Power Protection - Uninterruptible Power Supplies
Updated: December 10, 2012

Use of Uninterruptible Power Supplies
in home entertainment applications

Is it possible to make use of the more affordable
computer-grade UPS in the Home Theater
as an alternative power protection solution?

Good quality computer-grade uninterruptible power supplies are reasonably priced—surely significantly cheaper than home theater power centers and power line conditioners. Yet a good quality UPS still provides the desired automatic voltage regulation and moderate surge protection in addition to EMI/RFI noise filtering; and this is apart from a battery backup that gives you the time to switch off your system in the right order should a mains power failure occurs.

It sounds as if a computer UPS represents a suitable alternative power protection solution to expensive home theater grade power line conditioners. The purist will definitely not agree. But if you are on a tight budget, a computer-grade power protection solution may very well represent a better alternative than just opting for a cheap surge protection power strip.

Cyberpower PP2200SW UPS - 2200VA/1500WCyberpower PP2200SW UPS
 2200VA/1500W PureSine AVR Boost/Buck 8-Outlet RJ11/RJ45 Tower EMI/RFI USB

This line interactive uninterruptible power supply comes with full automatic voltage regulation over a wide range of AC input voltages, 1796-joule surge suppression, built-in overload voltage circuit breaker, and lifetime connected equipment guarantee of $350,000.

Would about a computer-grade uninterruptible power supply as part of a power protection solution in the home theater?

In their quest to protect sensitive and expensive home theater gear, many system owners do not foresee the option of using computer-grade power protection as part of a possible solution to their needs. For many, it is as if uninterruptible power supplies and surge suppressors designed to protect expensive and sensitive computer equipment, will do a poorer job in the home theater.

In this article, we investigate the possible use of a computer-grade uninterruptible power supply as part of a power protection solution for audio and video applications. 

There is a lot of controversy surrounding the use of computer-grade power equipment in home theater applications, in particular because most of these UPS systems produce a stepped sinewave AC output.

Yet computer UPS systems come at a significantly cheaper price-tag than their AV-grade counterparts; therefore, for the budget conscious, a computer-grade power protection solution may still represent a possible alternative.

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In our opinion, this is a technically acceptable approach, but only as long as one is aware of a few possible limitations that may arise in this respect.

The Computer-Grade UPS Power Protection Solution

From a budget perspective, for the money spend on a suitable home theater power center with surge suppression and automatic voltage stabilization, it is possible to buy a good quality 'line-interactive' or better still an 'online' computer-grade uninterruptible power supply (UPS); whether it is one or the other depends mainly on the power ratings in question.

Home theater power protection solutions with line conditioning and ac voltage regeneration technology (please refer to our How-it-Works: Power Line Conditioners article for more information) are much more expensive. Yet from a technology perspective, a UPS is basically an AC Voltage Regenerator similar in principle to that found on high-end power line conditioners; the real basic difference between the two is that the UPS solution comes with the added battery backup.

However, prior to continuing with this discussion, it is important to note that not all computer-grade uninterruptible power supplies support the desired functionality to act as a suitable replacement for an AC Voltage stabilizer/line conditioning solution in the home theater. To better understand the whole issue, we will first discuss the most common UPS technologies presently available for computer use.

Different UPS Technologies

Surprising as it may seen, not all uninterruptible power supplies provide the much desired AC line conditioning and power protection for your electronics. In its cheapest form, a UPS will only provide a battery backed AC supply when either there is a mains failure or when the AC supply voltage is outside the set limits.

Therefore, having an understanding of the different UPS technologies is important if you are seriously considering the more affordable computer-grade UPS option as part of a home theater power protection solution.

There are three main types of Uninterruptible Power Supplies; these are:

Type 1: Standby UPS

Type 2: Line-Interactive UPS

Type 3: Online UPS

The 'Standby' Uninterruptible Power Supply

A standby UPS system, also known as an off-line uninterruptible power supply, powers equipment directly from the AC outlet. In the event of either a complete power failure, or a variation in the input AC voltage that exceeds pre-set limits, the UPS power circuitry kicks in and the unit goes to battery operation. In the process, there is a small delay of a few milliseconds for this switching over to take place.

