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Matching Battery Backup "Waveshape" to the Right Equipment? 37

Posted by Cliff
from the if-everthing-has-to-have-a-UPS dept.
Controlio asks: "I see all sorts of battery backups out there, from as low as $100 to the multi-$1000 range. One difference I've noted in battery backups is the 'waveshape' it outputs (stepped sine wave, trapezoid, etc). I've heard different types of outputs are good for different types of equipment, and certain types of equipment can be destroyed by the wrong UPS (motors, etc). So what's the best type of output for different kinds of electronic equipment? I'm looking at what exactly I can backup in my room - from computers to TiVos to a rather large TV, large speaker amp, etc etc etc. Are there any deadly combinations that I need to avoid when making my purchase?"
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Matching Battery Backup "Waveshape" for the Right Equipment?

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  • This is utter nonsense. I personally won't attach electronic devices to anything other than sine wave or nearly sine wave. All other wave forms can destroy electronic equipment!

    The power supply of a computer for example works with a switching power supply which transforms the voltage via a very high frequency intermediate signal. The best thing to transform into high frequency is - a sinus wave. All other wave forms aren't really standalone waves, they are mixtures of different sine waves with different frequencies. For example a square wave consist of infinite sine waves. Now image what might happen if you transform such a bad signal.

    Don't do it. Don't attach expensive electronic equipment to a sheap USV. The person who wrote this is _completely_ wrong, even with his motor hints. A motor is generally no problem, regardless of the wave form. I would put a motor, a light bulb or a electric shaver (which is little more than a motor) onto a odd shaped current, but never ever electronic equipment.

    Remember: You won't be able to sue this guy for destroying your electronic equipment by his bad advice.

  • You may restate it as long as you like, but it will never became the truth.

    None-Sine Wave Forms can cause heavy spikes into switching power supplies effectively harming or destroying them.

    If you don't respond to things like this, than don't do it. But don't tell the people nonsense which can destroy their equipment.

    Fact is, that UPS mostly does nice enough waveforms which will not destroy your equipment. Of course because of this they can give you an warranty.

    But you said that the waveform in general does not do any difference and that is dumb shit! No UPS designed for computers or electronics will output for example square wave or similar bad waveforms because this WILL destroy the equipment.

    So, yes, you can use almost any UPS which is out there, which is sold for computer usage. And, no, it is not irrelevant which wave form a generator does output.

    If you can't get this straight, don't post.
  • To clarify this: Yes, there are UPS out there, which are not designed for computer or electronics usage. Watch out!

    A nonsense quote like 'waveform doesn't matter' won't give you a false feeling that you can buy anything which is sold.

    Get a UPS with sine-wave or near sine-wave (sometimes called pseudo sine-wave), get one which is sold for computer usage. Get some brand name device. It might be more expensive, but do you want to sue a noname taiwan manufacturer because his bad designed UPS has fried your electronics?

  • I've written a fairly detailled comment to both you and fwc here [slashdot.org]. Instead of copying and pasting it again, I've just made a link. Looking forward to comments.
  • Unless, of course, you've got some special application in mind that doesn't need much current, like keeping an ISDN line up during short blackouts or somesuch.

    Actually telco equipment is designed to run off of -48VDC for precisely this reason. They can use the mains to float charge the batteries and if power goes, oh well. :-)

  • A 130 volt MOV connected to a 120 VAC (RMS) outlet is going to blow within a few tenths of a second.

    Actually it won't blow that fast. I'm hunting around for a power supply I can rip apart so I can cross the part to show you that I'm right but at this time I can't. Maybe later tonight I'll get back to you; depends on what the kids get into. :-)

    Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed.

    Hmmm, I guess that's why we have the current go through the roof when you're driving a pump and go to reduce phase angle, right? (I suppose you could say that when you reduce the phase angle you're changing the synchronous speed...) In the case of driving a motor with the UPS you can cause the bus to rise if you're in a high inertia situation. (pushing a heavy piston up and then gravity assists it in falling, this will push you past your synchronous speed as well.)

    I can't speak for the designers of all UPS's, but any unit with either a pi-network or L-network (inductor input) output filter is going to soak up those spikes before they leave the box.

