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| UPSonNet NewsLetter June 2010 |
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UPS Inverter Waveform & New Computer Servers
Editorial Topic: Potential Problems using Non Sinusoidal UPS Inverters in Stand-By and
Line Interactive UPS systems with new computer servers.
Energy Star, a joint program of U.S. Environmental Protection Agency (EPA) and U.S. Department
of Energy has published in June 2009 computer server specifications, which require to increase
server's input power factor (PF) to 0.95 from the common figure of about 0.65. This requires
introduction of Active Power Factor Correction (APFC) circuit in each server.
The resulting effect on UPS system, using the new Energy Star server specification, accepted by
other legislative authorities and server manufacturers all over the globe, was discussed in UPSonNet
June 2009 Newsletter. Considerations, that buyers should take in account when purchasing UPS
systems, are presented in our article titled Mind Watts and Volt Amperes when Specifying a UPS.
On 16 February 2010 EPA started a project to Evaluate UPS labeling , asking manufacturers to
comment on UPS Specification Framework document. The request and manufacturers comments are
displayed on the relevant Energy Star UPS page.
Energy Star specification considers only Power related issues of UPS systems; however Energy Star
requirement to increase server's power factor have significant importance not only on UPS Real and
Apparent or Total Power, but also on UPS output waveform, not treated by Energy Star.
Standby UPS systems and particularly Line Interactive UPS types became popular because of
considerably lower price when compared to online UPS solutions. The lowest price units, which are
also the most popular when compared to all other UPS types, reduce the price further on account of
non sinusoidal inverter output waveform.
Standby (called also battery backup) UPS systems connect the protected load normally to the input
utility Mains (Line) power. Whenever mains voltage deviates beyond a preprogrammed window; (
generally +/10% from its nominal voltage value), the load is switched to the output of a DC to AC
Inverter, which supplies the critical power from backup batteries
Line Interactive UPS systems operate in similar way, but here an additional transformer is included
which acts as automatic voltage regulator (AVR) interacting with the input line, enabling to extend the
input voltage window size beyond +/- 10%. This ability enables the Line interactive UPS to solve
almost 95% of voltage excursions before transferring to UPS Inverter (battery operation), and is
therefore considered a cost effective solution for most consumers including servers.
For more information please see: UPS Basics article.
As long as the Mains voltage is within voltage window limits, the loads are driven by sinusoidal
waveform from the mains. Upon mains excursion beyond the input window, including the case of
power outage, the Inverter kicks in and dictates the voltage waveform supplied to the load.
An Inverter with sinusoidal output voltage waveform should be the preferred solution. Such
waveform doesn't have harmonics, it is identical with the mains voltage, and complies with the
requirements of all systems designed to work from the utility, including also computer servers.
Sinusoidal Inverters are standard in Online UPS types, and in certain more expensive line interactive
systems. Economical considerations however, cause most UPS manufacturers to use Inverters
either with square type waveform implemented generally in simple battery backup systems, or with
rectangular pulse width modulated waveform, generally called Modified Sine Wave, or Semi
sinusoidal waveform, implemented in most popular Line Interactive types.
The square type voltage waveform has about 45% total harmonic content, and cannot be regulated,
whereas the width of the pulse in Modified Sine Wave can be adjusted to decrease voltage harmonics
to about 25% while enabling by varying the width of the pulse to stabilize Inverter's output voltage,
as well as to limit the output current in order to protect the inverter from overloads.
The "modified sine wave" waveform despite the name, given by UPS manufacturers is far from
resembling a sinusoid. Such Inverters are not designed to work with numerous loads such as, as, air
conditioning units, fans, vacuum cleaners, stereos, DVD players, computer monitors, laser printers,
or rotary field engines, that use condensers for generation of an auxiliary phase such as refrigerators,
washing machines, dishwashers. They won't work properly with Fluorescent lamps having series
choke to limit the operating current, nor with consumers that have built-in clocks pacing time based
on line voltage zero crossing such as clock radios, alarm clocks, coffee makers, thyristor regulated
chargers and more.
UPS systems with modified sine wave inverters work however properly with simple uncontrolled
diode type rectifier circuits with capacitive filters implemented in most Personal computers and
conventional servers. Such UPS systems are therefore widely used in personal computers, work
stations and data center servers.
Introduction of servers with Active PFC circuits poses a new problem. An active PFC controls the
input current of the load to get current waveform proportional to and in phase with mains voltage
sine waveform. Server's APFC circuits, designed to comply with the new legislations, are not
designed to operate with a rectangular voltage waveforms. The possible behavior when driving APFC
servers from modified sine wave inverter, depend on the particular APFC design and cannot be
predicted.
