Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
On Tue, 07 Mar 2017 20:27:10 -0500, firstname.lastname@example.org wrote:
It's a good question, since the OP is right that a power supply seems
pretty well isolated by all that plastic encasement, and the output is low
DC at relatively low amps (< 10 or so amps most of the time).
There's no power transformers anymore due to the switching power supply
And yet ... ... ...
I wonder if the electronics of the switching power supply require a really
The switchers do have transformers in them. They are usually after some
of the switching circuit and are very small compaired to what they are
if they were on the 60 HZ side.
The electronics will work fine without a ground. The ground is for
safety, and it does help with the filtering of the hash the switchers
generate that is fed back on the power wires.
It may also pay a small part to help prevent surges coming in from the
They have done that for many years, or in some cases like priners and
modems the power supply is seperte so they can just ship seperate
supplies depending on the country.
Many computers and some other devices have a switch for 120 or 240 volts
and that universal socket on the device. The suplies are really not
even that particular about the voltages, just get into the ball park
with them. Going 20 or 30 volts either way is fine.
These days the switchers are very wide mouth and can take anything
from 100-250v at any frequency, even DC although they are not labeled
that way. The first thing that happens is the input is converted to DC
immediately anyway. Then it is chopped to something in the 10s of
thousands of hz, fed through a small toroid transformer, regulated,
rectified and comes out at the desired voltage. When went to New
Zealand, all I needed was a plug adapter to run every electronic
device I had (laptop, phone, camera, MP3 player, tablet etc) All of
the chargers were 100-250v.
SO OLD. Virtually everything in the last20 years anyway is
"universal" or "auto switching" in the small SMPS world. Virtually
all my laptop powes supplies and switch mode wall warts are listed as
100-240 or the odd one 85-250 volts The odd PC power supply still has
a switch (Del and HP up until at least a few years ago) but Acer has
been full auto for at least that long. I've got8 nyear old acers that
are full automatic, for sure
Tue, 07 Mar 2017
21:29:46 GMT in alt.home.repair, wrote:
Filtering perhaps? Limited surge supression components? Redundant
safety...I've got a few laptops around here that have the 3 prong and a
couple that don't. I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.
Sarcasm, because beating the living shit out of deserving people is
I've suspected the issue is a ground loop based on prior experience
with that...I haven't tried to open one of these and take a look
inside, so it's entirely possible it is connected, but, due to some
filtering circuitry in between, I'm unable to do a simple continuity
test on it. By unable, I mean that it doesn't read as completing a
circuit when tested in that manner.
This works well to remedy the problem...
(Amazon.com product link shortened)
Sarcasm, because beating the living shit out of deserving people is illegal.
Reading with a meter you will be looking through the filter so YMMV on
what kind of continuity you see but at 60hz there will be some pass
through. I have had that problem with desk tops that feed amps,
particularly if there are other things in that loop like a TV.
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