Square waves from UPS into transformer increase heating?

[Neil]

I have a transformer for my laptop, presumable output several volts. Whether
charging or not, it warms up some of course from agitation of the ferrite
domains, but not really hot. However, when I plug it from my APC brand UPS, I am
quite sure it gets hotter than usual. The manual for the UPS states that output
is a stepped-wave (square steps) approximation to sinusoidal output. Presumably
that works OK in computers and most things, but I wonder: each of those sudden
little jumps is a rapid dV/dt, and I figure that stresses and heats the
transformer more than a sine wave. Think so? Heard or thought about this? The
manufacturers don't warn about this. I think it could be degrading the
transformer, because it gets very hot and I don't run it off the UPS anymore. I
also wonder if transformer output is a nice sine wave, or shows distortion from
stepped input. Could this type of voltage output from UPS be damaging equipment
out there, and not appreciated?

 

[r5]

little jumps is a rapid dV/dt, and I figure that stresses and heats the

The harmonics due to these little jumps are going to be very weak.
How many pulses are being used to define the sine wave? I assumed
100 pulses and calculated the MSE between the pulsed sine wave and
an ideal sine wave over a single cycle to yield roughly 6.5e-4.
I don't think a transformer is going to heat up due to 0.065% of
the input waveform energy being in higher order harmonics, at least
for the example of the 100 pulse sine wave.

 

[Jim Ghrist]

If your laptop is like mine, the output from the ac adapter is dc, not ac.
My adapter is a Toshiba Model PA245OU with 100-240 vac input and 15 vdc
output. While the adapter may run a little hotter with a high harmonic
content source like your UPS, I doubt if this will have a significant effect
on the life. If you have a good battery on your laptop, I see no need to
use a UPS, however.

 

[[email protected]]

I have a transformer for my laptop, presumable output several volts. Whether
charging or not, it warms up some of course from agitation of the ferrite
domains, but not really hot. However, when I plug it from my APC brand UPS, I am
quite sure it gets hotter than usual. The manual for the UPS states that output
is a stepped-wave (square steps) approximation to sinusoidal output. Presumably
that works OK in computers and most things, but I wonder: each of those sudden
little jumps is a rapid dV/dt, and I figure that stresses and heats the
transformer more than a sine wave. Think so? Heard or thought about this? The
manufacturers don't warn about this. I think it could be degrading the
transformer, because it gets very hot and I don't run it off the UPS anymore. I
also wonder if transformer output is a nice sine wave, or shows distortion from
stepped input. Could this type of voltage output from UPS be damaging equipment
out there, and not appreciated?

Highly unlikely it is the tiny harmonics doing this.

More likely it is your line voltage is low while the UPS always puts out
117-120 volts.

A quick measurement of the line voltage versus the UPS output voltage
will confirm or refute.

 

[Nam Paik]

However, when I plug it from my APC brand UPS, I am

quite sure it gets hotter than usual. The manual for the UPS states that output
is a stepped-wave (square steps) approximation to sinusoidal output. Presumably
that works OK in computers and most things, but I wonder: each of those sudden
little jumps is a rapid dV/dt, and I figure that stresses and heats the
transformer more than a sine wave.

Any waveform other than sinewave will stress transformers & other
parts in the power supply more (thus extra heat generated). UL 1778
is the standard which applies to UPS systems, and for that reason, no
longer than 30 minutes of operation in stepped wave (modified
squarewave) is allowed under UL 1778.

This 30 minute limit is somewhat arbitrary since some power supplies
will work fine for hours whereas other power supplies might be damaged
even after 5 minutes. So, my recommendation would be to just operate
it on UPS for 1 minute or so for orderly shutdown and wait until
utility AC is restored. Then, UPS will send the utility power (which
is sinewave AC) to your power supply & everything will be OK.

To run any device for over 1 or 2 minutes without overheating (& thus
damaging the power supply in the equipment), you need to use UPS with
Sinewave Output Inverter - so that you get sinewave output even if UPS
is running on battery.

 

[Roy McCammon]

I have a transformer for my laptop, presumable output several volts. Whether
charging or not, it warms up some of course from agitation of the ferrite
domains, but not really hot. However, when I plug it from my APC brand UPS, I am
quite sure it gets hotter than usual. The manual for the UPS states that output
is a stepped-wave (square steps) approximation to sinusoidal output. Presumably
that works OK in computers and most things, but I wonder: each of those sudden
little jumps is a rapid dV/dt, and I figure that stresses and heats the
transformer more than a sine wave. Think so? Heard or thought about this?

Yes, it is a well known phenomena. It doesn't have to be that way, but
to save money, space and weight, power transformers are run very close
to saturation. The few extra volt seconds in the square wave may go
ahead and saturate the core. At that point, it is only the winding
resistance that limits current and you get a nasty current spike through
the primary winding.