    Perhaps it's because I'm in large industrial controls but would a 700W filter not be rather large and bulky?

    *Unless it is a single-phase motor and you get it up to the speed where the start winding disconnects. If that happens, a single-phase induction motor will happily run backwards.

    We (Benshaw [benshaw.com]) can get a three phase motor to rotate backwards with a six-SCR starter through a cycloconvertor type of firing algorithm. (actually the standard set of software will do 7 and 14% of full speed forward and 20% reverse.) We sell this feature quite a bit for bucket inspections and positioning as the client usually doesn't have need for a full-blown drive and doesn't want to pay 2.5x the price for one.

  • Explain "reducing phase angle" in English.

    Power a three-phase motor via a six-scr power stack. When the SCRs are fully phased-on (i.e. triggered at 0 degrees through 180) the motor will have full line power, minus the volt or so the SCRs drop the line. By "reduce the phase angle" I mean to start phasing back the SCRs... instead of turning on at 0 degrees, turn them on at 45 degrees (3/4 of the half-sine wave) -- If the motor is driving something like a pump or a high inertia load the current will rise quite a bit.

    If the motor were supplying power back to the mains your current would drop, as the sign of the real power component went through zero (then it would rise again). If you run the motor backwards the effective inductance of the motor drops and your reactive current goes way up; your slip ratio is climbing beyond 1 and you're probably way down the tail of the real-power curve

    We're not running backwards; the load is turning the motor in the same direction it was originally going (high inertia load) or trying to turn it in the opposite direction (think of a mile of water trying to push back against the pump). In the second case (where I am more familliar) you are moving back up the speed/torque curve and, in most instances the current will rise and rise until you just don't have the voltage there anymore (as you are phasing back and turning off the power to the motor as you decel).

    Depends on the what you have to filter, doesn't it? Depending on the harmonic output of the inverter, I could see the filter being smaller than a car-alternator hash filter.

    I agree but if you're using PWM waveforms to generate a sinusoidal current waveform you are going to have very steep edges (as you switch from +bus to gnd and back) and the only way to get nice steep edges is to have lots of harmonic content. Now Don Lancaster is pushing something called Magic Sinewaves [tinaja.com] which are just PWM waveforms which are engineered to reduce or eliminate specific harmonics. From what I have read of them (he's been into them for a few years now), they look really interesting for fixed amplitude waveforms, like in UPSes and the like. Hell some of them are even delta-friendly.

  • by tzanger (1575) on Tuesday April 10, 2001 @06:22AM (#303654) Homepage

    and am running an AT power supply off a Modified-Sine Wave. There has been no problem what so ever.

    Squarewaves don't hurt transformers and equipment. They stress them. Your 120VAC 60Hz transformer was made to work at 60Hz. Throw a squarewave at it and you'll increase its temperature as it is now having to deal with 180Hz, 300Hz, 420Hz... The 60Hz transformer is not efficient at these frequencies and it will heat up due to eddy currents in the laminations and so on.

    The equipment on the other side won't see much since the transformer is blocking most if not all of these nasties. However that transformer is now likely running out of spec.

    If you want to be nice to your equipment and are running it off of a stepped-wave inverter, just take a pair of 120V-24V (or whatever) transformers which are larger than they need be (rule of thumb: if you need 20VA make these 30 or 40VA each) and hook them up back-to-back. i.e. your inverter output goes to the 120V side of the first transformer. Now the 24V side goes to the 24V side of the other, and the 120V side of the second transformer goes to your equipment. You've now just made an isolation transformer and, in addition to isolating the equipment from your electrical system (ground it yet!), you've also made a very handy (but inefficient as hell) 60Hz filter. Since the transformers are oversized you won't run into much trouble. Keep an eye on the temp (run the computer at full tilt for a number of hours to get the heat rise on the isolation transformer) and add a fan to them if needed.

    To summarize: Squarewaves do affect equipment not designed for them.

  • by tzanger (1575) on Tuesday April 10, 2001 @06:11AM (#303655) Homepage

    Most inverters spit out a sinusoid-like CURRENT waveform because they have a large inductor or transformer to smooth out the current (inductors oppose fast current changes). The industry hasn't made linear-mode UPSes for at least a decade now, as the losses are too high.

