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#1
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OT a bit - matching UPS with one's pc
I'll probably be buying a UPS for my pc soon and need to learn how to
size and match a UPS with my pc, but there's a lot of unclear info out there. Complicated but probably more exact method - add up the amps each device in my pc uses to calculate the minimum size UPS. I've found some calculators out there that follow this method. Variation to that method - add the number of watts each of the various devices need, add 10% as a safety margin and divide that number by 12 to derive amps needed from a UPS. Simplistic method - My brother said use the specs posted for my pc's PSU regarding amps and pick a UPS based on that number - his explanation being that all the devices in the pc are ultimately powered through the PSU and it therefore incorporates everything needed by the individual components of the pc so that the amps it provides can be thought of as the minimum amps that a UPS should provide. My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A, +5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean much to me. If I add them together, the sum totals 123 Amps, but using the second procedure yields roughly 50 Amps. For simplicity, call it a 100% difference. My pc has an Asus M4A89GTD Pro mobo, an AMD Athlon II x3 440 CPU, a Radeon 6750 video card, 4x4Gb DIMMs, a DVD and 2 500 Gb hds. As far as my needs go, I think I want to use a UPS just for my pc and leave my monitor and cable modem on a surge protector. I might choose a UPS that can instruct my pc to shutdown when power goes out. My biggest concerns in my neighborhood are rolling brownouts. It promises to be a very hot summer. I don't need the UPS to power my pc for extended periods of time, just enough time (minutes) to safely shut down. My brother's suggestion seems the most practical way (KISS) to decide how much UPS I need, but I feel like I'm doing something wrong to add up to 123 Amps using the PSU specs whereas dividing 550 Watts by 12 = 47 Amps. Are there other considerations I should keep in mind? Thanks, John |
#2
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OT a bit - matching UPS with one's pc
Yes wrote:
I'll probably be buying a UPS for my pc soon and need to learn how to size and match a UPS with my pc, but there's a lot of unclear info out there. Complicated but probably more exact method - add up the amps each device in my pc uses to calculate the minimum size UPS. I've found some calculators out there that follow this method. Variation to that method - add the number of watts each of the various devices need, add 10% as a safety margin and divide that number by 12 to derive amps needed from a UPS. Simplistic method - My brother said use the specs posted for my pc's PSU regarding amps and pick a UPS based on that number - his explanation being that all the devices in the pc are ultimately powered through the PSU and it therefore incorporates everything needed by the individual components of the pc so that the amps it provides can be thought of as the minimum amps that a UPS should provide. My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A, +5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean much to me. If I add them together, the sum totals 123 Amps, but using the second procedure yields roughly 50 Amps. For simplicity, call it a 100% difference. My pc has an Asus M4A89GTD Pro mobo, an AMD Athlon II x3 440 CPU, a Radeon 6750 video card, 4x4Gb DIMMs, a DVD and 2 500 Gb hds. As far as my needs go, I think I want to use a UPS just for my pc and leave my monitor and cable modem on a surge protector. I might choose a UPS that can instruct my pc to shutdown when power goes out. My biggest concerns in my neighborhood are rolling brownouts. It promises to be a very hot summer. I don't need the UPS to power my pc for extended periods of time, just enough time (minutes) to safely shut down. My brother's suggestion seems the most practical way (KISS) to decide how much UPS I need, but I feel like I'm doing something wrong to add up to 123 Amps using the PSU specs whereas dividing 550 Watts by 12 = 47 Amps. Are there other considerations I should keep in mind? Thanks, John In simplistic terms, when you buy a 550W supply, it draws anywhere from 0 watts to 550W from the wall. Imagine, for a moment, you have the PSU sitting on the bench, with nothing connected to the wires. We would hope the supply draws very close to zero, with no load on it. There is little heat coming out of the back of the PSU. The PSU converts AC power to DC power, but only converts enough to supply the load. That's why it draws zero when nothing is connected. And at the other extreme, by carefully tweaking a load box, we can force it to supply up to 550W. Any more than that, it'll shut down. Now, your PC parts don't draw 550W. They draw some intermediate value. And that intermediate value, is the one you'll be buying the UPS for. Depending on your budget and level of curiosity, you could buy a Kill-O-Watt meter, and remove all uncertainty. This one is about $20, and measures the power for you. You can use it later for your other appliances. If you run the computer off a power strip (plug in computer, plug in monitor), then plugging the power strip into the Kill-O-Watt, totals all the power used. http://www.amazon.com/P3-Internation.../dp/B00009MDBU This is a spec sheet for a Kill-O-Watt meter. It measures both watts and VA, the two units of measure we need. http://ec1.images-amazon.com/media/i...L000010953.pdf "Also displays Volts, Amps, Watts, Hz, VA" ----- -- ******* The UPS has two specs. It was watts (real component, no imaginary component) and VA (ignores phase angle). http://en.wikipedia.org/wiki/Volt-ampere "When a UPS powers equipment which presents a reactive load with a low power factor, neither limit may safely be exceeded." The old ATX power supplies, had a power factor of 0.7. The newer supplies, with power factor correction, are 1.0. When the power factor is 1.0, watts is equal to VA. A light bulb is power factor 1.0, and its watts are the same as the VA. ******* Just taking the first UPS I'm offered on Newegg as an example... http://www.newegg.com/Product/Produc...82E16842101311 750 VA 450 Watts You have to work out both of those, to determine if you're exceeding the limits of the unit. Here, someone works out the KVA (kilo-volt-amps) by multiplying the power in watts, by the inverse of the known power factor of the load (office building full of PC power supplies). The person doing the estimate, used a PF of 0.8. http://forums.apc.com/thread/5643?start=0&tstart=0 110kW * 1/pf = 110*1/0.8 = 137.5kVA So it is possible to estimate this for yourself, where PF=0.7 for a very old PSU, and PF is close to 1 (and it may state in the specs it is power factor corrected). The UPS companies make a web page available, for picking a UPS, and it nicely ignores those specs, and picks a unit for you. Naturally, such a web page is filled with bad assumptions. But it will likely get you a UPS that works. If you use a Kill-O-Watt meter, and run a 100% computing load (i.e. playing Crysis, running Prime95 or the like), then the meter can simply print out on its screen, the number of watts and the number of VA. And then you can compare those to the UPS specs. Another nice aspect of the Kill-O-Watt meter, is it does the vector math for you, if you have multiple loads, all with different power factors. If you connect a desk lamp, the LCD monitor, the computer, all to the power strip, the Kill-O-Watt will still read out the total Watts and VA for you. Very accurately. ******* Now, what is the danger of doing it this way ? You end up buying a $50 UPS, because the math says that's all you need. I didn't buy mine that way. I bought a mid-tier UPS, to avoid the "bottom feeding junk" in the $50 range. So on the one hand, doing the math is reassuring from an "I only bought as much as I needed" point of view. But, the product quality simply may not be there, by being so cheap. By the time you move upscale a bit, you have enough power capacity that the math is less of an issue. This one has a runtime rating of 5 minutes at 780W. $160 http://www.newegg.com/Product/Produc...82E16842101421 This one runs for 12 minutes at half load (half of 1500W). $509 Weights 69 pounds. http://www.newegg.com/Product/Produc...82E16842102068 Now, if you get your Kill-O-Watt, make the measurements, it is always possible a unit like this will fit the bill. But it could be a false economy, depending on what the customer reviews say. Runs 2.1 minutes at 257W. $52. It might be barely enough to do the job. I could spend my time estimating your load (X3 440 95W, HD 6750 86W [bad estimate], 50W mobo, 12W disk drive), but that'll get me 243 watts / efficiency = perhaps 304 watts at the plug, and we know the video card really doesn't draw that amount of power. So estimating is going to be error prone, due to the people who normally measure the power, not having measured it for HD 6750. But this might be an example of what you would buy, if using maths on it. 2.1 minutes is probably enough time to shut down. http://www.newegg.com/Product/Produc...82E16842101349 If you're going to skimp that much, I'd use the Kill-O-Watt to be sure. A couple reviews had problems with that UPS, which is actually pretty good. I expected to see more trouble reports. When we bought 100 units of some junk at work, we had a 10% failure rate. I guess it's all right, if yours was one of the 90 working ones :-) So it's about $20 + $50, if you do it the Kill-O-Watt way, or maybe $160 if you just buy a mid-tier unit. Years ago, when I bought mine (2002?), they were more expensive than they are now. I guess that's the Chinese batteries in them, "paying dividends". Or maybe it's the competition from CyberPower :-) Your choice, Paul |
#3
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OT a bit - matching UPS with one's pc
On 6/10/2013 1:19 AM, Yes wrote:
I'll probably be buying a UPS for my pc soon and need to learn how to size and match a UPS with my pc, but there's a lot of unclear info out there. Complicated but probably more exact method - add up the amps each device in my pc uses to calculate the minimum size UPS. I've found some calculators out there that follow this method. snip... Thanks, John Safe way: measure the actual power consumption of the equipment you need for minimal functioning and work from that. This equipment would include the computer + monitor + whatever equipment is needed to connect to the Internet (modem, router, switch or whatever other bits your situation calls for). Add at least 20% to that although doubling it won't hurt. Then buy yourself a UPS which will support that load. You should not include power hogs like printers, especially lasers. Keep in mind that the power rating of the UPS is not terribly informative about how well it will serve your purpose. A massive power output rating simply means that it will put out that much power but not for how long. A 1000W UPS which only runs for one minute is not terribly useful; at the very least the UPS needs to keep everything going for long enough to tell the computer to shut down safely. A UPS which supports your equipment and runs for 20 minutes would be a better value. I have standardized on 1200W CyberPower units not because any of my equipment consumes anything like that (maybe 350W max) but because the are have proven to be reliable, have a good number of outlets (both battery and surge protected), they are line-interactive and handle brownouts well and they go on sale pretty regularly so they are affordable. I program the shutdowns so that when the batteries have maybe 5 minutes of support left the computer does a safe powerdown. I have 5 of these units as well as a couple of 12VDC units supporting network infrastructure but I live in an area with obsolete power distribution, lots of storms, and huge trees so what seems like overkill is actually just barely enough. |
