Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Spinning disk meters are becoming a thing of the past. However, I believe that very few utilities are billing residential customers for kVAR. Many do charge residential demand and time-of-day rates. Eric, you may want to comment further. Chuck WB2EDV - Original Message - As I stated in an earlier post, the rotating-disk kWH meter on the typical residence measures only true power. It does this magic by combining the magnetic fields of two coils: a voltage coil that is connected in parallel with the load, and a current coil that is in series with the load. The angular displacement of these coil windings is precisely set so that only currents that are exactly in phase with the voltage result in a torque to turn the aluminum disk.
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
I have a site where for many years the only load was a battery charger feeding a battery to power up the equipment. For many years the power meter DID NOT MOVE! It started moving when I substituted a GE Mastr II base station power supply with backup battery. My theory (correct me if I am wrong) is that the very short duty cycle current pulses drawn when the sine wave is at the crest of the cycle (when the diodes conduct) is why the meter was not moving. The GE Power supply is ferro resonant and draws current over the whole cycle although the power factor is pretty bad. The GE supply also uses a filter choke which reduces the current pulsing when the diodes conduct to a minimum. 73 - Jim W5ZIT --- On Tue, 9/16/08, Bob M. [EMAIL PROTECTED] wrote: From: Bob M. [EMAIL PROTECTED] Subject: RE: [Repeater-Builder] Volt-Amp(Re: APC UPS Charging Power) To: Repeater-Builder@yahoogroups.com Date: Tuesday, September 16, 2008, 10:31 PM Thank you Eric. This was the explanation I was looking for. The UPS is saving me money when drawing 181 Volt-Amps, yet the electric meter is only recording and charging me for 31 Watts. I wonder if APC did this on purpose. I don't know how much current is actually being fed to the batteries; they've been in there for a couple of months and should be fully charged by now, so it should just be trickling them (eight 12V 7A SLA cells in series/parallel for 48V). Bob M. == --- On Tue, 9/16/08, Eric Lemmon [EMAIL PROTECTED] net wrote: From: Eric Lemmon [EMAIL PROTECTED] net Subject: RE: [Repeater-Builder] Volt-Amp(Re: APC UPS Charging Power) To: Repeater-Builder@ yahoogroups. com Date: Tuesday, September 16, 2008, 9:21 PM Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator' s starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY ___
Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
More likely the meter simply failed to register well on light loads. It doesn't happen with the newer meters. Chuck WB2EDV - Original Message - From: Jim Brown To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 17, 2008 10:06 AM Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) I have a site where for many years the only load was a battery charger feeding a battery to power up the equipment. For many years the power meter DID NOT MOVE! It started moving when I substituted a GE Mastr II base station power supply with backup battery. My theory (correct me if I am wrong) is that the very short duty cycle current pulses drawn when the sine wave is at the crest of the cycle (when the diodes conduct) is why the meter was not moving. The GE Power supply is ferro resonant and draws current over the whole cycle although the power factor is pretty bad. The GE supply also uses a filter choke which reduces the current pulsing when the diodes conduct to a minimum. 73 - Jim W5ZIT
Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Thank you Eric Lemmon ! Your explanation is the most precise I've read thus far. The last line of your last paragraph said what folks want to hear. I started to respond to this thread earlier, but after a few minutes of organizing my thoughts, my aging pea-brain said, Forget this and go get another gin tonic ! What's another few brain cells anyway ? de WD7F John in Tucson - Original Message - From: Eric Lemmon [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Tuesday, September 16, 2008 9:59 PM Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) John, You are correct that when the power factor is 1.00, the current is in phase with the voltage, as it will be in a purely resistive circuit. In this unique case, watts equals volt-amperes. However, when the load is reactive, the current either leads or lags the applied voltage. A typical case is a lightly-loaded induction motor, which may exhibit a power factor around 0.65, which is considered to be a poor PF. Some of the current drawn by this motor is used to create torque and perform actual work, and this current is nearly in phase with the applied voltage. Some current causes heating of the copper windings and the field core, and this current is also nearly in phase with the applied voltage. Both of these currents consume true power and are measured in watts. However, a significant amount of current does nothing but magnetize the field windings during part of the AC cycle, and that reactive energy is returned to the source as the magnetic field collapses just before the field is built up with the opposite polarity during the other half of the AC cycle. There are additional reactive losses, such as eddy-current and hysteresis losses, but the magnetizing currents are lagging the applied voltage, so they are the cause of apparent power which is expressed in volt-amperes reactive, also known as VARs. As was discussed at great length in this forum several months ago, one cannot measure true power with separate voltage and current meters. That is because the readings of separate meters are not synchronized in time. Even if one uses two true RMS DVMs to measure voltage and current, one still winds up with nothing more than apparent power based upon volts times amperes, or volt-amperes. To measure true power, one must use an AC power meter that synchronously measures current and voltage throughout the entire cycle. This can be performed by a device called a four-quadrant