BE VERY CAREFUL DOING THIS!!!!!
This advice is specific to a single product form one manufacturer. Each
laptop manufacturer has different battery maintenance circuitry, and
they operate off different voltages, usually NOT 13.8V! Input voltages
tend to vary between 12 v and 30 v depending on manufacturer. As an
example, Apple PowerBooks and iBooks need about 25 volts. Applying 20V
to a 12V input WILL cause undesired effects. Applying 12V to an 18V
input MAY cause undesired effects.
Also, be sure that any power adapter you use will provide enough power
to run the laptop. Laptop power supplies started out at about 20 watts
many years ago, and generally run around 45-65 watts these days.
I would STRONGLY advise that anyone wanting to run their laptop from a
12V battery source purchase a commercial power adapter for their
laptop. These are available from many sources, including your local
neighborhood computer store.
On Aug 29, 2004, at 11:14 AM, Bob Tellefsen wrote:
Hi don
I have two laptops here, and both can be run from an external battery
source.
HOWEVER, I need to run them through a small inverter to bring the
voltage up to around 13.8v. I checked this with my variable
voltage bench power supply to find out where the laptop switched
from external power to internal. It is usually above normal
battery voltage by 1-2 volts, hence the small inverter.
I built the one from Sam Ulbing, N4UAU. It was written up in QST
as "My All-Purpose Voltage Booster". He sells the kit for a very
reasonable price. You can find him on the web under his call.
I used mine on Field Day, and it was extremely quiet. Not a trace of
hash
anywhere. A side benefit in running on batteries in the field is that
the
converter is regulated. As the input voltage drops, the output stays
pretty near constant.
This would not be a problem in the shack with a fixed supply. I
suggest
you check your laptop using a variable voltage power supply and find
out how low you can go before it switches over to the internal battery.
Good luck and 73
Bob N6WG
- Jack Brindle, WA4FIB
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