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Uninterruptible Power Supply Questions and Answers


Once you figured out that you need an uninterruptible power supply (also known as UPS), you probably have a bunch of questions that still may require an answer. In this section of Questions and Answers, I will try to guide you through several things that you need to consider in order not to overpay for your UPS system or under-protect your critical equipment.
There are several basic steps that you need to take in order to choose a proper UPS system. I hope the following questions will help you navigate through loads of information and guide you in the right direction:

1. Equipment questions

The first step in choosing your UPS system is to list all of the equipment that you would like to be backed up during power failure.

  • Question #1. What devices do I need to backup?

2. Questions about power

The second step is to calculate your Watt requirements.

  • Question #2. Where do I find the watt rating?
  • Question #3. What is the power factor?

3. UPS sizing

The third step is to match your power needs with a proper UPS size.

  • Question #4. What capacity of UPS do I need?
  • Question #5. How do I size UPS equipment?

4. Type of UPS you need

The fourth step is to match your needs with a proper UPS type.

  • Question #6. What are uninterruptible power supply types?

Now, let’s look at the answers:

Question #1. What devices do I need to backup?

If you are not running a large center with servers and networking equipment, you can usually get away with just powering your computer (or computers), modem, and router. The idea behind having a UPS (Uninterrupted Power Supply) system is to give yourself or your staff enough time to save the information that you were working on and safely shut down the equipment.

In this case, having a desktop UPS system will be sufficient. Following are examples of equipment that this type of system is suitable for:

  • Personal computer
  • Workstation
  • Small server
  • Printers
  • Scanners
  • Modem and routers
  • Small electronics

If your business or work requires to be ONLINE all the time and downtime is not an option (data centers, telecommunications, factory equipment), you may need to consider a network/server UPS. Check if any of the following applies to you:

  • Your equipment is mission-critical and any downtime will result in bad customer service.
  • Your load is greater than 750 watts.
  • Your equipment requires a pure sine wave.
  • You require UPS to be installed on the rack.
  • You require remote management of your UPS.
  • You require your UPS to support an optional external battery.

Network/server UPS systems are designed to handle larger loads, provide your equipment with sine wave power, and are optimized for rack installations. These types of systems will also give you a remote management option and the ability to extend their run time by adding optional external batteries (few desktop versions do that as well).

So, how do you determine your backup power needs?

In order to answer this question, you need to find out which devices are essential for you to use during a blackout. You may need to use a computer, for example, but using a printer can wait until you get power restored.

Also, your devices will not be used all at once! Some of them will only need power when they are being turned on, others do not consume much power in the standby mode.

Question #2. Where do I find the watt rating?

You probably noticed that some electronics do mention Watt rating:

… while others mention Amp rating:

For a more accurate rating, you can use an energy meter (also known as an electricity usage monitor). Just plug it in between your equipment and the wall outlet in order to get a reading of your complete energy consumption (from initial spikes to a standby mode usage).

How to use a Kill A Watt and save money

You can use Kill-A-Watt 4460 (paid link), which is perfect to use for that purpose. It’s inexpensive, not bulky, has an internal battery, and is conveniently sold on Amazon 😏. You can also use this device to find out how much your equipment costs you in energy usage.

A quick reminder not to forget to calculate ALL equipment that is being plugged in, including the ones that are not being plugged in directly into UPS (Uninterrupted Power Supply), but one into another.

Question #3. What is the power factor?

The power factor is the efficiency of your power equipment. If you divide real power that your device is able to produce (Watts) by apparent power (VA – which is how much power your unit is taking in), you will get a Power Factor (which ranges from 0 to 1.0 and gives a % of how much potential power you will actually be using):

Power Factor = Watts / VA

The better the power factor (0.9-1.0), the less energy will have to be drawn by your equipment from the utility to produce the same result. Here is a video on that:

Power Factor Explained - The basics what is power factor pf

Knowing the power factor is important since it is not always provided by the manufacturer. If you have trouble figuring out the power factor of your equipment, give yourself 40% more power than you actually require.

