Yes, it'll run 12 (or 14v) from the car, but it'll be
in 'assist mode', but if you try to get it to run at
full speed and charge the battery at the same time, I
won't work.
But all people are after (in this thread at least) is to be able to USE the MacBook (Pro) in-flight. One thing about the Apple portables is that they do have a good power management system that allows for things like limiting the power drawn from the supply (so as to be able to use different wattage supplies to best effect for example). IF the management processor has the capability to control power demand to 75W and run the system from 14V then there is no need for the electronics - just a simple cable and appropriate identification is all that required.
Why do you think they are having so much
problems with the inverters, etc?
Because it's the wrong way to tackle the problem ! If you want to run from an aircraft supply that is limited to 75W, then the right way to do it is for the system to control it's draw to 75W - you can't achieve that effect reliably if the system thinks it's OK to draw 85W so you end up drawing 90+W after the extra conversions.
I find it hard to belive that apple designs an
adapter that outputs 16/18v just for the heck of it.
No they don't, they select the input voltage to suit the requirements. I don't know the battery voltage for the MacBook Pros, but the G4 17" is 12V. It makes the conversion circuitry simpler if you only have to convert one way (eg step-down) rather than two ways (ie step down or step up). Since the voltages used internally are all probably 5V or lower, then it's still a down-conversion from 12/14V.
That doesn't mean that they can't design the system to cater for other voltages with some loss of functionality - such as accepting a lower input voltage but losing the ability to charge the battery.
Why else all of a sudden it jumped up to 85w for
the macbook pro line?
For the same reason the G4 PowerBooks hiked it to 65W from the previously standard 45W - it takes more power to run the system than to run the older ones. However, I can tell you that the G4 17" does run very happily from a 45W supply (it will even charge the battery), but it will draw more power from the battery to satisfy peak demands than it will running from a 65W supply.
That is the way Apple portables (and probably many other makes) have always worked - they rely on the battery being there to cover peaks in demand that would otherwise take them over the capacity of the PSU. When the peak is over they will top up the battery again. That BTW, is the reason Apple has always stated that their portables should not be run without the battery - and I assume that would be the same for the newest models.
Bottom line, in order to get the laptop running at
top speed and at the same time rapidly charge the
battery in ~couple of hours or so, they need the
higher voltage.
It would IF that is what people are asking for, but if you go back and read the thread, people are not looking to charge the battery, just to be able to use the system on a flight that's longer than the unassisted battery life.
I'd be very surprised if a 14V supply limited to 75W couldn't supply at least 95% of the systems power requirements - that means at least 20 times the battery life, well enough for a 10 to 20 hours flight. After that, you recharge the battery wherever you can find a mains socket (hotel room anyone ?).
Currently the 85w adapter output a constant 6v when
unpluged. As soon as it senses resistance, it jumps
up to 16v and since it can output 18v, I bet it'll
sense that and step up if needed.
What is needed is some real technical details, without those then it's all just speculation. Unfortunately, the way Apple has gone over the years I don't expect them to release those details without extracting a sizable wad of cash and a non-disclosure agreement.
