Questions RE UPS for computers

[Boomzilla]

I have a UPS on my computer system. The two printers (one laser, one ink jet) are NOT on UPS - only on surge suppressors. The equipment that IS on UPS includes:

One laptop computer
One desktop computer
A cable modem
A telephone modem
A 12 port Ethernet router
Two external HDDs
A powered USB breakout box
A powered KVM switch

My questions include:

1. How much VA capacity do I need to run this stuff? I don't plan on continuing to use the gear after the power is down, but I do want enough time to shut everything down safely.

2. How often should I replace the UPS to avoid reduced run-time?

3. What brands of UPS are the most reliable?

I've tried to research these questions on Google, and find that there's no particular consensus on any of them. One site recommends nothing but one brand of UPS, another recommends another brand. I know that SOME of you on the lounge work in IT, and probably have experience with multiple brands of UPS boxes. What do you think?

My current boxes are between two and four years old, and I think I'd just like to pick a reasonable interval, and replace them periodically. Since I live in a university area, I can donate my old UPS boxes to the local thrift store that helps battered women, and there will always be students willing to buy the used UPS boxes, since they still work. The only reason that I'm reluctant to just replace batteries is that I worry that the internal surge suppressors' MOVs may be degraded and I'd just as soon replace them also.

Thanks for the feedback.

Boom

[novisnick]

UPC HAS ALWAYS been good to me. The larger the better and these are connected to the PC with programming that does periodic testing and gives you a report as to battery condition, watt calculator and a few more useful reports. I’ve replaced the batteries a few times without regret.
I employ 3 1500 series units throughout the house. One specifically for the modem for when the power goes out. As long as you power the modem your internet will work unless a tree takes down those lines as well. That doesn’t usually happen believe it or not. 

[donh50]

Add up the VA or Watt ratings for everything from the back panels and get a UPS sized with at least 20% margin. It gets tricky since you may have a mix of W and VA... To avoid a bunch of engineering explanations that don't really help just assume VA = W * 1.7 and you'll be in the ballpark. Add up all the VA numbers and get a UPS sized to that. But realize your 800 W computer power supply is likely running at half or less of that most of the time thus 20% margin is reasonable IME. You only need a few minutes to shut things down so extended run capacity is not a big deal. Also, remember your normal 15 A wall outlet can only provide 1800 W max and chances are you are way below that. My guess is something in the 1000 VA range would be plenty. For a single computer or TV with a cable box and maybe DVR I have found 500-750 VA is enough, but I mostly buy 1500 VA models. Those I can swap around the house without really worrying about the load so the extra cost is worth it when a critical one dies. They are about twice the cost of the smaller units, however. But in turn about half the cost of the big 2 kVA models. Prices tend to jump steeply from <1 kVA (<$100 USD) to better sinewave approximation (cleaner output) 1.5 kVA models (~$200 USD). For brief periods you don't need the cleaner output and probably not the higher power.

What wears out in most UPS units is the battery. They can only be charged and discharged so many times (typically sealed lead-acid batteries are used). Expect 2-3 years before you have to replace the batteries.

I used APC for many years but the past few years have been vexed by their reliability and support. Too many failures and replaced batteries only to have something else fail. The third or fourth time, I started trying other brands. That said, we use them extensively at work and they are doing OK there. We do go through a lot of batteries... I replaced batteries in one unit after about three years only to have another fault occur a few months later and had to replace the unit. It was out of warranty and the service price was more than an equivalent new unit. They said it would be cheaper to get a nice new unit so I did - just not from APC. I have been using CyberPower lately. A little cheaper and with cleaner output signal (not a big deal since, like you, they are mainly to give me time to shut things down cleanly). I think my last one was ~$200 USD from Amazon, not on sale as another UPS died and I needed a replacement right now (one of the bigger APCs, with six-month old batteries, grrr). Another well-regarded company is Tripp Lite -- I have used them in the past but not recently, but they worked well for me in commercial installations and at home.

HTH - Don

[RichGuy]

I've had a Belkin 1500VA F6C1500-TW-RK for my computer for many years now, I forget exactly how long but it's been well over 10. The batteries are easily replaceable, I've replaced them numerous times now, they last about 3 years and are easy to find online when it's time to replace them. This has really been a nice power source for my main desktop computer. This model has been discontinued but I do see that used ones sell on ebay. I'd recommend looking for something similar and that has replaceable batteries.