    Motors don't harm UPSes, UPSes harm motors. (more on this later.) A UPS is essentially a cheap VFD (Variable Frequency Drive). Unlike DC motors, you can't get full torque out of an AC motor by just reducing the voltage. The frequency and voltage must be kept in a specific ratio in order to keep the torque characteristics of the motor.

    Unfortunately for UPSes, the voltage waveform they spit out is more or less a nasty-ass chopped up PWM waveform. Bad for anything, really. With motors (and most inductors) you will end up breaking down the insulation on the first few windings of the stator (in the case of a motor). That's why motor manufacturers (I'm talking 3-phase here) use "inverter-grade" wire; the insulation is better and can withstand this nasty voltage spiking.

    And no, the more expensive UPSes still spit out a nasty-ass voltage wave form. You are paying for either a) a higher switching frequency, b) better PWM control (meaning a more balanced waveform), c) more stages (instead of just on-off, on, 1/2way and full) and/or c) heavy inductors or output transformers to smooth out the current waveform. I haven't seen a commercial step-like UPS in ages (too many components for not much advantage). Stick a scope probe across your high-end UPS; it's still got a nasty voltage waveform but chances are it's giving you a truer (closer to sine) current output than your $100 special.

    Most PCs come with cheap-ass switchmode power supplies. There are MOVs in almost all equipment. Unfortunately most suppliers use 130V MOVs. The peak-to-peak voltage on standard North American outlets is about 170VAC (120VRMS is 170V p-p) -- those MOVs eventually fail because they're turning on at the peaks of each cycle for the briefest of moments. Sketch out a sinewave with 84V peaks; the amount of time you're over 60 degrees is only a few tens of degrees. Depending on the construction of the power supply you'll either blow the shit out of the MOV or the internal fuse eventually. I've fixed countless computer power supplies by replacing the MOV and/or fuse.

    What's that got to do with inverters and UPSes? Simple, really: the PWM voltage output has lots of nice sharp edges and causes all kinds of ringing in any length of cable. It can help lead to premature failure of power supplies but when it does fail it looks no different than a normal equipment failure. Yeah there's a $25k replacement value given but that's only from lightning strike or power surge on the incoming side of the UPS. Read the fine print; it does not cover failures as I've described.

    The only time that an AC motor will cause grief to a UPS is if you're powering it and your load is actually driving the motor; i.e. you're using a motor to power an uphill conveyor and the load on the conveyor gets to great as to start moving the belt downhill and drive the motor. This causes the motor to generate instead of.. uh.. "motorate" and raises the bus voltage on your poor UPS which was NOT designed to do so. This usually overvoltages the caps and as I've seen many times in our power lab, things come apart.

  • As computers run off rectified and filtered {2[245]0,110}(*sqrt(2))V DC internally... would it not be just as good to feed them straight DC instead?
  • Which UPSs ('smart' and otherwise) have software (GPL'd) that works with Linux? Also there's the question of quality of the UPS hardware...anybody? Anybody?
  • Actually...

    Some nuclear reactors (eg Magnox) are refuelled in a continuous progress (ie a few fuel elements a day) to created a nice "flat" radial neutron flux.

    And yes, in Britain there are still some Magnoxes running. They are Bradwell (Essex), Sizewell A (Suffolk), Dungeness A (Kent), Oldbury (Gloucestershire), Calder Hall (Sellafield, Cumbria), Chapelcross (Dumfries, Scotland) and Wylfa (Anglesy, Wales).
    Bradwell is to close next year.
    Hinkley Point A (Somerset), Berkeley (Gloucestershire), Trawsfynydd (Wales) and Hunterston A (Ayrshire, Scotland) are all closed already.

