Uninterruptible Power Supplies (UPS) – An Introduction

Uninterruptible Power Supply or UPS. The questions are what are they, where are they used, do I need one or more and what type?

What Are They?

The function of a UPS is to mask or remove any changes to your AC supply that have the potential to damage your electronic equipment. They do it by monitoring the incoming AC power and:

1. Smoothing out AC power voltage fluctuations (up or down)
2. Correcting line frequency (double conversion types ONLY)
3. Filtering out unwanted AC power noise, noise spikes and general interference
4. Helping to suppress AC power surges and line lightning strikes
5. Taking over if your AC power is completely lost and running off their DC batteries. (for a short time)

While some types of UPS can continually correct for small AC power voltage changes without using their batteries, most residential UPS supplies are only “active” as a short term stop-gap measure. Its job is to keep things running until either the power returns after a few minutes or gives you those same few minutes to safely turn all your equipment off.

Where Are They Used?

A UPS provides AC power protection for your electronic equipment including;

• Projectors
• TV’s & displays
• AVR’s
• Phono amps
• Power amplifiers (maybe)
• DVD and CD players
• PC’s
• Gaming devices
• Networking hardware – switches, routers
• Signal processing devices  – EQ, delays etc.

when there are changes to the incoming AC supply that might damage them, especially if they are powered up when the power issue occurs. These changes include:

• Surge – A brief, but intense, spike in electricity commonly caused by lightning. Surges can damage and destroy electronics, and the intense “spike in electricity” or spike in voltage and current harms circuit boards and components.
• Blackout – A power outage lasting anywhere from seconds to days. These are most commonly caused by severe weather, utility power shortages, accidents, and power grid failures.
• Brownout – An intentional or unintentional drop in voltage for an extended period of time. In emergency conditions, power companies may lower the voltage of your electricity to reduce strained resources and avoid a total blackout.
• Voltage Sag – A sag is also a type of under voltage, but, unlike a brownout, it’s sudden and brief.
• Over Voltage – Occurs when incoming voltage is higher than normal and lasts longer than a surge but not high enough to be classified as a surge, spike or lightning strike.
• Line Noise – Line noise also known as frequency noise can disrupt or degrade the performance of a circuit by injecting abnormalities into the system.
• Frequency Variation – Not a common problem with most power company supplies, but it can occur when using generators and power frequency fluctuates more than desired.
• Harmonic Distortion – A departure from the ideal electrical signal on a given power source.

For most AV/HT equipment the occasional loss of power will not damage it, especially if it is powered off when it occurs. Lightning however can be very destructive if not prevented from entering your HT electrical system and it doesn’t matter if it is turned on or off. Also rapid on/off AC power cycling can be very damaging. Bulb projectors and to a lesser extent LED projectors are particularly sensitive to power loss as they need the air from their internal fans to cool the bulb/LED’s and electronics when in use and after use when they power down. Some computer systems and HT systems like mine, require a specific equipment shutdown sequence in order not to loose data or cause equipment damage. This requires a short period (a few minutes) of continued power after the main AC power is lost in order to execute the correct sequence.

Do I Need One, Or More?

A UPS does not improve the audible performance of any home HT equipment, even if it includes filtering, unless you have a terribly noisy AC mains feed. If your supply is very noisy but stable there are several high quality purpose designed noise and lightning arrestor solutions available. The UPS function is to protect your equipment from those AC power anomalies listed above. Many people will not require a UPS if their utility power is generally quite stable. However, if you live in an outlying region, like me, it is quite common to loose power during storms from lightning strikes and fallen tree limbs. You need to asses your own tolerance of the number of times your household looses power and decide…..do I need a UPS for my HT/AV and computer systems? None of my household computers nor my family room AV system is on a UPS, my HT room equipment requires two.

If you decide to use one you will need to determine which devices you are going to connect to it, are they all going to be connected to just one and what type of UPS design you will require – see later comments.

Networking and computer devices including monitors will often benefit as it allows for an orderly shut down of the system with no data loss or corruption. Some UPS designs can even facilitate this shut down themselves.

HT devices that should be protected with a UPS would include; projector, TV (maybe), pre-amp, AVR, DVD/CD player, any external signal processing devices that feed your speakers like delays and equalizers, any stand alone analog power supplies for phono amps etc. and networking devices. Due to the amount of power that power amplifiers and active speakers, including subs, require, it is not cost effective nor technically required to power them from a UPS.

