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#21
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Observations on a UPS - follow up to a previous post
Arfa Daily wrote:
But that's my point. You can't have a 'true' sine-based RMS figure for power consumers that draw a pulsed current. Just because it is a sine wave that's *available*, it doesn't mean that the load will draw anything like a sinusoidal current, from it. The only items that will are those that are totally 'passive' in nature, such as light bulbs. Even power supplies that are transformer based, are likely to draw current in pulses from the available sinusoidal supply, and switch mode power supplies, on which most modern consumer electronics are based, most certainly won't draw a sinusoidal current from the supply. Arfa ICs to do the true RMS conversion are dirt cheap these days. http://www.analog.com/library/analogDialogue/archives/34-01/rmsarticle/index.html http://www.analog.com/en/subCat/0,2879,773%255F866%255F0%255F%255F0%255F,00.html -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#22
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Observations on a UPS - follow up to a previous post
"David" wrote in message
et I have a "Kill-A-Watt" and it appears to display true RMS for voltage and current readings. The voltage reading for a modified sine wave from a standard UPS displays the actual RMS voltage. It is speced to deliver true RMS readings. It will also display power factor. I do not know what crest factor it can handle Can't find it in the manufacturer's detailed specs. but displays power factors of considerably less than unity for most consumer electronics with DC rectifiers off of the line voltage. It is a very nice unit for the price. Agreed. |
#23
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Observations on a UPS - follow up to a previous post
On Mon, 13 Aug 2007 04:42:02 -0700, "William Sommerwerck"
wrote: Lead-acid batteries (like is [sic!] in your car) have major issues if they are completely drained, these are also the common battery in cheap, well, just about everything. The _only_ consumer products I've owned that used lead-acid batteries were an early Sony Discman, and two APC SPSs. They are not common in consumer products. They provide relatively high capacity at a low cost (which is why they're used in SPSs and UPSs), but they are too-easily damaged by a full discarge. I accidentally ruined a $45 batter for the Sony D-T10. Practically all consumer grade UPS use lead-acid batteries. Other common items using lead-acid batteries are some of the handheld halogen spotlight (flashlights), and automotive portable power station "thing-a-majigs" like those that can jump a car or have a flashlight/pump/inverter. A few transportation devices have them also like a kid's motorized big-wheels or skateboard or motorized bike, etc. Any decently designed UPS will cut off power before the lead acide battery is drained to a critical level, although it is still much harder on the battery to drain to any significant extent, a large % of total capacity instead of the UPS turning off as soon as possible. |
#24
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Observations on a UPS - follow up to a previous post
On 13 Aug 2007 01:07:28 GMT, Arno Wagner
wrote: In comp.sys.ibm.pc.hardware.misc Doc wrote: Recently I asked about suggestions regarding a UPS. I ended up getting an 875 VA 525 Watt "Geek Squad" model from Best Buy - yeah, yeah, everyone says Geek Squad stuff is overhyped junk, but at $69 on sale, the price seemed right. The price is all wrong. Nobody can build a decent product with these specs for that price. You cannot even buy the components needed in decent quality for that price. Depending on your definition of "decent", this may be true, but it's going to be roughly equivalent to what you'd buy from APC as a 500VA for about $50 so if that's what the budget allows, it's not an exceptionally low price (also considering you can sometimes get the APC discounted or with rebate putting it closer to $20-30 than to $50. It seems to handle my 2 computers fine - a PIV 2.4 gig and a PIII 933 mhz sharing a monitor. With both machines and the monitor on, the onboard readout shows them well below the unit's max capacity, drawing about .250 - .260 kw (which I assume translates to 250 - 260 watts) , with an estimated run time of 9 minutes with both computers. More than enough to get me through short hit outages with both machines running. And with the el-cheapo battery in there, that figure will be down to 1 minute in no time. And you would be well advised to test the claim. Software can be made to lie to you, you know. There's no reason to belive the battery is especially cheap, it's going to be a standard lead-acid which is quite a mature technology today, a commodity item essentially and all that's really at question is whether the manufacturer conservatively rated the unit or if it's unlikely to meet the specs due to design budget constructions. Either way, it's probably $70-100 worth of UPS, it will likely do as well as anything else available for the same price. If one were to pay = 2X as much, naturally the expectation would be it's either fancier or higher capacity or an online type, etc, but there is no expectation the battery is inherantly any higher quality per se, though probably higher capacity due to being a larger size or a series of two batteries. |
#25
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Observations on a UPS - follow up to a previous post
"James Sweet" wrote ...
