Inverters

How many watts do I need from an inverter to run my laptop computer?  Most of the ones I see are rated at 50 watts. I have a Compaq Presario 1030, CD Rom, etc. I want to use an inverter in my car to power the laptop for use with GPS. Compaq Tech Support says I need 240 watts, but that doesn't seem right. I am totally confused. Will one of those $50 units from Circuit City do the job, or do I need one capable of 250 watt output?  HELP?
bboseleyAsked:
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speed_54Connect With a Mentor Commented:
highly recommend the 250w inverter, because if you use the laptop for modeming while travelling, the modem tends to suck the juice lots...
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paulvaneykelenCommented:
Why do you need an inverter to run your laptop. A lot of the laptops can be directly connect to the battery of your car, (they can use DC to charge the battery). The only thing you need is a special cigarette lighter plug. I don't know what your GPS system needs, but I figure, it needs something similar.
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bboseleyAuthor Commented:
I appreciate the answer, however it didn't address the question. I have a particular need
for an inverter, and the question concerned the wattage requirement - not whether or
not I should use an inverter.
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rmarottaCommented:
If you don't believe the people who made it, who will you believe?

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bboseleyAuthor Commented:
Wow, this is getting sorta personal. But the comment about "who made it" is valid. The
problem is that I happened to get someone at Compaq who clearly didn't know what he
was talking about. (He had never heard of an inverter!!!)  The laptop does not draw 240 watts. After a few minutes (Compaq charges $2.00 per minute) it was clear I was not
going to get a correct answer, so I gave up. I will admit I know nothing about electricity.
Volts, Amps, Watts, etc.  If I did I could no doubt determine how many watts my laptop requires.
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rmarottaCommented:
They don't have to know anything about inverters.  
All you need to know is how much power their computer uses.
Now I don't know this for sure, but I think it's required to print such information on an electrical device's nameplate.
Have you looked closely on the AC adapter?
Regards,
Ralph
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cumboCommented:
bboseley,

I second Raph's suggestion about the AC Adapter. If it doesn't show wattage it will say what the current and voltage are. A simple rule of thumb is to multiply the amps x voltage for a ball park wattage. Add 10% to the total for a fudge factor.

Cumbo
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speed_54Commented:
p.s. there's nothing wrong with having extra capacity on an inverter anyway - it could be useful to run other stuff in the car
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mark2150Commented:
Look on the *data plate* on the equipment. It will give you the draw in either watts or Volts & Amps. Since wattage is Volts times Amps the computation is a simple one. A computer with a standard monitor can certainly pull 240W and then some. A laptop would normally be less. If the data plate is not on the computer itself it will be on the power supply module. Make sure your inverter has at least 20% more capacity than the data plate shows. Don't write back that there is no data plate, they're required by *law* and if you can't find it you're not looking hard enough.

M

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rmarottaCommented:
bboseley,
You said:  "The laptop does not draw 240 watts."

What do you base that statement on?
Ralph
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publicCommented:
Get a 100W square wave inverter. These are called modified sine wave inverters by sales people. Typical cost is $35. You can run the laptop with the ac adapter. Running it directly is risky, since car power may have large spikes, and laptops have little protection.
ps If the laptop dissipated 240W, the plastic case would melt and smoke.
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