Developer Forum

I've read a few posts on using 115 VAC 400Hz power (commonly found on
aircraft) with a standard laptop power brick. Everything I've seen
basically amounts to "try at your own risk" or "didn't hurt my
laptop". Does anyone have switching power supply design experience
that may be able to shed a little light on why this would or would not
be a good idea for a modern laptop power brick. My extremely limited
testing with a multimeter/oem power brick/400Hz input shows that the
the power brick outputs the correct DC voltage. I would feel a little
better plugging it into the $6000 laptop we bought if I could check
for ripple output voltages at 400Hz compared to 60Hz with a scope. If
that turns out to be a non-issue then then the next worry would be
early failure of the power brick (minor concern) and safety issues
such as the brick catching on fire (slightly less minor concern).

Any info or reading suggestions much appreciated.

Laptop switch mode power supplies (or indeed any switch mode supply) will
work quite happily off a 400 Hz supply. We do it all the time. The ripple
will be more or less the same as the power supply part is separated from the
mains input by a DC bridge. The rating plate says 50-60Hz simply because
that is what will be encountered by the vast majority of users. As it
happens, they also work perfectly from DC (but do require a higher voltage
~150 volts for US supplies and ~300 volts for Europe - though most supplies
are universal).

Power supplies containing a mains transformer won't work at all from 400Hz
(but otherwise sustain no damage). These power supplies must not be run
from DC.

>>
>> >> >> >>>> I've read a few posts on using 115 VAC 400Hz power (commonly found on >>>> aircraft) with a standard laptop power brick. Everything I've seen >>>> basically amounts to "try at your own risk" or "didn't hurt my >>>> laptop". Does anyone have switching power supply design experience >>>> that may be able to shed a little light on why this would or would not >>>> be a good idea for a modern laptop power brick. My extremely limited >>>> testing with a multimeter/oem power brick/400Hz input shows that the >>>> the power brick outputs the correct DC voltage. I would feel a little >>>> better plugging it into the $6000 laptop we bought if I could check >>>> for ripple output voltages at 400Hz compared to 60Hz with a scope. If >>>> that turns out to be a non-issue then then the next worry would be >>>> early failure of the power brick (minor concern) and safety issues >>>> such as the brick catching on fire (slightly less minor concern). >> >>>> Any info or reading suggestions much appreciated. >> >> Laptop switch mode power supplies (or indeed any switch mode supply) will >> work quite happily off a 400 Hz supply. We do it all the time. The ripple >> will be more or less the same as the power supply part is separated from the >> mains input by a DC bridge. The rating plate says 50-60Hz simply because >> that is what will be encountered by the vast majority of users. As it >> happens, they also work perfectly from DC (but do require a higher voltage >> ~150 volts for US supplies and ~300 volts for Europe - though most supplies >> are universal). >> >> Power supplies containing a mains transformer won't work at all from 400Hz >> (but otherwise sustain no damage). These power supplies must not be run >> from DC.

Also, you can check for any ripple in the output DC by setting your
DMM or VOM to AC and measure across the DC output - if it reads 0.0
you have no ripple.
Paul

>>
>> >> >> >>>> I've read a few posts on using 115 VAC 400Hz power (commonly found on >>>> aircraft) with a standard laptop power brick. Everything I've seen >>>> basically amounts to "try at your own risk" or "didn't hurt my >>>> laptop". Does anyone have switching power supply design experience >>>> that may be able to shed a little light on why this would or would not >>>> be a good idea for a modern laptop power brick. My extremely limited >>>> testing with a multimeter/oem power brick/400Hz input shows that the >>>> the power brick outputs the correct DC voltage. I would feel a little >>>> better plugging it into the $6000 laptop we bought if I could check >>>> for ripple output voltages at 400Hz compared to 60Hz with a scope. If >>>> that turns out to be a non-issue then then the next worry would be >>>> early failure of the power brick (minor concern) and safety issues >>>> such as the brick catching on fire (slightly less minor concern). >> >>>> Any info or reading suggestions much appreciated. >> >> Laptop switch mode power supplies (or indeed any switch mode supply) will >> work quite happily off a 400 Hz supply. We do it all the time. The ripple >> will be more or less the same as the power supply part is separated from the >> mains input by a DC bridge. The rating plate says 50-60Hz simply because >> that is what will be encountered by the vast majority of users. As it >> happens, they also work perfectly from DC (but do require a higher voltage >> ~150 volts for US supplies and ~300 volts for Europe - though most supplies >> are universal). >> >> Power supplies containing a mains transformer won't work at all from 400Hz >> (but otherwise sustain no damage). These power supplies must not be run >> from DC.
>>From what I read last night, what you've said makes sense including
running the power supply off of DC. I'm a little confused by your
last comment though. If you're immediately stepping down the mains
voltage with a transformer designed to to run at 60 or 50 Hz wouldn't
it easily handle the same voltage at 400Hz?

