49 lines
3.0 KiB
Plaintext
49 lines
3.0 KiB
Plaintext
MiniSport Laptop Hacker - Vol 12, 6 Apr 1993
|
|
Copyright(C) 1993 by Brian Mork.
|
|
|
|
>>> PORTABLE POWER OPTIONS
|
|
Twelve volt DC universality has again raised its head. A number of peo-
|
|
ple seem to be interested in running their computer from 12v DC, whether
|
|
from the cigarette lighter or from portable batteries. No problem! The
|
|
pinout (pinin?) of the power connector on the left side of the computer
|
|
is very simple. The Zenith manufactured power supply meant to plug into
|
|
this connector is a switching power supply; be careful measuring its
|
|
voltages, if you do that to compare with my numbers. Switching power
|
|
supplies only regulate voltages well when they're under load.
|
|
The round shield of the connector is ground. It's more than a
|
|
shield--it actually carries the return current. It is electrically con-
|
|
nected to the forward contact on the batter pack, becoming the BLACK pow-
|
|
er line inside the computer.
|
|
The single smaller hole is a 5v DC (TTL) input that indicates when the
|
|
AC adapter is being used. If you're interested in running off a portable
|
|
battery, leave this unconnected. I'm not sure how (or if) this actually
|
|
gets into the computer. Apparently the battery pack itself has some cir-
|
|
cuitry that requires the 5v signal.
|
|
The bottom of the two large holes is a 9v DC input providing power di-
|
|
rectly to the computer. This 9v doesn't electrically connect to the bat-
|
|
tery pack at all. It is mechanically routed to the center conductor on
|
|
the bottom of the battery pack, becoming the RED power line soldered to
|
|
the main CPU board inside.
|
|
The upper, rearward large hole is a 6v DC, used to recharge the battery
|
|
pack. Directly, or indirectly through a few components, it makes its way
|
|
to the rearward contact of the battery pack and subsequently the YELLOW
|
|
power lead inside the computer.
|
|
I claim ignorance on the inside of a battery pack. Does anybody have a
|
|
torn-open pack? What exactly is the 5v signal used for? Are there any
|
|
compenents built into the pack or is it just batteries and wires?
|
|
In any case, I've had complete success running the computer from a 9v
|
|
wall-wart transformer. Large size paper clips happen to be exactly the
|
|
correct size to make the 9v contact and rub in place next to the ground
|
|
connection. The Zenith power supply indicates that maximum of 2A is tak-
|
|
en from the 9v supply. Use an adjustable 3-terminal regulator to bring
|
|
the 12v DC down to 9v. If you're running straight from the cigarette
|
|
lighter, put some huge inductance in line (a lamp ballast works fine) and
|
|
a large capacitor on the car side of the inductor. A 1 amp diode put
|
|
backwards (banded end toward the car side) will clamp any high voltage
|
|
spikes from arcing into the connector if you pull the paper clip out,
|
|
making the magnetic field of the inductor collapse.
|
|
|
|
73, Brian Mork (Opus-OVH) KA9SNF@wb7nnf.#spokn.wa.usa
|
|
Internet ka9snf@jupiter.spk.wa.us
|
|
6006-B Eaker, Fairchild, WA 99011
|