Typically for Class A amp builds DIYers are using aluminum extruded heat sinks for which the base and the fins are part of a single block of metal.
What if a heatsink is built up using a 6mm -8mm base plate with smaller heat sinks with fins bolted on? Would there be a lot of efficiency loss and concerns on thermal performance?
I have attached pics of a flat bar/ rectangular plate and smaller sized heat-sinks for reference. The heat sinks are 60 mm tall and 179 mm long - if we stack two and attach it to flat rectangular piece, then we can get a heat sink which 120 mm tall and 179 mm long. The pics are for reference purposes only. Ideally the heat-sinks can have a thinner base (4mm - 6mm)to keep cost (and weight) down.
What if a heatsink is built up using a 6mm -8mm base plate with smaller heat sinks with fins bolted on? Would there be a lot of efficiency loss and concerns on thermal performance?
I have attached pics of a flat bar/ rectangular plate and smaller sized heat-sinks for reference. The heat sinks are 60 mm tall and 179 mm long - if we stack two and attach it to flat rectangular piece, then we can get a heat sink which 120 mm tall and 179 mm long. The pics are for reference purposes only. Ideally the heat-sinks can have a thinner base (4mm - 6mm)to keep cost (and weight) down.
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Hello zman01,
done many, many times by amplifier- builders. Connecting heatsinks by a heatspreader (the aluminum plate/flatbar).
You should try to get a good thermal contact between your aluminum flatbar and the heatsinks connected.
It will not be 100%ly the same as one heatsink.
Mount your Powertransistors (Fets, BJTs) to the aluminum flatbar. Best 1/3 from bottom of heatsink (measured vertical), 2/3 of heatsink above.
Check some tests of Pass Labs- amps with fotos showing the inside of the heatsinks/Heatspreader and transistors...
Cheers
Dirk
done many, many times by amplifier- builders. Connecting heatsinks by a heatspreader (the aluminum plate/flatbar).
You should try to get a good thermal contact between your aluminum flatbar and the heatsinks connected.
It will not be 100%ly the same as one heatsink.
Mount your Powertransistors (Fets, BJTs) to the aluminum flatbar. Best 1/3 from bottom of heatsink (measured vertical), 2/3 of heatsink above.
Check some tests of Pass Labs- amps with fotos showing the inside of the heatsinks/Heatspreader and transistors...
Cheers
Dirk
Thank you Dirk.
To function well, what is the minimum thickness that the heat-spreader should be? The smaller heat sinks can have thick bases too (6mm - 10mm) depending on make and model.
Jeffh01,
I recall reading that article by Rod Elliot a long time back; involves a lot of work to get a nice unit using that many pieces. 🙂
To function well, what is the minimum thickness that the heat-spreader should be? The smaller heat sinks can have thick bases too (6mm - 10mm) depending on make and model.
Jeffh01,
I recall reading that article by Rod Elliot a long time back; involves a lot of work to get a nice unit using that many pieces. 🙂
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Generally, thicker is better. Depending on the manufacturing process for the sink and if the back of the sink is simply extruded or extruded then milled, you may have some work to do to make mating surfaces more flat to improve the contact area for better heat transfer. Valve lapping compound can help here. A thin but thorough layer of thermal paste is definitely necessary as well.
You might be able to find “narrow and tall” sinks to mount side by side rather than “wide and short” sinks to “stack.” This might make construction easier. This is what I did with my big Aleph-X amps, link to my construction is in my signature.
I'd say that if the heat spreader is 5-6 mm thick and the base of the heat sink is 3-4 mm think then you have plenty of aluminum to conduct the heat. Aluminum is very conductive both of electricity and heat. As @JMFahey just said, make sure the surfaces are flat and then apply a light coat of thermal grease before bolting everything together. You need just enough grease to fill the voids and scratches.
Play with this heat sink calculator for a bit: https://heatscapecal.com/natural. I tricked it into calculating the temperature drop across a 5 mm aluminum sheet by setting the base height to 5.0 mm and the overall height to 5.2 mm (fin height: 0.2 mm).
Tom
Play with this heat sink calculator for a bit: https://heatscapecal.com/natural. I tricked it into calculating the temperature drop across a 5 mm aluminum sheet by setting the base height to 5.0 mm and the overall height to 5.2 mm (fin height: 0.2 mm).
Tom
