UNINTERRUPTABLE POWER SUPPLY

An uninterruptable power supply (UPS) is a device with a built-in battery that sits between the power supply and your server(s). It protects your equipment from power outages, brownouts, sags, surges, bad harmonics, etc., which can adversely affect the performance of the system. UPSs are available in numerous configurations. A UPS that can protect a single web server will cost around $250. If you have a network of servers, UPS costs can run into thousands of dollars.

There are two types of website — the ones that have had a power problem and the ones that will have a power problem. A UPS will be one of the most important pieces of equipment you will install to help ensure the reliable operation of your website.

Standby Power Supply

There are many UPSs with varying capabilities. A “standby power supply” or “offline UPS” is not a true UPS. It won’t protect your web server. This standby power supply’s power comes directly from the power line, until the power fails, then a battery-powered inverter takes over. The time required for the inverter to start providing electricity to your server varies greatly. Some servers might tolerate a standby power supply, but don’t chance it.

Hybrid UPS

A “hybrid UPS” is a device that uses a ferroresonant transformer to maintain a constant output voltage between the power source and your server, protecting against line noise. It can maintain output relying on its battery (a secondary power source) for a limited period of time. If power is not reinstated, a total outage occurs. It is questionable whether this type of device can actually respond when needed without an accompanying interruption in power. There is some debate as to whether a UPS’s ferroresonant transformer will interact with the ferroresonant transformers in your equipment, producing unexpected results. The hybrid UPS system is comparatively cheap, but, if you choose it, be sure to test it thoroughly with all of your equipment before going on-line.

True UPS

All e-commerce operators should use “true” UPS systems. While these systems are more expensive to purchase and maintain than the others we have examined thus far, this system continuously operates from an inverter with no switchover time and offers good protection from power problems.

A true UPS has internal batteries and can absorb small power surges. It continues to provide power during line sags, negates noisy power sources, and provides power for a set length of time during a power loss. It provides continuous power independent of the outside power supply. The minimum support you want from any UPS system is 30 minutes, enough to survive short outages and other power inconsistencies. Keep in mind though, as you design your server system that a true UPS generates quite a bit of heat; so don’t put it in a closed space.

HOW TO ASSESS YOUR UPS REQUIREMENTS

How much will you pay for the reliability of a true UPS? To find the answer, decide the minimum and maximum amount of time you want to keep your equipment running after the power goes down. To assess the amount of time your system might need supplemental power support—which can be considerable with tape back-up and CD burners—add up the power requirements of the hardware you are running by using the equipment manuals (not the rating plates on the equipment). If power is stated in Watts, then multiply that figure by 1.5 (some experts say 2.0) to get the VA rating, which is the maximum number of Volts Amps the piece of equipment can deliver.

The energy delivering capacity of a power system is measured in Volt-Amps (VA). In the U.S., a standard electrical system outlet for the home is rated at 120 Volts of Alternating Current (120 VAC) and 15 amps (depending upon the thickness of the wire), and thus has a rated VA capacity of 120V x 15A = 1800VA. Exceed that limit and you’ll trip a circuit breaker or cause a fire.

Similarly, for a UPS, an expensive, heavy-duty 300VA device has a lot more capacity than an inexpensive 100VA device. If you use a 100VA rated device anyway and exceed its rating you could blow its fuse or it will not work correctly when called upon during a power failure.

In high school you may have been taught that Watts = Volts x Amps, so you might jump to the conclusion that VA = Watts. It isn’t quite that simple.

Transformer- and capacitor-operated devices have a spec called the “power factor,” which is a number between zero and one. The power factor represents the ratio of the energy used by the system to the energy required by the system to make it operate properly. Light bulbs, space heaters, toaster ovens, etc., use all of the raw energy put into them and so these devices have a power factor of one. Devices based upon more delicate and complicated electronic components do not necessarily use all their power rating, all the time, and thus have a power factor of less than one, generally 0.5 or 0.6. Thus, a computer may need 160VA to run correctly but it actually only uses 80 Watts so the power factor is 80 / 160 = 0.5. Another way to find the VA is to remember that VA = Watts / Power Factor.

