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-   -   The "Uninterrupting" Uninterruptible Power Supply (UPS) Guide (https://www.overclock.net/forum/31-power-supplies/1305395-uninterrupting-uninterruptible-power-supply-ups-guide.html)

tompsonn 09-13-2012 04:37 AM


Following what I call from last night as "UPS night" (at least for GMT+8!) due to a more-than-usual spark of questions about UPSes, I am going to take the time to quickly describe the functionality of a UPS and their various types and some certain factors to consider for yourself when purchasing a UPS - but in a way that should be easier to understand than some convoluted resources you may find by hunting around the Internet.


What is this Uninterruptible Power Supply (UPS) thing, anyway?

Put simply a UPS is device that, when functioning correctly, helps to ensure that power supply to your components is not disturbed. Of course there is more to it than that, right? Indeed there is. A UPS does this by supplying the load using batteries (or a series of batteries). The load could be desktop computers, servers, audio and video equipment, or even peripherals. The primary advantage of a UPS is that it provides power to a computer so that it can stay running long enough for the operating system that is running on it to shutdown cleanly. Contrast this to a sudden loss of power where unsaved data will be lost and things may possibly get corrupted! (and even hard disk heads can crash, although that is rare now).

But many UPSes can also function as a power conditioner - this means that some are capable of filtering noise in the power line and also correcting for brownouts (under-voltage) or power surges (over-voltage). If you know your AC supply is prone to these issues (including frequent blackouts), a UPS would be a wise investment to protect your expensive technology!

My personal recommendation is that at the very least all high-end and relatively expensive equipment should be behind the protection of a quality UPS unit. But how will I know what type and size of UPS to buy? Like computer power supplies, there are so many and I bet it has something to do with wattage, right? It sure does, but that is not all. Please, continue reading...


So before I decide to get a UPS, how exactly do they work?

While there are possibly thousands of UPSes on the market, they are generally classified into three different sub types. These sub types describe the type of technology that the UPS uses to protect your equipment and how it functions to switch to an external source of power (as mentioned, usually one or more batteries). I will briefly list and explain these three types of UPS below. Note that there are other more commercially oriented types of UPS that I will not describe here as they are beyond the scope of this guide.

Standby UPS

This is the most basic type of UPS system. More often than not, power starts by being fed through various circuits that control surge and line-noise filtering. A secondary component, a battery charger, ensures that the internal battery is kept fully charged for when it is ready to be used (hence "standby"). In this very simple system, when a mains/AC power failure, brownout or over-voltage is detected by the system redirects the power output through an inverter which engages the battery and converts the DC output from the internal battery into AC output that your equipment requires. Sometimes over-voltage scenarios simply send the extra current out to the ground via the ground pin on the plug in the wall.

Note: The output of a standby UPS is almost always a simulated sine-wave as this makes them cheaper to produce. See the end of this guide for information on why a simulated sine-wave may not be suited to your equipment.

Power flow diagram of a Standby UPS

Image courtesy of Wikipedia page at http://en.wikipedia.org/wiki/Uninterruptible_power_supply

Line-interactive UPS

This type of UPS is very similar to that of a standby UPS system. These systems are often advertised as having automatic voltage regulation (or AVR). Like a standby UPS, power starts by being fed through various circuits that control surge and line-noise filtering. After this however, the line-interactive UPS adds an additional component called a multi-tap auto transformer (which can automatically adjust/regulate voltage usually within a range of 90-140V. In different countries such as Australia where mains supply is 240V, this range is usually different, but the principle is the same). The advantage of this type of UPS is that in most cases during a brownout or over-voltage surge, the battery reserve does not need to be drained in order to compensate for the voltage fluctuation.

In the meantime, just like a standby UPS, a battery charger ensures that the internal battery is kept fully charged for when it is ready to be used. With this UPS type, when a brownout or over-voltage occurs the UPS will select different "taps" on the auto transformer which adjusts the voltage output (lower for over-voltage and higher for a brownout). If the brownout or over-voltage does not fall within the range that the auto transformer can automatically adjust, the UPS will revert to that of a standby system - either engaging battery supply, or directing current to the ground.

It is this tap selection by the auto transformer that causes line-interactive UPSes to make a distinct clicking sound. A main/AC failure functions identical to that of a standby UPS. Most consumer UPS systems do have line-interactive technology as it is rather cheap to implement.

Note: The output of a standby UPS is almost always a simulated sine-wave as this makes them cheaper to produce (although I am commonly seeing even line-interactive UPS systems with pure sine-wave output). See the end of this guide for information on why a simulated sine-wave may not be suited to your equipment.

