UPS sine wave vs square wave output?

[jsmith]

Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?

 

[Don Pearce]

On Tue, 22 Feb 2005 17:04:21 -0500, "jsmith" <juddo@ix.netcom.com>
wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?

Because the power supplies in the equipment it is powering have all

been designed to accept a sine wave from the mains supply. There is no
guarantee how they would behave when presented with a square wave.

d

Pearce Consulting
http://www.pearce.uk.com

 

[Larry Brasfield]

"jsmith" <juddo@ix.netcom.com> wrote in message
news:1109109248.47a9b4f4aabdc28f3a2836c54efe85d7@sonicnews...

Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?

Many devices are over-stressed when powered from
square waves, or approximations thereof. For example,
a simple diode rectifier feeding a resevoir capacitor will
experience much higher RMS current when fed that way.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Luhan Monat]

jsmith wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?


Probably the same marketing company that claims you need 'pure

rocky-mountain spring water and high country barley'.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm

 

[Charles Edmondson]

jsmith wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?


Basically because there are things attached to them that assume that

they have sine waves, and behave very badly when when they get other
waveforms...

Motors, transformers, some electronics, esp. power supplies are designed
around low harmonic content sine waves. Give them bad waveforms, and
they loose efficiency, get warm, release magic smoke from components...

--
Charlie
--
Edmondson Engineering
Unique Solutions to Unusual Problems

 

[Luhan Monat]

Luhan Monat wrote:

jsmith wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other
sort of
output wave form such as square wave?


Probably the same marketing company that claims you need 'pure
rocky-mountain spring water and high country barley'.

But seriously folks, I ran a complete hardware/software engineering lab

out of a motorhome for several years. My Trace 810 inverter (modified
square wave) ran everything just fine. Thats not to say that some
electonic equipent may have problems - especially AM radios.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm

 

[jsmith]

Why such insistence on a UPS having a "pure" sinewave vs any other sort
of
output wave form such as square wave?
-------------------------------------------------------
Because the power supplies in the equipment it is powering have all
been designed to accept a sine wave from the mains supply. There is no
guarantee how they would behave when presented with a square wave.

-----------------------------------------------------------Question:

How does one design a power supply to accept a sine wave but not a square
wave??

 

[jsmith]

Why such insistence on a UPS having a "pure" sinewave vs any other sort
of
output wave form such as square wave?

--------------------------------------------------------
Many devices are over-stressed when powered from
square waves, or approximations thereof. For example,
a simple diode rectifier feeding a resevoir capacitor will
experience much higher RMS current when fed that way.

-----------------------------------------------------------Question:

Wouldn't the filter capacitor enjoy receiving what amounts to alternating DC
in the form of a square wave?

 

[John Tserkezis]

jsmith wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other sort
of output wave form such as square wave?

Because the power supplies in the equipment it is powering have all
been designed to accept a sine wave from the mains supply. There is no
guarantee how they would behave when presented with a square wave.

How does one design a power supply to accept a sine wave but not a square
wave??

You don't. Not intentionally anyway.

A square wave input of the same RMS value of an equivalent sine wave will
have a much higher crest factor. That is, the peak value is *much* higher in
relation to the RMS value, as compared to a sine wave.

Most power supplies simply bridge rectify the AC input, and feed that
somewhat pulsating DC into the regulator that does the bulk of the work.

With a sine input, that peak DC at the filters will be 1.4 times the sine RMS
value.
With a stepped square wave, or worse still, a pure square wave input of the
same RMS value as your sine input will have a peak much higher.

Thus, if your components are only expecting a peak of X volts, and you force
feed it something significantly higher than X, it'll blow.
--
Linux Registered User # 302622 <http://counter.li.org>

 

[Roger Lascelles]

"jsmith" <juddo@ix.netcom.com> wrote in message
news:1109138630.ef131eba900a3bfb6cccf1babb4b7358@sonicnews...

So why not lower the peak voltage of the square wave to a safe level??

Its not just the peak level which matters. Imagine a disharged capacitor
connected to a low impedance squarewave generator. The squarewave goes up
fast and the capacitor voltage must follow. This means a large current
flows through the diode and the capacitor. Now imagine a sinewave : the
capacitor has to follow the sinewave as it climbs up. The current pulse is
stretched out and not as large in amplitude.

Result : Transformer, diode and capacitor RMS current is less, which means
less heating of these parts.

Roger

 

[Pooh Bear]

jsmith wrote:

Why such insistence on a UPS having a "pure" sinewave vs any other sort
of
output wave form such as square wave?
-------------------------------------------------------
Because the power supplies in the equipment it is powering have all
been designed to accept a sine wave from the mains supply. There is no
guarantee how they would behave when presented with a square wave.

