UPS Installation

How much UPS do you need?

Several of the manufacturers web pages have suggestions of how to calculate needed capacity. Most of them kind of describe a system, and say "A system like this needs a 400 VA UPS". To get a general idea of what you need, look at the label on your power supply and monitor. My power supply (200W) and monitor (100W) means I need 300 Watts, or about 375 VA (300W divided by 0.8). The guess is that a 400VA UPS will give me 10 or 15 minutes of protection.

These calculations seem to be rather generous. The SL Waber UPStart (250VA) claims to support a 150MH Pentium and 17" monitor for up to 5 minutes. My 17" monitor consumes 120W, and the Pentium system probably has at least a 250W powersupply. That works out to almost 470 VA. But, a bigger unit will support your system far longer than 5 minutes.

I guess the message is to get as high a VA rating as you can afford.

Another consideration is - How smart? You will need to know when power has failed, and you should be able to turn off the UPS's inverter. It is also nice to know when the battery is getting low, but if you don't try to stay up too long before shutting down, you can get by without it. So, my recommendation is, get a "Smart" UPS if you must, or if you can get programming details (BestPower makes the details and software sources available on their web page, for example). These UPS's can emulate Dumb UPS's so that the software available for Dumb UPS's can be used for Smart UPS's too.

Better might be a "Dumb" UPS, which is just cabable of toggling serial control signals, as it will provide the information you need, without a lot of information you can't use.

If you have a autistic UPS, perhaps a line powered relay can be constructed to inform the computer of a power failure.