Takes 2 batteries like this, about $35 for the pair to replace

[garbulky]

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanenetly producing square wave power through the battery.

[novisnick]

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanenetly producing square wave power through the battery.

At one time I had my DC-1 connected to one and never noticed a difference when I plugged the same DAC into the wall. Based on that I believe it passes electricity straight through. Only powers the two or three lines when tripped.  

[MusicHead]

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanenetly producing square wave power through the battery.

Yes, and the low cost one usually have a so called "modified square wave" output. That output is generally okay for the switching power supply on PCs and switching power supplies in general. 

Something like this:



The more expensive UPS have an actual sine output. For those interested, someone has built a database with actual output waveform tests of many of the popular models. 

www.hardwareinsights.com/database-of-ups-output-waveforms/

[garbulky]

May 5, 2019 22:01:49 GMT -5 MusicHead said:

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanenetly producing square wave power through the battery.

Yes, and the low cost one usually have a so called "modified square wave" output. That output is generally okay for the switching power supply on PCs and switching power supplies in general. 

Something like this:



The more expensive UPS have an actual sine output. For those interested, someone has built a database with actual output waveform tests of many of the popular models. 

www.hardwareinsights.com/database-of-ups-output-waveforms/

So yes it IS a passthrough with no square wave when the mains power is not off?

[Boomzilla]

I'm currently using an APC Back-Ups 700 purchased in March of 2014. I think I got my money's worth out of that one...

Since it has been adequate for my needs, I'm thinking that I probably need nothing any more powerful. And since the APC brand has served me well, I think I'll also stay with them.

So thank all of you kindly for your feedback - the output waveform database was particularly helpful.

One other stupid question, if I may... Is there any reason not to "daisy chain" UPS boxes? In other words, Box 1 would be connected directly to the wall socket, and box 2 would be plugged into the back-up outlet of box 1. It would seem, in such a case, that if power was lost at the socket, that box 1 would continue to supply power until it failed, at which time box 2 would begin supplying power until its battery was also depleted.

Why do this if I don't really need the battery-operated run time? Because the power conditioning of BOTH boxes would be functional at all times, and in the event of a real surge (lightning strike, etc.), the older box (1) would sacrifice its MOV and hopefully protect the newer box (2) from surge damage.

If this theory is sound, would I accomplish the same thing by putting an inexpensive (and sacrificial) surge suppressor strip in place of Box 1? If so, could I run two (or more) inexpensive surge-suppressors in series upstream of the UPS? This would (theoretically) allow a LOT of joules to be dumped to ground before the surge ever got to the UPS itself. Of course, this also brings up the question of response time of the MOV chips... Would the surge travel through the entire chain before the MOVs had a chance to trigger?

Any EEs on the Lounge?

Thanks - Boomzilla

PS: I found information on MOV degradation HERE.

I also found information on MOV activation speed HERE.

And finally APC recommends not plugging their UPS products into surge strips for two specific reasons:

1. If you have other equipment plugged into the surge strip, the UPS may see low voltage more frequently and trigger spuriously
2. The surge suppressor may interfere with the ground that the UPS needs.

Source for the two above items is HERE.

So to summarize, I think I've answered my own questions - Don't daisy-chain UPS boxes - Don't use a surge-suppressor upstream or downstream of the UPS - Don't expect the MOV in your UPS to protect your equipment from lightning - If you want lightning protection, buy a whole-house lightning arrestor.

[RichGuy]

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanenetly producing square wave power through the battery.

A UPS is great for protecting computer systems and projectors. A UPS is NOT good for plugging in your music and sound system and will normally poorly affect its sound quality, so a UPS is NOT what you want to us for your music or home theater system. But again a UPS is excellent for computers and projectors both which can sometimes suffer from immediate power loss.

[geeqner]

I have been involved in specifying and purchasing UPS Units for "Critical Applications" such as head-ends for Card Access Systems and Network Fire Alarm Command Centers.

