Gary KW4Z wrote:


Here's Today's problems and a few questions:

I got a laptop computer for Christmas. It uses an AC to DC adapter
(transformer) to get power and recharge the computer's batteries.

Unlike most modern electronics, this one has a non-polarized socket for
the charger and the power cord is non-polarized, non-grounded too.
Neither is there any kind of marking, such as a white stripe along the
cord that lets me know which is the hot/neutral side. From what I've
read, a white stripe usually indicates it is the polarized side (the
neutral) and goes into the longer slot on the wall socket. The longer
slot is always neutral. Is that right?

The instructions say, plug the charger into the computer and then that
into the wall socket.
When I did it, there was an arc from the wall socket's left slot. I
thought that's strange. (This is one of the three prong, polarized,
grounded (but not really) sockets.)

I left it plugged in for a day or so. I unplugged it. Later, when I
plugged it back in, without paying attention to the orientation of the
plug, there was no spark. I thought, "strange," again. So, I flipped
the power cord plug over, plugged it in that way and sure enough, a
spark from the left slot of the wall socket. --bright blue and snappy.

The power adapter doesn't care how you plug in the cord and it is
transformer isolated from the computer. To DC a Transformer is a short
and
for a moment to AC it's a short but only for a moment. It's not uncommon
to have a small arc when plugging in a computer transformer, no matter the
orientation of the plug. This is especially true when the computers
battery is discharged, that is the spark will be more profound, if there
is one.



The one thing your missing though is laptop supplies are not usually a
transformer, they are typically a switched power supply otherwise they
would be much larger and heavier. A typical switching power supply will
switch the hot side on and off thousands of times a second and very the
pulse width to get the proper output voltage. I oversimplified but I hope
you get the idea that since there is no transformer the characteristics
will be different.