    Do I get Nerd Points for this?
  • This sure sounds like somebody's nutty idea on how to ride out a rolling blackout. If it is, and you're looking to power everything but the kitchen sink for a 1-2 hr period, a UPS ain't gonna cut it. Get a generator, or better yet a solar array. I did the rough math for my house, I use about 500kwh/month. Some rough estimates of a solar array were around $7-10k. The cool thing is, if I generate more than I use, PG&E is required by law to buy it from me. For the moment I'm holding on to see what happens. With power rates capped around $0.13/kwr, it's not yet fully cost efficient to go solar. But, if the PUC or Bankruptcy judge allows rates to approach $0.20/kwr I get close to the break-even point. So, if they get their rate increase, it makes the grid power expensive enough to justify my generating my own, with the added benefit of immunity to blackouts... But, for somebody who just *has* to be able to watch the boob tube when power is out, cost efficiency isn't the whole story.
    Regards,
  • by yabHuj (10782) on Tuesday April 10, 2001 @12:33AM (#303660) Homepage
    The main advantage of non-sinewave voltage conversion lies in the simpler setup of the conversion electronics. For rectangular you only need a switch and an inversion switch - then cycle off, on, off, reversed on, ...

    The major disadvantages of non-sinewave compared to pure sinewaves are:

    • worse efficiency - transformators work best with pure sine. Non-sinewave cause a number of useless spikes and inductive resistance.
    • unwanted & dangerous spikes - any non-smooth waveforms causes transformators or motors to create high-voltage spikes that can harm or even destroy your equipment
    • humming - with a pure sinewave you only have the standard AC frequency of 50/60 Hz. Other waveforms - especially rectangular - consist of a number of overtones (have a look at the waveform's FFT) that can make it easily through the filtzers (designed for 50/60Hz). This will be especially distracting for music equipment.
    Pure sinewave UPS come with a cost, though...
  • I just want to know I'm not nuking the little motor.

    Actually, most fishtank air pumps don't have motors (last time I checked). It's usually just an electromagnet that turns on and off, which pulls on (and releases) a metal strip that pumps a rubber bellows. The only moving parts are the bending and unbending of the metal strip and the rubber bellows. (Does anybody even make piston air pumps for fishtanks any more?)

    Given that, I wouldn't THINK there's any harm to the air pump from being attached to any UPS...as far as I know.


    ---
  • by adolf (21054) <flodadolf@gmail.com> on Monday April 09, 2001 @11:34PM (#303662) Journal
    First, let's define some terms. A UPS (in its most basic form) consists of a battery, a battery charger, and an inverter. For this discussion, we only care about the inverter, for that is what takes the low voltage DC provided by the battery and converts it into standard AC (at whatever voltage is typical where you live).

    Switching power supplies (such as that in your PC) are, these days, remarkably unaffected by being powered with an odd waveform. At best, they work justfine. At worse the odd waveform confuses them to such an extent that they shut down harmlessly, or they just run a little warm. In theory, anyway. :^)

    That said, what the electronics really want is a pure 60 or 50Hz sine wave. It is, after all, precisely what they were designed for.

    I forget what sort of waveform my (old) APC Back-UPS 450 uses (sine, square, stepped square, sawtooth, whatever). I did at one point attempt to drive a relatively serious audio system, an aquarium, lava lamp, and a bunch of computers from it.

    The computers worked fine. The stereo produced a low 60-cycle hum, but functioned otherwise. The flourescent lights in the aquarium got pissed and flickered. The pumps made noises of certain distress. The lava lamp produced a figure of startling likeness to Roseanne Bar, and was promptly disconnected.

    I've done similar experiments with a Best Ferrups 800 that I happened across, which offers a real-live sinewave output. Nothing budged; no lights flickered, the aquarium filter continued to run silently, Roseanne Bar did not appear, and there was much rejoicing. I did note an increased buzzing sound from the Best box, but it was quickly overcome by the sounds of Iron Butterfly's Inna Gadda Da Vida (my 17-minute, 6-second treat for my otherwise dark, silent, and powerless neighbors during an inexplicable outage).

    Given this experience, there's a -lot- of things I don't trust to a non-sine inverter like my Back-UPS. For this reason it sits disconnected in the corner of the room (also, because it once rebooted a machine as the power went out - hint, hint). On the other hand, there's absolutely nothing I would hesitate to plug into the Ferrups.

    Most other good UPSs (mid-grade APC, Best, Tripplite seems OK) should fair about as well at powering whatever you feel like plugging them into, the key being that it output a sinewave.

