advice on chassis as heatsink

dsavitsk · 27th April 2005, 03:41 AM

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.

-d

Stocker · 27th April 2005, 04:20 AM

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.

dsavitsk · 27th April 2005, 04:37 AM

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.)

-d

Stocker · 27th April 2005, 04:40 AM

That's just what I meant.

Nuuk · 27th April 2005, 12:53 PM

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.

tiroth · 27th April 2005, 01:07 PM

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.

autoexec · 27th April 2005, 01:31 PM

whats the thickness needed for? i cant see it adding much surface area

ROVSING · 27th April 2005, 01:35 PM

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.

Nuuk · 27th April 2005, 01:35 PM

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.

ROVSING · 27th April 2005, 01:57 PM

Well maybe you have a point there nuuk but aluminium is a rather "dead" material, not that sensitive to vibrations.

27th April 2005, 03:41 AM	#1
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	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. -d

27th April 2005, 04:20 AM	#2
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	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. __________________ Jesus loves you.

27th April 2005, 04:40 AM	#4
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	That's just what I meant. __________________ Jesus loves you.

27th April 2005, 12:53 PM	#5
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

27th April 2005, 01:35 PM	#8
ROVSING diyAudio Member Join Date: Sep 2004 Location: Fyn Odense	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. __________________ Frandsen


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27th April 2005, 04:37 AM	#3
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	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.) -d

27th April 2005, 01:07 PM	#6
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	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.

27th April 2005, 01:31 PM	#7
autoexec diyAudio Member Join Date: Oct 2003 Location: Maroubra, Sydney, Australia	whats the thickness needed for? i cant see it adding much surface area

27th April 2005, 01:57 PM	#10
ROVSING diyAudio Member Join Date: Sep 2004 Location: Fyn Odense	Well maybe you have a point there nuuk but aluminium is a rather "dead" material, not that sensitive to vibrations. __________________ Frandsen

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