Garland Gray II wrote:

Well now... I hadn't really considered that there was an inverter in my
laptop.

All laptops have something like that to stabilize, smooth and adjust the
input voltage and send it to a few major components, sometimes at
different voltages. Your laptop probably takes about 14V from your AC
to DC adapter and outputs 12V or so to the battery charging circuit and
has two other outputs (typically 5V and 12V) to the primary components
like motherboard, drives, etc.

To charge your 10.8V battery, you need a little higher voltage and it
needs to be stabilized and at a given amperage and the internal DC-DC
inverter takes care of all that. The charging voltage may be monitored
by the DC-DC inverter and tailed down or turned off when the charging
process is complete. Your laptop is probably running off the internal
battery at all times. When the battery is fully charged it stays fully
charged with the AC adapter connected.

If you can find the specs for the OEM DC-DC adapter your laptop, you'll
probably find it has an output voltage of 14 Volts or so (at a specified
Amperage) and that it will use an input voltage of 11-15V or so. So you
want a DC-DC adapter that will provide the same output.

So if I'm running it off the inverter now, the current would be going from
dc to ac to dc back to ac ??

At the end of the line, the laptop only needs DC voltages. The only AC
to DC conversion is to convert AC power to DC power for the jack on the
laptop. It does not really matter if that DC input power is converted
by an AC adapter or DC adapter as long as it is stable and at the right
voltage with adequate amperage.

The laptop will tolerate some variation in the input voltage, maybe a
volt or two or so. Then it changes that voltage as necessary and passes
it around.

The bottom line is that it is simpler to use a DC-DC adapter on a boat
that has 12V power available than it is to use DC to AC inverter so that
you can use your AC to DC adapter. Also the DC-DC process will use less
power, generate less spurious electrical noise (may bother radios,
radars, etc.), and is generally safer (lower voltages/less risk of
shock) in a marine environment.

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)