All electronics that use a switching power supply (commonly all IT equipment) are divided into two categories:

  • Power Factor Corrected (PFC). In the mid-’90s, the Power Factor Corrected (PFC) switching supplies were introduced with a power factor rating of 0.99 to 1.0 (meaning the Watts are equal to VA). 
  • Capacitor input power supplies. This equipment has a power factor rating of 0.65 to 0.85 with Watts being equal to 0.65 to 0.85 times the VA rating:

Watts = VA * Power Factor

Now you can find Power Factor Corrected power mainly in large computing and networking devices, such as servers, drive arrays, switchers and routers. Small computing equipment, such as personal computers, hubs, and other accessories, are powered by Capacitor Input power supplies.

Large, older equipment (prior to 1996), uses capacitor input technology as well, which makes it less efficient than newer versions. Use this formula to determine the full capacity of your equipment:

VA = Watts / Power Factor

It is quite common for equipment to have a Watt rating at about 60% of the VA rating. Keep this in mind when sizing your UPS (Uninterrupted Power Supply) in order to avoid overloading.

Question #4. What capacity of UPS do I need?

Before we get started, it’s a good idea to determine the overall environment that you will be setting your UPS (Uninterrupted Power Supply) in:

  • If outages in your area are not quite common and last no longer than 5 min, you can get away with using a Watt rating that matches the total Watts number of your equipment.
  • If the outages in your area last longer (and occur more frequently), oversizing your UPS would be advised or purchasing an additional battery pack.

In order to determine the size of UPS required to keep your equipment safe from power outages, you will need to calculate the total amount of wattage needed and then match it to the appropriate UPS unit.

By checking the runtime of this UPS unit at the maximum load, you will know if it suits your needs and if it’s not enough for you, get a bigger unit (it will survive a longer outage) or consider adding external batteries.

To be on the safe side, you may want your UPS to run at 80% of its maximum load capacity. This will help with unavoidable power demand fluctuations and reduces chances for overload (while leaving yourself room for additional equipment).

Also, older equipment pulls out much more energy than newer ones and certain types of equipment have more energy-consuming spikes during startups than others (ex: laser printer).

Question #5. How do I size UPS equipment?

If you want protection during a blackout, you cannot plug in more devices than your UPS (Uninterrupted Power Supply) can handle and that’s why proper sizing is important.

Two ratings are generally used to classify UPS equipment and they are VA (VoltAmps) and Watts. This is actually a quite confusing issue, so here is some explanation:

VA vs Watts: The difference between volt amperes and watts by Professor Wattson

Is VA the same as watts? The quick answer is: “No”, even though they are both used to measure the power capacity of your UPS system.

  • Watts – the real power that UPS can produce and supply your devices with. Mathematically, it is Volts multiplied by Amps. In simple words, this is the actual power that you are purchasing.
  • VoltAmps (VA) – the apparent power of the device. This is the power that is supplied to the circuit. It’s a Watt rating divided by the “Power Factor” (or efficiency) of the device.

Here is the example (that is taken from the actual box) that mentions both Watts and VA (VoltAmps) ratings :

Power factor can be anywhere from 60% to 1% and this is exactly by how much VA rating will be different (either equal to or greater) than Watt rating.

Question #6. What are uninterruptible power supply types?

There are three basic UPS (Uninterrupted Power Supply) technology types:

  1. Off-line (or stand by). Least expensive. This is a standby unit that offers no surge protection.
  2. Line-interactive. This is a standby unit that protects from voltage spikes and surges.
  3. Online (or double-conversion). Most expensive. Always online and power transition from utilities to UPS battery is seamless. It converts electric current twice and filters it before it gets to your equipment.

The article here will give you more details on these three UPS systems (link to another article). So, what type of UPS technology do you really need?

If your needs are basic, a couple of computers and routers, getting an online UPS system would make sense. Your computers will be always protected from power disturbances and in case of a blackout, they will not crash (giving you an opportunity to save your work).

Even though the online UPS system is more expensive, you don’t have hundreds of computers to backup, and the peace of mind that you will have with this system is invaluable. Here are some advantages of using an online UPS system (link to another article).

If you are running a center with a bunch of servers or telecom equipment that is connected to SMPS (Switch-Mode Power Supply), then a line-interactive UPS system will be a proper match for you. The reason for this is that the capacitor (which is a part of the SMPS system), stores enough power to give you a seamless transition to UPS during a blackout in a similar way online UPS will.

Not to mention, if your business requires many UPS units, having a system that is not ON all the time and reasonable in cost, will save you quite a bit in upfront money and energy bills.

Feel free to check out the advantages of using a line-interactive UPS system(link to another article).

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