The problems encountered when APFC power supplies are fed from modified sine wave UPS
systems are now frequently discussed on UPS related user's forums and in user's experience related
articles. To illustrate, here is a description of experience learned by a user named Bruce Berls when
he changed his old computer, with a new Dell computer with APFC power supply, to the same APC
Line Interactive Back UPS system:
"Within a few days, it rebooted spontaneously and presented me with a login screen. It did it again a
couple of days later. Very shortly it was happening frequently, as often as once a day. It happened a
couple of times while I was using the computer – either the computer froze hard or it went black and
restarted. In each case there was no warning and nothing in the event logs to explain what was going
on. "
Bruce checked deeper, finding out that the problem occurs due to connecting the new Dell computer
to APC's Back UPS UPS which has a modified sine wave inverter. Bruce says that : " Dell is
acknowledging the issue but quietly so far – for example, this now appears in the fine print about the
Precision T7500:
"The system uses a very efficient Active Power Factor Correction (APFC) power supply. Dell
recommends only Universal Power Supplies (UPS) based on Sine Wave output for APFC PSUs, not
an approximation of a Sine Wave, Square Wave or quasi-Square Wave (see UPS Technical
Specifications). If you have questions, please contact the manufacturer to confirm the output type."
Bruce's specific problem can be solved by using for instance APC's Smart UPS type instead, which
has a sinusoidal inverter. But the real problem is considerably more complicated, much beyond the
additional cost of a sine wave UPS, due to the following reasons:
1. Line Interactive systems available at the local store or computer dealers are mainly of the Modified
Sine Wave inverter type.
2. Most sellers and dealers have no idea what kind of output wave form is supplied in the UPS which
they sell.
3. Type of UPS waveform doesn't always appear in most UPS brochures, and isn't always declared
in technical specifications.
4. Most users do not know about, and do not understand the problem.
As evidenced by Bruc'es article titled :" Powered by pure sine waves!" ( Bruce mistakenly uses the
term Modified Square-Wave, instead of Modified Sine-Wave).
Please read on to see how we intend to help users to select the right system.
Remark: Certain links in this and future e-mails refer to archived and other restricted information on
UPSonNet website, requesting members to log-in. UPSonNet membership offers unrestricted access to
entire website. Dramatic, limited time, discount is now offered to newsletter subscribers
See Member Sign-UP page.
UPSonNet Website News
We have recently introduced on Our Website an Online UPS Features and Prices Guide , which
compares Single Phase systems from main USA manufacturer's, temporarily available to all website
visitors . The publication was accompanied by Press Release which gained significant publishing as
can be seen by entering on Google the phrase: UPSonNet Launches Features and Price Guide.
To help users to select a sinusoidal line Interactive UPS, we intend to present also a "Line Interactive
UPS Guide".
We are now preparing also a similar guide concerned with Three Phase UPS Systems, which will
include most global 50/60Hz voltage systems.
We welcome suggestions concerned with the content of any or both guides, as well as requests from
manufacturers, or recommendations to include specific product lines. Please e-mail to
denis@upsonnet.com
UPS Industry News
Two news items published in our June News deserve attention:
Emerson has eventually made it, by convincing Chloride to accept its new buy out offer. Chloride's
investors made it big, when their shares price boosted from 205 pence/ share in April to the current
price of 373 pence/share. As indicated in the relevant news, initial Emerson's $ 1.1 Billion offer in
April , Chloride's board reaction, the effect of Chlorides financial results for 31 March 2010, ABB's
role when placing an offer, and finally Emerson's decision to increase its offer to $ 1.5 Billion, all tell
an interesting story about bargaining and company valuation.
May 2010 Newsletter topic titled Best UPS Battery Technology, was dedicated to comparison of
GE's sodium metal halide UPS batteries to lead acid battery, indicating how GE's batteries offer a
solution which solves most lead acid battery drawbacks.
In June, Sony announces Lithium Ion rechargeable batteries for UPS use, which offer another
alternative to conventional lead acid solution. The modular structure, with the ability of parallel or
serial module connection, and self-monitoring function, is of particular interest as it offers a new
solution, which deserves user's attention.
Remark : Certain links on UPSonNet website are available only to subscribed members. For
Unrestricted access to the entire site please Sign-UP.
We welcome remarks on any Newsletter issue. Please e-mail to: denis@upsonnet.com
_________________________________________________________________
To receive this newsletter in your e-mail, please subscribe
Please forward this Newsletter to your friend, that might be interested.
