Enclosure Cooling
Eric Nelson said:
I always have the fan blowing air INTO the enclosure, rather than sucking it OUT. A little positive pressure prevents sucking dust "into every available crack"
Well consider this: Most "Filters" allow plenty of particles over 100 u to blow straight into your enclosure. For those of you unfamiliar with microns, 25 u equals .001".
Power Supplies, due to ionization are magnets for dust, and guess where these 100 u+ particles wind up? On every ionized surface in your cabinet.
My first choice is always positive air pressure, but I always prefer Positive Air Pressure enclosure dessication to fans. Fans burn out, fans don't get replaced, fans don't provide reliable positive air pressure.
I prefer to route in 5 psi of CDA (Compressed Dry Air) monitored by a SCCM Flow meter, and create a positive pressure that way. Ideally .25 - .4 " H20 of positive pressure.
Does this air have a charge? Yes or No? Yes, but in the lesser of evils department, I prefer air over fans.
With regards to heat dissipation:
Automation Direct DL06 units are gauranteed to Operate up to 138 F. Well that is still pretty dang warm. A lot of my heat sinked 7815's run upwards of 150 F (which I don't like). Anyway - lots of heat dissipated.
My rule of thumb is try to keep the cabinet as close to ambient temperature as possible. It is repeated heating and cooling stress which destroys solid state devices in the long run, all other things being "Normal".
Just for laughs try using these equations and guides to determine what Heat Load your cabinet is generating, or for BTU/hr heat dissipation of your cabinet:
http://www.exair.com/cabinetcooler/cc_page.htm
Check out Exair Vortex Cabinet Coolers:
http://www.exair.com/vortextube/vt_page.htm