"Doc" wrote... Maybe, but a lot of people seem to swear by the Kill-A-Watt meter, which can be had all day for around $25 online, eBay etc. EE friend of mine compared one to a $2500 power analyzer at work, found that the Kill A Watt performance is pretty much inline with the specs printed for it. It's not as good as the professional equipment, but it's really very impressive for what it is and certainly adequate for consumer use. The wonders of modern microelectronics, it's amazing what they can do with one inexpensive chip and a handfull of passive components. I still remember when a pocket calculator was $300, then a few years later $50 would buy one just as effective, and not long after that they were under $20 and those are all more capable than large machines costing many thousands just a few decades earlier. Agree completely. They are great when used with the regular sine-wave mains power grid. However note that many have been fried beyond repair when used with any kind of square- wave source: inverter, UPS, etc. even "stepped sine" waveforms. The problem appears to be the capacitive voltage divider used to power the Kill-A-Watt electronics. The high frequency harmonics deliver way too much power to the shunt regulator through the capacitor and something fries. |
#26
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Observations on a UPS - follow up to a previous post
Doc wrote:
"William Sommerwerck" wrote: My experience -- at least where I live -- is that the power is off for a fraction of a second, or hours. There's rarely anything in-between. In general, I'd say that's my seat of the pants impression too, though not always. I also notice they'll often come in clusters. The transformer - if that's the correct term for it - big gray basically cylindrical unit on top of a power pole - near my house blew once. Powerful **BOOM** and a huge column of flame. Not sure what the fuel for the flame was, do they have oil in them? Also a bit disconcerting since anyone nearby surely would have been in jeopardy from flaming debris. Needless to say, power was out for a while on that one. About 30 years ago a friend of mine was in a neighborhood where multiple houses were supplied from one undersized transformer, and the power company just ignored all requests to replace it. The residents got together, and all turned on air-conditioners, ovens, whatever, and then went outside to watch the transformer blow. It did, and the scheme produced a new proper sized transformer. -- Chuck F (cbfalconer at maineline dot net) Available for consulting/temporary embedded and systems. http://cbfalconer.home.att.net -- Posted via a free Usenet account from http://www.teranews.com |
#27
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Observations on a UPS - follow up to a previous post
"David" wrote in message . net... "Arfa Daily" wrote in message ... "David" wrote in message et... But be aware that in general, these cheap 'power' meters are expecting 'traditional' sine-draw loads. I have seen wildly inaccurate standby figures being given for equipment, by eco-campaigners that have been let loose with one. A lot of modern equipment that makes use of switch mode power supplies, handles standby mode by brief bursts of full draw operation. This can confuse a simple power calculating algorithm that's expecting continuous draw. Also, the draw by many cheapo switchers is very asymmetric and 'dirty', and may also not produce a true reading. I wouldn't connect a UPS to a fridge. These things are notorious for pulling a short-term startup current of tens of amps, as they get the compressor turning over. The UPS would probably fall over before being able to supply this, and might, as someone else suggested, even sustain damage. Arfa I have a "Kill-A-Watt" and it appears to display true RMS for voltage and current readings. The voltage reading for a modified sine wave from a standard UPS displays the actual RMS voltage. I do not know what crest factor it can handle but displays power factors of considerably less than unity for most consumer electronics with DC rectifiers off of the line voltage. It is a very nice unit for the price. David But that's my point. You can't have a 'true' sine-based RMS figure for power consumers that draw a pulsed current. Just because it is a sine wave that's *available*, it doesn't mean that the load will draw anything like a sinusoidal current, from it. The only items that will are those that are totally 'passive' in nature, such as light bulbs. Even power supplies that are transformer based, are likely to draw current in pulses from the available sinusoidal supply, and switch mode power supplies, on which most modern consumer electronics are based, most certainly won't draw a sinusoidal current from the supply. Arfa Arfa, I know that the current draw on these things is anything but sinusoidal. My point was that the "Kill-A-Watt" seems to actually compute the RMS value for that complex current waveform as well as non-sinusoidal voltage waveforms. David OK. I'm not sure that 'RMS' is the right term to attach to any value derived from a ragged-arsed waveform, as it is a mathematical function normally associated with symetrical waveforms, which the draw by a SMPS may very well not be, but I see what you're saying. What I am trying to say is that a chip which is designed to produce an RMS reading from a sine wave, may well produce a meaningful figure from a non-sinusoidal waveform also, but *only* if it is still symetrical. Arfa |