>>
>> >> >> >>>> I've read a few posts on using 115 VAC 400Hz power (commonly found on >>>> aircraft) with a standard laptop power brick. Everything I've seen >>>> basically amounts to "try at your own risk" or "didn't hurt my >>>> laptop". Does anyone have switching power supply design experience >>>> that may be able to shed a little light on why this would or would not >>>> be a good idea for a modern laptop power brick. My extremely limited >>>> testing with a multimeter/oem power brick/400Hz input shows that the >>>> the power brick outputs the correct DC voltage. I would feel a little >>>> better plugging it into the $6000 laptop we bought if I could check >>>> for ripple output voltages at 400Hz compared to 60Hz with a scope. If >>>> that turns out to be a non-issue then then the next worry would be >>>> early failure of the power brick (minor concern) and safety issues >>>> such as the brick catching on fire (slightly less minor concern). >> >>>> Any info or reading suggestions much appreciated. >> >> Laptop switch mode power supplies (or indeed any switch mode supply) will >> work quite happily off a 400 Hz supply. We do it all the time. The >> ripple >> will be more or less the same as the power supply part is separated from >> the >> mains input by a DC bridge. The rating plate says 50-60Hz simply because >> that is what will be encountered by the vast majority of users. As it >> happens, they also work perfectly from DC (but do require a higher voltage >> ~150 volts for US supplies and ~300 volts for Europe - though most >> supplies >> are universal). >> >> Power supplies containing a mains transformer won't work at all from 400Hz >> (but otherwise sustain no damage). These power supplies must not be run >> from DC.

Also, you can check for any ripple in the output DC by setting your
DMM or VOM to AC and measure across the DC output - if it reads 0.0
you have no ripple.

--------------

If it reads 0.0 you most likely have a dead multimeter. Unlike an
osilloscope, which has a blocking capacitor when set to AC, most multimeters
actually detect the average or RMS (depending on the meter) of the input
when set to AC. The DC output itself has both an average value and an RMS
value that is not zero. In the case of the average sensing instrument, it
is calibrated to read the RMS value, but only for a sine wave. The meter
will read either the DC voltage or a value 1.11 times the DC voltage. If it
does read only the AC ripple, then you actually do have one of the few
meters that block the DC (no true RMS instrument will do this). The really
good ones (and expensive) offer 3 options, DC, RMS AC or RMS DC+AC.

Of course, you can always add a blocking capacitor of your own in one of the
leads. A few tens of nanofarads should be adequate for a switch mode
supply. I would be very surprised if the ripple were any different (but it
won't be zero - not for a switch mode supply).

>>> I've read a few posts on using 115 VAC 400Hz power (commonly found on >>> aircraft) with a standard laptop power brick. Everything I've seen >>> basically amounts to "try at your own risk" or "didn't hurt my >>> laptop". Does anyone have switching power supply design experience >>> that may be able to shed a little light on why this would or would >>> not be a good idea for a modern laptop power brick. My extremely >>> limited testing with a multimeter/oem power brick/400Hz input shows >>> that the the power brick outputs the correct DC voltage. I would >>> feel a little better plugging it into the $6000 laptop we bought if >>> I could check for ripple output voltages at 400Hz compared to 60Hz >>> with a scope. If that turns out to be a non-issue then then the >>> next worry would be early failure of the power brick (minor concern) >>> and safety issues such as the brick catching on fire (slightly less >>> minor concern). Any info or reading suggestions much appreciated. >>> >> >> Laptop switch mode power supplies (or indeed any switch mode supply) >> will work quite happily off a 400 Hz supply. We do it all the time. The >> ripple will be more or less the same as the power supply part is >> separated from the mains input by a DC bridge. The rating plate says >> 50-60Hz simply because that is what will be encountered by the vast >> majority of users. As it happens, they also work perfectly from DC >> (but do require a higher voltage ~150 volts for US supplies and ~300 >> volts for Europe - though most supplies are universal).

OUCH! Your ignorance is showing; that is NOT why the 50/60Hz spec exists!
Doing so completely disregards heat dissipation and output current
limitations in most switching supplies. You need to quit spewing garbage
and learn a little about these things. Also, because ONE worked, does not
mean the next one will.
If you bother to look, you'll also find that some are capable of 400Hz by
spec, and some are not. Most are capable of operating with no load on them
too, but not all.
>> >> Power supplies containing a mains transformer won't work at all from >> 400Hz (but otherwise sustain no damage). These power supplies must >> not be run from DC.