As stated earlier - "cheapo" UPS Units provide a modified "Stepped" approximation of the Sine Wave that would be present in your AC source from the Power Utility.
Better ones provide more of a "Pure Sine Wave" Output (or something close to it). For things like Television and Audio - IF you were to use a UPS, these would probably be a better choice, since some of the equipment internally synchronizes to the AC waveform and the circuitry that does this is expecting a "normal" sine wave input.

As for how they work internally - there are (3) Main Types:

BASIC "STAND-BY" UPS = your typical inexpensive "APC Back-UPS".
NORMAL MODE - these units more or less simply "Pass" the AC In from the plug to the Output Outlets with maybe some elementary Surge Supression.

AC FAIL MODE - The Inverter Circuits, which Generate the (normally "Stepped) AC Output from the Batteries are designed for Intermittent use
(designed to only run for a few minutes / a few hours at a time)

BATTERY HEALTH - Most of these hardly do anything to monitor the health of the battery(s) - you will usually find that your batteries are "dead" when
AC fails and your equipment "crashes".

LINE REACTIVE UPS = a Solid "Middle-of-the-Road" UPS - like "APC SMART-UPS" / Tripp-Lite.
NORMAL MODE - these units usually incorporate a Ferro-Resonant Autoformer and more sophisticated AC Correction / Filtering.
They can usually compensate for Line Frequency anomalies and brown-out protection.
So, even when they are in stand-by mode - they are "conditioning" the AC Power that is being fed to the protected equipment.

AC FAIL MODE - The Inverter Circuits, which Generate the AC Output from the Batteries are usually considerably more robust, but are
still designed for Intermittent use (designed for a few hours at a time)

BATTERY HEALTH - Most of these usually do a better job of monitoring the health of the batteries.
They will usually tell you about / have utilities to allow you to see the health / charge status of the Batteries.
These will usually give you some sort of Alert or Alarm if your batteries deteriorate to a point where they will not work properly.

DOUBLE-CONVERSION UPS = (As the Line-Reactive types become better, these are becoming less common) - Think Large Data Center:
These units CONSTANTLY RUN via their internal Inverter Circuits.
Because of this - the Inverter Circuits are designed for CONTINUOUS DUTY (ALWAYS Running) and these circuits are ROBUST -
Designed to run under "worst-case" scenarios. 

They are usually intended to provide Carry-Over between Primary AC and a Generator for Critical Loads (Life Safety / Emergency Response, etc.)

NORMAL MODE - these units Generate AC Waveform from the Inverter Circuits (bypassing the batteries while maintaining charge)

AC FAIL MODE - Essentially the same as "Normal Mode" - except the Inverters are getting their power from the Batteries

BATTERY HEALTH - Usually about the same as a high-quality Line-Reactive

UPS BATTERIES:
Most UPS Units use "Immobilized-Electrolyte Lead-Acid" type batteies - more commonly known as "Gel-Cells".
Such batteries under good temperature control conditions will usually last around 4 to 5 years.
Testing them with a Volt Meter only tells you about HALF (or less) of the story
(A cell that reads "good" Voltage can still "poop-out" when subjected to a load.)
People who maintain Fire Alarm Systems have "Automatic Load Testers" that actually read-out the Amp-Hour Capacity of 6 and 12-Volt Cells.
I replace the batteries in my UPS every 5 years - whether they say that they need it or not

[donh50]

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanently producing square wave power through the battery.

I'll try to quickly answer this and a couple of other questions. UPS units are not my day job but I use them and have researched them a bit. I am an EE if that matters but power electronics are not my area of expertise by a long shot.

There are several types of UPS units falling generally into "off-line" and "on-line" types. The off-line types charge the battery constantly but only switch to power the outputs during a power outage. That is the vast majority of consumer units sold.

On-line units provide power from their internal circuits all the time. The advantage is no switch-over time, which may be important in some applications. They tend to be much more expensive since the circuits are always powering the load and must handle continuous duty.

Similarly, there are a range of units with different output purity. The simplest use a pulse train bearing little resemblance to a sine wave. Better units add filtering to smooth the output, then go to adding additional steps to provide a smoother signal. Think of a DAC going from 3 steps to five or more. Some add resonant transformers and extensive filtering to provide a "better than wall" output. Price goes up commensurately. A "pure sine" UPS unit is typically 2x or more the price of a basic stepped-sine off-line unit. Examples would be to compare APC's BackUps to their SmartUPS line, then on up to pricier high-end professional units.

