Car Adapter: Calculating Laptop Power Consumption required

Leonedes

Hello,

I'm thinking of buying a DC/AC Inverter for my Car [i.e 400 Watt 12 Volt DC To 110 Volt AC], especially to charge and use my Alienware laptop in the car. I cant seem to figure out how much wattage the laptop consumes.

To be clear, I will need to actually use my laptop adapter in the car, and not use a special laptop charger designed for the car, as the inverter needs to serve multiple cases.

On the back of my laptop adapter, it says 100-240V, 50-60Hz, ~2.5A .

Since my inverter will be giving out 110V , would that mean that the outputted wattage would be
P = U x I = 110*2.5 = 275 W .

Is that true ? I'm lost cause while reading amazon reviews, most people had laptops that require < 100W to function. Is mine so high due to the high current required ? (2.5 A)
Is the 275W the maximum power ? A constant ?

Should I stick with a 400W or would a 300W inverter do the job ? and finally; can those inverters be trusted or would they damage my cars battery/laptop in anyway, what I'm getting costs around 40$ and needs to be directly connected to the battery due to the high wattage required.

Sorry for the many many questions!

Edit: I found on cnet that average power consumes 125W ... how is that even possible ?! http://reviews.cnet.com/laptops/alienware-m15x-intel-core/4505-3121_7-33772443.html#reviewPage1

I also found my laptop adapter online, the title says "150-Watt 3-Prong AC Adapter with 6 ft Power Cord for Dell Alienware M15x" Does that mean its max consumption is 150W or is that its output ?! http://reviews.dell.com/2341n/330-5830/dell-150-watt-3-prong-ac-adapter-with-6-ft-power-cord-for-dell-alienware-m15x-alienware-m17x-alienware-m17xr3-xps-l702x-xps-m2010-laptops-reviews/reviews.htm?sort=rating&dir=asc

xazbrat

You don't need 300 or 400 watts--that would be overkill. Look at your AC adapter and see how much that requires in WATTS. They are usually anywhere from 80-125 watts, and that's all that you need. I have one and have used with no problems for a few years (got it in the US), 120 watts no problems with my Dell laptop.

yasamoka

xazbrat wroteYou don't need 300 or 400 watts--that would be overkill. Look at your AC adapter and see how much that requires in WATTS. They are usually anywhere from 80-125 watts, and that's all that you need. I have one and have used with no problems for a few years (got it in the US), 120 watts no problems with my Dell laptop.

If I'm not mistaken, they label only power delivery and not power requirements. Considering that such power supplies are often not really efficient, shouldn't power draw be a bit on the high side?

xazbrat

yasamoka wrote
xazbrat wroteYou don't need 300 or 400 watts--that would be overkill. Look at your AC adapter and see how much that requires in WATTS. They are usually anywhere from 80-125 watts, and that's all that you need. I have one and have used with no problems for a few years (got it in the US), 120 watts no problems with my Dell laptop.
If I'm not mistaken, they label only power delivery and not power requirements. Considering that such power supplies are often not really efficient, shouldn't power draw be a bit on the high side?

Power requirements are also listed--usually in 100-240v and also a wattage number. This figure will be around 120, but will vary on the type of charger. Anything that you have to attach directly to the battery will be overkill--that's the kind of adapter people use to power TV's or other small appliances.

Leonedes

Well unfortunatly nothing is written on the laptop adapter. Anyway check out the links I posted in "EDIT" one says its 150W (which is alot if standard laptops are around 100) and another says regular consumption is 125W.

xazbrat

Leonedes wroteWell unfortunatly nothing is written on the laptop adapter. Anyway check out the links I posted in "EDIT" one says its 150W (which is alot if standard laptops are around 100) and another says regular consumption is 125W.

After doing some digging, it seems that the "standard" wattage for the Alienware M15x is 150 watts. You can use 65 watts if you go into stealth mode. If you can find an AC adapter rated at 150watts, you should be good to go. You may want to get one rated higher at 180 or 200 watts just to be on the safe side. These are plugged into the cigarette lighter and don't require you to connect it to the battery.

The Alienware series being a higher performance laptop, do require more voltage than other standard laptops.

Leonedes

Excellent info xazbrat :) thanks alot , never really knew stealth mode was that efficient, i guess its a bonus for my case. By the way anything more than 120 W needs to be connected directly to the cars battery else you might blow the cig plug's fuse .

xazbrat

Leonedes wroteExcellent info xazbrat :) thanks alot , never really knew stealth mode was that efficient, i guess its a bonus for my case. By the way anything more than 120 W needs to be connected directly to the cars battery else you might blow the cig plug's fuse .

Get an adapter with a fuse then--it will prevent damage. Make sure that it provides continuous power at the wattage that you need (150w) something like this http://www.knighton-tools.co.uk/acatalog/POWER_INVERTORS_12DC_TO_110V_240V_AC.html (the first one)

or get something like this http://www.laptoppartsexpert.com/i-88518-auto-boat-adapter-150w.html

Good Luck

Leonedes

One last question though, in this case, what the hell does P = U * I represent ? The maximum value that the laptop adapter can output with no resistance ? Im purely trying to guess since the formula did not serve us in any way.

az09za90za

Leonedes wrotewhat the hell does P = U * I represent ?

its The maximum value with resistance.

Leonedes

Then to know what were looking for its P = U*I - R*I^2 ? It doesnt make much sense, again purely guessing