[tmcgee]

They make chargers for netbooks that plug into 12v lighter sockets. It's likely to be less money than an inverter.

If you do want to calculate power requirements, you need to know how much power the charger (+ the inverter) draws, then use Ohm's law: P=IE

 

[PTRider]

Yak, on your charger or on the netbook it will list amperage or wattage. The rule mcgee quotes can be turned around:
watts = volts x amps
amps = watts ÷ volts

Also to be considered is the parasitic loss of the inverter. It will consume some power just making itself hum and get warm. Probably an inverter 50% higher capacity than the netbook charger is wise; no less than 20% greater is probably minimum. A car charger remains the best bet.

 

[OydnaR]

I have this 70 watt inverter that I charge my survey instruments with

Amazon.com: Schumacher PI-70 70 Watt Power Inverter: Automotive

 

[Yak]

Thanks guys. so the charger output (what it sends to the computer) is 19 volts at 2.15 amps, giving a draw of 40.85 watts. I have a 75 watt inverter, so even with parasitic power loss, it should do fine. Someone (salesman) suggested I needed a 400 watt inverter.

 

[tmcgee]

Thanks guys. so the charger output (what it sends to the computer) is 19 volts at 2.15 amps, giving a draw of 40.85 watts. I have a 75 watt inverter, so even with parasitic power loss, it should do fine. Someone (salesman) suggested I needed a 400 watt inverter.

Yeah, you should be fine assuming the rating is calculated properly and the 75 watts is output rather than input. Nothing wrong with the 400 watt suggestion though. Higher capacity means things run cooler.

 

[Valentine]

Advice

Cheap inverters give you a Square Wave output. A square wave output will NORMALLY not cause any problems on the device to which it is attached. However, some computers are sensitive and require the normal sine wave output.

I decided to purchase a sine wave inverter just to be save. Unfortunately, pure sine wave inverters are about 50% more expensive than an equal capacity square wave inverter.

 

[OydnaR]

Cheap inverters give you a Square Wave output. A square wave output will NORMALLY not cause any problems on the device to which it is attached. However, some computers are sensitive and require the normal sine wave output.

I decided to purchase a sine wave inverter just to be save. Unfortunately, pure sine wave inverters are about 50% more expensive than an equal capacity square wave inverter.

like myself, the op is just charging batteries

 

[Fyrman]

I picked up this last week to use on the drive home from vacation. Worked fine and was on sale for $15. Not sure if it still is but worth looking into.

 

[Yak]

That's the same one I have. I got it on sale for $9.95.