-----------------------------------------------------------Question:

How does one design a power supply to accept a sine wave but not a square
wave??

Start by considering the difference between the rms and peak voltage values
for each waveform.


Graham

 

[Fabio G.]

John Tserkezis <jt@techniciansyndrome.org.invalid> ha scritto:

but mass production wins every time: square or stepped square inverters are
much more popular

However for medium/high power (>3-4 kVA) they are always sine wave
inverters (PWM bridge + LC filter)

--
Per rispondermi via email sostituisci il risultato
dell'operazione (in lettere) dall'indirizzo

 

[Guy Macon]

Terry Given wrote:

Which is why the 900W OEM UPS' I worked on in MA had extremely long
switching times - the "square" waves had edges of around 500us - 1ms.
Think I=C*dV/dt. In our case the "problem" that steep edges caused was
the X capacitor in the downstream equipment, just like Larrys voltage
doubler.

It also helps that many "square wave" UPSs don't just go from full
pluss to full minus, but instead go plus -> zero -> minus -> zero
-> plus -> and so forth. I seem to remember reading about a few
that would have five or seven voltage levels instead of three.

 

[John Tserkezis]

Fabio G. wrote:

but mass production wins every time: square or stepped square inverters are
much more popular

However for medium/high power (>3-4 kVA) they are always sine wave
inverters (PWM bridge + LC filter)

Perhaps because of the higher price tag for units of that power, the
additional cost of sine is less significant than for a lower power inverter?
--
Linux Registered User # 302622 <http://counter.li.org>

 

[Guy Macon]

Ken Smith wrote:

Most "square wave" converters don't really make a square wave.
They make a signal like this:

ASCII Art:

...******............******.......
..................................
..................................
***......***......***......***.... 0V
..................................
..................................
............******............****

Something just occured to me as being the sort of thing I should
already know; during the 0V periods, is the output high impedence
as one would expect with minimum FETs, or is there an extra set of
FETs that clamp it to 0V? If it is high impedence, I would expect
some interesting waveforms as the inductance of the load drives
the line. If it is clamped to 0V, it would be interesing to see
hopw they derive that 0V in single phase hot/neutral systems where
the bottom trace is zero volts relative to earth/ground.

 

[John Tserkezis]

gwhite wrote:

A square wave input of the same RMS value of an equivalent sine wave will
have a much higher crest factor.

Huh? The crest factor of a sq-wave is 1 (0 dB). The crest factor of a
sine-wave is 1.414 (3 dB). Why do you believe what you wrote?

Because your statement only holds true for a square wave operating at 100%
duty. That certainly is not the case for most of the time and probably not the
case for ANY of the time in many cases.
--
Linux Registered User # 302622 <http://counter.li.org>

 

[John Woodgate]

I read in sci.electronics.design that Ken Smith
<kensmith@green.rahul.net> wrote (in <cvlu0a$ms$1@blue.rahul.net&gt about
'UPS sine wave vs square wave output?', on Fri, 25 Feb 2005:

Newer supplies rectify the
input and run the pulsating DC with nearly no filtering into a DC-DC
converter that is designed so that over the period of a few cycles its
input current is proportional to the applied voltage. This regulator
does not regulate very well and is followed by a large filter capacitor
and a second DC-DC converter. This is how modern power supplies make
themselves appear to be resistive loads to the power grid.

What are these power supplies used for? What is the incentive to make
the load resistive (outside Europe)?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Ken Smith]

In article <OGU23mDax0HCFwrJ@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
[...]

Indeed, the EMC requirements in this case gel with sensible design
decisions. However, there are no harmonics emission requirements for 1
kW lab power supplies. YET.

I was using a <Name deleted> power supply in a rack mounted system. I
discovered that the fool thing made about 1V spikes from corner to corner
on its chassis when running. ie: with the lid on, if you grounded the
scope to the back of the metal cover and probed the front of the very same
chunk of aluminum, you'd see the spike.

The frequency content of this noise would drift around until it landed in
the bandwidth of interest.

Even without a government action, there is a limit to the emissions. It
is when the thing you are trying to run won't operate if the supply is on.

--
--
kensmith@rahul.net forging knowledge

 

[John Woodgate]

I read in sci.electronics.design that Ken Smith
<kensmith@green.rahul.net> wrote (in <cvomgc$9dq$3@blue.rahul.net&gt
about 'UPS sine wave vs square wave output?', on Sat, 26 Feb 2005:

Even without a government action, there is a limit to the emissions. It
is when the thing you are trying to run won't operate if the supply is
on.

Presumably that spike wasn't associated with mains harmonics, but your
statement is correct. 'Auto-EMC' can be quite a problem with compact
designs, especially with mixed technologies as well.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk