UPS
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From: chrisisasavage on 29 Sep 2005 13:26 This is the first time I am looking for a UPS for a small server room. We need a UPS for our phone system. We do not have a generator, so we'd like to use a UPS as batter backup for a couple hours. I know this isn't going to be cheap, but it's our only solution in the suite we're at. I opened the side of the voicemail server to see the power usage on the power supply. It rated 115V/10a. This seemed excessive, but I double checked it was the actual input rating, and considering it's function I'm assuming it's correct. When selecting a UPS for a computer should I use those numbers or the number of Watts the supply is rated at? I don't have a way to test it to check it's actual draw. A 1150va and 300W Power supply don't seem to correlate very well, any idea why the input is rated so high? The next question is with our phone switch. It's rated 117V 6A. Generally, should I use 702va to figure the power usage of this device? I've had problems getting help from the manufacturer on how the power usage would work. The next questions is on the monitor for the voicemail server, which happens to be a Compaq v570, which I've seen listed as 75W. The back of the monitor shows the device voltage as 100-240V 1.2A. If it's 100V that would be 120VA, right? Sorry I sound ignorant (and am ignorant) on this one. I've read and read and read trying to figure out what I need. Is Watts or VA better to figure power by. It's not going to be cheap (we're looking in the range of 2 hours), so I'm ready for that. Thanks for any help, answers, or ANY information you can pass on. Thanks.
From: Bennett Price on 29 Sep 2005 23:12 I think you should spend $20 and get a clampon ammeter from Radio Shack, model # 22-602 along with a short 3 wire extension cord, preferably the sort with 3 parallel wires, (glorified zip cord). An air conditioner extension cord is the sort you want. Split the three wires apart, without knicking the insulation. You'll have to power off the equipment to do the following. Put each of the loads on the extension cord and clamp the ammeter around each of the 3 wires and let the equipment boot up. You should get identical readings on two of the wires and zero on the third. Either of the identical readings is how many amperes your equipment is consuming, (don't double the reading because you measured it twice.) 120 volts times the sum of your amperes is the VA. As you suspect, the ratings on the equipment may bear little relation to what you measure. They may simply reflect how many amperes the line cords and power switches are rated to carry, not how many amperes they are carrying. Also, if power is out, is the server room likely to overheat due to no ventilation? chrisisasavage(a)yahoo.com wrote: > This is the first time I am looking for a UPS for a small server room. > We need a UPS for our phone system. We do not have a generator, so > we'd like to use a UPS as batter backup for a couple hours. I know > this isn't going to be cheap, but it's our only solution in the suite > we're at. > > I opened the side of the voicemail server to see the power usage on the > power supply. It rated 115V/10a. This seemed excessive, but I double > checked it was the actual input rating, and considering it's function > I'm assuming it's correct. When selecting a UPS for a computer should > I use those numbers or the number of Watts the supply is rated at? I > don't have a way to test it to check it's actual draw. A 1150va and > 300W Power supply don't seem to correlate very well, any idea why the > input is rated so high? > > The next question is with our phone switch. It's rated 117V 6A. > Generally, should I use 702va to figure the power usage of this device? > I've had problems getting help from the manufacturer on how the power > usage would work. > > The next questions is on the monitor for the voicemail server, which > happens to be a Compaq v570, which I've seen listed as 75W. The back > of the monitor shows the device voltage as 100-240V 1.2A. If it's 100V > that would be 120VA, right? > > Sorry I sound ignorant (and am ignorant) on this one. I've read and > read and read trying to figure out what I need. Is Watts or VA better > to figure power by. It's not going to be cheap (we're looking in the > range of 2 hours), so I'm ready for that. Thanks for any help, > answers, or ANY information you can pass on. Thanks. >