#28
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Observations on a UPS - follow up to a previous post
Doc wrote:
On Aug 12, 8:45 pm, "William Sommerwerck" wrote: My experience -- at least where I live -- is that the power is off for a fraction of a second, or hours. There's rarely anything in-between. In general, I'd say that's my seat of the pants impression too, though not always. I also notice they'll often come in clusters. The transformer - if that's the correct term for it - big gray basically cylindrical unit on top of a power pole - near my house blew once. Powerful **BOOM** and a huge column of flame. Not sure what the fuel for the flame was, do they have oil in them? Also a bit disconcerting since anyone nearby surely would have been in jeopardy from flaming debris. Needless to say, power was out for a while on that one. TRMOAS (that reminds me of a story)... Years ago, when Atari ST computers were common, friends of mine lived in and old house with just such a transformer on the adjacent pole. Buddy had been trying for ages to get his girlfriend to start learning to use the computer, but she was always afraid she'd "break something". Finally one day, he convinced her to sit down and give it a try. She took a deep breath, put her hands on the keyboard... as the room was lit up by a brilliant flash through the window, shaken by a magnificent **BOOM!**, and the computer screen went black. Poor girl was in a complete panic, she was SURE it was her fault... As it turned out, a drunk speeding down the road outside in his van had gone THROUGH two nearby power poles and finally stopped just shy of hitting a third; the first impact brought the lines down and was sufficient to explode the transformer just outside their window. ....took her years to ever touch a computer again |
#29
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Observations on a UPS - follow up to a previous post
Arfa Daily wrote:
.... snip ... OK. I'm not sure that 'RMS' is the right term to attach to any value derived from a ragged-arsed waveform, as it is a mathematical function normally associated with symetrical waveforms, which the draw by a SMPS may very well not be, but I see what you're saying. What I am trying to say is that a chip which is designed to produce an RMS reading from a sine wave, may well produce a meaningful figure from a non-sinusoidal waveform also, but *only* if it is still symetrical. Oh? Try a square wave, for example. Nice and symetrical. You are over-simplifying. -- Chuck F (cbfalconer at maineline dot net) Available for consulting/temporary embedded and systems. http://cbfalconer.home.att.net -- Posted via a free Usenet account from http://www.teranews.com |
#30
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Observations on a UPS - follow up to a previous post
"Richard Crowley" wrote in message
"James Sweet" wrote ... "Doc" wrote... Maybe, but a lot of people seem to swear by the Kill-A-Watt meter, which can be had all day for around $25 online, eBay etc. EE friend of mine compared one to a $2500 power analyzer at work, found that the Kill A Watt performance is pretty much inline with the specs printed for it. It's not as good as the professional equipment, but it's really very impressive for what it is and certainly adequate for consumer use. The wonders of modern microelectronics, it's amazing what they can do with one inexpensive chip and a handfull of passive components. I still remember when a pocket calculator was $300, then a few years later $50 would buy one just as effective, and not long after that they were under $20 and those are all more capable than large machines costing many thousands just a few decades earlier. Yup. I logged lots of hours on mechanical calculators, Wang shared-logic desk calculators, and the HP35. Agree completely. They are great when used with the regular sine-wave mains power grid. However note that many have been fried beyond repair when used with any kind of square- wave source: inverter, UPS, etc. even "stepped sine" waveforms. News to me. I've used mine with UPSs, but the application was not long-term use. The problem appears to be the capacitive voltage divider used to power the Kill-A-Watt electronics. The high frequency harmonics deliver way too much power to the shunt regulator through the capacitor and something fries. You're aware that capacitive voltage dividers have flat frequency response, right? |
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