The uninterruptible power supply – or UPS – is one of the most misunderstood components of the IT and power infrastructure. Yes, it can save your bacon, but it can also be an intimidating piece of technology. As Eaton product manager David Windsor once put it, “You don’t have to have an engineering degree to understand it, but it helps.” Whether you’re on the verge of implementing your first UPS or are gearing up for your next upgrade or replacement, this guide can help you make sense of things.
What it is and why it’s awesome
A UPS is a battery-based power supply that keeps your critical equipment running in the event of a power outage. A UPS is generally used to provide enough power to allow a graceful shutdown of your equipment when the power goes out. In situations where no downtime can be tolerated, a UPS can be used until systems can be cutover to a backup site or until an alternate source of power, such as a generator, can be brought online.
But wait – there’s more! Depending on the type of UPS you have, it can also protect equipment against power surges and power “sags,” which is important because both can wreak havoc on sensitive IT systems. This process of regulating incoming power to eliminate surges and sags is sometimes known as “power conditioning.”
Depending on your environment – and your budget – you may want to protect every system in your infrastructure with a UPS of some kind. Or you may have to prioritize and protect only the most business-critical components.
Most UPS devices fall into three basic categories:
A standby UPS allows your equipment load to switch quickly to battery power when power through your normal sources is disrupted. There can be a micro-second delay while the UPS takes over. Depending on what equipment you’re supporting with your standby UPS, this blip may not hurt anything. This is the base model UPS, and it may or may not regulate incoming power to even out surges and sags.
A line-interactive UPS does the same thing as a standby UPS in terms of switching quickly to battery power after a micro-second delay. But unlike most standby UPS devices, a line-interactive UPS regulates incoming power before passing it through to protected equipment. You’ll pay a little more for this type of UPS, but it offers better protection against power fluctuations.
A full-time UPS (also known as an “online UPS”) is always ready to take up the load and therefore can take over seamlessly when a power outage occurs. This is the kind of UPS you want when your equipment cannot tolerate the momentary blip of a standby or line-interactive UPS. A full-time UPS provides the best power protection – and is also the most expensive.
Line-interactive and standby devices that regulate incoming power are known as “single-conversion” devices. A full-time UPS is known as a “double-conversion” UPS because it does more than just regulate power as it comes through – it converts the AC power to DC, then converts it back to AC again before passing it through to protected equipment. The purpose of this process is to completely isolate the IT equipment from the original power source. It may help to think of the line-interactive device as a power filter – and the full-time UPS as a power purifier.
Mixing it up
What if you need full-time UPS protection for some equipment but not others? Mix it up! Since full-time UPS protection is the most expensive, it doesn’t make sense to use it for your entire infrastructure. Use a full-time system to protect your most sensitive workloads, then provision a line-interactive or standby system to protect the rest.
Nowadays you can also buy what’s known as a “multi-mode” system that can act as either a line-interactive or a full-time UPS device, depending on the power situation. This is more of an enterprise or data-center solution, though. For the average SMB, it will probably be cheaper just to divvy up your systems based on the protection they need and buy separate devices.
Key terms you should know
Before you jump into any UPS discussion – either online, with colleagues, or with a vendor – there are a few key terms you should be familiar with:
VA: VA stands for volt-amperes and is how the power rating for a given UPS is expressed. A small UPS might have a rating as low as 500 VA. Giant ones have ratings in the millions. The average SMB is probably looking at closer to 20,000 to 100,000. Also, don’t confuse VA with wattage, as they are completely different things!
Single-phase vs. three-phase: These terms are referring to the type of power delivered to your facility by your power utility. Generally, residences receive single-phase power, and businesses receive three-phase power. The UPS you choose will likewise be single-phase or three-phase. Of course, single-phase UPS devices are cheaper than three-phase, but they are only appropriate for protecting relatively low-amperage systems (less than 20,000 VA).
Output load: In simplest terms, this is the load your UPS is capable of supporting in the event of a power outage. Keep in mind that you don’t ever want to have to run your UPS at 100% of its capacity. You could easily overload it and cause everything running on it to fail. Aim to run your UPS at no more than 80% load to give yourself some breathing room.
Runtime: This is the length of time that the UPS will support the load you have assigned to it. The higher your output load, the shorter your runtime. Likewise, the lower your output load, the longer your runtime. Needless to say, if your runtime is too short, you won’t have enough time to react when a power failure occurs. Supporting appropriate output loads, most UPS devices are designed to provide five to fifteen minutes of runtime. Make sure your UPS will give you sufficient runtime to get your IT affairs in order.
Rightsizing your UPS
How do you know what size of UPS to buy? That’s the $64,000 question, and it’s one you should probably get a UPS vendor to help you answer. But here is a fun math calculation you can do on your own to help you know if you’re in the ballpark:
- Identify all the equipment the device will be protecting, then use OEM information to determine the volts and amps each device draws.
- Multiply volts by amps to get the VA of each device, then add them all together.
- Multiply that figure by a minimum of 1.2 to allow for breathing room. If your business is growing quickly or you’re planning to add or upgrade servers in the next few years, you’ll want to use an even higher number.
You should also have an idea of whether you prefer a rack-mounted UPS or a freestanding device. Depending on the size of UPS you need, you can probably have your choice of form factor.
Need more than the standard five-to-fifteen minutes of runtime? You can always augment your UPS with supplemental external battery modules. Depending on the capacity, these can give you hours of emergency runtime instead of mere minutes.
Replacing batteries vs. replacing the UPS
According to industry averages, most organizations will get eight years of reliable life out of their UPS device and will need to replace the batteries once during that lifespan. If your batteries are more than four years old or the UPS itself is more than eight years old, you may be starting to press your luck, especially if you’re seeing any alerts or errors. Both age and errors dramatically increase the risk that your UPS will fail when you need it most. And an unreliable UPS defeats the purpose of having one! That said, a well-made and well-maintained UPS has been known to provide upwards of 20 years of safe and reliable service, assuming it’s still sized correctly to meet the output load.
They say up to 85% of UPS failures are caused by battery failures. It’s a depressing thought that the UPS itself can be fine but the batteries can conk out, rendering the entire device useless. But that’s exactly how it works: The batteries are the heart of the UPS, and they have to be in good shape if the UPS is going to do you any good. Keep in mind, however, that batteries represent roughly 80% of the cost of the UPS. So if the UPS itself is nearing retirement age and has already had the batteries replaced once, you may want to seriously consider replacing the entire unit instead of just replacing the batteries, especially if it’s time to reconsider your output load.
reprinted from Spiceworks.com