multiplier which, as its name implies, performs the multiplication of current and voltage through 360 degrees of phase rotation. One such instrument is a VIZ Instruments WD-767 Digital Wattmeter, which sold for about $925. Another device which has become very popular with Hams is the Kill-A-Watt meter that costs about $20 from several Internet vendors. Although not as accurate as the WD-767, it does perform quite well. As I stated in an earlier post, the rotating-disk kWH meter on the typical residence measures only true power. It does this magic by combining the magnetic fields of two coils: a voltage coil that is connected in parallel with the load, and a current coil that is in series with the load. The angular displacement of these coil windings is precisely set so that only currents that are exactly in phase with the voltage result in a torque to turn the aluminum disk. A small permanent magnet is placed near the disk so that the speed of the disk is proportional to the amount of true power being consumed. Since speed is movement over time, the disk is geared to a register that accumulates the number of rotations, which represents power over time, which is energy. Thus, the meter measures kilowatthours. You pay only for the true power that you actually use; you do not pay for apparent power since volt-amperes is not true power. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Barrett Sent: Tuesday, September 16, 2008 9:13 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) This doesn't mesh up with what I've learned about power factor -- the impression that I got was a perfect power factor was 1 (one) (current in phase with voltage, equipment using everything the the power company charges you for to do useful work). Anything other than PF=1 meant that the equipment was using the power less efficiently, and therefore you were paying more in KWH than the work actually performed. That description excludes the possibly that the equipment could use more power than the power company records as being delivered (heck, conservation of energy says that in any case). any load reactance (inductive or capacitive) and the very low PF numbers stated sound more like what I get off my linear power supplies
Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Eric, Kudos on a great explanation Doug - Original Message - From: Eric Lemmon To: Repeater-Builder@yahoogroups.com Sent: Tuesday, September 16, 2008 11:59 PM Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) John, You are correct that when the power factor is 1.00, the current is in phase with the voltage, as it will be in a purely resistive circuit. In this unique case, watts equals volt-amperes. However, when the load is reactive, the current either leads or lags the applied voltage. A typical case is a lightly-loaded induction motor, which may exhibit a power factor around 0.65, which is considered to be a poor PF. Some of the current drawn by this motor is used to create torque and perform actual work, and this current is nearly in phase with the applied voltage. Some current causes heating of the copper windings and the field core, and this current is also nearly in phase with the applied voltage. Both of these currents consume true power and are measured in watts. However, a significant amount of current does nothing but magnetize the field windings during part of the AC cycle, and that reactive energy is returned to the source as the magnetic field collapses just before the field is built up with the opposite polarity during the other half of the AC cycle. There are additional reactive losses, such as eddy-current and hysteresis losses, but the magnetizing currents are lagging the applied voltage, so they are the cause of apparent power which is expressed in volt-amperes reactive, also known as VARs. As was discussed at great length in this forum several months ago, one cannot measure true power with separate voltage and current meters. That is because the readings of separate meters are not synchronized in time. Even if one uses two true RMS DVMs to measure voltage and current, one still winds up with nothing more than apparent power based upon volts times amperes, or volt-amperes. To measure true power, one must use an AC power meter that synchronously measures current and voltage throughout the entire cycle. This can be performed by a device called a four-quadrant multiplier which, as its name implies, performs the multiplication of current and voltage through 360 degrees of phase rotation. One such instrument is a VIZ Instruments WD-767 Digital Wattmeter, which sold for about $925. Another device which has become very popular with Hams is the Kill-A-Watt meter that costs about $20 from several Internet vendors. Although not as accurate as the WD-767, it does perform quite well. As I stated in an earlier post, the rotating-disk kWH meter on the typical residence measures only true power. It does this magic by combining the magnetic fields of two coils: a voltage coil that is connected in parallel with the load, and a current coil that is in series with the load. The angular displacement of these coil windings is precisely set so that only currents that are exactly in phase with the voltage result in a torque to turn the aluminum disk. A small permanent magnet is placed near the disk so that the speed of the disk is proportional to the amount of true power being consumed. Since speed is movement over time, the disk is geared to a register that accumulates the number of rotations, which represents power over time, which is energy. Thus, the meter measures kilowatthours. You pay only for the true power that you actually use; you do not pay for apparent power since volt-amperes is not true power. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Barrett Sent: Tuesday, September 16, 2008 9:13 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) This doesn't mesh up with what I've learned about power factor -- the impression that I got was a perfect power factor was 1 (one) (current in phase with voltage, equipment using everything the the power company charges you for to do useful work). Anything other than PF=1 meant that the equipment was using the power less efficiently, and therefore you were paying more in KWH than the work actually performed. That description excludes the possibly that the equipment could use more power than the power company records as being delivered (heck, conservation of energy says that in any case). any load reactance (inductive or capacitive) and the very low PF numbers stated sound more like what I get off my linear power supplies with big capacitance and no power factor correction. In any case, anything other than PF=1 should mean that you are paying for more power than you are actually using. Tell me where I goofed this up ?? Bob M. wrote: Thank you Eric. This was the explanation I was looking
Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
--- On Tue, 9/16/08, Albert [EMAIL PROTECTED] wrote: From: Albert [EMAIL PROTECTED] Subject: [Repeater-Builder] Volt-Amp(Re: APC UPS Charging Power) To: Repeater-Builder@yahoogroups.com Date: Tuesday, September 16, 2008, 5:12 PM Hopefully you will forgive me hijacking the post but this brings up a question I have had for a long time. What on earth is a volt-amp. My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is is? Confused. Albert If you only have a resistance element then the watt and volt-amp are the same. It should really be VAR or volt-amp reactive. If the load has a very high reactance (capacitive or inductive) , the volt and amp will be out of phase. That is the maximum point on a voltage curve will not be at the same time as the maximum amp point. When you turn on a switch from a battery going through a resistor and put a voltmeter across the capacitor and an amp meter in series, the voltmeter will slowly start to rise and the amp meter will read maximum and then fall. This is a crude example as how the current and voltage get out of phase.
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Thank you Eric. This was the explanation I was looking for. The UPS is saving me money when drawing 181 Volt-Amps, yet the electric meter is only recording and charging me for 31 Watts. I wonder if APC did this on purpose. I don't know how much current is actually being fed to the batteries; they've been in there for a couple of months and should be fully charged by now, so it should just be trickling them (eight 12V 7A SLA cells in series/parallel for 48V). Bob M. == --- On Tue, 9/16/08, Eric Lemmon [EMAIL PROTECTED] wrote: From: Eric Lemmon [EMAIL PROTECTED] Subject: RE: [Repeater-Builder] Volt-Amp(Re: APC UPS Charging Power) To: Repeater-Builder@yahoogroups.com Date: Tuesday, September 16, 2008, 9:21 PM Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert
Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
This doesn't mesh up with what I've learned about power factor -- the impression that I got was a perfect power factor was 1 (one) (current in phase with voltage, equipment using everything the the power company charges you for to do useful work). Anything other than PF=1 meant that the equipment was using the power less efficiently, and therefore you were paying more in KWH than the work actually performed. That description excludes the possibly that the equipment could use more power than the power company records as being delivered (heck, conservation of energy says that in any case). any load reactance (inductive or capacitive) and the very low PF numbers stated sound more like what I get off my linear power supplies with big capacitance and no power factor correction. In any case, anything other than PF=1 should mean that you are paying for more power than you are actually using. Tell me where I goofed this up ?? Bob M. wrote: Thank you Eric. This was the explanation I was looking for. The UPS is saving me money when drawing 181 Volt-Amps, yet the electric meter is only recording and charging me for 31 Watts. I wonder if APC did this on purpose. I don't know how much current is actually being fed to the batteries; they've been in there for a couple of months and should be fully charged by now, so it should just be trickling them (eight 12V 7A SLA cells in series/parallel for 48V). Bob M. == --- On Tue, 9/16/08, Eric Lemmon [EMAIL PROTECTED] mailto:wb6fly%40verizon.net wrote: From: Eric Lemmon [EMAIL PROTECTED] mailto:wb6fly%40verizon.net Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Date: Tuesday, September 16, 2008, 9:21 PM Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Hi Eric, I agree with most of what you say, except the bit about generators and horsepower. I've always understood poor power factor to be a problem because the generator and distribution system needs to carry higher currents to deliver the same energy into a poor load. That's a problem because the power companies either suffer higher resistive (and financial) losses in their systems, or they need to use heavier distribution wiring and thicker wires in their transformers and generators (increasing the infrastructure costs). To offset these costs they financially discourage anyone from using poor power factor loads. It's the same in a generator set. The difference between the 1,000 Watt/ 1250 KVA rating is that with a bad load up to 250 Watts are wasted in resistive losses in the generator windings, requiring a bit more torque from the engine to provide the extra 250 Watts and some extra energy to further cool the generator. Electronic power supplies, especially older switch modes, cause a whole new set of problems. While they show up as poor power factor loads, they also create harmonics in the supply network, and that could show up on electronic power meters very inaccurately! Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Wednesday, 17 September 2008 11:22 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert Yahoo! Groups Links