#4
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OT a bit - matching UPS with one's pc
On Monday, June 10, 2013 1:19:04 AM UTC-4, Yes wrote:
I'll probably be buying a UPS for my pc soon and need to learn how to size and match a UPS with my pc, but there's a lot of unclear info out there. Generally sum the amps or watts. Then remember a UPS battery typically degrades in three years. So, for example, if your system consumes 350 watts, then the UPS should be sized about 500 watts. So the the three year old battery can still provide enough power. And for other technical reasons. Now, the power rating on the label for most engineer designed appliances is good enough. However many put 800 watt power supplies into computers that consume only 200 watts and never more that 350 watts. To get a better idea, read what others measured with their Kil-A-Watt in: http://forums.anandtech.com/showthre...1#post34917091 BTW, a UPS connects your equipment directly to AC mains when not in battery backup mode. Many rumors are based in hearsay that is discussing a UPS costing on the order of $1000 or higher. Cleanest power come when the UPS connects your computer directly to AC mains. And finally, power from a UPS in battery backup mode is so 'dirty' as to sometimes be harmful to motorized appliances. But electronics are so robust as to not care. |
#6
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OT a bit - matching UPS with one's pc
On Sunday, June 9, 2013 10:19:04 PM UTC-7, Yes wrote:
need to learn how to size and match a UPS with my pc, Complicated but probably more exact method - add up the amps each device in my pc uses to calculate the minimum size UPS. I've found some calculators out there that follow this method. Variation to that method - add the number of watts each of the various devices need, add 10% as a safety margin and divide that number by 12 to derive amps needed from a UPS. Simplistic method - My brother said use the specs posted for my pc's PSU regarding amps and pick a UPS based on that number - his explanation being that all the devices in the pc are ultimately powered through the PSU and it therefore incorporates everything needed by the individual components of the pc so that the amps it provides can be thought of as the minimum amps that a UPS should provide. My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A, +5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean much to me. If I add them together, the sum totals 123 Amps, but using the second procedure yields roughly 50 Amps. You can't just add up amps but instead have to add up powers (amps X volts), but it's a lot more realistic to plug your computer and monitor (but not the printer, scanner, or audio system) into a Kill-A-Watt ($15-25) and run a worst-case power test (video game). Then note the maximum Volt*Amp and watt numbers the Kill-A-Watt reports. Add 50% to those numbers to get the VA and watt ratings you'll need from a backup power supply. Generally backups have a watt rating that's about 60% of its VA rating. |
#7
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OT a bit - matching UPS with one's pc
On 06/10/2013 12:19 AM, Yes wrote:
I'll probably be buying a UPS for my pc soon and need to learn how to size and match a UPS with my pc, but there's a lot of unclear info out there. Complicated but probably more exact method - add up the amps each device in my pc uses to calculate the minimum size UPS. I've found some calculators out there that follow this method. Variation to that method - add the number of watts each of the various devices need, add 10% as a safety margin and divide that number by 12 to derive amps needed from a UPS. Simplistic method - My brother said use the specs posted for my pc's PSU regarding amps and pick a UPS based on that number - his explanation being that all the devices in the pc are ultimately powered through the PSU and it therefore incorporates everything needed by the individual components of the pc so that the amps it provides can be thought of as the minimum amps that a UPS should provide. My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A, +5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean much to me. If I add them together, the sum totals 123 Amps, but using the second procedure yields roughly 50 Amps. For simplicity, call it a 100% difference. My pc has an Asus M4A89GTD Pro mobo, an AMD Athlon II x3 440 CPU, a Radeon 6750 video card, 4x4Gb DIMMs, a DVD and 2 500 Gb hds. As far as my needs go, I think I want to use a UPS just for my pc and leave my monitor and cable modem on a surge protector. I might choose a UPS that can instruct my pc to shutdown when power goes out. My biggest concerns in my neighborhood are rolling brownouts. It promises to be a very hot summer. I don't need the UPS to power my pc for extended periods of time, just enough time (minutes) to safely shut down. My brother's suggestion seems the most practical way (KISS) to decide how much UPS I need, but I feel like I'm doing something wrong to add up to 123 Amps using the PSU specs whereas dividing 550 Watts by 12 = 47 Amps. Are there other considerations I should keep in mind? Thanks, John Yes...UPSes are typically rated in VA (volt amp) which is not the same as watts. If you assume a power factor of .65 a 1000VA UPS is good for 650 watts. http://www.rapidtables.com/convert/e...va-to-watt.htm |
