# Opinions sought on Heatsink rating (see photo)

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#### Nicwix

Hi

I to build 2 x 2 channel 30W Aleph's - which I understand means each channel will draw 100W. I have eight of the heatsinks in the photo and would like to use 2 heatsinks per channel, ie 50W.

Each heatsink is 10cm x 10cm x 10cm and the weight (OK, mass) is approx 700g.

I am thinking of mounting four on top of each two channel amp - possibly with some lightly forced air coming up through holes under each heatsink.

I have no data on these heatsinks - any bets on the heatsink rating (C/W) and hence operating temperature???

Nix

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• heatsink 640 x 480.jpg
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#### schizeckinosy

rule of thumb

Hi Nix,

There is a rule of thumb for heatsinks, which can be found here:

http://www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm

Basically, with natural convection you can get 1deg/W cooling with a heat sink 500-800 cc's, and bigger heatsinks are more effective. For yours, I'd ignore the center section, and add the 2 densely finned wings up. They look like 10x10x3 cm to me, so for both, you would have 600cc's. This is within that range, so I'd guess they are at least 1deg/watt or a little better. So, dissapating 50 watts would give a rise of 50 degrees at the heat sink. Add in the thermal resistance of the junction, insulator, etc., and you will get the junction temp.

Cheers, Dan

#### tiroth

I've also seen

deg C/W = 50/sqrt(A)

where A is the surface area in cm^2.

#### schizeckinosy

tiroth said:
I've also seen

deg C/W = 50/sqrt(A)

where A is the surface area in cm^2.

Yeah, but try adding up all those nooks and crannies

Dan

#### roddyama

Hi Dan,

You should be able to find a heat sink with a simular profile as the the ones you've shown us at the following link. This link has many links to heat sink sources. Most are heat sinks for microprocessors but some have all types.

Hope this helps,
Rodd Yamashita

#### Nelson Pass

Paid Member
I see a heat sink with a 1.5 deg C per watt rating.

With a breeze, they'll be half that.

#### Nicwix

Thanks to all for your thoughful responses.

Nelson, your reply was so almost Haiku, I had to finish it in the traditional format (seventeen syllables written in three lines divided into 5-7-5.):

I see a heat sink
One point five its rating be
With a breeze, halved

1 deg C/W or lower should be OK - so some small fans (possibly thermostatically controlled for faster warmup) should do it.

I am thinking of a layer cake design:
Layer 1 - Transformers & rectifiers & fans
Layer 2 - Pi filter (caps & chokes)
Layer 3 - Driver electronics
Layer 4 - Heatsinks & output devices

Looks like it will be about 300mm cubed. Alternatively, I could do a wedding cake and put some air between the layers

BTW, I paid US\$0.35 each for the heatsinks

Nic

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