This also means that Watts = VA x Power Factor. You might be tempted to look at your computer, see the Watt rating of 80 Watts, then run to your friendly neighborhood computer store and buy an 80 Watt UPS. Bad idea! Things are not that simple, since Watts = VA x Power Factor, so 80 Watts = 160VA x 0.5 for our imaginary computer. This means that you need a 160VA unit to protect and supply power for an 80 Watt computer. Unfortunately many UPS manufacturers use a generous power factor of 1.0 when they advertise the ratings of their VA devices and are thus listing the rating in Watts instead of in VA capacity. They figure that “Watts” is a more familiar electrical term to non-techies than VA and, besides, a power factor of 1.0 gives the largest value for the Watt rating, so 80VA x 1.0 = 80 Watts. This causes the unsuspecting consumer to buy an underpowered UPS. An “80 Watt” UPS may really be an 80VA unit that can actually only handle a 40 Watt computer! To protect a 160 Watt computer, you would have to buy a 320VA UPS.

And even if you think you’ve “figured out” what the right size is for your UPS, be sure to add another 20% capacity for good measure.

What this all comes down to is that, if you want your website to be up and running during a blackout, then you will need a very robust UPS. Your UPS will rely on its battery (DC) to AC converter, which means an expenditure of power. Just to give you an idea at what you are looking at, the author will hazard a guess that a 1250 VA UPS could probably operate during a blackout for around 5 hours and a 2000 VA UPS could operate during a blackout about 8 hours.

Before purchasing a UPS, be sure to ask the vendor about guarantees; if the guarantees don’t fit your needs, find another vendor.

Included in the “true” UPS category are systems that provide:

• Automatic shutdown and restart of your website’s equipment during long power outages.
• Monitoring and logging of the status of the power supply.
• Display of the voltage/current draw of the equipment and the voltage currently on the line.
• Alarms on certain error conditions.
• Short circuit protection.

How to Rate UPSs

When researching your UPS requirements and the various brands and configurations available, make certain that the UPS vendor offers a support and/or maintenance contract. If not, go to another vendor. There are many options you may wish to consider before purchasing your UPS. A manual bypass switch is helpful so that when the UPS is out of operation, power can pass through it to your web server. You also should know how close the AC output of the UPS is to a sine wave.

An inverter is an electronic device that converts a battery’s DC output to AC through a switching process, producing a “synthesized” AC, which can be charted as a waveform on an oscilloscope or graph paper. Inverters produce two types of waveforms: The so-called “modified sine wave” and the “true sine wave.”

True sine waves, or sinusoidal signals, are the most common waves that exist. They’re called sine waves because they have the same shape as the graph of the sine function used in trigonometry. Sine waves look the way they do because they are produced by rotating electrical machines such as generators and, indeed, a sine wave’s intensity (amplitude) at any given instant can be represented by a point on a wheel rotating at a uniform speed since waves are perfectly “balanced” over successive time intervals.

On the other hand, a “modified sine wave” is not actually a sine wave, but a stepped wave, which is the kind of wave a pendulum produces, and is not as smooth as a sine wave. But “mod sine” inverters cost half the price of sine wave inverters, thus lowering the cost of a UPS. However, they can cause electrical noise on a circuit, and digital clocks and timing circuits can be confused or even be occasionally damaged.

Sine wave inverters in a good UPS deliver true sine wave AC output power with high efficiencies from storage batteries. They have high surge ability and low idle current draw. Because of the pure sine wave, the expense is greater than a modified sine wave inverter.

If your UPS does not output a pure sinusoidal waveform, do not put a surge protector between the UPS and the server since a surge protector can mistake the nonsine waveform as a power surge and send it to ground; that will damage the UPS. Some experts think that most computers use a switching-type power supply that only draws power at or near the peak of the waveform, therefore the shape of the input power waveform is not important. It is the authors’ opinion that it is worth spending a little more for a UPS with pure sinusoidal output especially for a UPS that must continually provide a waveform to the computer.

Check what useful operational information the UPS itself provides via displays, etc., such as the power or percentage load the unit is drawing, the battery level and power quality. Most UPSs use lead-acid batteries with a life span of only a few years but no battery memory. Therefore they should be run “dry” as few times as possible.

Maintenance

As your UPS ages, its battery life will become shorter. Be vigilant in monitoring the active support time. When your website has no one accessing it (or you can take it off the Internet for a few minutes) and you’ve completely backed up you hard drive(s), test your UPS and its failure modes. Simulate a power outage by throwing the circuit breaker that has the UPS on it (don’t pull the plug from the wall) to check the UPS. If you don’t have your UPS-protected website on an isolated circuit, you could install a Ground Fault Interrupter (GFI) socket (GFI sockets are the electrical switches with a red and a black button you have in your house or office).

Power problems are inevitable and beyond your control. Therefore, a UPS is one of the most crucial items you can purchase to keep your website up and ready for action.