Batteries are charged as long as there is mains power available. These units provide protection against AC supply voltage fluctuations that fall outside the pre-set operating range; they also include some minimal protection against spikes and switching transients. But the power protection offered by these inexpensive UPS computer systems is not on par neither with power line conditioners nor with true surge protectors. In particular, cheaper models do not include adequate line noise filtering and surge protection.

The 'standby' uninterruptible power supply is the least suitable for use in the home theater as it does not provide sufficient protection against voltage sags or burnouts (drop in the electrical power supply voltage) and overvoltage surges. The reason is that these units generally allow for too wide a range in AC supply fluctuations before the battery back-up kicks in. This does not constitute a problem with most switch-mode power supplies used in computer systems; but it will definitely be a problem with the more conventional power supplies used in premium quality audio systems.

'Line-Interactive' Uninterruptible Power Supply

The basic difference between a line-interactive and the cheaper standby type is that line-interactive uninterruptible power supplies provide a voltage boost on sags without utilizing the batteries. These are hybrid devices that offer a higher level of performance by adding better voltage regulation and filtering features to the standby UPS design.

Cyberpower CP500AVRLCD 1500VA/900W UPSCyberpower CP1500AVRLCD 1500VA/900W line-interactive UPS

Examples of line interactive UPS systems include the 1500W Cyberpower PP2200SW UPS featured on top of this page and the 900W Cyberpower CP1500AVRLCD UPS pictured here.

These UPSs are designed for mid to high-end computer systems and feature dynamic line conditioning with automatic voltage regulation in addition to surge protection and battery backup in the in the event of brownouts or total power loss. These are also equipped with full phone, fax, Ethernet, and DSL protection. And all this is backed up by a 'Connected Equipment Guarantee' of $500,000 for the 900W model and $350,000 for the 1500W UPS system.

Line interactive uninterruptible power supplies make use of a 'tapped' or a 'ferroresonant' transformer to maintain the required output voltage. These are special transformers that provide voltage regulation by operating on the non-linear portion of the magnetization curve of the metal core. The transformer provides voltage regulation and minimal power conditioning for disturbances such as electrical line noise.

This setup allows for continuous line conditioning, increases battery life, and reduces electronic noise. These units also provide some surge protection, though again, the surge protection provided is often not on par with dedicated surge protection strips. The exception here is the 1500W UPS model which includes a modest surge suppression rating of 1796 joules.

As with standby uninterruptible power supplies, complete elimination of line noise and frequency variations work only when the unit switches to battery operation. In addition, these systems are not very much effective against unstable frequency variations and sudden current changes.

'Online' Uninterruptible Power Supply

Online uninterruptible power supplies provide the highest quality power protection. This is done via a double power conversion technique; the online UPS takes incoming power, converts it to DC, conditions it, and converts it back to AC. In such a setup, there is no delay to switch to battery. It is like having a standby-type or line-interactive UPS in tandem with a dedicated power line conditioner using AC regeneration technology; the difference is that the online UPS solution would turn out cheaper than the two-component setup.

These systems offer complete protection and isolation from all types of power problems, problems like power surges and power sags, high-voltage spikes, switching transients, electrical line noise, frequency variations, etc.

Online UPS systems are capable of delivering TRUE sine wave power, independent of whether these operate on the AC supply or on battery mode. Instead, stand-by and line-interactive systems generally deliver a simulated stepped sinewave output (as we will explain further on in this article) rather than a true sinewave when in battery mode. Only some of the more expensive line-interactive UPS systems (like the 1500W Cyberpower model referred to above) provide a pure sinewave, and again only when in battery mode. True sinewave represents the optimum power for most AV electronics as it only delivers the 60Hz (or 50Hz) voltage with no presence of unwanted harmonics on the AC line feeding your gear.

In view of the higher expense, increased weight, and size associated with online UPS systems, use of online uninterruptible power supplies is normally restricted for critical applications, high availability servers, etc. However, in view of its capability to deliver TRUE sinewave power output at all times, online UPS systems also represent the ideal UPS solution for use as part of a home theater power protection setup.

There is one major problem though...

Unfortunately, the 'online' uninterruptible power supply is the most expensive of the trio, with a price tag that often renders it unfeasible with respect to a dedicated Home Theater Center solution using AC regeneration technology.

Is a Computer UPS really a 'No-Go' Solution?  

