The Great Mr. Kurtz [David A. Gatwood] wrote:

> Questions:
> 
> 1. What VA rating would you suggest to achieve that (the system's power
> supply is rated at 3 amps max, no idea what the real drain is, though),

This is from my fading EE knowledge, so it may be a little off. 
Anyone chime in if they have a better memory than this.

VA=Volt Amps
Watts=Volts * Amps

Why the difference? Well, in certain industries they use
VA instead of watts to signify that the value is relating to 
peak voltages, as opposed to RMS voltages, for AC curent.
(This can be confusing, since most people and specification
use 'watts' when talking about AC circuits in a house or 
business.)

1 watt is about 1.4 VA.

So, if your system draws 3 amps max on a 120 volt circuit,
the draw for the system is ~360 watts (max). This is approx.
360 * 1.4 = ~500 VA. If this is on a machine that has a 
few unused  PCI slots it will be less than this (since the 
3 amps. is a max.), but it's always better to overestimate 
your power draw initially.

Looking at my handy APS user's manual, their Model 1400
can supply approx. 500VA for approx. 29 minutes.

Note that when I set up some of this stuff recently, I found 
that using the max. amp values for calculations resulted in 
a safety margin of 2-3 times. That is, I over estimated the 
actual power draw by 2 or 3 times. This means that I can either 
run the systems longer or I could have gotten a lower-end UPS. 
YMMV.

Also, I personally would recommend that you don't spend the
money on keeping the systems up for more than 5-10 minutes.
This will handle quick flickers of the power and brownouts,
but it the power is off more than 5 minutes it's usually
going to be off for a while. Plus the UPSs can get 
fairly expensive as you push the "on-time" up. That extra
20 minutes usually isn't worth the extra cost, although it
of course depend on the application.

Later,
	--John