaps some low-profile types under the chassis, of if there is ventilation, some larger ones inside? If there is room for that, then try it and see how hot it runs.
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Old 27th April 2005, 03:37 AM   #3
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There's plenty of room (the inside of the case is about 12"x12"x3") I just don't happen to have sinks around, and want to get this thing running without placing yet another order for parts.

I do have some fairly large TO-220 sinks, but they are too narrow to attach the chips to. I thought about attaching them to the chassis right next to the chips, but I am not sure this would actually do any good. (as I reread your post, maybe this is what you are suggesting. Perhaos I'll give it a try.)

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Old 27th April 2005, 03:40 AM   #4
Stocker is offline Stocker  United States
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That's just what I meant.
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Old 27th April 2005, 11:53 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Just use a piece of flat aluminium or copper, about 3 inches by two inches by 1/4 inch thick (or thicker ) under each chip. Then connect this strip to the case bottom with bolts and heatsink compound.
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Old 27th April 2005, 12:07 PM   #6
tiroth is offline tiroth  United States
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If you run 8 ohm loads at moderate power, I don't think you'll have problems just using the plate as a sink. 12"x12" is pretty big. Just make sure you have some feet to allow airflow under there.
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Old 27th April 2005, 12:31 PM   #7
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whats the thickness needed for? i cant see it adding much surface area
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Old 27th April 2005, 12:35 PM   #8
ROVSING is offline ROVSING  Denmark
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Placing the chips horisontally on the bottom plate will work fine in this case, only thing is that hot air goes upwards in this case around the chip, dissipation would be better if you placed the chips vertically, on a heatzink or a piece of alu/cubber.
LM3875 doesnt, really need much heatzink.
But still - it will work fine....maybe you could drill some holes in the bottomplate to get some airflow, but i don't really think that it is necessary.
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Old 27th April 2005, 12:35 PM   #9
Nuuk is offline Nuuk  United Kingdom
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Quote:
whats the thickness needed for? i cant see it adding much surface area
If he joins the chip to that flimsy piece of aluminium base, it is going to pick up all the vibration. Adding something more substantial will help minimise microphony and 'take away' the heat.
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Old 27th April 2005, 12:57 PM   #10
ROVSING is offline ROVSING  Denmark
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Well maybe you have a point there nuuk but aluminium is a rather "dead" material, not that sensitive to vibrations.
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