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heat management in abs enclosure
heat management in abs enclosure
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Old 25th November 2020, 05:59 AM   #1
ultrachrome is offline ultrachrome  United States
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Default heat management in abs enclosure

I stuffed an old, cheap ebay dac in an ABS Hammond enclosure and noticed the area above the LM7805 heatsink became rather warm.

With a non-contact thermometer it reached 40C while a thermocouple on the heatsink reached 67C after 45 minutes and stayed there. With the lid off, the heatsink dropped to 60C so it doesn't seem like the PSU is suffering due to lack of ventilation.

There's about 15mm between the top of the heatsink and the lid.

Is this too hot for the ABS? It looks like the molding temp of ABS is 40-80C so I'm wondering if the ABS might begin to deform.
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Old 25th November 2020, 08:59 PM   #2
duncan2 is offline duncan2  United Kingdom
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ABS ( plastic ) is formed by injection molding which means high hydraulic pressure and heat ( I have repaired the machines ) .


Once formed the chemical composition is fixed and second heating will cause burning and burning will make it brittle .


If you are that worried about a cheap casing increase the size of the LM708 heatsink.
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Old 25th November 2020, 11:42 PM   #3
ubergeeknz is offline ubergeeknz  New Zealand
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ABS should be okay with those temperatures. Glass transition should be somewhere north of 80 C

If you want to get the temps down, use a bigger heatsink and/or make some holes in the case to allow for ventilation
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Old 26th November 2020, 12:59 AM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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I would have gone for a vented case.
I wouldn't be worrying about the box but the die temperatures of the regulators.
They might be 60+ on outside but inside a good few degrees warmer.
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Old 26th November 2020, 01:12 AM   #5
ultrachrome is offline ultrachrome  United States
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I think I determined the root cause.

I realized that I used a transformer with 15VAC secondaries when only 9VAC is called for.

I'll order a new one.
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Old 26th November 2020, 01:14 AM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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Ahh the elusive detail !
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Last edited by nigelwright7557; 26th November 2020 at 01:17 AM.
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Old 26th November 2020, 03:47 AM   #7
ultrachrome is offline ultrachrome  United States
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It was an impulse buy from 2008 and I had the transformer on hand. I hastily mounted it all to a plank and used it off and on until my first son was old enough to crawl.
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Old 26th November 2020, 05:29 AM   #8
BillWojo is offline BillWojo  United States
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Plastic cases conduct heat rather poorly. I know you will probably be ok at the much lower voltage but keep that in mind for your next project.



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Old 1st December 2020, 09:48 PM   #9
andrewdw22 is offline andrewdw22
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Quote:
Plastic cases conduct heat rather poorly. I know you will probably be ok at the much lower voltage but keep that in mind for your next project.



Billwojo
yes but I'm personally never had a problem with them
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Old 2nd December 2020, 01:05 AM   #10
rabbitz is offline rabbitz  Australia
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I use a lot of these Hammond cases and if heat is an issue, drill a series of vent holes top and bottom.
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