Dell D-series Power Supply

may be this is a bit off topic here but I bought a 3 year old D-Series
lattitude leasing laptop D600 in Ebay. My old notebook had a 2 pin power
connector and the switching supply worked down to 12 Volt. Only battery
charging was disabled if power supply was not 18 Volt. From this reason I
always used a direct 12V supply in my car without step up converter. 

I tried to do the same with my D-series Dell and it did not work. First
suprise was a 3 pin connector at the well sealed power supply. I found the
pins for GND and +18Volts but the appliance switches off at a threshold of
of only 17,5 Volt. No chance without step up converter. Therefore I tried a
simple switcher from National Semiconductor and I can switch on the Dell
with it. After that an error message from the BIOS appears becouse of
unknown power source. From this reason I tried to find out the signal of
the 3rd pin. No success with ohm meter or meassuring volts at this pin.
Therefore I opened the well sealed primary switched power supply with brute
force using a saw blade. Luckily I hit only the aluminum heat sink and the
power board is still working for further analyses.

The secret of Dells third pin is a custom chip with supsicious similarity to
the Dallas DS2401 2 wire silicon serial number. See datasheet at 
maxim-ic.com. Probably it is a DS2401 with its content factory lasered for
Dell. Disassembly of Bios shows that the number is checked to distinguish
between 60Watt and 80Watt power supply models. The D800 works only with 80
Watt Power supply and the D600 works with both models. 

There are still many open questions an maybe anyone else is able to give
some hints: 

- what circuit is inside the Li-Io battery pack? 3 cells make 11,2 Volt but
there are additional active control pins in use. Even if I have a power
supply in parallel the computer switches of after one second when removing
the battery pack. In general it must be possible to run the computer
directly from 12 Volt source.

- the BIOS is CRC32 secured and flash memory contains a service tag and
optional passwords. Dells support is using a tool what can calculate a
password from the service tag what resets all user passwords. Anybody
already disassembled the Bios or knows more about this feature ?

- the port replicator can power up the laptop with closed display. Anybody
found something for the pin assignement of the port replicator? That would
be an interesting feature if the notebook is used in the car under the seat
(with external monitor and keyboard)