Power flow diagram of a Line-interactive UPS

Image courtesy of Wikipedia page at http://en.wikipedia.org/wiki/Uninterruptible_power_supply

Online and double conversion UPS

Although once reserved for very high power requirement installations (more than 5-10kW), the online and double conversion UPS is available (albeit with a hefty price tag) today as a consumer product if desired. At the consumer level it is also the highest level of power protection available. Unlike a standby UPS, the inverter in an online UPS is always engaged (online) 100% of the time. Power enters the system and is then componentized, after which the inverter perfectly reproduces/reconstructs it at the other end. Due to this action, the line is completely eliminated of any noise and brownouts and over-voltage scenarios are automatically compensated. All online UPS systems produce true sine-wave output.

An online and double conversion UPS works very similarly to the line-interactive standby UPS type (basic technology of auto transformers are used), although they are much more expensive because the quality of various components such as inverter and battery charger are much higher due to the fact they run continuously (i.e online). In an online UPS, the battery unit(s) are always connected to the inverter and this means that absolutely no power switches are necessary - a requirement for very sensitive devices which cannot handle even microseconds of a switch like in standby systems.

Power flow diagram of an Online UPS

Image courtesy of Circuits Today at http://www.circuitstoday.com/ups-uninterruptable-power-supplies


Now I know how they tick, what UPS should I get?

Here comes the fun part where we get to decide what UPS will be right for a certain scenario. In general we must consider three factors:
  1. The amount of power that planned power-protected equipment require.
  2. The amount of backup time desired (e.g. just enough to shutdown, or enough to finish working on that complicated spreadsheet).
  3. Line-interactivity (automatic voltage regulation) and simulated sine-wave vs. pure sine-wave.

How much power will my devices require? And what the hell is the difference between VA rating and wattage rating?

There are many ways to calculate how much power you require with all of your devices. Some methods include adding the manufacturer wattage consumption (if specified) of each device, estimating, or using a device such as a kill-a-watt to measure power draw from the wall. Because this is a relatively simple task to accomplish I won't discuss it in this thread, and will assume you have some sort of indication of how much power in watts you will require. So if all of my devices in total require approximately 400W, how big of a UPS should I purchase?

At first you might be confused because most UPS systems advertise their capacity in both VA (vole-amperes) and watts and these two values are always different from each other. But hang on a minute, isn't a volt-ampere dimensionally equivalent to the watt? Why, yes it is, however in UPS power ratings a different convention is used. Because it is recommended that you should not use more than 60% of a UPS's capacity (in VA), the wattage rating of a UPS is actually roughly 60% of the VA rating. For example a 2000VA UPS will actually be rated to supply 1200W (2000 * 0.6 = 1200).

Now that we have that cleared up, we can simply just focus on the wattage rating advertised by the UPS. In the rare scenario only the VA is mentioned, we can easily work it out from the explanation above. Back to our example - we have a 400W load that we would like to put behind a UPS. At first you may think to get a 400W (usually 750VA, a little more than 60%) - but this wouldn't be recommended at all. It is always wise to overshoot by about 20-25% and so instead we should go for about 500W (25% overshoot of 400W), or approximately 850VA.

A second method (and my preferred method) is to only use the VA rating. Because the 60% rule is not a standard but only a convention, some UPS vendors do not follow it completely, and instead their wattage ratings may be more than 60% of the VA rating. In this method we use 60% as an absolute minimum and convert our required wattage to "UPS VA" by adding 60%. In our example, 400W becomes 640VA (400 * 1.6 = 640). Now of course we don't just go out and get a 640VA UPS, so we overshoot this by 20-25% too and we are left with a recommendation of about 800VA (or 480W) which is within our 20-25% oversight.

Note: If some of your devices specify their power consumption in amps, simply multiply this by the voltage supply of your mains (for example 240V in Australia or 120V in the US).

I would like longer backup time, how do I achieve that?

Many line-interactive UPSes can have the facility for capacity expansion (i.e. adding additional batteries or replacing the battery for a larger one).
Another way to achieve higher backup time is to purchase a UPS with a higher VA rating (see above for more information on VA and wattage in UPS specifications).

An online and double conversion UPS can typically provide much more backup time than a normal standby or line-interactive UPS - but they are expensive.

Do I need features like line-interactive (AVR), data line protection and what about outlets?

On smaller and thus cheaper UPS systems it is common to only one or two outlets and sometimes only one of them is actually actively providing backup power protection, while the second outlet only performs surge protection (this means that if the power goes out, the components on the second outlet will not continue to run). For the record, it is OK to connect a power strip/power board to a UPS outlet however be mindful that you do not overload the UPS - most good quality UPS systems will shut down and jump up and down (i.e. beep) like a Jack Russell terrier if you do, however!