    [ObRant: it's presently more expensive to produce a high-current, high-voltage sinewave than any other waveform. In other words, all of these units are bloody expensive. And, it's the harmonics that make the rest of them so bothersome to use, but I'll leave those anecdotes to some other less-tired poster. Also, UPS makers have a bad habit of making a big deal out of the VA rating of a UPS, possibly the single most useless figure in a home computing enviroment, while they should be pushing battery size (in Amp-Hours) and inverter efficiency. Oh, and that too-good-to-be-true $99 super-whizbang 1.6kVa UPS you saw at some online discount whore really is too good to be true. If you can carry it around with one hand, it's not worth having, and is akin to replacing the battery in a car with a 12 volts worth of D-cell NiCads and expecting it to fire. Unless, of course, you've got some special application in mind that doesn't need much current, like keeping an ISDN line up during short blackouts or somesuch.]
  • I'm wondering with all the talk of motors and the like... is it bad to hook your fish tank's air pump (and possibly filters) up to a UPS? If the air pump and filters are off for any length of time, the least robust fish tend to suffer oxygen starvation and die. I just want to know I'm not nuking the little motor.
  • The VoltAmp spec CAN be useful, if it's coupled with numbers like what KIND of power factors the UPS can deliver the VAs into, and with what kind of distortion

    That said, I used to work for a company that made REALLY high grade UPS systems, but it's been more than 10 years since I worked there.

    There are UPS units out there that will deliver a pure sine wave (.002% THD) into any load from pure inductive to pure capactive - BUT your looking at BIG units, at BIG dollars

  • by Tower (37395) on Tuesday April 10, 2001 @06:08AM (#303665)
    Well, the APC UPSs are supported quite nicely through several tools on Linux:

    The free apcupsd (I think this is the one that ships with Mandrake)
    http://www.sibbald.com/apcupsd/ (among other places)

    or even from APC:
    http://www.apcc.com/tools/download/index.cfm

    There are some nifty network UPS monitoring tools, but I seem to have lost the link for those (they allow you to check all the UPSs on your network via a web browser).
    --
  • what you want is one of these:

    Coleman Powermate [colemanpowermate.com]
  • This is really an electronics engineering problem, and not a computer engineering problem. If you tranform the time domains waveform of both a sine and square wave into the frequency domain you will see two very different waveforms. The Sine wave will be represented by a single "peak" at its fundamental frequency (ie 60Hz), whereas the square wave will have a "peak" at its fundamental frequency as well as harmonics present at each odd harmonic of the fundamental. Linear power supply transformers act as low pass filters (inductive) and if you watch the output of a transformer you will see some filter effects on a square wave inputted. Additionally, once you rectify the signal, it is typically put through another lowpass filter (capacitive or inductive) which cleans up the signal even more. The regulator circuit cleans it up significantly from that point on. The concern is the initial "spike" needed to create the rising edge of the square wave. Ideally (as was posted before) we don't generate that "spike". However, if you've done any transformer theory, you know it takes time to build up the flux in the core of the transformer. The difference is that the flux will build up faster with a square wave than with a sine wave and introduces the chance of saturating the transformer. If you saturate the transformer, it will stop 'transforming' and the output will drop off prematurely. You also risk overheating the transformer (ie letting the smoke out.) Most manufacturers build their transformers capable of handling the flux generated by a square wave. The key here is that YMMV. Also, square waves are audibly and spectrally noisy when going through transformers. As for switching power supplies, the input power is rectified first (as noted by a previous poster), filtered and then "switched" to generate the output. A square wave input will not harm the rectifiers in any way. Here's the catch. The control circuit of a switching supply would NOT be able to handle the square input. There are too many harmonics. This is where "modified sine wave" more accurately labelled "stepped square wave". The aim in that system is to reduce the number of harmonics and their intensity and the average voltage of the waveform. A sine wave's average voltage is lower than that of a square wave as is its RMS voltage. This is so that more sensitive equipment can be connected to the UPS. One final note. I recommend getting a "True On-Line UPS" instead of a Traditional UPS (ie Back-UPS). The difference is that a "true on-line"'s inverter is always running and usually generates a truer sine-wave. The Power supply portion drives the inverter and keeps the battery charged. The traditional type switches the inverter on and into the circuit if the power dips below a certain threshold. The engineers of these UPSs have done an excellent job making sure that power isn't interrupted in the switching process, but let's face it, anytime you switch a power source, you generate spikes which could damage your data, equipment or crash your system(s). The "true on-line"s do no switching. For them, the power supply shut off, but the batteries are still supplying power. It is completely transparent to the end equipment.
  • It is not to try and run things while waiting for the power to come back. You'll go thru a lot of expensive batteries that way!

