On 7/2/06, Peter Todd wrote: > On Sun, Jul 02, 2006 at 10:20:29AM +0300, Vasile Surducan wrote: > > > If the boxes are not hermetically sealed, drill drain holes in the > > > bottoms. I'm not kidding!! > > > > > > Even the boxes are hermetically sealed, what make you think will not be > > moisture inside ? Huge temperature variations will create sweat > > inside a hermetical sealed box as well in an opened one. > > Critical temperature is 7-8C when the temperature is increasing from 0C. > > Not that I've ever done this sort of work but what's wrong with throwing > a couple bags of dessicant in the boxes? It's aparently good enough to > keep surface mount chips from going pop. Sure, but as I said, the moisture is still there, now in the silica-gel pack. I've just want to point to a problem which exist, no matter what you're doing, except if some radical solutions are used, which are far away too difficult and too expensive. A hermetically sealed box with a PCB inside, running one day in open sun could have even water inside in the next morning. One example (nothing in common with the topic). I've used a 250W 220V bulb as a flooding device for opening and closing a valve (something more or less identical with the classical closet reservoir). The water temperature insidethe tank was between 10C and 90C. The bulb works in this way one year. After one year inside the bulb I found water, filling about 10% from the bulb volume. The bulb WORKS after that when I supply it (with the bulb kept in a position where water does not touch the filament. Conclusion: the porosity of the bulb's glass allows bidirectional gas/fluid transfer. More or less on this principle, the glass PH-meter is built using a very porousive glass. Why a hermetically sealed plastic box can't have the same behaviour? :) greetings, Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist