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Mounting of modules on heatsink
Mounting of modules on heatsink
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Old 1st April 2018, 06:25 PM   #1
Vrystaat is offline Vrystaat  South Africa
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Default Mounting of modules on heatsink

Hallo all,
Which of the mounting of the amp modules would be the best and preferred method to dissipate the heat ?
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Old 1st April 2018, 06:34 PM   #2
scottjoplin is offline scottjoplin  Wales
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The first one
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Old 1st April 2018, 07:09 PM   #3
dlvoots is offline dlvoots  United States
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Here's the rule of thumb I've used for the projects I've built:

One of the most critical factors is the orientation of the fins. I can't tell in your pictures whether they run the long dimension of the heat sink (I'll call it "the lenght"), or whether they run the short dimension of the heat sink (I'll call it "the width"). Regardless, when you install the heat sink on the chassis you want to make sure the fins are oriented vertically when the chassis is in operation.

The object of the game is to create a convection engine, where the bottom of each fin is relatively cool and sits in relatively cool air. The devices you want to keep cool are mounted at approximately the half way point from the bottom of the fins, give or take maybe 20% lower. That means you can mount the devices approximately 20% lower than halfway if you need to, but try not to go higher than half way.

As the devices get hot, they pass the heat on to the heat sink and then to the fins. They will get a bit warm below the devices, but most of the heat will rise to the top half of the fins. That creates a system where cool air passes the bottom of the fins and is pulled upwards across the upper half of the fins, carrying the heat away and cooling the overall heat sink. That self-pulling air mechanism is your convection engine.

Here's an example for you -- If your heat sink has 4 inch fins, you can mount the active devices anywhere from say.........1.5 inches from the bottom of the fins to the two inch mark.

Hope this helps.

Dave
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Old 2nd April 2018, 06:46 PM   #4
Andersonix is offline Andersonix  Sweden
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Mounting of modules on heatsink
I like the second one better, as it avoids fin-sharing and distributes the heat better along the full breadth of the whole hs. This is assuming we are looking at the hs from the underside. It's not ideal though, as the transistors are a bit close to the bottom edge, but it's still intuitively better than the first option...
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Old 2nd April 2018, 06:53 PM   #5
scottjoplin is offline scottjoplin  Wales
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Neither of them is great, the main thing is to have the transistors as even spaced as possible. It would be better if in the first picture one board was rotated 180 degrees and then them both shifted across to get the transistors nearer the centre
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Old 2nd April 2018, 07:09 PM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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The transistors should be in the middle of the heat sink so there is most metal beneath them.
Given there are two modules then they need to be apart from each other.
So the first picture is the way I would go but with the pcb's slightly closer together.
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Old 2nd April 2018, 07:34 PM   #7
Vrystaat is offline Vrystaat  South Africa
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Thanks guy's, I did it as in the first pic, I had both modules running at idling for 2 hours at ambient temp which is 21 deg C, winter coming. Heatsink temp were 28deg C which is 75mA per module, I will apply load and see what happens.
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Old 4th April 2018, 03:00 PM   #8
speaker is offline speaker  United States
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Quote:
Originally Posted by Andersonix View Post
I like the second one better, as it avoids fin-sharing and distributes the heat better along the full breadth of the whole hs. This is assuming we are looking at the hs from the underside. It's not ideal though, as the transistors are a bit close to the bottom edge, but it's still intuitively better than the first option...
I like this one too.
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Old 4th April 2018, 03:53 PM   #9
scottjoplin is offline scottjoplin  Wales
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Why? Heat distribution in an aluminium heat sink is governed more by conduction than convection
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