At 10:51 AM 8/11/97 +0200, you wrote:

>They are a serious liability if you have a 0.5 to 2 second drop out.
>The typically very effective NTC thermistors that go close to short circuit
>a few seconds after switch on.  Problem is when they are hot/short-circuit
>and you have a dip, the primary switcher capacitor discharges and when the
>power comes back the inrush current is now NOT moderated by the
>thermistor and relies on the slo-blo of the fuse not to rupture.

Good point. So I don't cycle the power on my systems within 60 seconds.
And where possible I'd use a UPS in the event the local kids throw
steel cable up onto those power poles - Yuk !

>There are hundresds of thousands of switchers that are unatended
>all over the world in all sorts of industries, The Internet lives
>on them and I would say that at least half of them are unatended
>overnight and weekends.  I think you are beeing a bit too cautious
>unless you have a national monument that cannot handle any risk of
>fire.

True - my main system is at my home, thats my monument - see my other
post in respect of sweat shop manufacture etc. If I had to fit out a lab
which NEEDED unattended operation then I'd quite happily manage the
setup to avoid a fire in the rare event of ignition and there are lots
of neat ways to approach this goal etc.

>> So if I wished to have a PC in a unattended environment I'd design my
>> own supply with a heck of a lot of safeguards...
>
>What I find is that the FAN is very important.  I have had switchers
>fail in service but only those that do not have a fan or if the
>fan has failed.  Dust is the main enemy of a fan.

I agree - I don't like Fans much - if I had to use one in my design, then
it would be in an 'open region' where dust could not accumulate - ie the
standard upside down smooth surface approach. The rest of the cooling I'd
arrange as far as possible to be convection, radiated, transmissive to
that large heatsink of a case. I've got some great large enclosure
designs using hefty aluminium extrusions for an inverter currently
being evaluated - no pesky continuous rated fans in that setup...

Rdgs

Mike
Perth, Western Australia