David, did you mean to say DC notebook adapters are quite "in"expensive?

You can get a DC adapter that plugs into the cigarette lighter for less than
11 bucks with free shipping.
Doesn't get much cheaper than that.
http://tinyurl.com/agfkzd

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David Kao
Sent: Friday, February 27, 2009 12:32 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Invertor ?

Notebook computer vendors normally have DC power adapters for
use in cars to power notebooks. They take DC 13.8 volt input
and generate DC 19 volt (for HP notebooks) 3 - 4 amp output to
power notebooks. Such DC power adapters are quite expensive.
There are aftermarket DC inverters that are cheaper to get.

Using an inverter (13.8 volt DC in, 120 volt AC out) to power
a notebook AC adapter then power the notebook is indeed less
efficient. That's two stages of inverters.

If the setup is used only for charging the notebook you probably
will lose maybe 3 - 5 watts of power due to the inefficiency.
This will not be too much a concern really. But the reliability of
the inverter will be one to worry. Most cheap ones are over rated.
When they go bad they can cause damage to the device they power.

David