Uninterruptible Power Supplies (UPS)

See model ratings below. Also see standalone inverters.

WHAT DOES A UPS DO?: An uninterruptible power supply (UPS) is a battery powered inverter that supplies AC voltage for a short period of time when the main power fails or flickers. A UPS is used between a computer & the wall plug, when computer information could be lost if power is lost, or where improper shutdown might cause data corruption if there was a sudden power loss. A UPS often will also filter the line Voltage for spikes that could cause damage to computer components, but most UPS's only have limited line filtering capabilities, so you might want to also use a really good power bar with excellent surge protection of 2000 Joules or more. Some UPS's will also bump up the Voltage (Automatic Voltage Regulation) when it is too low (called a "brown out"), or cut back on Voltage level if it is too high, but the less expensive units don't usually do this function very well. In North America the typical level is 117 AC Volts at 60 Hz cycles & in Europe it is 220 AC Volts at 50 Hz cycles. Most computer power supplies are designed to accept a wide range of input Voltages (often 100 - 240), but if the Voltage falls outside that range, weird computer malfunctions can occur. I recommend the use of a half decent UPS for your computer & monitor for many business applications were power failures could cost big bucks & especially for professional video editing computer applications where hours worth of rendering could be ruined by a 3 second power interruption.

HOW LARGE SHOULD A UPS BE?: It is quite important to choose a UPS that is large enough (larger is better). As a minimum the UPS must be able to support your computer & monitor for several minutes, which gives you time to save files & close down the computer properly, or allows the software to do this for you (through the RS-232 serial port connection if the UPS comes equip for auto shutdown). UPS's have a VA size rating. Usually VA means "Volts times Amps" which is Watts, but in the case of a UPS the VA rating does not mean that this is how many Watts the UPS can sustain. Often the UPS literature will indicate that the actual maximum Wattage handling capabilities is about 50-60% the VA rating, but my experience is that on smaller UPS's it's even lower than that. For example, the CyberPower 650SL mentioned below is rated to be able to handle 350 Watts, but if you were to plug a 225 Watt device into this fully charged 650VA UPS (rated for 350 Watts) & unplug the UPS from the wall, the power from the UPS to the 225 Watt device would shut off immediately. Only when I lowered the device load to 175 Watts was the UPS able to sustain the load for a period of time. So for smaller UPS's in the 650VA range & lower, it is probably a good idea not to expect to get reliable coverage if your Wattage is higher than 25% of the VA rating (i.e. 650VA should handle 163 Watts). When using a UPS for a new computer & large monitor, I would recommend a minimum 700 VA rating or larger if you can afford it.

TYPICAL COMPUTER & MONITOR WATTAGES: A small computer with 1 hard drive might draw as little as 60 Watts when idle & a dual Pentium Zeon 2.4 GHz computer might draw about 135 Watts when idle & both will draw plenty more when in heavy duty use. A 19" CRT tube computer monitor might typically draw about 93 Watts, a 17" CRT monitor about 70 Watts & an 18" LCD flat panel monitor typically about 43 Watts. If you estimate the total idle Wattage of your computer & monitor, then multiply by 4, that will give you the minimum VA rating you should use for the UPS in your computer setup. If you can afford to buy a larger UPS, do so because the ability of the batteries to handle the load diminishes over the years as the batteries age. You can expect to get 6-7 years from the rechargeable batteries of a UPS if treated properly & the batteries are not left in a discharged condition for many hours after a power failure. The batteries use gel lead acid technology which is similar to the battery in your car & they must always be recharged right away if you expect long life from them.

TEST THE UPS: After you buy a UPS & before you plug the auto shut down serial cable into your computer, charge the UPS for at least 8 hours, then plug your computer & monitor into the UPS with the UPS still plugged into the wall outlet, boot the computer but don't open any applications & wait at least 3 minutes for things to stabilize. Unplug the UPS from the wall & time how long the UPS can supply power before it shuts off. Do not use the applications in the computer while doing this test. This will give you the maximum time your UPS can support the computer & monitor under the most ideal conditions. If this is acceptable to you, install the RS-232 serial cable & UPS software & set the automatic shutdown time for 1/2 or less of the time you just got under ideal conditions. If you add other devices to draw power from the UPS, redo this test. Once a year repeat this test & adjust auto shutdown time accordingly.

