This article appeared in the May 2003 WYSIWYG newsletter.
Uninterruptible Power Supply
by Don VanSyckel
Well it looks like winter is finally behind us and spring is really going to happen. I know spring is actually half over according to the calendar but it never seems like spring until it warms up and we start having those spring showers. Speaking of spring showers and those power outages, how about a little insurance. We all buy auto insurance, home insurance, life insurance, and health insurance among others. I suggest you consider computer insurance in the form of an Uninterruptible Power Supply (UPS). These devices were quite expense in times past but integrated circuits (chips) and wide usage (higher production rates) have caused the price to drop to a very reasonable level. What a UPS does, in short, is protect your computer from power outages and surges and protects your data from being corrupted by having your computer powered off in the middle of writing to the hard disk. The UPS plugs into the wall (your house power) and then whatever is currently plugged into the wall, plugs into the UPS. The UPS has a battery and circuitry in it.
A UPS passes the wall power through to its socket and monitors it. If the input wall power stops for longer than a specified time, usually a couple of power cycles, the UPS disconnects its socket from the input wall power and turns on an internal inverter. This inverter uses the internal battery power to generate 60 hertz power which looks something like the wall power. All this is done in another couple of power cycles. The entire interruption is short enough that the power supplies in your computer and other equipment don't fade enough to affect the equipment's performance. When the wall power is restored the UPS circuitry monitors it for a few cycles to make sure its stable and actually back. At this point the internal inverter is turned off and the input wall power is connected to the UPS socket . The last part of the UPS is a battery charger which will charge the battery back to full charge. Most UPSs also include surge suppression circuitry.
For most people, I would put the computer and monitor on the UPS output and leave the printer connected directly to the wall power. With this type set up a 350 VA UPS should be enough. If you want to add other items such as the printer or scanner, you will need to check the specifications of the device and add power requirements to the power requirements of the computer and monitor. When you choose the UPS model don't be too tight give yourself some extra capacity. Namely if the power requirements you calculate are close to the capacity of one model UPS buy the next model up. From what I see, The 350 VA model is the most popular and the 500 VA model is second. So if you want to protect more devices it might be cheaper to buy a couple of 350 VA models or a 350 VA and a 500 VA instead of moving up to a 750 VA model or whatever. You get the idea.
I have a 350VA model under the table in the den with the cable modem and the internet router / wireless access point plugged in. I have another 350 VA model in the basement with the network switch, cable TV booster, alarm system, and sprinkler system controller all plugged into it. Then I have a third 450VA model where I have my computer.
All my UPSs are from American Power Conversion (APC). They have been in the business for a long time and have an impeccable reputation. More recently a number of UPSs have appeared in the market from other companies. When the power goes off is not the time to find out you've bought an inferior product. Do yourself a favor and check out the product reviews for any UPS you are consider purchasing from a company
other than APC. Before you thing I've spent a small fortune on UPSs, I bought one of them on sale with a rebate for a total cost of $10. The normal price for a 350VA model currently is running between $40 and $80.
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