Get a larger model with a few plugs and more power. Cheaper ones have a
noisy fan. You can run them with the car off but risk being unable to
start the car of course so I got an extra car battery for that scenario.
I paid too much for my noisy one at Radio Shack, have heard others found
better for cheaper.

Bill

You might want to look at
" XPower Powerpack 300 Plus  Plug in to portable power anytime, anywhere, at
home or on the road. Use this sealed 20-amp-hour/200 CCA battery and
300-watt inverter combo system to jump start vehicles, run 115-volt AC or
12-volt DC accessories and even power your home security system in a power
failure. Built-in 250 psi air compressor inflates tires and small sports
equipment. Battery recharges from a standard 120-volt household outlet or
12-volt accessory outlet."

http://www.campingworld.com/browse/skus/index.cfm?deptID=&subOf=55&skunum=26
434&src=TSC

Or
http://tinyurl.com/c4td8

Sounds like it might be a good for this type of job. It looks like a little
12 volt battery that also has 300 watt invertor built in. You can charge it
from 110 or off a running car. So you could use it and if it kills the
battery no problem, you could just charge it again.

Although you need to be aware of low cost invertors are not very good for
Hard drives, but should be OK with a Laptop transformer.

I have never used this item and do not know anyone who has. I just ran
across it a while back and your needs seemed it might work.

Paul Wilson

On 8/1/05 4:48 PM, in article
1122929337.772386.137760@g44g2000cwa.googlegroups.com, "Bill Hilton"
<bhilton665@aol.com> wrote:

DC-to-AC inverters come in several varieties.

The fancy ones produce pure sine-wave output, just like you get at home.
They will run just about anything as long as you don't exceed the power
rating.

The cheap ones produce a square-wave output, which is incompatible with
many electronic/electrical devices and can even destroy them. This is a
common problem with solar-powered houses. I have seen it reported that
laptops are pretty tolerant of square-wave power, except for some Macs. I
have had square-wave power fry a battery charger; some other chargers just
don't work.

Also available are "modified square-wave" inverters, which give you
in-between power quality for an in-between price.

For my Dell laptop, I got a DC powerpack which converts 12V DC into the
same DC voltage provided by the laptop's AC powerpack. However, the laptop
also works fine when I plug the AC powerpack into a square-wave inverter.

For delicate low power devices such as cell phone and camera chargers, and
presumably your external HD, I'd recommend a low-power pure sine-wave
inverter.

A laptop will discharge a car battery in roughly 10 hours, so this is an
issue. The hours add up pretty fast.

HTH

Pete

Bill,
I have run numerous things off of DC to AC converters, from computers
to scientific instruments, to battery chargers.  The one point I would
consider is not to get too much capacity as efficiency of the
converter might be low and a lot of power dissipated as heat in
the converter.

I have run a telescope (motor driven) with autoguider (custom
computer and CCD sensor) all night with no problem.

For laptops, I buy the DC converter designed for the laptop.
I've also done a microwave (600 watt converter).

Get everything well before you go and test all of them.  I was
running a laptop and GPS once and about an hour into first time
use of the laptop converter, the converter went up in smoke.
I had to jump out of the car quickly and get it out before
it caught other things on fire!

While I have run numerous battery chargers from DC to AC converters,
I have not tested the 1D Mark II charger (yet).

I also have a nifty solar cell that can charge a car battery
in a day.  I use it when camping for a long time and needing
continuous power.  It has no model number as I got it used from
a do-it yourselfer.

I have never had a problem with square wave converters.

Roger