Noise on the AC Line

For the purists in audio and video systems, the use of a computer-grade UPS is simply a no-go approach. They would argue that uninterruptible power supplies designed for computer use might add more noise and distortion in the audio band.

To a certain extent, this may be true in that computer-grade power protection gear would normally incorporate only EMI/RFI high-frequency noise filtering; computer type UPS systems would not normally filter out any AC harmonics present on the line.

Yet, it is also a fact that even most mid-range power line conditioners designed for home audio, often fail in this respect. Filtering of noise in the audio spectrum present on the AC line is far from a straightforward job.

Yet there is more to the filtering of noise and unwanted AC harmonics on the line. Most of these UPS systems deliver a simulated stepped sinewave instead of a pure sinewave when in battery operation.  The stepped output is typical in digital circuits and leads to a simplified inverter output stage on the UPS.

Unfortunately, the 'stepped output' is a good source for higher order harmonics that would appear across the UPS output. These added harmonics are in effect an added source of noise that would find its way into AV system if not filtered out.

Surge Protection:

Although most computer uninterruptible power supplies incorporate some surge suppression on their AC input, the surge protection capabilities of a computer grade UPS are in most cases, far from adequate.

Main Advantage of using a UPS-based Power Protection Solution

While 'off line' uninterruptible power supplies do not provide much added value in home theater power protection, the use of 'line-interactive' and even more so 'online' UPS systems, would guarantee a regulated AC power output independent of the fluctuations or waveform distortions on the AC power line feeding your system.

Protection against power line fluctuations in the home theater should not be underestimated. Fluctuations on the AC line can turn out to be a serious problem as prolonged fluctuations may lead to overheating and occasional damage.

Fluctuations by as much as ±10% of the nominal AC line voltage may cause a 200W amplifier to deliver 160W in output.  Large power amplifiers found in subwoofers, multi-channel power amplifiers, projectors, and RPTV systems, are extremely power hungry, and therefore fluctuations of this magnitude on the AC line would mean a dimmer picture for a projector during a bright scene, or a significant loss of power for an amplifier during a loud passage of music.   

Concluding Remarks 

Computer vendors can provide reasonably priced uninterruptable power supplies that may represent a better value for the home theater on-a-budget. It is all a question of analyzing what you will get when investing in a computer-grade uninterruptible power supply as against an equally-priced protection system specifically designed for home theater use.

We are not saying that high-end AC regenerator based systems designed for home theater such as the 'Monster Cable MP PRO AVS2000 featured elsewhere under this section or the Furman IT-Reference 15i, are not worth the investment. These products are capable of delivering remarkable results, exceptionally clean power, and come with a level of build quality that is difficult to match, but...

There is a price to pay; expect to pay anything between $1,500 and $3,000 for these products. It is all a question of available budget; if you are working within a tight budget, the computer-grade UPS solution may be the way to go. And...

You can always improve on the 'raw' computer uninterruptible power supply solution and still end up with a less expensive alternative to the 'dedicated' home theater power line conditioner. All you have to  do is add additional filtering to the output of a computer-grade UPS.  Inexpensive units such as the $40 Monster MP HT800G PowerCenter would provide enhanced surge suppression on both the AC line as well as protected connections for the phone line and the coax TV input.

Tripp Lite HT10DBS Home Theater 10 Outlets 3570 Joules RJ11/45 Surge SuppressorFor a little bit more, you can get an enhanced power protection strip such as the Tripp Lite HT10DBS Home Theater 10-Outlet power strip; this comes with a 3570-joule rated surge suppressor, and incorporates multiple-line coaxial, phone/modem, and even network surge protected connections.

The use of a hybrid power solution based on a surge protector strip and a computer-grade line-interactive uninterruptible power supply surely represent a cost effective and highly efficient power protection solution for any home theater setup.

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 Article Content

Issues discussed in this article:

Blue bullet  Introduction: Would you consider a computer UPS as part of a home theater power protection solution?

Blue bullet  Uninterruptible Power Supplies: Discussing the different types of UPS supplies, from standby and line-interactive to online UPSs

Blue bullet  Is it really a viable alternative? What are the pros and cons of using an uninterruptible power supply in the home theater?

Blue bullet  Concluding remarks:: Ways of improving on the UPS solution as part of a home theater power protection setup

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