American Power Conversion APC XS 1000 (BX1000), has a 1000VA or 600 Watt rating  Although the box & user manual mention that this unit has surge protection, nowhere does it mention how much surge protection, so I will make an assumption that it is minimal.. The spike filtering protection is 825 Joules & the maximum surge current is 36,000 Amps. It has 6 electrical outlets that are battery protected (spaced far enough apart to accommodate some mole transformer blocks), 2 electrical outlets & a phone/DSL/modem/fax port that are surge protected only. There is a ground fault test light built in. Comes with a data port connection, USB to RJ-45 cable & software in case you prefer to install the automatic shut down software (not tested). The box says that the "on battery Voltage" should be 115 VAC + or - 8% (i.e. 105.8 - 124.2 VAC when wall power is out & UPS is driven from the battery) however it did not comply with this range except during the last several minutes of power. The box says that the Automatic Voltage Regulation (AVR) increases on-line Voltage by 12% when utility Voltage is 94 - 107 Volts. I test this & found that .... This unit does not seem to have very good AVR (Automatic Voltage Regulator) despite it's advertised claims. It mentions on the box that it protects in brownout situations (under 112 Volts) (which means that it should prop up the low line Voltage & bring it back up near nominal 117 VAC levels) & overvoltage situations (over 130 Volts). I tested brownout conditions with a stepping transformer & this UPS did not kick in when it should & prop up the Voltage until it got quite low (didn't cut in at 107.5 Volts, but did prop up Voltage when the input was at 102.8 Volts) (it's suppose to kick in when Voltage goes below 112 VAC). When I tested this UPS 1 minute after unplugged from the wall under a 100 Watt load (light bulb), the Voltage level dropped to about 101.5 Volts. (unacceptable). which isn't adequate in my opinion for many devices & certainly not what I would have expected for a unit that advertises it's tight Automatic Voltage Regulated to be between 114 - 126 Volts when the UPS is drawing from the batteries (120 Volts +-5%). The Voltage didn't even start rising from 88 Volts for 8 minutes & never got above 100 Volts until 20 minutes, so clearly the AVR in this UPS isn't well designed for low Wattages of 100. This UPS lasted 59:45 minutes under a 100 Watt load, which is a lower load than most computers with a monitor. When tested unplugged from the wall at 173 Watt load, this UPS dropped as low as 98 Volts which is marginally acceptable & it went higher within 3 minutes as the battery started to drain, so obviously there is some kind of low quality crude Voltage regulation. This UPS lasted 32 minutes under a 174 Watt load which is more typical of the load that an average computer & large monitor would be. That is substantially less than the 24-28 minute quote on the box for a desktop PC with a 21" monitor & also less than the manual which states that this UPS should power a 200 Watt load for 17 minutes. At 231 Watts load it went as low as 100.3 Volts but within a minute the Voltage started going higher. The AVR clearly works better under a heavier loads, but Voltage dips under heavier loads, as was evident by a light bulb that flickered. This UPS lasted 23:50 minutes under a 236 Watt load which is typical of the load that a more powerful tower PC & 19" monitor might draw. When I loaded the UPS with various Wattage's up to 365 & unplugged it from the wall, the UPS did handle the load without immediately shutting off.  This unit sells for $200. CDN. at Future Shop & it is the minimum size I would recommend for most modern computers with a monitor. It's not a great UPS, especially for low Wattage loads (100 Watts) because of poor quality Automatic Voltage Regulation, but it is marginally acceptable for higher Wattage loads (150 - 230 Watts). I purchased this UPS for 150. CDN. at Costco in January 2004.

CYBER POWER 700AVR, has a 700VA or 350 Watt rating. The spike filtering protection is 825 Joules & the maximum surge current is 36,000 Amps. It only has 2 outlets that are battery protected (3 or 4 would have been handier). This unit does not seem to have very good AVR (Automatic Voltage Regulator) despite it's advertised claims. It mentions on the box that it protects in brownout situations (under 112 Volts) (which means that it should prop up the low line Voltage & bring it back up near nominal 117 VAC levels) & overvoltage situations (over 130 Volts). I tested brownout conditions with a stepping transformer & this UPS did not kick in when it should & prop up the Voltage until it got quite low (didn't cut in at 107.5 Volts, but did prop up Voltage when the input was at 102.8 Volts) (it's suppose to kick in when Voltage goes below 112 VAC). When I tested this unit unplugged from the wall under a 100 Watt load, the Voltage level dropped to about 88 Volts (unacceptable) which isn't adequate in my opinion for many devices & certainly not what I would have expected for a unit that advertises it's tight Automatic Voltage Regulated to be between 114 - 126 Volts when the UPS is drawing from the batteries (120 Volts +-5%). The Voltage didn't even start rising from 88 Volts for 8 minutes & never got above 100 Volts until 20 minutes, so clearly the AVR in this UPS isn't well designed for low Wattages of 100. At 100 Watts load, this UPS lasted 30:24 minutes (less than the manual claims). When tested unplugged from the wall at 173 Watt load, this UPS dropped as low as 98 Volts which is marginally acceptable & it went higher within 3 minutes as the battery started to drain, so obviously there is some kind of low quality crude Voltage regulation. This UPS lasted only 12:34 minutes under a 173 Watt loadwhich is more typical of the load that an average computer & large monitor would be. That is substantially less than the 24-28 minute quote on the box for a desktop PC with a 21" monitor & also less than the manual which states that this UPS should power a 200 Watt load for 17 minutes. At 231 Watts load it went as low as 100.3 Volts but within a minute the Voltage started going higher. The AVR clearly works better under a heavier loads, but Voltage dips under heavier loads, as was evident by a light bulb that flickered. This UPS lasted only 8:00 minutes under a 231 Watt load (manual claims 12 minutes under a 250 Watt load). When I loaded the UPS with various Wattage's up to 365 & unplugged it from the wall, the UPS did handle the load without immediately shutting off.  This unit sells for $200. CDN. at Future Shop & it is the minimum size I would recommend for most modern computers with a monitor. It's not a great UPS, especially for low Wattage loads (100 Watts) because of poor quality Automatic Voltage Regulation, but it is marginally acceptable for higher Wattage loads (150 - 230 Watts).

