UPS

Work From Home Essentials: Choosing a UPS for Your Computer System

I’ve always used a UPS (Uninterruptable Power Supply) to protect my Mac and peripherals from loss of power, electrical surges, brownouts, and noise and glitches on the power coming into my Mac. Having this basic protection had likely kept me from losing data when power failures occurred, extended the life of my Mac, and allowed me to laugh in the face of danger, or at least the thunderstorm heading our way.

A UPS is something that everyone should have to protect his or her computer(s) and equipment. In this Rocket Yard guide, we’ll take a look at UPS basics, features, and how to size a UPS for your needs. In today’s work from home (WFH) environment, it is more necessary than ever.

UPS: An Introduction

At its most basic, a UPS is a battery-powered system used to provide the needed electricity to your Mac and peripherals should the normal power fail. The UPS monitors the incoming utility power, and should it go down quickly, switches the power source to its internal battery. This prevents a sudden shutdown and the stress it can cause to your Mac and peripherals. It also gives you time to save the data in open applications and perform a controlled shutdown of your Mac.

Basic standby UPS
A Standby UPS monitors the AC input, and provides a battery backup should the power go out.

By avoiding the perils associated with suddenly losing power, a UPS can prevent data loss, corruption of files and the system, damaged components, and a shortened lifespan.

UPS devices also have built-in surge protection to handle routine electrical surges that often occur in commercial and residential settings.

UPS Types

UPS devices are usually available in three broad categories, with each type providing different levels of protection. Each UPS manufacturer may use a slightly different name for each category:

Standby UPS: This is the most basic type of UPS. It passes the utility power on to your Mac while monitoring the incoming voltage levels. If the incoming electrical levels fall below a predetermined level, the UPS changes the power source from the incoming utility voltage to the internal battery. Standby UPS usually can protect from surges, blackouts, and brownouts.

Line Interactive UPS: This type of UPS goes a bit further than the basic type. It monitors the incoming voltage for surges, blackouts, and brownouts, but it will also use the internal battery to supplement under-voltage conditions, and prevent over-voltage conditions from being passed on the devices connected to the UPS. You can think of this UPS category as allowing connected devices to use the normal incoming utility power as long as it is stable and within acceptable levels, but as soon as those levels are overstepped, the internal battery takes over.

Double Conversion UPS: With this type of UPS, your connected devices always run off the internal battery of the UPS, regardless of the state of the incoming line. The incoming line voltage is used primarily to keep the battery charged. This type of UPS offers all the protection of the Line Interactive, as well as protection against most line noise, frequency variations, and harmonic distortions. It’s possible for a Double Conversion UPS to provide the cleanest power to your devices.

CyberPower BRG1500AVRLCD
A Line Interactive UPS can offer more features, such as displays, USB charging ports, and automatic voltage regulation.

Which Type of UPS to Use?

Any UPS type is better than none, and each type can provide good service to your hardware, depending on the type of power problems you are likely to experience:

Stable electrical environment: This is likely a residential setting in an urban or suburban area. The power tends to stay on year-round but may go off if a big storm rolls through. You don’t have industrial machinery operating nearby, and the biggest source of electrical noise is your refrigerator, washing machine, or AC turning on or off. In this type of environment, any of the UPS types will meet your needs, including the basic Standby UPS.

Mostly stable: You live in a residential setting in a suburban or rural environment. You may lose power once in a while from storms. You may be a good distance away from an electrical substation, or in the last group of homes on a power feed. You notice occasional brownouts when the weather is hot. You may also be near commercial or agricultural properties that use large electrical machinery. While the power stays on most of the time, it’s likely not very clean, having over- and under-voltage conditions. A Line Interactive or Double Conversion type of UPS is appropriate for this setting.

Mixed: The area you live in has enough power outages that you have, or are considering installing, a backup generator, or make use of alternate electrical energy sources. In this type of setting, your electrical system can experience line noise, frequency variations, and harmonic distortion. A Double Conversion UPS is the best choice for this environment.

Note: Not sure where you fall in the above list? A Line Interactive UPS is the most popular and meets the needs of most people.

Sizing a UPS

The UPS needs to be big enough to not only run all of the devices you connect to it but to allow for enough runtime after a power outage occurs to give you time to perform a controlled shutdown on all of the devices. To properly size a UPS, you will need to know the capacity of the UPS and the size of the load connected to it.

OWC Envoy Pro EX
Bus-powered external drives, such as the OWC Envoy Pro EX, use power from your Mac, so it isn’t necessary to include their power needs in the load calculations.

This would seem to be a trivial exercise; add up all the loads and compare that to the UPS capacity. The problem is that UPS capacity and device loads are usually measured in two or more different units. It’s not uncommon for your devices to use watts to indicate the load, and a UPS to use VA (Volt-Amps) to indicate capacity. The two measurements are not directly interchangeable, although sometimes they are. The key is a third measurement known as PF or Power Factor. Unfortunately, equipment manufacturers rarely publish the PF rating. That leads us to use a generalization that the wattage rating is generally 60 percent of the VA rating.