#8
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OT a bit - matching UPS with one's pc
You are making the assumption that the UPS is one of those crappy
modified sine wave types. They should simply be avoided. I would rather lose power than use a modified sine UPS. I use a double conversion UPS, not all that different from the $500+ unit the other poster listed from newegg. Double conversion true sine is the only way to go. Otherwise, don't use a UPS. Your gear SHOULD be able to handle the crappy signal from the cheap inverter, but some devices can be damaged. Basically the modified sine, which is practically a square wave, causes increased surge current in the capacitors of the computer power supply. The thing to note with a true sine wave double conversion UPS is that it is running all the time. It has fans and thus noise. Think of a computer server room at a business, then imaging that in your house. I'm using an optiups 1500b. About 4 or 5 years old at this point and thus far no problem. It can run a desktop and a few very low power computers. That is, 1500va is a lot of power. Most of your computer power supplies, unless they are bargain basement PCs, will have power factor correction. So they will look resistive to the UPS. http://en.wikipedia.org/wiki/Power_factor Everything I build uses 80plus rated power supplies. But a lot of the low power accessories will not have active power factor correction. That shouldn't be an issue since the key phrase here is low power. But it wouldn't be surprising for all the wall warts and such to add up to a hundred watts. BTW, I also agree having a Kill-A-Watt is a good idea. Get the cheapest model since the fancy ones have features that really aren't all that useful. http://www.newegg.com/Product/Produc...82E16842107015 I see they still make it. OK unit, but I don't like how the front panel attaches. It doesn't attach firmly. That is my only complaint. It is one of the quieter double conversion units around since the fans are variable speed. Still it is damn loud. Tomshardware has review of it and a few others. Note the opti can work off of serial or usb. The deal is if you have a number of devices on the supply, serial is better since that one signal can be bussed around. That is, for a UPS to be completely effective, all your attached devices need to be able to sense the power failure signal. This can also be done via lan instead of serial port, but the serial port scheme requires the least brain power. http://www.tomshardware.com/reviews/...t,2785-12.html Note it has the best voltage regulation because it was the only double conversion unit in the test. It was also the most expensive. However, it will last hopefully for use over at least two different computer systems for the average home user that gets a new PC every 5 years. Maybe three if you change computers more often. Note that the double conversion scheme gives you true surge protection since it comes for free given the design. That is, the raw AC is rectified then filtered. At the filter stage, you can really do decent surge protection because you are dealing with DC. Filter the bejesus out of it. Big ass caps are not a problem. Then you convert the DC to AC with the true sine inverter. |
#9
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OT a bit - matching UPS with one's pc
On Monday, June 10, 2013 5:58:25 PM UTC-4, Paul wrote:
Power rating is not the same thing as runtime. ... A dumb manufacturer, could use the battery from a 450W unit, in a 1200W product. And if the 1200W load was applied (with that flimsy battery in place), it would run out of juice in less than a minute. And that unit would immediately shutdown three year later as the battery further degraded. It would not have power necessary to provide 1200 watts long enough to do anything useful. All electronics are so robust that a modified sine wave UPS is sufficient and ideal power. Many get hyped by hearsay (as another demonstrates by not saying why power must be 'cleaner'). Spend massively for a double conversion UPS or a double conversion that still outputs 'dirty' sine waves. (Latter costs less, is double conversion, and still has a crappy output.) Spending all that additional money accomplishes nothing useful. Since any advantage from a double conversion UPS is already done better inside electronics. UPS is temporary and 'dirty' power during a blackout. It must be sized so that it will provide sufficient power even when seriously degraded in three years. Other engineering factors also say why a 350 watt load means a UPS maybe 500 watts or larger. |
#10
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OT a bit - matching UPS with one's pc
The double conversion scheme is a power conditioner and UPS at the same
time. If you understand electronics, it is far easier to absorb a surge at DC versus AC. Seriously, those modified sine wave UPSs are so ****ty it is far better to suffer a power outage. Look at the modified sine waveform. It is more like a modified square wave. The steep edges will stress the power supply since i=C*DV/DT, and the DV/DT of a square wave is infinite. Of course the modified sine doesn't have an infinitely fast rise time, but it is faster than the design criteria of 2*pi_60Hz. |
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