CYBER POWER 650SL, has a 650VA or 350 Watt rating. The spike filtering protection is only 585 Joules & the maximum surge current is 36,000 Amps. This unit does not seem to have sufficient AVR (Automatic Voltage Regulation) even though it mentions on the box that it protects in brownout situations (which means that it would not prop up the low line Voltage & bring it back up near nominal 117 VAC levels). I simulated brownout conditions with a stepping transformer & this UPS did not kick in & prop up the Voltage until it got quite low. When I tested this unit unplugged from the wall under a 100 Watt load, the Voltage level at times dropped as low as 102.6 Volts which is adequate in my opinion for many devices, but not what I would consider tight Voltage Regulated. When tested at 173 Watt load this UPS dropped as low as 112.7 Volts but went higher as the battery started to drain, so obviously there is some kind of low to medium quality crude Voltage regulation. The Volt & Watt meters verified this, as did the light bulb which briefly dimmed (almost a flicker) frequently. The box says that the output Voltage when running on the battery should be 120 Volts +-5% (which is 114 - 126 Volts), but it didn't even come close to the specs. This UPS lasted 25:20 minutes under a 100 Watt load, but would last far less under the load of most computers with a monitor. This UPS lasted only 9:20 minutes under a 173 Watt loadwhich is more typical of the load that an average computer & monitor would be. That is substantial less than the 14-18 minute quote on the box for a desktop PC with a 21" monitor. A major shortcoming was evident when I loaded this UPS with 225 Watts & unplugged it from the wall, the UPS did not handle the load, it immediately shut off. In my opinion, a UPS that is rated to be able to handle a 350 Watt load during a power outage, should not immediately shut down when it only has a 225 Watt load during a power outage with a fully charged battery. If that is all this UPS can do under new charged conditions, what's it's performance level going to be like in a few years as the battery ages? This unit sells for $150. CDN. at Future Shop, but I do not recommend it.

BELKIN 520VA (model F6C520-SER-LC, or P56373-A, or BEK-65-0073) has a 520VA or 312 Watt rating. This unit is not part of Belkin's better line called "Gold Series", so this unit does not claim to have AVR (Automatic Voltage Regulation), which means that in a brown-out situation (low line Voltage) it would not prop up the Voltage & bring it back up near nominal 117 VAC levels. When I tested this unit fully charged & unplugged from the wall under a 100 Watt load, the Voltage level at times dropped as low as 91.5 Volts which is unacceptable in my opinion, though many computer power supplies might still be able to function properly at this low Voltage level. When tested at 173 Watt load this UPS dropped as low as 104.7 Volts but went higher as the battery started to drain, so obviously there is some kind of crude Voltage regulation. The manufacture's stated operating range is 93 to 135 Volts. The spike filtering protection is only 320 Joules & the high frequency ENI/RFI filter is 10 dB at 0.15 MHz or 50 dB at 30 MHz. This UPS lasted 18:45 minutes under a 100 Watt load, but would last far less under the load of most computers with a monitor. This UPS lasted only 6:50 minutes under a 173 Watt load. The box indicates that this UPS will provide 28 minutes of back-up power, but it doesn't say under how much load & since even the simplest computer with a small monitor will draw more than 100 Watts, the manufacturer's claim of 28 minutes is clearly deceptive & nowhere near what you will actually get. The manual says this UPS will last 5-28 minutes with a PC computer & a 15" monitor plugged into it. When I loaded the UPS with 225 Watts & unplugged it from the wall, the UPS did handle the load without immediately shutting off. This UPS was on sale at Compusmart for $70. CDN (regularly $100. CDN). I do not recommend this unit for a computer & monitor as it is too small.

See also INVERTERS that create AC Voltage for household appliances from a battery.

By Doug Hembruff.
Last updated July 5, 2005