[Mobile-Portable] Re: Laptops Near Mobile Rigs

[Hsu, Aaron (NBC Universal)]

Doc,

>>> I have observed that laptops designed for 19VDC will not operate
some accessories, e.g. network cards, if the voltage is too low.  I am
guessing that the system "sees" low voltage as a sign of the battery
discharging and lowers demand accordingly.

Hmmm, never even thought about that possibility, though most everything
past the laptop's internal DC-DC converter should be running at "native"
voltages - generally 3.3v, 5v, and 12v.  Even if the battery is a higher
voltage, it's converted to the native voltages via the DC-DC converter -
the higher voltage battery probably allows more headroom for voltage
drop during surge conditions.

>>> There has also been a concern expressed that low voltage = higher
current and higher current = more heat on tiny traces and in sensitive
tiny components thus raising the probability of early failure.

Quite possibly, but not likely.  Again, all power going "in" to the
laptop usually goes straight to a DC-DC coverter to generate native
voltages.  Yes, if you drop voltage, current goes up, but the only
components or traces that see this change are the power connector and
any traces leading into the DC-DC converter and these should be able to
handle any current needs of the laptop.

>>> Also, I am told that some of the laptop batteries are not even 12vdc
so a high enough charging voltage should not be an issue but that tells
me that there could be a dc-dc converter in the laptop that is engaged
when the battery is used for power.

As mentioned above, all laptops I(AFAIK) have a DC-DC converter to
generate native voltages.  With laptops using Li-On or Li-Poly cells,
the batteries voltages will be a multiple of 3.6v or 3.7v.  The voltage
requirement going "in" to the laptop is generally higher than the
battery voltage (usually by 20% or more) so that the battery can reach
full charge.  Many companies use a common design point voltage that will
work with any of their products to keep costs down.  They then design
the internal DC-DC converter with this in mind.  For example, *all* of
HP/Compaq's "business" laptops manufactured since (c.)1998 use a common
18.5v power supply (though they have bumped the current capability up to
match total wattage needs) and the batteries are either 11.1v or 14.4v.
The laptops themselves will run with DC as low as 11v, but the battery
charging circuitry (in the batteries themselves) will not engage until
supply voltage reaches about 15v.  HP/Compaq even has a "direct" cig.
lighter cord that plugs straight into the laptop and feeds 12v - this
allows the laptop to run, but doesn't charge the battery.

>>> To keep things simple I am looking for a 12vdc (12-15vdc) native
laptop.  I will sell my three IBM Thinkpad 600-series laptops once I
find a 12vdc native replacement.

I'm sure there are some out there - wish you luck in your search.  You
might want to consider building a small 12v PC instead.  I've seen some
DIY projects on the net that use SBC (small board computers) and used
LCD panels to build custom MP3 players for the car.  Most SBC
motherboards I've seen will mount directly to a 5.25" drive (though they
don't really exist anymore <g>).  SBC's are designed for industrial
control, so small size comes in handy.  Depending on how portable you
want the system to be, this might be a good alternative.

73,

  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {aaron.hsu}@nbcuni.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"