Care must be taken when using a UPS on your AVR as it includes several powerful amplifiers that can consume a lot of power. If your system remains active after it switches to UPS power excessive current could be drawn by the AVR if the music/film is still playing, causing the UPS to close down or even damage it. This is not an issue for a pre-amp driving active speakers.

Remember that even if you have a standby electrical generator a UPS will still be required to bridge the time it takes for the generator to startup and for the transfer switch go over to generator power, generally ten seconds or more.

What Type of UPS Do I need?

First lets get noise and surge suppression out of the picture. Virtually all UPS’s provide some level of noise and surge suppression. The issues are their effectiveness and energy absorption capability. You are really at the mercy of the manufacturer as to how good the devices noise EMI/RFI suppression is, where as manufacturers will often quote the number of joules of energy that the over voltage/lightning arrestor system can absorb, typically between 800-6000joules. The more joules the better.

UPS supplies come in two distinct types:

1. Double conversion
2. Single conversion

Double conversion supplies are only needed in specialized power critical environments where there can be zero power disruptions of any kind. These UPS’s are effectively online all the time. They take the incoming AC power, process it and feed it out as the main AC feed using batteries to support the conversion process in the case of AC power loss. These supplies can be quite noisy, create heat, are expensive and are NOT recommended for anything other than professional/medical environments.

Single conversion supplies are only truly active when AC power is lost and typically take 4-10mS to come online. Unlike double conversion supplies, they do not correct the frequency of the incoming AC power. Single conversion supplies have two design approaches:

1. Offline also known as Standby or Battery Backup
2. Line Interactive

Offline supplies do not normally make any corrections to the incoming AC voltage if it goes up or down. They usually only become active and go online when power is lost or the incoming AC voltage is outside its expected range. However, some models have built in automatic voltage regulation (AVR) that can boost the incoming voltage, within a small range, without using any battery power to support brownouts and voltage sags.

Line interactive supplies use an (auto)transformer and automatic voltage regulation (AVR) to electronically correct the incoming voltage, within a small range, without using any battery capacity, thereby extending the batteries life. They will only come online and use battery power when they cannot correct the incoming AC voltage level or AC power is lost.

For both approaches their AC outputs are directly connected to their AC inputs (via any filtering etc.) using switching when the power is stable and within an acceptable voltage range. This function is often marketed as being Green as the UPS is now bypassed and uses little power.

UPS designs are split into two output types:

• Sine Wave
• Simulated Sine Wave or PWM Sine Wave

All AC supplies delivered to homes and businesses are a 60Hz (USA/JP) sine wave, (50Hz UK/Europe). However, in many cases they slightly digress from a perfect sine wave due to power line and noise issues and the frequency may not be “spot on”. So the ideal replacement for a sine wave AC supply is a sine wave UPS. However, a sine wave UPS is considerably more expensive than a simulated sine wave UPS and quite a lot of equipment doesn’t mind which type of waveform it receives.

• Sine Wave UPS

These supplies use sophisticated digital and analog electronics with (auto)transformers to reconstruct their 60Hz AC sine wave output voltage from either the incoming AC power or their DC batteries.

Pure sine wave

The additional electronics and in particular the (auto)transformer cause these supplies to be two to three times more expensive than the equivalent simulated sine wave UPS.

All equipment will work perfectly on this design of UPS. I use the rack mounted, line interactive, CyberPower PR750LCDRM1U to run most of my rack equipment including:

• Denon AVR A1
• DVD Oppo players x3
• Phono amplifier
• Analog power supplies x4
• Analog signal processing for my subs – delays, equalizers and voltage balancing amps.

My Genelec active speakers and SVS subs are all connected directly to the mains AC power.

• Simulated Sine Wave or PWM Sine Wave UPS

These supplies use digital switching circuitry to reconstruct a digital representation of the analog sine wave.

Simulated sine wave

Comparison of a simulated sine wave to a pure sine wave

When compared to an analog sine wave the resulting waveform has periods where there is no voltage change. This can be problematic to some equipment power supplies.

ENERGY STAR or 80PLUS standards require that manufacturers of desktop and workstation computers and displays incorporate Active Power Factor Correction (Active PFC) as part of the engineering design. Devices with Active PFC power supplies usually require sine wave AC power for guaranteed trouble-free operation. (Check with your device vendor if not sure)

Simulated or stepped sine wave power, provided by entry-level UPS systems, may be problematic for Active PFC devices. Sine wave power varies smoothly and continuously from positive to negative. A simulated wave only mimics a sine wave using a form of pulse wave modulation, a squared-off approximation, that can cause a zero power gap. This interruption may not be recognized by an active PFC system and could cause the system to unexpectedly shut down or sustain system component stress. Also some simulated sine wave UPS’s cannot supply active PFC devices even if they are run well under the maximum wattage of the UPS, it may simply shut down or make strange noises!