 

[Neil]

The harmonics due to these little jumps are going to be very weak.
How many pulses are being used to define the sine wave? I assumed
100 pulses and calculated the MSE between the pulsed sine wave and
an ideal sine wave over a single cycle to yield roughly 6.5e-4.
I don't think a transformer is going to heat up due to 0.065% of
the input waveform energy being in higher order harmonics, at least
for the example of the 100 pulse sine wave.

Thanks to all for their replies. However, you don't all agree, and most of the
others are saying that there is a noticeable effect. One says it's from the UPS
giving out a bit more voltage than I get from the socket, some others say it is
indeed the stepping in some way. I'm not sure how you calculated exactly, but
doesn't it matter how fast the step rises, not just how many steps there are?
I'm not sure how to evaluate the theory and opinions, but the bottom line for me
is, I am sure the transformer gets hotter.

 

[DarkMatter]

Highly unlikely it is the tiny harmonics doing this.

If they were indeed tiny.

More likely it is your line voltage is low while the UPS always puts out
117-120 volts.

That shouldn't change the behavior of a device plugged into the UPS.
Otherwise, the UPS is out-of-spec.

A quick measurement of the line voltage versus the UPS output voltage
will confirm or refute.

That would or could confirm that he is feeding a different voltage
to the module. This WOULD be a factor. If the UPS put out more
voltage than the line, the module would likely waste more than at
nominal or low line conditions.

Besides, it isn't the UPS transformer getting hot, it is the small
laptop module that he states is heating more. Input line sags would
not cause this, if as you stated, the UPS is always supplying 120VAC
or whatever constant voltage..

Also, the harmonic content of square waves through a transformer made
for 50 - 60Hz is not "tiny".

 

[[email protected]]

If they were indeed tiny.

Which they are in a modern UPS.

That shouldn't change the behavior of a device plugged into the UPS.
Otherwise, the UPS is out-of-spec.

Say the line voltage is 109 and the UPS output is 119 just for arguement
sake. Why would you not think a device plugged into the UPS is dissipating
more power than the same device plugged into the line?

That would or could confirm that he is feeding a different voltage
to the module. This WOULD be a factor. If the UPS put out more
voltage than the line, the module would likely waste more than at
nominal or low line conditions.

That is the whole point.

Besides, it isn't the UPS transformer getting hot, it is the small
laptop module that he states is heating more. Input line sags would
not cause this, if as you stated, the UPS is always supplying 120VAC
or whatever constant voltage..

Sigh. The module gets hotter plugged into the UPS than it does plugged
into the line. When your are plugged into the line, you see the sags.

Also, the harmonic content of square waves through a transformer made
for 50 - 60Hz is not "tiny".

True, but modern UPSs don't put out square waves, they put out stepped
sines.

 

[[email protected]]

news:[email protected]...

Thanks to all for their replies. However, you don't all agree, and most of the
others are saying that there is a noticeable effect. One says it's from the UPS
giving out a bit more voltage than I get from the socket, some others say it is
indeed the stepping in some way. I'm not sure how you calculated exactly, but
doesn't it matter how fast the step rises, not just how many steps there are?
I'm not sure how to evaluate the theory and opinions, but the bottom line for me
is, I am sure the transformer gets hotter.

There is no way to tell for sure without some measurements and/or experiments.

If you really want to know, measure the temperature rise. Put an AC line
filter between the UPS and the transformer and measure the temperature
rise again.

Measure the line voltage and the UPS output voltage. Get a variac and
put it between the transformer and the line. Measure the temperature rise
at nominal line voltage and at nominal UPS voltage.

Report back with your findings.

Doing this as a calculation that has any validity would require a hell of
a lot more information, and equipment to get that information, than the
simple experiment outlined above.

 

[DarkMatter]

Say the line voltage is 109 and the UPS output is 119 just for arguement
sake. Why would you not think a device plugged into the UPS is dissipating
more power than the same device plugged into the line?

In your own words, you state that the UPS voltage is constant, and
refer to the line voltage being low, not the UPS output voltage.

UPSs by their nature, put out a constant AC output voltage from
fed-thru-ac power to full-on-battery power, all the way down to the
low line spec for the battery voltage as it discharges. That entire
time, the output AC voltage won't move more than 1.2 volts.

The device dissipates the same power on it's output side either way.
The question is what are the costs of operation.

At low line, the device should usually be the least lossy (read most
efficient), so your argument fails.

If the UPS puts out a higher voltage than the line does, the device
might be warmer on the UPS.

 

[DarkMatter]

True, but modern UPSs don't put out square waves, they put out stepped
sines.

What frequency does it get quantisized / step modulated at?

 

[[email protected]]

In your own words, you state that the UPS voltage is constant, and
refer to the line voltage being low, not the UPS output voltage.
Yes.