The more expensive UPS systems that have higher VA ratings often supply more than two outlets and they are almost always all backup-power supplied.

Automatic voltage regulation is present in line-interactive and online UPS systems and is recommended for all provisions. See above for more information on line-interactive and AVR technology. Data line protection is an optional feature of some systems that protects things like TV lines (coax), Ethernet and DSL/phone line lines from surges. Depending on application this feature may or may not be necessary and is not a critical requirement.

One last thing - what about true sine-wave output versus simulated sine-wave output?

Whether you need a true sine-wave UPS or not is mainly dependent on the power supply in your computer. Many power supplies (or rather, any decent modern power supply) utilize a feature called active power factor correction, or active PFC (the intrinsic of which is beyond the scope of this guide). Put simply, power supplies that employ active PFC can drop the load and reboot the system when a simulated sine-wave UPS system is used. Another issue with simulated sine-wave with active PFC power supplies is that the PSU efficiency will drop tremendously.

Whether or not your power supply uses active PFC should be marked on the manufacturer specification sheet or website. In these scenarios I would recommend to purchase a true sine-wave UPS - in line-interactive models they are generally not much more expensive. Where possible I personally recommend the use of true sine-wave output UPS units - I have seen a few consumer line-interactive units with this capability.


Bonus reading

"The Different Types of UPS Systems" - http://m.softchoice.com/files/pdf/brands/apc/SADE-5TNM3Y_R6_EN.pdf (Thanks Duckie!)
Real-world UPS set up (Thanks to axipher!)

I hope you have found this content useful. Please post for additions or any addendum.

KhaoticKomputing 09-13-2012 04:38 AM

Nice write up, + rep.

tompsonn 09-13-2012 04:42 AM

Quote:
Originally Posted by KhaoticKomputing View Post

Nice write up, + rep.

Thanks! smile.gif

axipher 09-13-2012 05:23 AM

As an electrical engineer, I approve this message thumb.gif

 

 

 

But seriously, great article man.  Of course with anything there is always more to add, but as usual (from al the help you've provided me), you provide all the needed information.

 

Only things that I think people might be interested in as additional sections:

  • Data protection and how it works (RJ-11, RJ-25, COAX, Serial, etc.)
  • Software interaction with UPS (USB, Network, Serial, etc.)
  • Extra Features (Back-up powered USB ports)
  • Power/Time curves for common sizes (500, 750, 1000, 1500 VA or similar)

 

 

 

As a long time UPS user, I highly recommend everyone use them.  At my new place, I got lucky and my room mate had a nice beefy UPS so we are able to have both our servers on a rather large consumer UPS, all our network equipment and a network printer on another UPS, and a third smaller one for mini-appliances in a real emergency or simply powering a lamp to provide light at night.


tompsonn 09-13-2012 05:40 AM

Quote:
Originally Posted by axipher View Post

As an electrical engineer, I approve this message thumb.gif

Phew! biggrin.gif
(I totally forgot!)

DuckieHo 09-13-2012 05:54 AM

Good whitepaper by APC about additional UPS types: http://m.softchoice.com/files/pdf/brands/apc/SADE-5TNM3Y_R6_EN.pdf


Also, you might want to note any decent modern PC PSU utilizes active PFC.


I wish supercapacitors where avaliable large enough for UPSes..... I hate spending $100 on a unit and having to spend over 60% of it costs every few years for battery replacement.

tompsonn 09-13-2012 05:57 AM

Quote:
Originally Posted by DuckieHo View Post

Good whitepaper by APC about additional UPS types: http://m.softchoice.com/files/pdf/brands/apc/SADE-5TNM3Y_R6_EN.pdf
Also, you might want to note any decent modern PC PSU utilizes active PFC.
I wish supercapacitors where avaliable large enough for UPSes..... I hate spending $100 on a unit and having to spend over 60% of it costs every few years for battery replacement.

Added smile.gif

Original Sin 09-13-2012 08:07 AM

Excellent guide... stickie applied. smile.gif



ps. you might wanna' add a few lines about Delta Conversion units too. wink.gif

tompsonn 09-13-2012 08:12 AM

Quote:
Originally Posted by Original Sin View Post

Excellent guide... stickie applied. smile.gif
ps. you might wanna' add a few lines about Delta Conversion units too. wink.gif

wheee.gif

Duckie's PDF link in Bonus reading has some stuff on delta units I think... smile.gif

Thanks!

nleksan 09-13-2012 08:14 PM

Awesome, thanks so much! +rep


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