    It is to allow you to perform a safe shutdown on your devices.

    A TV does not need a safe shutdown. Just kill the power.

    I don't know about the Tivo; it may be designed to safely deal with power cuts, since after all it is a consumer device.

    I can't see any difficulty with connecting UPSes to a Linux box; liable to be a lot easier than an NT box, since it should be simple to write some code that checks for a signal on the serial port and issues a shutdown -h now when it sees it.
  • by hansendc (95162) on Monday April 09, 2001 @10:47PM (#303669) Homepage
    Let me get this right: When you have a power outage, you want to make sure that you can watch your really big TV, and use your "large speaker amp"? On my UPS [sr71.net], (yes that is a boat battery which it uses) I only have my 2 important systems and one 13 inch monitor. That way, it can last longer. I don't need my big MP3 machine or my 19 in. monitor running when the power goes out, I only need to be able to safely shut the important machines down if I have to. You put the bare minimum of stuff on a UPS.

    For your purposes, I recommend an old mainstay of power backups: a nuclear reactor [britannica.com]. That way, you only have to refuel it every 20 years or so, AND you don't need a connection to the lousy power grid!
  • The "jet" ones are usaully a magnetic impeller... I don't think the UPS will hurt that...
  • by JonesBoy (146782) on Tuesday April 10, 2001 @04:36AM (#303671)
    If you want to power all of this stuff, why are you using a UPS system anyway? I am using a APC 700 on just a computer and flat panel monitor, and it barely holds it for more than 10 mins. If you had a TV, computer, radio, etc. you won't get anything done before the batteries die. If you want high performance, you are better off buying all the parts separately. Get some deep cycle RV batteries (they are better than car batteries for this application), a battery tender, and a power inverter with the best effiency you can afford. Each lead acid RV battery will only set you back about 50 bucks, and give you tons of power. I know a lot of people who use this type of setup for their HAM radio shacks for use during emergency service assistance. One setup had a relay wired in so he didn't have to flip switches when the power went off. Be sure to use acid proof battery boxes and proper ventilation! Charging batteries can produce hydrogen gas! Check out some HAM and ARRL web pages for more info on sucessful setups.
  • by fwc (168330) on Tuesday April 10, 2001 @01:34AM (#303672)
    I usually don't respond to stuff like this, but...

    Let me prefix this with I fully agree that the closer you can get to a True Sine Wave UPS, the better. However, I fully feel that my original comment is correct and true.

    A couple of Data Points:

    Almost all UPS manufacturers include a Equipment Protection Warranty. If the UPS's bad waveform fries your equipment they will replace it. See http://www.apcc.com/support/service/equipment_prot ection_policy.cfm [apcc.com] for an example. If the pseudo-sinewave that they put out really caused that much grief do you think they would warrant your equipment against damage up to $25,000?

    Also, the first thing all modern switching power supplies do is to rectify the incoming AC and then filter it with a capacitor, ending up with about 370 or so volts DC, which it then chops up to produce the lower +- 3.3-12 Volts used in PC's. The resulting output of the rectifier and Filter Cap (and power factor correcttion, EMI/RFI filtering, etc. etc. etc.) is virtually identical regardless of the input waveform - whether sine or pseudo-sine. I would have to do some nasty math to determine which waveform would be better - my guess is that it would be a toss up.

    For a more technical information than you probably ever wanted to know about switching power supplies, I wholehartedly recommend the ON Semiconductor SWITCHMODE Power Supply Reference Manual at http://www.onsemi.com/pub/Collateral/SMPSRM-D.PDF [onsemi.com]

    I'll also stand by my statement about motors. I'll restate to make myself more clear: Switchmode Power Supplies and UPS's get along just fine. Anything else you might have problems with.

  • by fwc (168330) on Monday April 09, 2001 @11:14PM (#303673)
    As a general rule, if you are using just electronic devices, about any UPS should be fine.