UPSs by their nature, put out a constant AC output voltage from
fed-thru-ac power to full-on-battery power, all the way down to the
low line spec for the battery voltage as it discharges. That entire
time, the output AC voltage won't move more than 1.2 volts.
Yes.

The device dissipates the same power on it's output side either way.
The question is what are the costs of operation.
Yes.

At low line, the device should usually be the least lossy (read most
efficient), so your argument fails.
How?

If the UPS puts out a higher voltage than the line does, the device
might be warmer on the UPS.

Exactly the point.

The device gets hotter plugged into the UPS than it does plugged into the
line.

Now do you get it?

 

[[email protected]]

What frequency does it get quantisized / step modulated at?

Depends on the UPS model and who made it, you tell me.

In general, a bit higher than 60 Hz.

 

[Paul R. Mays]

Thanks to all for their replies. However, you don't all agree, and most of the
others are saying that there is a noticeable effect. One says it's from the UPS
giving out a bit more voltage than I get from the socket, some others say it is
indeed the stepping in some way. I'm not sure how you calculated exactly, but
doesn't it matter how fast the step rises, not just how many steps there are?
I'm not sure how to evaluate the theory and opinions, but the bottom line for me
is, I am sure the transformer gets hotter.

I think this is one place I might have 1 up on this subject....

Its depend... On type of UPS.. Switching UPS that uses a
offline inverter use generally a SCR or triac switches that
directly feed the load side with a bit of a filtered output.

Best Product and Sola brands are the system most often that
use the offline method.. They have a output inductor that
is resonant with the line freq. This allows the inductor to
maintain output voltage for the one or two cycles it takes
it switch the inverter on and transfer the load to the
battery powered inverter.

In this method is very cost efficient requiring no power
to run the inverter until required.. But it means that the
inverter Must run at really close to input line voltage
because you would see a voltage and current spike when
the system switched from line to inverter.


The second method for solid state UPS is isolated
input where the input voltage is rectified to DC ...
That voltage is tapped to trickle charge the batteries and
contentiously run a inverter that supplies the load...

This type ( Exide, Deltec,Leibert, Seimens ect.) have no switching
time because the battery plant is parallel with the Input DC..
And care's little where the DC source comes from...

This means you can have a very high input voltage ( smaller
wires , cheaper input systems like breakers ect) and have
a much lower output voltage.. Say a 480vac in and a
120vac out.. The two voltages have no relationship ...


There are also Rotary UPS ( General Power, PSE and some others)
Where there is a AC motor and DC motor and a Generator...
These also isolate the input from the output ( even completely
electrically isolating ) That's why the are preferred for secure
high value data centers because data can't be captured from
the RF feed back of the data being process out on the power grid.

Paul Mays

 

[Paul R. Mays]

In sci.physics.electromag DarkMatter

By the time the load see it... Its a sine wave.. at least in
most systems.. the output inductor filter and cap banks
smooth out the step waves that are produced but the inverter
which most are pulse width modulated.

Depends on the UPS model and who made it, you tell me.

In general, a bit higher than 60 Hz.

Yup... The faster the step freqency the more steps per full wave
at 60 or 50 hertz ... So the more steps the less filtering required
to clean up the wave form... So you can have any freq ya want..

So has to be much higher at 60hz you would get a square wave
at 120hz you get 1 step each 45deg of rotation of the wave form
and so on.....

 

[DarkMatter]

Exactly the point.

The device gets hotter plugged into the UPS than it does plugged into the
line.

Now do you get it?

Look, ASSWIPE, you said that fluctuating line voltage would change
the module temp plugged into the UPS.

It will not. When will you get it?

 

[DarkMatter]

Depends on the UPS model and who made it, you tell me.

In general, a bit higher than 60 Hz.

Like duh, ya friggin dope.

 

[[email protected]]

Look, ASSWIPE, you said that fluctuating line voltage would change
the module temp plugged into the UPS.

It will not. When will you get it?

What I said was the module sees one voltage plugged into the line and
another plugged into the UPS.

Learn to read.

 

[Joel Kolstad]

To run any device for over 1 or 2 minutes without overheating (& thus
damaging the power supply in the equipment), you need to use UPS with
Sinewave Output Inverter - so that you get sinewave output even if UPS
is running on battery.

This is patently untrue. I'm sure you can find me devices that really do
object to so-called 'modified' sine waves, and I can imagine the UL has
enough spare time on their hands that they write up standards that are
useful for certain applications, but I can also guarantee you that there's
tons of really cheap inverters out there making pretty nasty looking
pseudo-sine waves that's used to power lots of dirt cheap equipment, and the
vast majority of the time nothing 'bad' happens.

Although you probably could convince me that statistically there might be
some impact on the life time of the equipment... but still, for many
applications, a true sinewave output inverter isn't worth the (significant)
additional cost.

---Joel Kolstad