Editorial Topic: Potential Problems using Non Sinusoidal UPS Inverters in Stand-By and
Line Interactive UPS systems with new computer servers.
Energy Star, a joint program of U.S. Environmental Protection Agency (EPA) and U.S. Department
of Energy has published in June 2009 computer server specifications, which require to increase
server's input power factor (PF) to 0.95 from the common figure of about 0.65. This requires
introduction of Active Power Factor Correction (APFC) circuit in each server.
The resulting effect on UPS system, using the new Energy Star server specification, accepted by
other legislative authorities and server manufacturers all over the globe, was discussed in UPSonNet
June 2009 Newsletter. Considerations, that buyers should take in account when purchasing UPS
systems, are presented in our article titled Mind Watts and Volt Amperes when Specifying a UPS.
On 16 February 2010 EPA started a project to Evaluate UPS labeling , asking manufacturers to
comment on UPS Specification Framework document. The request and manufacturers comments are
displayed on the relevant Energy Star UPS page.
Energy Star specification considers only Power related issues of UPS systems; however Energy Star
requirement to increase server's power factor have significant importance not only on UPS Real and
Apparent or Total Power, but also on UPS output waveform, not treated by Energy Star.
Standby UPS systems and particularly Line Interactive UPS types became popular because of
considerably lower price when compared to online UPS solutions. The lowest price units, which are
also the most popular when compared to all other UPS types, reduce the price further on account of
non sinusoidal inverter output waveform.
Standby (called also battery backup) UPS systems connect the protected load normally to the input
utility Mains (Line) power. Whenever mains voltage deviates beyond a preprogrammed window; (
generally +/10% from its nominal voltage value), the load is switched to the output of a DC to AC
Inverter, which supplies the critical power from backup batteries
Line Interactive UPS systems operate in similar way, but here an additional transformer is included
which acts as automatic voltage regulator (AVR) interacting with the input line, enabling to extend the
input voltage window size beyond +/- 10%. This ability enables the Line interactive UPS to solve
almost 95% of voltage excursions before transferring to UPS Inverter (battery operation), and is
therefore considered a cost effective solution for most consumers including servers.
For more information please see: UPS Basics article.
As long as the Mains voltage is within voltage window limits, the loads are driven by sinusoidal
waveform from the mains. Upon mains excursion beyond the input window, including the case of
power outage, the Inverter kicks in and dictates the voltage waveform supplied to the load.
An Inverter with sinusoidal output voltage waveform should be the preferred solution. Such
waveform doesn't have harmonics, it is identical with the mains voltage, and complies with the
requirements of all systems designed to work from the utility, including also computer servers.
Sinusoidal Inverters are standard in Online UPS types, and in certain more expensive line interactive
systems. Economical considerations however, cause most UPS manufacturers to use Inverters
either with square type waveform implemented generally in simple battery backup systems, or with
rectangular pulse width modulated waveform, generally called Modified Sine Wave, or Semi
sinusoidal waveform, implemented in most popular Line Interactive types.
The square type voltage waveform has about 45% total harmonic content, and cannot be regulated,
whereas the width of the pulse in Modified Sine Wave can be adjusted to decrease voltage harmonics
to about 25% while enabling by varying the width of the pulse to stabilize Inverter's output voltage,
as well as to limit the output current in order to protect the inverter from overloads.
The "modified sine wave" waveform despite the name, given by UPS manufacturers is far from
resembling a sinusoid. Such Inverters are not designed to work with numerous loads such as, as, air
conditioning units, fans, vacuum cleaners, stereos, DVD players, computer monitors, laser printers,
or rotary field engines, that use condensers for generation of an auxiliary phase such as refrigerators,
washing machines, dishwashers. They won't work properly with Fluorescent lamps having series
choke to limit the operating current, nor with consumers that have built-in clocks pacing time based
on line voltage zero crossing such as clock radios, alarm clocks, coffee makers, thyristor regulated
chargers and more.
UPS systems with modified sine wave inverters work however properly with simple uncontrolled
diode type rectifier circuits with capacitive filters implemented in most Personal computers and
conventional servers. Such UPS systems are therefore widely used in personal computers, work
stations and data center servers.
Introduction of servers with Active PFC circuits poses a new problem. An active PFC controls the
input current of the load to get current waveform proportional to and in phase with mains voltage
sine waveform. Server's APFC circuits, designed to comply with the new legislations, are not
designed to operate with a rectangular voltage waveforms. The possible behavior when driving APFC
servers from modified sine wave inverter, depend on the particular APFC design and cannot be
predicted.
