> From: Mike Bilow <zvmr.pthe@sendrata.com>
>
> See my earlier comments. I especially don't see the need for a
full-blown
> DC/DC converter when a simple regulator will suffice. Converters are
handy
> when stepping up in voltage, but that's not the issue when you are
starting
> with a 24V supply.
My aim was to get a handle on the size of the problem and I think we're
agreed that starting with new parts would soon get you to a comparable
price of an off the shelf one.
The DC-DC converter would be a reasonably efficient way to get down from
24V to a regulated 5 and 12V. A linear 24V to 5V regulator would dissipate
a lot of power but for cost reasons you might choose to do it this way
(especially for a low power system).
>
> This makes a fundamental error in assuming that the "200W" power supply
in a PC
> uses anything approaching 200W. In general, you can expect a motherboard
to
> consume about 10W at most, and then only when loaded up with a fairly
fast CPU
> and lots of RAM. Sure, there are horrible exceptions such as the Cyrix
6x86
> <snip>
Yep, this is the main thing I didn't know and haven't measured. Another
factor is that the rated capacity of a battery is generally given for a
discharge over 20 hours at room temperature when it is new. At faster
rates the capacity goes down. Dunno how much. Switching on APM, avoiding
the CDROM and so on would have a very significant effect on the battery
run-time. The electronics would have to cope with the worst case though.
Perhaps adding a little more "smarts" to a basic UPS is the way to go. I
guess there's not really that much info you need, maybe just two bits: AC
power's failed, battery is getting low. Battery dead is pretty self
evident :-)
Sorry to wander off the linux-hams path...
Andy
--------------------------------------
Andy Dachs
Email: fsf@kerailya.tunkki.fi
Web: http://www.ee.surrey.ac.uk/EE/CSER/UOSAT/