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Will this heatsink concept work?
Will this heatsink concept work?
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Old 19th September 2019, 11:35 PM   #1
Stvrob63 is offline Stvrob63  United States
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Default Will this heatsink concept work?

I bought an inexpensive amplifier kit on Amazon, It is a MX50 SE and the main power transistors are D1047 and B817, for which I need to fabricate a heatsink. I found these two CPU heatsinks at a rummage sale (see pictures). I don't have a power supply yet but I'm hoping to find something in the +/- 30V to +/-40V range. I'm guessing roughly 70-90W/channel but not exactly sure. The two heat sinks are not identical, one is aluminum, the other, appears to be steel and is much heavier. Together they weigh 21 oz.

My idea was to sandwich the four transistors (two each channel) between these two heatsinks, with a bolt through each transistor. (As in the 4th picture) Does anyone have any ideas how much heat I might dissipate with this arrangement? Or is this a nonstarter right off the bat? What about if I used a fan? Or would that be a mistake?

Also, is it OK to locate these transistors away from the PCB board if it fits the chassis better? (at the moment I have no chassis)

Thanks for your input.
'Steve
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Old 19th September 2019, 11:59 PM   #2
rayma is offline rayma  United States
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One sink per channel would be much better. The front of the power device is not intended
to be a thermal interface. If the sinks run too hot, fans are not optional.

Last edited by rayma; 20th September 2019 at 12:02 AM.
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Old 20th September 2019, 12:14 AM   #3
Stvrob63 is offline Stvrob63  United States
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Quote:
Originally Posted by rayma View Post
One sink per channel would be much better. The front of the power device is not intended
to be a thermal interface. If the sinks run too hot, fans are not optional.
Thanks rayma. I was trying to find a way to make it work using two different heat sinks with almost certainly differing thermal properties. Still, this was only my first rummage adventure, so I will keep looking for something.
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Old 20th September 2019, 01:44 AM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by Stvrob63 View Post
Thanks rayma. I was trying to find a way to make it work using two different heat sinks with almost certainly differing thermal properties. Still, this was only my first rummage adventure, so I will keep looking for something.
The two different sinks may work, but one may have a lower thermal resistance (and run cooler)
than the other. Hard to say until you try it.
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Old 20th September 2019, 08:36 AM   #5
russc is offline russc  England
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1 - heatsink should be mounted so rising air current passes through the fins.
2 - use the supplied electrically insulated pads.
3 - I'd cut the ali heatsink in half at right angles to the fins & use half per amp. Then your transistors mount easily in pcb & heatsinks are optimally orientated.
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Old 21st September 2019, 09:32 PM   #6
Andersonix is offline Andersonix  Sweden
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Will this heatsink concept work?
Heat sinks with close fin spacing as shown are designed for fans and won’t cool well with only natural air flow.
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Old 21st September 2019, 11:13 PM   #7
mandu is offline mandu  Singapore
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The heatsinks you are trying to use is the bonded type and is better than extruded type due to very large heat transfer area per weght. However you need to verify the thermal resistance is suitable for your application. For unmarked heatsinks you can check similar sized models with any manufacturers to get a rough idea. Worst case you can use a small fan with some serial resistor just to move the hot air.
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Old 22nd September 2019, 01:03 AM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by rayma View Post
One sink per channel would be much better. The front of the power device is not intended
to be a thermal interface. If the sinks run too hot, fans are not optional.
The front is often hard plastic so not a good thermal conductor.

Either buy a couple of proper none fan heatsinks with fins further apart.
Or buy fan type heatsinks with fans.
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Old 25th September 2019, 02:05 PM   #9
Mark Tillotson is offline Mark Tillotson
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The front is always epoxy and is always a bad conductor of heat - 99% of heat goes out through the tab anyway, a front heatsink would be better placed in themal contact with the other heatsink to help it.
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Old 26th September 2019, 12:10 PM   #10
Kay Pirinha is offline Kay Pirinha  Germany
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Or you mount the devices using a isolated solid aluminium or copper bar along the front sides of the tabs and coupling the 2nd sink to this bar.
Best regards!
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