The problems encountered when APFC power supplies are fed from modified sine wave UPS
systems are now frequently discussed on UPS related user's forums and in user's experience related
articles. To illustrate, here is a description of experience learned by a user named Bruce Berls when
he changed his old computer, with a new Dell computer with APFC power supply, to the same APC
Line Interactive Back UPS system:
"Within a few days, it rebooted spontaneously and presented me with a login screen. It did it again a
couple of days later. Very shortly it was happening frequently, as often as once a day. It happened a
couple of times while I was using the computer – either the computer froze hard or it went black and
restarted. In each case there was no warning and nothing in the event logs to explain what was going
on. "
Bruce checked deeper, finding out that the problem occurs due to connecting the new Dell computer
to APC's Back UPS UPS which has a modified sine wave inverter. Bruce says that : " Dell is
acknowledging the issue but quietly so far – for example, this now appears in the fine print about the
Precision T7500:
"The system uses a very efficient Active Power Factor Correction (APFC) power supply. Dell
recommends only Universal Power Supplies (UPS) based on Sine Wave output for APFC PSUs, not
an approximation of a Sine Wave, Square Wave or quasi-Square Wave (see UPS Technical
Specifications). If you have questions, please contact the manufacturer to confirm the output type."
Bruce's specific problem can be solved by using for instance APC's Smart UPS type instead, which
has a sinusoidal inverter. But the real problem is considerably more complicated, much beyond the
additional cost of a sine wave UPS, due to the following reasons:
1. Line Interactive systems available at the local store or computer dealers are mainly of the Modified
Sine Wave inverter type.
2. Most sellers and dealers have no idea what kind of output wave form is supplied in the UPS which
they sell.
3. Type of UPS waveform doesn't always appear in most UPS brochures, and isn't always declared
in technical specifications.
4. Most users do not know about, and do not understand the problem.
As evidenced by Bruc'es article titled :" Powered by pure sine waves!" ( Bruce mistakenly uses the
term Modified Square-Wave, instead of Modified Sine-Wave).
Please read on to see how we intend to help users to select the right system.
Remark: Certain links in this and future e-mails refer to archived and other restricted information on
UPSonNet website, requesting members to log-in. UPSonNet membership offers unrestricted access to
entire website. Dramatic, limited time, discount is now offered to newsletter subscribers
See Member Sign-UP page.
UPSonNet Website News
We have recently introduced on Our Website an Online UPS Features and Prices Guide , which
compares Single Phase systems from main USA manufacturer's, temporarily available to all website
visitors . The publication was accompanied by Press Release which gained significant publishing as
can be seen by entering on Google the phrase: UPSonNet Launches Features and Price Guide.
To help users to select a sinusoidal line Interactive UPS, we intend to present also a "Line Interactive
UPS Guide".
We are now preparing also a similar guide concerned with Three Phase UPS Systems, which will
include most global 50/60Hz voltage systems.
We welcome suggestions concerned with the content of any or both guides, as well as requests from
manufacturers, or recommendations to include specific product lines. Please e-mail to
denis@upsonnet.com
UPS Industry News
Two news items published in our June News deserve attention:
Emerson has eventually made it, by convincing Chloride to accept its new buy out offer. Chloride's
investors made it big, when their shares price boosted from 205 pence/ share in April to the current
price of 373 pence/share. As indicated in the relevant news, initial Emerson's $ 1.1 Billion offer in
April , Chloride's board reaction, the effect of Chlorides financial results for 31 March 2010, ABB's
role when placing an offer, and finally Emerson's decision to increase its offer to $ 1.5 Billion, all tell
an interesting story about bargaining and company valuation.
May 2010 Newsletter topic titled Best UPS Battery Technology, was dedicated to comparison of
GE's sodium metal halide UPS batteries to lead acid battery, indicating how GE's batteries offer a
solution which solves most lead acid battery drawbacks.
In June, Sony announces Lithium Ion rechargeable batteries for UPS use, which offer another
alternative to conventional lead acid solution. The modular structure, with the ability of parallel or
serial module connection, and self-monitoring function, is of particular interest as it offers a new
solution, which deserves user's attention.
Remark : Certain links on UPSonNet website are available only to subscribed members. For
Unrestricted access to the entire site please Sign-UP.
We welcome remarks on any Newsletter issue. Please e-mail to: denis@upsonnet.com
_________________________________________________________________
To receive this newsletter in your e-mail, please subscribe
Please forward this Newsletter to your friend, that might be interested.
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