John Weston wrote:
surfnturf, in article kcxYf.218601$sa3.159619@pd7tw1no,
says...
Good points John.

Typical rated power to the AC adapter for a laptop is close to 150W,
but output to computer is in order of 65W. Explains why the damn
things get hot.

Direct power may well be worth investigation, rather than using DC
to AC to DC.


A good power supply design shouldn't just dump the excess
power as heat. That's what linear regulators do, not the more
usual switching regulators. However, even they loose
something as heat so, in my opinion, just the one converter,
to provide the laptop's DC input needs directly is best

I use a DC-DC converter (12Vdc battery to approx 18Vdc) to
power my laptop since there is only one conversion loss
(+heat). It seems more efficient to me. Others prefer going
all the way up to 120/240Vac (+heat) to power the laptop AC-DC
power brick (+more heat) which goes back down to the 18-24Vdc
needed by the laptop.

I'm looking at replacing this with a 12V battery driven mini-
ITX when I get a round tuit now my laptop is faulty... I'll be
sailing on a boat with a shuttle-based system this summer so
will see how well it works

The laptop's power brick plus an inverter is far better at dealing with the
voltage "spikes" that an alternator can put out, as I found to my cost a
couple of years ago, blowing the system board using one of these DC-DC
converters.