From: Mike Walsh on 30 Sep 2005 22:00 A clampon meter is not necessary. If you have a regular digital multimeter you can cut the hot wire and use the meter to measure the current. The neutral should have the same reading. The one that should not have any current is ground. Voltage times current equals watts. VA is not watts, but comes from some formula that give an inflated number. This plus the fact that a UPS is rated for peak, and not continuous power means that the VA rating should be twice the actual wattage required, and should be four times if you want to have a decent battery run time. E.g. with a PC that requires 200 watts you should have a UPS with a 800 VA rating. Bennett Price wrote: > > I think you should spend $20 and get a clampon ammeter from Radio Shack, > model # 22-602 along with a short 3 wire extension cord, preferably the > sort with 3 parallel wires, (glorified zip cord). An air conditioner > extension cord is the sort you want. > > Split the three wires apart, without knicking the insulation. > You'll have to power off the equipment to do the following. > Put each of the loads on the extension cord and clamp the ammeter around > each of the 3 wires and let the equipment boot up. You should get > identical readings on two of the wires and zero on the third. Either of > the identical readings is how many amperes your equipment is consuming, > (don't double the reading because you measured it twice.) 120 volts > times the sum of your amperes is the VA. > > As you suspect, the ratings on the equipment may bear little relation to > what you measure. They may simply reflect how many amperes the line > cords and power switches are rated to carry, not how many amperes they > are carrying. > > Also, if power is out, is the server room likely to overheat due to no > ventilation? > > chrisisasavage(a)yahoo.com wrote: > > > This is the first time I am looking for a UPS for a small server room. > > We need a UPS for our phone system. We do not have a generator, so > > we'd like to use a UPS as batter backup for a couple hours. I know > > this isn't going to be cheap, but it's our only solution in the suite > > we're at. > > > > I opened the side of the voicemail server to see the power usage on the > > power supply. It rated 115V/10a. This seemed excessive, but I double > > checked it was the actual input rating, and considering it's function > > I'm assuming it's correct. When selecting a UPS for a computer should > > I use those numbers or the number of Watts the supply is rated at? I > > don't have a way to test it to check it's actual draw. A 1150va and > > 300W Power supply don't seem to correlate very well, any idea why the > > input is rated so high? > > > > The next question is with our phone switch. It's rated 117V 6A. > > Generally, should I use 702va to figure the power usage of this device? > > I've had problems getting help from the manufacturer on how the power > > usage would work. > > > > The next questions is on the monitor for the voicemail server, which > > happens to be a Compaq v570, which I've seen listed as 75W. The back > > of the monitor shows the device voltage as 100-240V 1.2A. If it's 100V > > that would be 120VA, right? > > > > Sorry I sound ignorant (and am ignorant) on this one. I've read and > > read and read trying to figure out what I need. Is Watts or VA better > > to figure power by. It's not going to be cheap (we're looking in the > > range of 2 hours), so I'm ready for that. Thanks for any help, > > answers, or ANY information you can pass on. Thanks. > > -- Mike Walsh West Palm Beach, Florida, U.S.A.