Note: Wattage ratings of your equipment can be found either on a sticker attached to the equipment, or in the device’s manual, technical specifications, or environmental report.

As an example, the following desktop Mac with two external drives:

Total wattage: 262 + 36 + 0 = 298

VA rating: 1.6 × 298 = 476.8

This results in a UPS with a minimum VA rating of 476.8. But that’s just the minimum; the next step is to determine the runtime and over-provisioning.

Runtime is how long you want the UPS to be able to run the connected load before it depletes the battery and turns itself and your system off. To calculate runtime, you need to know the efficiency rating of the UPS, another specification that’s rarely published. Instead, it’s easiest to use configuration tools provided by the UPS manufacturers

Over-provisioning is how much additional load you want to be able to add to your system without adversely affecting the UPS. Some manufacturers allow you to specify over-provisioning in their tools while others do not. If you don’t see an over-provisioning option, add additional wattage to represent items you may add in the future to the total wattage calculation above.

Runtime graph
Runtime estimates from the CyberPower tools show our 298-watt example having a 21-minute runtime when paired with a CP1500AVRLCD UPS.

Additional UPS Features to Consider

There are additional UPS features you’ll need to consider, including some basic items, such as:

AVR: Short for Automatic Voltage Regulation. This feature is used to compensate for over- or under-voltage conditions. In most cases, a UPS with AVR will be a Line Interactive type of UPS. 

Sine Wave or Simulated Sine Wave: The UPS battery’s output is DC and is converted by the UPS to either an approximation of an AC waveform (Simulated Sine Wave) or a true Sine Wave output. Some devices may require a true Sine Wave power source to operate correctly; this is especially true for devices that use active PFC (Power Factor Correcting) power supplies. Check with the device manufacturer to see if a true Sine Wave is required for the AC input, or if PFC power supplies are listed as a feature.

Software: Some UPS devices include an app that allows the UPS to communicate with your computer, informing the computer that the UPS is running on battery, how much runtime is left, and to initiate shutdown. The Mac has basic UPS support built-in, though the UPS software may offer more options. Using either the UPS-supplied or the Mac’s built-in power management software is a good idea, as it will allow for the Mac to be shut down gracefully during a power outage, even if you aren’t present.

Energy Saver preference pane showing UPS settings.
The Mac’s built-in UPS power management can shut down your Mac based on criteria you specify.

Power Outlets: Most UPS devices have a mix of outlets, some connected to the battery, and others that are just surge protected. Make sure the number of outlets matches up to your needs. Also, make sure the outlet arrangement will account for the use of power bricks your equipment may use.

Charging Port: A UPS may offer one or more USB ports specifically for charging mobile devices.

Noise: Larger UPS devices may have fans that can be annoyingly loud when you’re running on battery power. Check the manufacturer for noise ratings.

Alarms: A UPS may use an audible alarm to indicate that power has been removed, and the UPS is running off the battery. Check to see if the alarm can be disabled. It’s not pleasant to spend a night listening to the UPS alarm going off.

Displays: Some UPS devices include informational displays that indicate current conditions, such as voltage, battery charge, available runtime, and battery health.

Replaceable batteries: Batteries in UPS devices have a limited lifetime. Being able to replace the battery is a better choice than replacing an expensive UPS just because the battery has failed. In addition, some UPS devices allow you to add larger or multiple batteries to increase runtime.

USB: A UPS will usually communicate to the computer using a USB port. Make sure you have a free USB port on your Mac to support the UPS.

UPS outlets
UPS power outlets are usually divided up between battery backup and surge protection. Make sure there is enough of each type for your needs.

Other UPS Uses

So far, we’ve assumed that you’re using the UPS with your computer setup, but a UPS can be used to protect just about any type of electronic device, including TVs, home theater, security systems, networking equipment (routers, modems, wireless access points, switches), and gaming systems.

UPS usage has some restrictions; the consumer versions usually should not be used to power devices such as printers, copiers, and scanners that use motors or toner fusing systems. These types of devices tend to draw large amounts of energy in short bursts that can quickly overload a UPS. It’s OK to use UPS surge-only outlets to protect these devices, but don’t connect them to the battery outlets of the UPS.

What’s your experience with a UPS? Let us know in the comments below.


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Tom Nelson
the authorTom Nelson

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4 Comments

  • Very informative and concise article. Thank you.

    Please note there is an error in calculating the minimum VA capacity of the UPS. You should divide by 0.6, instead of multiplying by 1.6, as the maximum wattage from the load would be 0.6 of the minimum VA capacity. The resulting number will be 6.7% higher.

  • Execellent article on UPS. I have used them for years and would add the comment to label them with the month/year put into service. Very easy to forget when you added them to your system.

    Also if the worst happens make sure to keep your receipt and file the claim on the warranty. I had a lightening strike and the warrant paid for the damaged printer and replaced the UPS!