Hello, I made a research on google about 500 watt online and serial (not pararell) UPS and couldn't find anything conclusive.

I decided that I want to buy that kind of UPS but there's no such info at stores and manufacture's website. Is there any offline or online pararell UPS avaiable yet?

Also, my computer needs 500 watt (at max consumption), so do I must buy a 500 watt model or just calculate the X kVA needed?

Appreciate any help.

Skuzye

Hello skuzye

You are right to be cautious. UPSes vary greatly.

The best are what are called "online" here in India. They feed the mains (220 V 50 Hz here) directly when the mains is within voltage and frequency limits. When the mains is cut or otherwise goes outside limits they very quickly switch over to taking power from the batteries, inverting (converting) battery energy to mains voltage and frequency. The issue is that "very quickly", with the best ones doing it quickly enough to keep even the poorest "power brick" or "wall wart" type power units going. This is important for ADSL modems which typically take ~2 minutes to get back on line. If the ISP provides a different IP address by DHCP that means losing connections to many servers (it depends on the server -- a few keep the connection despite the IP address change). Computer PSUs store some energy so are more tolerant of a "slow" online UPS giving a short break in the mains supply. It varies between PSUs. Some online UPSes keep the mains supply going better at higher loads -- counter-intuitive!

Less good (not "online") UPSes always take energy from the batteries and invert it to mains. The downside is that there is an energy loss because the mains has to be converted to battery voltage in the charging circuit. Say ~10% loss.

We have recently taken delivery of an experimental device which will sit on the mains side of our "slow" online UPSes and hopefully kick in and keep the supply going during the short break.

Regards the VA you need, inverters are tolerant of high overloads for short times. The limiting factor is heat build up in the transformer so it takes a while.

Ideally you will measure what your computer uses. Usage varies widely but is mostly well below peak demand. If your voltage is 120 the USA-made Kill-a-Watt is good and great value for measuring actual power consumption.

Here in India we have a lot of UPS models to choose from but very few informative technical specifications. APC are good but expensive, perhaps manufactured in USA where APC are based. We do not have any APC UPSes; I know this from discussions.

None of the UPSes I have experience of have serial or parallel connections.

Some UPSes (the very bad ones) do not provide a true sine wave. They are described in various creative ways but are no use for modern electronics.

Best

Charles

From what I've heard, the serial connection would be like this:

and pararell would be:

So with serial you always get a continuous power source independent of variations in eletricity supplied by the power company. Also, you wouldn't have any delay.

The trouble is finding whether a UPS is or not pararell or serial or even whether it is online or offline.

So, even if they say it is for 350w e.g. I can use it with my 500w power supply. Is that right?

Skuzye

Ah! That's what you mean by serial and parallel! I was thinking you meant what sort of cable between computer and UPS; some UPSes had/have serial connections, presumably so software running on the computer could display things like battery state-of-charge and, more importantly, could shut the computer down when the UPS was going to cut power supply because taking more charge from the battery would damage the battery.

When you say "parallel UPS", it is the same as when I say "on-line UPS".

If your loacal suppliers don't provide that information then, yes, that's a trouble! Does it matter to you if the UPS is serial or parallel (online) as long as it works for you? I am "green" and work with a "green" NGO so wasting 10% of the power used matters to us -- especially if it is solar-generated. If your computer works on a 500 W supply and you are not using it intensively (as a hard-working file-server or backup-server, games with full-on graphics ...) then it probably doesn't use more that 250 W maximum, most of the time. 10% of 250 W is 25 W, not huge for the bank balance or the environment ... ? Our rule-of-thumb whean calculating power requirements is that the average office computer pulls 100-150 W; most of them are fitted with at least 350 W power supplies.

Are your local suppliers willing to demonstrate the UPS, ideally at your place? That would be one way to find out if it does the job. It won't tell you if it is serial or parallel but you can get some idea how much energy it is consuming from its heat output.

A 500 W power supply should (TM) be capable of delivering 500 W, when it will be draw ~10% more than that, 550 W. But your computer is unlikely to be using that much; the PSU draws only what it needs from the mains. If your computer is taking 200 W from the PSU then the PSU is taking ~220 W from the mains. Like I wrote before, the best is if you can measure what it is actually taking. A simple meter, measuring AC Amps, is "good enough" for what you are trying to do now.

Ok, thank you. It helped a lot. I'll try to hit a store and try making them testing it for me on my own computer.