From: Bennett Price on 1 Oct 2005 12:26 The original poster seemed inexperienced at matters electrical; hence I suggested a clampon ammeter as much safer than cutting all 3 wires and then trying to determine H-N-G. Also, some inexpensive DVM's don't measure AC current. I don't agree that UPS' are rated at Peak; in general they are rated at operating conditions - whether in VA or Watts. VA is Volts times Amperes - not some 'inflated number'. Watts are V x A x Power Factor (which can be anywhere from zero to one); thus watts are equal to or less than VA. Since it is difficult to know the PF or true wattage of a load, purchase a UPS based on its VA rating and throw in some more fudging factor. Keep in mind that long run time can be achieved either by buying an oversize UPS or buying one of the appropriate VA/wattage rating with extra large or supplemental batteries. The VA capacity of a UPS is determined in part by its batteries but also by its internal components. You can put the biggest battery on a 350 VA UPS; it will still only put out 350VA but it may do so for days. Similarly, if you have enough flashlight batteries, you can run a 5KVA UPS, but only for seconds. Mike Walsh wrote: > A clampon meter is not necessary. If you have a regular digital multimeter you can cut the hot wire and use the meter to measure the current. The neutral should have the same reading. The one that should not have any current is ground. > Voltage times current equals watts. VA is not watts, but comes from some formula that give an inflated number. This plus the fact that a UPS is rated for peak, and not continuous power means that the VA rating should be twice the actual wattage required, and should be four times if you want to have a decent battery run time. E.g. with a PC that requires 200 watts you should have a UPS with a 800 VA rating. > > Bennett Price wrote: > >>I think you should spend $20 and get a clampon ammeter from Radio Shack, >>model # 22-602 along with a short 3 wire extension cord, preferably the >>sort with 3 parallel wires, (glorified zip cord). An air conditioner >>extension cord is the sort you want. >> >>Split the three wires apart, without knicking the insulation. >>You'll have to power off the equipment to do the following. >>Put each of the loads on the extension cord and clamp the ammeter around >>each of the 3 wires and let the equipment boot up. You should get >>identical readings on two of the wires and zero on the third. Either of >>the identical readings is how many amperes your equipment is consuming, >>(don't double the reading because you measured it twice.) 120 volts >>times the sum of your amperes is the VA. >> >>As you suspect, the ratings on the equipment may bear little relation to >>what you measure. They may simply reflect how many amperes the line >>cords and power switches are rated to carry, not how many amperes they >>are carrying. >> >>Also, if power is out, is the server room likely to overheat due to no >>ventilation? >> >>chrisisasavage(a)yahoo.com wrote: >> >> >>>This is the first time I am looking for a UPS for a small server room. >>>We need a UPS for our phone system. We do not have a generator, so >>>we'd like to use a UPS as batter backup for a couple hours. I know >>>this isn't going to be cheap, but it's our only solution in the suite >>>we're at. >>> >>>I opened the side of the voicemail server to see the power usage on the >>>power supply. It rated 115V/10a. This seemed excessive, but I double >>>checked it was the actual input rating, and considering it's function >>>I'm assuming it's correct. When selecting a UPS for a computer should >>>I use those numbers or the number of Watts the supply is rated at? I >>>don't have a way to test it to check it's actual draw. A 1150va and >>>300W Power supply don't seem to correlate very well, any idea why the >>>input is rated so high? >>> >>>The next question is with our phone switch. It's rated 117V 6A. >>>Generally, should I use 702va to figure the power usage of this device? >>> I've had problems getting help from the manufacturer on how the power >>>usage would work. >>> >>>The next questions is on the monitor for the voicemail server, which >>>happens to be a Compaq v570, which I've seen listed as 75W. The back >>>of the monitor shows the device voltage as 100-240V 1.2A. If it's 100V >>>that would be 120VA, right? >>> >>>Sorry I sound ignorant (and am ignorant) on this one. I've read and >>>read and read trying to figure out what I need. Is Watts or VA better >>>to figure power by. It's not going to be cheap (we're looking in the >>>range of 2 hours), so I'm ready for that. Thanks for any help, >>>answers, or ANY information you can pass on. Thanks. >>> > >
From: kony on 1 Oct 2005 17:17 On Sat, 01 Oct 2005 16:26:58 GMT, Bennett Price <bjpriceNOSPAM(a)itsa.ucsf.edu> wrote: >The original poster seemed inexperienced at matters electrical; hence I >suggested a clampon ammeter as much safer than cutting all 3 wires and >then trying to determine H-N-G. Also, some inexpensive DVM's don't >measure AC current. > >I don't agree that UPS' are rated at Peak; in general they are rated at >operating conditions - whether in VA or Watts. Definitely the consumer grade units, including APC's, are not rated at operating conditions. AT least two APC units I have cannot output 500VA with fresh battery, yet that's their rating. With a load (system and monitor requiring roughly 300VA) they will shut down immediately.
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