Many devices like projectors, AVR’s, TV’s, amplifiers, DVD/CD players and wall wart or stand alone analog/switched mode power supplies will often run on simulated sine wave supplies. In my case I use the lower cost rack mounted, line-interactive, CyberPower OR700LCDRM1U to run my JVC projector, Darbee video processor and Panamorph lens sled.

NOTE: 4/17/23. The OR700 even with new batteries will no longer support the projector during power outages. I have to assume that aging of the UPS components has moved it out of spec so I have replaced it with a CP1500PFCRM2U sine wave UPS. See comments below.

As a “rule of thumb” I DO NOT use or recommend simulated supplies for any sensitive analog equipment NOR Apple iMAC computers.

Other UPS Features To Consider

• Transfer time – this is the time it takes for the UPS to sense the loss of power and switch to full battery backup. The faster the better, 4-5mS is good. You DO NOT want your equipment to turn off before the UPS comes on line.
• Control software – this allows you to control and monitor the status of your UPS over your network typically on a PC.
• Other connections – like USB, relay and serial for alarms etc.
• Overload circuit breaker – to prevent damage to the UPS if you draw too much current through it.
• Number of outlets and type – make sure the plug type matches yours, usually NEMA 5-15R and has enough to meet your needs.
• Run-time – length of time the UPS will run for when on battery. You will always want several minutes at your selected wattage load.
• Display features – quick easy local monitoring of the UPS main parameters like I/O voltage, battery charge/status/alarm and available run time.
• NOISE – single conversion supplies are silent in normal operation, only making a very small amount of noise for the short time when they become active.

Which Type is Suitable For My Needs?

How Do I Calculate The Size Of My UPS In Watts?

Finally you will need to know how many watts of power you need from your UPS before you go searching for your model, be it rack mount, tower or desktop. If you have looked at UPS power ratings you will have seen that they have two. The first is VA, the second is watts and neither must be exceeded. Simply put, most AC circuits  do not present purely resistive loads to their AC power supply, but have a reactive (inductive or capacitive) component. This reactive power requirement generally has a higher value than the purely resistive value and is measured in volt amps (VA). In most small business and household settings the VA rating can be ignored, also virtually all power ratings for HT equipment are given in watts, so that is what you add up when determining your power requirement.

MY EXAMPLES:

OR700 rating – 700VA/400W (simulated sine wave) – Replaced with CP1500PFCRM2U a 1000 watt sine wave UPS – see comment below.

• JVC RS640 – 380watts
• Darbee – 5watts
• Lens sled – 5watts

Total watt requirement – 390 watts, just inside the units maximum of 400watts. Even with new batteries, this UPS has recently (4/17/23) stopped supporting my JVC projector system. Apparently this power requirement is far too close to the UPS maximum wattage and CyberPower recommends that you do not run their UPS’s at more than 80% of their rated load for extended periods.

PR750 rating – 750VA/560W (sine wave)

• Denon A1 – 120v x 2amp=240watts
• Denon A100 – 55 watts
• Oppo 103 – 35watts
• Oppo 203 – 40watts
• Oppo 205 – 65watts
• Analog PSU 1 – 10watts
• Analog PSU 2 – 15watts
• Analog PSU 3 – 20watts
• Sub Digital Delay – 12watts
• L/C/R analog equalizers – 3x6watts=18watts
• Balanced/unbalanced voltage amp – 2 x 6watts= 12watts

Total watt requirement – 522 watts, well inside the units maximum of 560 watts. There is rarely more than one player active at any time, so a typical demand would be 392 watts or 70% of the UPS rated wattage.

Hopefully now there is enough information to set you on the right path to getting that protection.

Remember UPS power is not a one off cost. Most supplies use lead acid batteries that deteriorate over time and must be replaced every several years. You do not want your UPS to fail you when you most need it. Many supplies have displays that will show you the state of the batteries and warn you if they are failing. I typically manage 5 years per battery set. I also check the UPS supplies by deliberately turning off the appropriate breakers once every year, a stressful occasion!

Common Home AV/HT/IT UPS Suppliers:

The following UPS suppliers provide tables to assist you with selecting your UPS and have technical departments that can review your needs.

• Cyberpower and some HT UPS options
• APC
• Tripp Lite
• Eaton

For extreme RFI and surge protection, see this post on the Mcintosh MPC500 power controller.