Skuzye

I know a lot of people manage with the small CS, LS, RS, versions of UPSs but we've had some negative experiences with those. Most of the time they work fine and I would recommend it for a non critical application. However when there is a generator involved, most of the small 350-500VA APC UPSs aren't able to provide power. Also, if there is a sag or spike they're not able to regulate it. Again, for a home machine this is tolerable but if you need reliability it is not. Also, the budget is obviously an issue. If you get the higher end UPSs you will pay a bit more, so the application has to be worth it. Personally, I would recommend going with a minimum of a Smart UPS 750 Those are the line interactive type that output a sine wave, avr boost/drop and power filtering. They are also generator compatible. Personally, I would hunt around for a good deal on an used or refurbished UPS rather than spend money on a crappier new UPS. Of course the batteries need to always be brand new.


George

'True' sinewaves are very hard for inverters to generate and modified sinewave is safe and effective for all electronics.

From http://www.messaggeri.it/xalimentatori.htm#dctoac "The three most common outputs for inverters are square wave, modified sinewave (sometimes called a quasi sinewave), and sinewave outputs. Most devices with variable speeds such as electric drills, or devices with chargers such as cordless drills or screwdrivers, can behave irrationally when operating with modified sine or square wave inverters. Small wall based chargers (called wall warts) can have overheating problems with modified sine or square wave inputs. Some computers and stereo equipment use switching power supplies that utilize SCR’s and Triacs as well. These pieces of equipment may experience the same troubles with non-sinewave power. True sine wave output allows connected loads and equipment to operate the same as they would from utility supplied power. Unfortunately the true sine wave output inverters are more expensive than the ones which use square wave or modified sinewave".

From Northern Arizona Wind and Sun "Square wave inverters are usually only suitable for running some type of electrical tools and motors and incandescent lights. They are pretty rare nowadays, some of the old 1970's Triplite and a few others, and some old military surplus is about the only place you find it now.

Quasi-sine (modified sine, modified square) wave inverters have more circuitry beyond the simple switching, and put out a wave that looks like a stepped square wave - it is suitable for most standard appliances, but may not work well with some electronics or appliances that electronic heat or speed control, or uses the AC for clocks or a timer.

What May Not Run: Appliances that use electronics to control temperature or timers may have problems with modified sine waves. This includes anything - tool or appliance - that is variable speed, bread makers, some microwaves, some washers and dryers that use electronic timing for cycling. Most computers, TV's and similar items will have no problem. Anything with a motor will use about 20% more power with a modified sine wave than with a true sine wave.

Also, some of the chargers used for battery operated tools (such as Makita) may not shut off when the battery is charged, and should not be used with anything but sine wave inverters unless you are sure they will work. Sine wave inverters put out a wave that is the same as you get from the power company - in fact, it is often better and cleaner. Sine wave inverters can run anything, but are also more expensive than other types. The quality of the "modified sine" (actually modified square wave), Quasi-sine wave, etc. can also vary quite a bit between inverters, and may also vary somewhat with the load. The very bottom end put out a wave that is nothing but a square wave, and is too "dirty" for all but universal motor driven tools, coffee makers, toasters, and other appliances that have only a heating element.".

So a computer, especially one with a very goog PSU that does not use Silicon Controlled Recitifiers (SCRs) may be OK, even more efficient with a less-than-pure sine wave. It is for this reason that many specialist data-centre UPSes are less-than-pure sine wave -- they are relatively cheap and work -- but if you want the flexibility to power the standard SOHO devices using wall-warts (printer, switch, ADSL modem etc.) or maybe an audio-amplifier or HTPC then pure sine wave is the way to go.

All the usual devices are designed to work with mains electricity which delivers a (more-or-less!) pure sine wave.

Have you personally tried the modified sinewave?
i had my pc and chargers pluged into a modified sinewave inverter when our power when out a couple days ago, guess what:no overheating worked perfectly.

Yes, that's what we started with. Our grid power is unreliable and we have what may be the largest concentration of photovoltaic panels on the subcontinent, many more than 10 years old, and there are several local UPS and inverter manufacturers so we have accumulated a lot of experience. Second hand inverters that are not "pure" sine wave have almost no value; it's hard to give them away. Sure, some equipment (including perhaps most computers) runs just fine on them but an increasing amount doesn't.

Many Mac's do not function well with modified sinewave products. When the UPS goes to battery the Mac will either shut down, start emitting a buzzing noise or restart. The Mac power supplies just don't do well with those unit.


George

I absolutely agree. The better quality stuff is always the sinewave outputting ones. The square and simulated ones just aren't as good.

If you can afford the difference, why not buy something that's good?

we have eight UPS devices in our house protecting our computers
these are the Australian brand we use
http://www.powershield.com.au/
they are very good and many times keep our gear running when there are power cuts, which are not uncommon here.

The 650 VA will power a normal computer for a few minutes - long enough to shut down normally, while the 1200 & 1600 will power two computers long enough to shut down. The only time we turn them off is when there are nearby thunderstorms and then we unplug them as well.

hope this helps
floppy