All the UPS I have seen incorporate some filtering and spike protection. Simple MOVs such as found in cheap power strips do have finite lifetime and should be replaced after a major surge. Of course, you generally do not know if there has been a large voltage spike unless there has been a lightening strike nearby, so when to replace is an unanswerable question without test equipment. Better units use other types of spike suppression and/or high-power "resettable" MOVs with longer lifetime and lower let-through voltage (most MOVs will let through around 2-3 kV before they clamp). Their internal filtering makes external filtering redundant and potentially harmful since it can reduce current flow and such.

I have whole-house lightening and surge protection (two separate units). Virtually nothing will protect you from a direct lightening hit; it may not even come through the incoming service, and a bolt that has traveled a mile through the air is unlikely to be blocked by a short spark gap to ground. Many are installed without adequate ground wires, but even with heavy ground leakage from a direct hit is probably going to cause damage. That said, a bolt hit a tree about 50 feet from our house and perhaps 50 yards from our neighbor's house. We had no damage; they had several damaged components (TV, fridge, etc.) They added protection after that; better late than never.

Daisy-chaining is never recommended; APC has a good write-up on their website. There is no real benefit and can cause the two UPS units to cycle on and off as the first begins to die, leading to some nasty power glitches that can harm other components. Don't ask how I know this. I was not always an EE.

For simply powering the system long enough to shut it off most any UPS will do. If you actually expect to run it off the UPS then you will need a bigger UPS and probably one with a purer sine-wave output. I have one SmartUPS in the house to run my aquarium since motors tend to be more sensitive to the high distortion of a simple pulsed output (they get hot). Most components have an internal power supply that will reject incoming power noise. I do not hear noise in my system when running on the CyberPower "sinewave" UPS (the $200 model, not the $80 model). For several thousand dollars worth of components a couple hundred dollars for the UPS is worth it to me, mainly because my area has fairly frequent power glitches and I want to ride them out until I can turn stuff off or our generator kicks in.

HTH - Don

[KeithL]

Before deciding what UPS to buy to go with a computer you should take a good look at what you actually want it to do - and when.

For example, if you simply want a UPS that will prevent your computer from resetting if the power flickers, then one that will power the computer for five minutes is fine.

Likewise, if you always use your computer while you're sitting in front of it, then that sort is fine.

However, if you routinely leave long file copy operations running overnight, or long video or graphics rendering operations going, then you probably want one with a lot more capacity.

Another thing to consider is whether you're using your UPS for "protection" or "continuity".

If you want to be able to work, and not see a flicker, when the power wavers, then you need to put all of your equipment on the UPS.

And, if your area is subject to power surges, which may damage equipment, then you want everything plugged into something that will protect them.

But, if you're only worried about data problems, and not about damage from surges, then you need to have your computer, and your drives, on the UPS, but the monitor doesn't have to be.

(Note that many larger units will provide both high capacity outlets that have only surge protection and "protected" outlets powered by their UPS circuitry.)

It's also worth noting that, if you do really serious stuff, or run servers, there are more intelligent solutions - that cost more and require more effort to configure.

For example, most large server systems that aren't running critical applications have a UPS that can run the server for some number of minutes.

However, since many servers can be damaged by "pulling the plug", the sort of UPS used for server systems usually notifies the server when the battery is low, so the server can perform an orderly shutdown.

It's also worth noting that the needs of computers are somewhat different than those of audio equipment.

(Computers need "continuous steady" power - but most don't require power that is especially "clean" - which is why low level line noise isn't a major consideration for many computer UPS devices.)

[KeithL]

As donh50 said, MOVs have a finite life expectancy, and so actually "wear out" after stopping repeated surges.

(I'm personally a big fan of series-mode surge suppressors - which don't wear out.)

However, many units with surge suppressors actually feature some sort of indicator that tells you when they should be replaced (how the warnings work on various units, and how well, is another question).

Another thing worth noting is that large audio amplifiers draw a significant amount of current... and often draw a significant current surge, far above what they use on average, when first turned on.

Even most units that have "inrush limiting", like ours, draw more current for a few seconds when they start up than they do in normal operation.

While devices like circuit breakers and slow-blow fuses are designed to allow this, some power filters are not, and may have problems.