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Ooops - typo - should have written 1.250 KVA, not 1250KVA as that would mean 1.250 MegaVA ! Mark -Original Message- From: Mark Harrison [mailto:[EMAIL PROTECTED] Sent: Wednesday, 17 September 2008 2:54 PM To: 'Repeater-Builder@yahoogroups.com' Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hi Eric, I agree with most of what you say, except the bit about generators and horsepower. I've always understood poor power factor to be a problem because the generator and distribution system needs to carry higher currents to deliver the same energy into a poor load. That's a problem because the power companies either suffer higher resistive (and financial) losses in their systems, or they need to use heavier distribution wiring and thicker wires in their transformers and generators (increasing the infrastructure costs). To offset these costs they financially discourage anyone from using poor power factor loads. It's the same in a generator set. The difference between the 1,000 Watt/ 1250 KVA rating is that with a bad load up to 250 Watts are wasted in resistive losses in the generator windings, requiring a bit more torque from the engine to provide the extra 250 Watts and some extra energy to further cool the generator. Electronic power supplies, especially older switch modes, cause a whole new set of problems. While they show up as poor power factor loads, they also create harmonics in the supply network, and that could show up on electronic power meters very inaccurately! Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Wednesday, 17 September 2008 11:22 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert Yahoo! Groups Links
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
John, You are correct that when the power factor is 1.00, the current is in phase with the voltage, as it will be in a purely resistive circuit. In this unique case, watts equals volt-amperes. However, when the load is reactive, the current either leads or lags the applied voltage. A typical case is a lightly-loaded induction motor, which may exhibit a power factor around 0.65, which is considered to be a poor PF. Some of the current drawn by this motor is used to create torque and perform actual work, and this current is nearly in phase with the applied voltage. Some current causes heating of the copper windings and the field core, and this current is also nearly in phase with the applied voltage. Both of these currents consume true power and are measured in watts. However, a significant amount of current does nothing but magnetize the field windings during part of the AC cycle, and that reactive energy is returned to the source as the magnetic field collapses just before the field is built up with the opposite polarity during the other half of the AC cycle. There are additional reactive losses, such as eddy-current and hysteresis losses, but the magnetizing currents are lagging the applied voltage, so they are the cause of apparent power which is expressed in volt-amperes reactive, also known as VARs. As was discussed at great length in this forum several months ago, one cannot measure true power with separate voltage and current meters. That is because the readings of separate meters are not synchronized in time. Even if one uses two true RMS DVMs to measure voltage and current, one still winds up with nothing more than apparent power based upon volts times amperes, or volt-amperes. To measure true power, one must use an AC power meter that synchronously measures current and voltage throughout the entire cycle. This can be performed by a device called a four-quadrant multiplier which, as its name implies, performs the multiplication of current and voltage through 360 degrees of phase rotation. One such instrument is a VIZ Instruments WD-767 Digital Wattmeter, which sold for about $925. Another device which has become very popular with Hams is the Kill-A-Watt meter that costs about $20 from several Internet vendors. Although not as accurate as the WD-767, it does perform quite well. As I stated in an earlier post, the rotating-disk kWH meter on the typical residence measures only true power. It does this magic by combining the magnetic fields of two coils: a voltage coil that is connected in parallel with the load, and a current coil that is in series with the load. The angular displacement of these coil windings is precisely set so that only currents that are exactly in phase with the voltage result in a torque to turn the aluminum disk. A small permanent magnet is placed near the disk so that the speed of the disk is proportional to the amount of true power being consumed. Since speed is movement over time, the disk is geared to a register that accumulates the number of rotations, which represents power over time, which is energy. Thus, the meter measures kilowatthours. You pay only for the true power that you actually use; you do not pay for apparent power since volt-amperes is not true power. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Barrett Sent: Tuesday, September 16, 2008 9:13 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) This doesn't mesh up with what I've learned about power factor -- the impression that I got was a perfect power factor was 1 (one) (current in phase with voltage, equipment using everything the the power company charges you for to do useful work). Anything other than PF=1 meant that the equipment was using the power less efficiently, and therefore you were paying more in KWH than the work actually performed. That description excludes the possibly that the equipment could use more power than the power company records as being delivered (heck, conservation of energy says that in any case). any load reactance (inductive or capacitive) and the very low PF numbers stated sound more like what I get off my linear power supplies with big capacitance and no power factor correction. In any case, anything other than PF=1 should mean that you are paying for more power than you are actually using. Tell me where I goofed this up ?? Bob M. wrote: Thank you Eric. This was the explanation I was looking for. The UPS is saving me money when drawing 181 Volt-Amps, yet the electric meter is only recording and charging me for 31 Watts. I wonder if APC did this on purpose. I don't know how much current is actually being fed to the batteries; they've been in there for a couple of months and should be fully charged by now, so it should just be trickling them (eight 12V 7A SLA cells in series
