heat management in abs enclosure

[ultrachrome]

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.

 

[duncan2]

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.

 

[ubergeeknz]

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

 

[nigelwright7557]

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.

 

[ultrachrome]

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.

 

[nigelwright7557]

Ahh the elusive detail !

 

[ultrachrome]

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.

 

[BillWojo]

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

 

[andrewdw22]

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

 

[rabbitz]

I use a lot of these Hammond cases and if heat is an issue, drill a series of vent holes top and bottom.

 

[ultrachrome]

The 9VAC transformer seems to do the trick. Barely detect any warmth after about an hour.