Of course, the normal disclaimers apply: Don't do this without some experience in electronics, soldering, installs, etc, and I take no responsibility for damage to equipment, your car, your health, etc. I'm simply relaying my experience to interested parties.
So, I got this HP Advanced Docking Station and HP nc8230 laptop from work for $75, lightly used. I thought it would be great to have a docking station such as this one wired into my car to host USB, power on/off, VGA, extra drive bay, and whathaveyou, so that I could easily dock/undock the lappy without worrying about connections.
Trouble was, the AC adapter for the docking station is rated 135 watts (I figure 90 watts for the lappy plus overhead), and is of the "smart" type, where even if you apply an external 12v-19v DC/DC converter to the dock, it won't power on and charge the lappy. With the dock not powered on, the power switch on the docking station will switch the lappy on/off, and the dock will act as a USB hub only...it cannot charge the lappy nor provide power to it without a "smart" power connection. Without a "smart" connection, the lappy will power on from the docking station switch, but will only work off its own battery until it dies.
Some detective work was necessary to find out how to make the base station power on and charge the laptop while operating from an in-car 12v power source, where a simple 12v-19v adapter for notebooks wouldn't work. HP (nor anyone else, for that matter) does not make an auto adapter for the docking station (duh, they don't anticipate users putting docking stations in their cars). The trick was knowing something about the "smart" part of the existing AC adapter for the base station.
To see what was going on with the docking station's AC/DC power brick, I carefully cut the cable between the power brick and the power plug that makes entry into the docking station. I separated the conductors (3) within the cable coming from the brick, applied AC power to the brick, and went to work with my multimeter. I quickly found that the center (innermost) conductor coming from the power brick was the +19 volts that would eventually be fed to the laptop for power/charging purposes. The outer conductor sheath was ground...okay, that's pretty normal. The "smart" part of the adapter, which told the docking station it was okay to power on/charge on the 19 volts it was being fed, was located on the middle conductor within the cable. I found that it was a DC signal hovering around 12 volts, and could think of no other application besides signaling the base station that all was well...HP's way of making sure you were using approved HP equipment that cost many times more than what it should. Sure, it could be providing some power to the internals on the dock, but I couldn't figure why they would provide two separate DC voltages for charge/operation, when they could simply work from the same +19 every laptop I know of uses for input.
I figured that since this 12v middle conductor was providing nothing more than signaling, it was likely to be facing an extremely high impedance where it made entry to the base station. Basically, for signal purposes, you engineer your signal to present a voltage, but since you don't want to eat up a lot of energy communicating things like "okay to turn on", you present that "okay" signal with a very high input impedance at whatever you plug into, so as not to dump current where you don't need it...you're simply talking to a relay or something, not spinning a wheel, pushing speakers, heating bread, etc., so you don't need lots of current. On a whim, since there was presumably a very high input impedance at the other end, I figured I'd see how it dealt with +19 volts instead of the +12v it was expecting.
Using the cut off end of the cable that entered the dock, I simply spliced the middle and center conductors together into the +19v coming out of my 12v-19v DC converter (run-of-the-mill car adapter for laptops, about $15), and spliced the grounds together, being careful as always to keep them separate. I hooked up everything in my car for test and applied switched DC (turned the car on with the adapter in a cigarette lighter socket). It worked! The base station powered on and charged beautifully, and I've been using it in this configuration for the last 7 months or so.
So, to make a long story short, if you're looking to supply an advanced HP docking station with power for your in-car purposes, you need to:
1. Buy a 12v-19v DC to DC adapter rated at ~120 watts or better, or some other +19v DC source. It doesn't matter what type of plug is on the end, so long as have +19 volts on one conductor, and ground on the other. A "smart" in-car adapter for notebooks will not work with the docking station, I tried.
2. Snip the power cable on the existing AC adapter that came with the docking station, between the power brick and the docking station.
3. Splice together the innermost and middle conductors on the cable you have just cut (these will be fed +19 volts from your car adapter), separating these from ground (the outermost conductor).
4. Splice the +19v output of your car adapter from step 1 into the innermost and middle conductors which you spliced together in step 3.
5. Splice the ground from the adapter in step 1 to the outermost conductor on the cable from step 3.
Splicing into the power switch on this docking station is no different from most others. The only other install notes to pass on is that the HP docks don't really have a mechanism to hold the laptop locked down to the docking station (again, they don't anticipate in-car use and don't design their docks to withstand going over potholes, etc.), so you'll need a way to hold the lappy down to the station before you use it in-car. So far, the dock as well as the lappy have done very well to resist heat and mechanical shock while in-car. All my USB devices (external drive, Sirius, USB sound, touch screen, GPS) are operating off the dock without problem. Where applicable, USB applications requiring external 5 volts or 12 volts are being fed from a separate DC-DC converter.
I have too much time and too little aggravation in my life, so I built a carPC. ;)