J
jsmith
- Jan 1, 1970
- 0
Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?
output wave form such as square wave?
Because the power supplies in the equipment it is powering have allWhy such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?
jsmith said:Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?
jsmith said: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 thatjsmith said:Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?
-----------------------------------------------------------Question: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:-------------------------------------------------------->
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.
Probably the same marketing company that claims you need 'purejsmith said:Why such insistence on a UPS having a "pure" sinewave vs any other sort of
output wave form such as square wave?
jsmith said:-----------------------------------------------------------Question:
Wouldn't the filter capacitor enjoy receiving what amounts to alternating DC
in the form of a square wave?
But seriously folks, I ran a complete hardware/software engineering labLuhan said:Probably the same marketing company that claims you need 'pure
rocky-mountain spring water and high country barley'.
How does one design a power supply to accept a sine wave but not a square
wave??
<http://counter.li.org>John Tserkezis said: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.
jsmith said:So why not lower the peak voltage of the square wave to a safe level??
Larry said:That's a poor example, in the steady state (implied by
mentioning RMS). Consider instead the doubler used
in most off-line switching power supplies when strapped
to run off of 115 VAC. Your square waves will induce
much higher peak currents than the less steep wavefronts
of a sinusoid will.
sort of
Do a fourier transform on a square wave and you will find that it
represents the sum of the sine wave with same period, plus all the odd
hamonics of that sine wave, with amplitudes proportional to the
harmonic number - a 60Hz square wave is the sum of a 60Hz sine wave,
plus a 180Hz sine wave with one third of the amplitude, plus a 300Hz
sine wave with one fifth of the amplitude, and so on.
Put this into a transformer or a motor that is intended to be driven by
a 60Hz sine wave, and the higher harmonics excite extra eddy current in
the magnetic path, making the motor or the transformern run hotter than
it would have done if excited by a pure 60Hz sine wave.
The harmonics extend up to a frequency defined by the rise and fall
times of the square wave, which can be quite fast - fast enough to
interfere with local radio reception for a really cheap and nasty UPS.
jsmith said:So why not lower the peak voltage of the square wave to a safe level??
jsmith said:-------------------------------------------------------> >
-----------------------------------------------------------Question:
How does one design a power supply to accept a sine wave but not a square
wave??
John,jsmith said:-------------------------------------------------------> >
-----------------------------------------------------------Question:
How does one design a power supply to accept a sine wave but not a square
wave??
John Tserkezis said:but mass production wins every time: square or stepped square inverters are
much more popular
Terry said: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.