    I personally have had great luck with the APC brand, and as a general rule, I won't buy anything else. Your mileage may vary.

    Where you run into problems is where you start trying to run traditional "appliances". Fridges, Air Conditioners, Heaters, Microwaves, etc. etc.

    Most low-end UPS's (such as the APC Back-UPS) put out a pseudo sine wave, where as the more expensive ones (APC Smart-UPS for instance) put out a "real" sine wave. In theory the "real" sine wave models should work for even the fridge if there is enough wattage available, however, I wouldn't try it without taking to the UPS manufacturer first.

    Essentially the difference between the real sine wave and the pseudo one is that the real sine wave is the standard "smooth" sine wave you'd expect to see by plotting the sine function on a graph. The pseudo version is basically a modified square wave. The power is off (at zero) for a while, then at full positive power, then off, then at full negative power and then back to off, repeat. The ratio between on and off is set up so that the average voltage is the same as a real sign wave, and that the peak voltage is also identical.

    This works for almost 100% of the electronics out there. Quite frankly, a switching power supply or even an old fashioned transformer supply doesn't really care about the waveform as long as the voltage is in spec.

    The reason why some other loads do is that the waveform itself is important to the operation of the device. For instance, an AC motor actually operates by taking advantage of the reversing voltage to cause rotation. In addition, most inductive loads such as motors, etc. can cause spikes back into the UPS which may either blow the UPS up or cause it's regulation circuit grief.

    In short, if you're just wanting to run the electronics, just use any old UPS. If you're wanting to run applicances, well, good luck!

  • Try one of these! It's a 12,000 watt diesel generator [dct.com] made by honda. Not only can you watch TV in a hurricane (and microwave your li'l smokies - or hell do some metal artwork with an arc welder), but you can actually push power back onto the grid and get a paycheck from the light company each month! Batteries are for pussies!
  • Don't mess with that weak one I showed you... look at these [generac.com] and you can get a megawatt!
  • I would hazard a guess that he wants to protect the programming of the TV/video/receiver/whatever.

    If you lose power for an hour there's a good chance you'll have to go through and reprogram all the channel selections, VCR programming, etc.

    Also, UPSes do protect against low voltage (and somewhat against spikes), and if it's expensive equipment that might pay for itself.

    Finally, a decent-sized UPS might be able to cover a VCR recording for an hour.

  • I am working on putting a computer in my car,
    and am running an AT power supply off a Modified-Sine Wave. There has been no problem what so ever.
    Don't let these fools spend your money for you.

    All you use a UPS for is to safely shutdown your equipment, not to run your TV and Amp off when the power is down.

    I would suggest getting a SPS, they only kick in when the power goes out, and your power only goes through it when there is no power, any other time it is routed around it, just make sure you get one with a fast enough switching time (ie. >300ms)

  • I have 2 large battery backups in my home office, and I backup everything. 4 PCs, 3 monitors, TV, stereo, etc. Important or not, still like the option of being able to shut everything down properly if the power goes out, not just my primary workstation. Most power outages only last a few minuets around here anyway, so as long as I can get 10 minutes out of the battery backup, I'm fine.

    Try using a UPS from BestPower - their products are just as good as APC, but less expensive and easier integration with linux.
  • Let me get this right: When you have a power outage, you want to make sure that you can watch your really big TV, and use your "large speaker amp"?
    If he lives in California, it would be a great geeky thing to have all your electronics going even when the rolling blackouts hit your neighborhood. You could even host "blackout parties" and be the life of your block. It wouldn't be all that expensive to do; deep-cycle batteries are reasonably priced.
    For your purposes, I recommend an old mainstay of power backups: a nuclear reactor. That way, you only have to refuel it every 20 years or so...
    I hate to break this to you, but commercial nuke plants (PWRs) are refuelled on roughly a 2-year cycle. Then again, that's when they're cranking out a few GWthermal most of the time... if you had a Babcock and Wilcox unit all to yourself you could probably stretch it longer.
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  • Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed.
    Hmmm, I guess that's why we have the current go through the roof when you're driving a pump and go to reduce phase angle, right?
    Explain "reducing phase angle" in English. If the motor were supplying power back to the mains your current would drop, as the sign of the real power component went through zero (then it would rise again). If you run the motor backwards the effective inductance of the motor drops and your reactive current goes way up; your slip ratio is climbing beyond 1 and you're probably way down the tail of the real-power curve (unless you've got a wound-rotor motor and are playing games with the resistors).

    I know a mining engineer who got around regulations requiring "powered descent" capabilities for his ancient mine lift by upping the resistance on his rotor until the slip at loaded torque was > 1. (Loads normally went down on the brake.) The inspector shook his head and said something like "That's not how you're supposed to do it, but...." and signed him off. Clever guy.

    Perhaps it's because I'm in large industrial controls but would a 700W filter not be rather large and bulky?
    Depends on the what you have to filter, doesn't it? Depending on the harmonic output of the inverter, I could see the filter being smaller than a car-alternator hash filter. They'd have to pass similar amounts of power, and the hash filter doesn't have the luxury of having to only remove a small set of frequencies (odd multiples of 60 Hz).
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  • Explain "reducing phase angle" in English.
    Power a three-phase motor via a six-scr power stack. When the SCRs are fully phased-on (i.e. triggered at 0 degrees through 180) the motor will have full line power, minus the volt or so the SCRs drop the line. By "reduce the phase angle" I mean to start phasing back the SCRs... instead of turning on at 0 degrees, turn them on at 45 degrees (3/4 of the half-sine wave) -- If the motor is driving something like a pump or a high inertia load the current will rise quite a bit.
    That's a lot clearer. From your description it's pretty obvious that the harmonic content of the applied power increases radically as you begin chopping out the rising part of the sine curve. I'd have to do an analysis to check (and I'm not being paid to do this, so it isn't likely to get done anytime soon), but I suspect that the third harmonic is going to ground and the fifth harmonic is behaving like what you'd expect: trying to drive the motor at 300 Hz when it's turning at < 60 Hz, leading to behavior like it's running at a slip factor of 4 to 6 (consider the backward component of the 5th harmonic). You'd expect it to pull huge amounts of reactive current under those conditions, no?
    We're not running backwards; the load is turning the motor in the same direction it was originally going...
    I thought you were referring to a conveyor belt, which can typically move in either direction if the mechanicals aren't designed to forbid it. Sorry for any misconceptions.
    I agree but if you're using PWM waveforms to generate a sinusoidal current waveform you are going to have very steep edges (as you switch from +bus to gnd and back) and the only way to get nice steep edges is to have lots of harmonic content.
    If I recall correctly, there are resonant power-converter designs which allow switching of the power components at near-zero voltage. This would avoid most problems with steep edges. (I have not studied them much so I can't make any judgements about their suitability for any particular purpose.)

    Thanks for the pointer to Magic Sinewaves. I was going to cite them yesterday, but I couldn't remember exactly who was pushing them or what they were called so my quick Google search turned up nothing of interest.
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  • by Spamalamadingdong (323207) on Tuesday April 10, 2001 @10:52AM (#303683) Homepage Journal
    Simple, really: the PWM voltage output has lots of nice sharp edges and causes all kinds of ringing in any length of cable.
    I can't speak for the designers of all UPS's, but any unit with either a pi-network or L-network (inductor input) output filter is going to soak up those spikes before they leave the box.

    A 130 volt MOV connected to a 120 VAC (RMS) outlet is going to blow within a few tenths of a second. I have never seen such a device on the line side of a power supply. I have real difficulty taking the rest of your piece seriously after reading this.

    The only time that an AC motor will cause grief to a UPS is if you're powering it and your load is actually driving the motor; i.e. you're using a motor to power an uphill conveyor and the load on the conveyor gets to great as to start moving the belt downhill and drive the motor. This causes the motor to generate instead of.. uh.. "motorate" and raises the bus voltage on your poor UPS which was NOT designed to do so.
    Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed. If you are turning it in the backward direction, you are going to have current draw (both power and power factor) typical of a stall*. If you are powering it from an inverter and the inverter cannot handle a stalled motor on continuous duty, something's going to quit in the inverter (unless the motor's thermal cutout trips first).

    *Unless it is a single-phase motor and you get it up to the speed where the start winding disconnects. If that happens, a single-phase induction motor will happily run backwards.
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