Dell Dealer in KC

[Duane Attaway]

On Sat, 12 Oct 2002, Mark Hutchings wrote:

> No the power supplies for all C600 series is 75 watts and are the same.  My 
> C600 ran fine in a C/Dock II Expansion just fine with 75 watts.  But now, when 
> you order a dock with your C640, you get the exact same dock (or port rep) with 
> a 90 watt power supply to power both your dock and the PC, instead of the 
> standard 75 watt.  When you use the 75 watt one that comes with the laptop, 
> there's not enough juice for the dock and the 1.6Ghz power of the laptop.  It 
> knocks it down to 1.2Ghz.  So, I'm using the same dock as I got when I ordered 
> my C600, but now Im in need of a 90 watt power supply for it. Was hoping 
> someone in town would be cheaper than buying directly from Dell.  Cant find one 
> (90 watt power supply) on eBay.

How many volts and amps you need?  That is the real question to ask when 
looking for a power supply.

If you like living on the edge and doing things yourself:

Hint: since laptops have batteries with voltages that vary and power
supplies with long cords with connections that are unreliable, they all
have built in switching power supplies to provide the *exact* voltage
needed by the chips.  My laptops require anything from 15 to 19 volts with 
varying amperage.  All will run off a car battery, with voltages ranging 
from 11 to 16 volts when the car is running.  Despite the varying supply, 
the laptop's battery will still charge from this, even if the incoming 
supply is lower.

A fuse is required in any circuit delivering power to your notebook.  
Rate it to be twice the specified current.  The fuse will be called upon
by the laptop's protection circuit to remove itself from the evil source
if things go bad.  The laptop's internal power supply will actually clamp
down the supply in certain conditions and expects this fuse to be there.  
This fuse is part of the design.  It must be there.  Here is why:

Your notebook's internal power supply has a diode to clamp down on the
incoming supply if its wired up backwards.  This is why we have the fuse.  
Both work together to prevent a fire in case of this wiring problem.  
Also, excessive voltages will trip the SCR crowbar circuit.  If it sees a
voltage that is rediculous and will overheat the switching circuit, it
will feed the protection SCR to clamp the entire incoming feed to ground,
hoping to blow the fuse to remove itself from the evil source.

Also remember if you connect directly to a car's electrical system, your 
laptop will not be electrically isolated from the car's chassis.  This can 
be a problem as large electrical loads in the car, including the laptop 
itself can create voltage differences across the wires.  This is bad if 
one of your peripherals makes contact with something else with a few volts 
difference.  A CMOS chip can be biased in such a condition to electrically 
simulate a SCR and clamp its supply voltage to ground unintentionally and 
release a sweet aroma known as smoke...

Have fun!