(Unfortunately, the fancier and more expensive type, which regenerate the power waveform, are more likely to misbehave if you actually ask them to deliver more power than they are capable of.)

In short, if the device you purchase has specific recommendations, or certain outlets which are rated for "high current", you should always make sure to use those outlets for amplifiers and powered subs.

It's also worth remembering that, as with a laptop computer, or any other battery-operated device, UPS batteries DO eventually wear out and need to be replaced.

In general, you will receive some sort of warning when the battery is failing... although, with some units, the time they can remain alive without power will become significantly shorter before the battery fully dies.

(For that reason, if you're "deadly serious", you may want to consider replacing the battery on a schedule - like when you replace all the batteries in your emergency lights.)

(Some small low-cost UPS units are sealed... and you simply replace the whole unit when the batteries fail.) 

May 6, 2019 9:19:35 GMT -5 donh50 said:

May 5, 2019 21:44:13 GMT -5 garbulky said:

Does a UPS only produce power from its battery during loss of power? As in - is it in passthrough mode for house power the rest of the time? I heard that most UPS's produce square wave power and though I'm fine with it for short emergency power; I'd rather it not be on permanently producing square wave power through the battery.

I'll try to quickly answer this and a couple of other questions. UPS units are not my day job but I use them and have researched them a bit. I am an EE if that matters but power electronics are not my area of expertise by a long shot.

There are several types of UPS units falling generally into "off-line" and "on-line" types. The off-line types charge the battery constantly but only switch to power the outputs during a power outage. That is the vast majority of consumer units sold.

On-line units provide power from their internal circuits all the time. The advantage is no switch-over time, which may be important in some applications. They tend to be much more expensive since the circuits are always powering the load and must handle continuous duty.

Similarly, there are a range of units with different output purity. The simplest use a pulse train bearing little resemblance to a sine wave. Better units add filtering to smooth the output, then go to adding additional steps to provide a smoother signal. Think of a DAC going from 3 steps to five or more. Some add resonant transformers and extensive filtering to provide a "better than wall" output. Price goes up commensurately. A "pure sine" UPS unit is typically 2x or more the price of a basic stepped-sine off-line unit. Examples would be to compare APC's BackUps to their SmartUPS line, then on up to pricier high-end professional units.

All the UPS I have seen incorporate some filtering and spike protection. Simple MOVs such as found in cheap power strips do have finite lifetime and should be replaced after a major surge. Of course, you generally do not know if there has been a large voltage spike unless there has been a lightening strike nearby, so when to replace is an unanswerable question without test equipment. Better units use other types of spike suppression and/or high-power "resettable" MOVs with longer lifetime and lower let-through voltage (most MOVs will let through around 2-3 kV before they clamp). Their internal filtering makes external filtering redundant and potentially harmful since it can reduce current flow and such.

I have whole-house lightening and surge protection (two separate units). Virtually nothing will protect you from a direct lightening hit; it may not even come through the incoming service, and a bolt that has traveled a mile through the air is unlikely to be blocked by a short spark gap to ground. Many are installed without adequate ground wires, but even with heavy ground leakage from a direct hit is probably going to cause damage. That said, a bolt hit a tree about 50 feet from our house and perhaps 50 yards from our neighbor's house. We had no damage; they had several damaged components (TV, fridge, etc.) They added protection after that; better late than never.

Daisy-chaining is never recommended; APC has a good write-up on their website. There is no real benefit and can cause the two UPS units to cycle on and off as the first begins to die, leading to some nasty power glitches that can harm other components. Don't ask how I know this. I was not always an EE.

For simply powering the system long enough to shut it off most any UPS will do. If you actually expect to run it off the UPS then you will need a bigger UPS and probably one with a purer sine-wave output. I have one SmartUPS in the house to run my aquarium since motors tend to be more sensitive to the high distortion of a simple pulsed output (they get hot). Most components have an internal power supply that will reject incoming power noise. I do not hear noise in my system when running on the CyberPower "sinewave" UPS (the $200 model, not the $80 model). For several thousand dollars worth of components a couple hundred dollars for the UPS is worth it to me, mainly because my area has fairly frequent power glitches and I want to ride them out until I can turn stuff off or our generator kicks in.