Actually, this isn't true, either as there are a myriad of things that can
or maybe won't go wrong at 400Hz. It depends on the xfmr construction,
something you're apparently quite ignorant of. There will be an output from
the xfmr. Even audio xfmrs can be operated as a main xfmr under the right
circumstances, and they're rated to 20kHz and beyond.

>>>> I've read a few posts on using 115 VAC 400Hz power (commonly found on >>>> aircraft) with a standard laptop power brick. Everything I've seen >>>> basically amounts to "try at your own risk" or "didn't hurt my >>>> laptop". Does anyone have switching power supply design experience >>>> that may be able to shed a little light on why this would or would >>>> not be a good idea for a modern laptop power brick. My extremely >>>> limited testing with a multimeter/oem power brick/400Hz input shows >>>> that the the power brick outputs the correct DC voltage. I would >>>> feel a little better plugging it into the $6000 laptop we bought if >>>> I could check for ripple output voltages at 400Hz compared to 60Hz >>>> with a scope. If that turns out to be a non-issue then then the >>>> next worry would be early failure of the power brick (minor concern) >>>> and safety issues such as the brick catching on fire (slightly less >>>> minor concern). Any info or reading suggestions much appreciated. >>>> >>> Laptop switch mode power supplies (or indeed any switch mode supply) >>> will work quite happily off a 400 Hz supply. We do it all the time. The >>> ripple will be more or less the same as the power supply part is >>> separated from the mains input by a DC bridge. The rating plate says >>> 50-60Hz simply because that is what will be encountered by the vast >>> majority of users. As it happens, they also work perfectly from DC >>> (but do require a higher voltage ~150 volts for US supplies and ~300 >>> volts for Europe - though most supplies are universal). >> >> OUCH! Your ignorance is showing; that is NOT why the 50/60Hz spec exists! >> Doing so completely disregards heat dissipation and output current >> limitations in most switching supplies.

Yes, it does, 'cause they're irrelevant!!!

You might wanna check the mirror for signs of ignorance...

You need to quit spewing garbage >> and learn a little about these things. Also, because ONE worked, does not >> mean the next one will. >> If you bother to look, you'll also find that some are capable of 400Hz by >> spec, and some are not. Most are capable of operating with no load on them >> too, but not all. >> >>> Power supplies containing a mains transformer won't work at all from >>> 400Hz (but otherwise sustain no damage). These power supplies must >>> not be run from DC. >> >> Actually, this isn't true, either as there are a myriad of things that can >> or maybe won't go wrong at 400Hz. It depends on the xfmr construction, >> something you're apparently quite ignorant of. There will be an output from >> the xfmr. Even audio xfmrs can be operated as a main xfmr under the right >> circumstances, and they're rated to 20kHz and beyond.

You talk like this is a grand revelation. Audio transformers are
designed to run at 400 Hz...and 60 Hz...cause they're in the audio range. >> >> >> >> >>

"Pop`" < XXXX@XXXXX.COM > wrote in message
news:Liqwh.86100$Ss1.81445@trnddc07...

I clearly know more about these things than you ever will. It is you that
is showing ignorance. The whole point is that there is no mains
transformer. The first things encountered are a rectifier and then a
reservoir capacitor. The rectifier will work perfectly well from DC, 50Hz,
60Hz, 400Hz and a long way upwards (probably well into the megahertz, but I
haven't actually tried it). Once converted to DC, the original frequency
becomes totally irrelevant once it's switched into the converter
transformer. If the OP has a transformerless switch mode power supply (All
current manufacture laptop supplies are), I guarantee that it will work.
>>> >>> Power supplies containing a mains transformer won't work at all from >>> 400Hz (but otherwise sustain no damage). These power supplies must >>> not be run from DC. >> >> Actually, this isn't true, either as there are a myriad of things that can >> or maybe won't go wrong at 400Hz. It depends on the xfmr construction, >> something you're apparently quite ignorant of. There will be an output >> from the xfmr. Even audio xfmrs can be operated as a main xfmr under the >> right circumstances, and they're rated to 20kHz and beyond. >>

The mains transformer that is most likely to be encountered in a linear
power supply designed to operate from normal mains (i.e. 50 or 60 Hz) is
extremely unlikely to be constructed with the sort of features required for
400 Hz operation. For one thing the primary reactance will be far too high
to allow the sort of current that permits it to operate to flow. While it
is quite possible to construct transformers to operate from the wide
frequency range required, no manufacturer is going to go to that expense in
a cheap $5 power brick.