HTH - Don

[vcautokid]

May 5, 2019 11:20:39 GMT -5 novisnick said:

UPC HAS ALWAYS been good to me. The larger the better and these are connected to the PC with programming that does periodic testing and gives you a report as to battery condition, watt calculator and a few more useful reports. I’ve replaced the batteries a few times without regret.
I employ 3 1500 series units throughout the house. One specifically for the modem for when the power goes out. As long as you power the modem your internet will work unless a tree takes down those lines as well. That doesn’t usually happen believe it or not. 

I think you meant APC. I have trusted APC for over 25 years and they just do as they promise. Carefully assess your total computer devices draw and double the UPS as a minimum. More headroom, more time to properly close and save your work. We have to be careful on my Chinese home boys out there making Cheap UPSs'. Avoid at all costs. We are talking about lethal voltage and Current on top of your computer safety. Be smart! Be safe!
Good stuff is never cheap, and cheap stuff is never good.

P.s. I don't need to repeat all the awesome posts above mine. Just I have personally experienced a failure of a UPS at work, and it was Chinese-sium to the extreme. Just stupid that.

[garbulky]

May 6, 2019 9:19:35 GMT -5 donh50 said:

May 5, 2019 21:44:13 GMT -5 garbulky said:

UPS

THanks for the good write up Don.

So is that a yes or a no? (For cheap UPS's - is it always a square wave or is it only during power outages and the rest of the time it's a passthrough fro mains?)

[geeqner]

The square-wave / stepped square wave is usually ONLY when it's running on the Inverter Circuits.

Under "Normal" (AC is OK) - you get whatever AC you got

[novisnick]

May 6, 2019 10:13:08 GMT -5 vcautokid said:

May 5, 2019 11:20:39 GMT -5 novisnick said:

UPC HAS ALWAYS been good to me. The larger the better and these are connected to the PC with programming that does periodic testing and gives you a report as to battery condition, watt calculator and a few more useful reports. I’ve replaced the batteries a few times without regret.
I employ 3 1500 series units throughout the house. One specifically for the modem for when the power goes out. As long as you power the modem your internet will work unless a tree takes down those lines as well. That doesn’t usually happen believe it or not. 

I think you meant APC. I have trusted APC for over 25 years and they just do as they promise. Carefully assess your total computer devices draw and double the UPS as a minimum. More headroom, more time to properly close and save your work. We have to be careful on my Chinese home boys out there making Cheap UPSs'. Avoid at all costs. We are talking about lethal voltage and Current on top of your computer safety. Be smart! Be safe!
Good stuff is never cheap, and cheap stuff is never good.

P.s. I don't need to repeat all the awesome posts above mine. Just I have personally experienced a failure of a UPS at work, and it was Chinese-sium to the extreme. Just stupid that.

My Bad! 😲 You are correct my friend, APC is my unit of choice!  😁

[donh50]

May 6, 2019 11:00:07 GMT -5 garbulky said:

THanks for the good write up Don.

So is that a yes or a no? (For cheap UPS's - is it always a square wave or is it only during power outages and the rest of the time it's a passthrough fro mains?)

You're welcome.

Only during power outages; the rest of the time, the AC from the wall outlet is just passed through (albeit with a bit of filtering). No problem if the goal is to just get the stuff turned off, and for computer stuff not usually (like "never") an issue even for longer run times. That is what makes them great for this application -- doesn't affect normal operation, covers your gear when the power blips, cheap protection.

Mine keep my office PC, router, and cable modem up so if we lose power I still get internet. In theory, anyway; a lot of the time we lose power the cable is also out so we lose it all anyway. One reason we keep a landline and have not gone to IP phones, and the house is in a cell hole so cell phones are not reliable in a power outage (we have an IP repeater for the house -- when the 'net is up!)

[Boomzilla]

After adding up my wattage requirements and adding a generous safety factor, I figure that I could draw up to 275 watts. The 1,000 VA backups should give me over 13 minutes of battery run time (calculated by APC). So I think I'll opt for the 1000VA, APC Back-UPS Pro (BR1000MS) ($148.99 on Amazon) for my job. This is less than I'd planned to spend, but seems more than adequate, so the extra $50 in my budget can be applied to something else.

Thanks for the feedback.

Boom