12 DC - 240 AC Inverter

MajorPart

MajorPart

MajorPart

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I wish to use my laptop while travelling (not while driving tho, although detailed GPS Nav would be cool) and will not have a power connection on the routes when i stop.

I want to buy an inverter and it seems that most tend to be 150W.
I've checked my laptop charger (Fujitsu Siemens AMILO M 3438G)
I states 240V in is at 2A and the output at 20V is at 6A

Now from caluculating using the 240 figures

P=V*A = 480Watts!!

Now am i missing the mark here or would a 150W inverter just melt at the thought of my laptop charger?
 
No way a laptop is going to take 480W. That's just not happening. Even an average desktop won't take more than half that (by average, I don't mean an SLI/Crossfire system with a pair of Raptors and god knows what else :p).

The quoted figures are almost certainly maximums. You may well still be close to that 150W rating though.
 
Surely this is down to an inefficiency in the laptop power block...

it needs 240*2A in (480 watts) to produce 20*6A out (120 watts).

If you put less than 480 watts into the power adapter you'll get less than 120 watts out which might not be enough.

120/480 = 25% efficient.... hmm, odd, that'd mean it's giving off an aweful lot of heat.

Maybe that's not right afterall then...
 
That seems waay OTT to be honest matey, i have a 150w £20 invertor in my car which happily runs 2 notebooks at the same time, hasent ever batted an eye lid. My guess would be that a notebook is going to use what....40-50w? even with a rubbish psu it isnt going to drain 480w.
 
I would'nt worry about your lappy mate, I have a 150w inverter in my HGV, it runs a Microwave with no problems. ;)
 
Most invertors state the continuous power draw, you can get away with drawing a few more Amperes for a short time (peak).

150W is perfect for a laptop.
 
PeterNem said:
Surely this is down to an inefficiency in the laptop power block...

it needs 240*2A in (480 watts) to produce 20*6A out (120 watts).
Click to expand...

That would be a hideous inefficency, and if you think about it, no way in hell its going to be true, that would mean the charger would be putting 360w out as heat, and I'm sure you have felt how much heat comes out a 100w light bulb.... now, i'm not sure about your, but the charger for my laptop doesn't scorch the carpet :p

I'd imagine the 2A figure is to take account of the transients when the unit is first powered up, because switch mode power supplys contain capacitors...

You'll have no problem with a 150w inverter :)
 
Adam_151 said:
That would be a hideous inefficency, and if you think about it, no way in hell its going to be true
Click to expand...

I did think about it, hence the last 2 lines of my post...

... hmm, odd, that'd mean it's giving off an aweful lot of heat.

Maybe that's not right afterall then...
Click to expand...
 
I agree, an XPS Gen 2 definitely wouldn't, but not all laptops are made equal. Having said that, you're probably right.
 
Paulj said:
Dude, my XPS Gen 2 wouldnt even get near 150W.....
Click to expand...

It's pretty much the same system minus your funky lights.. ;)

It might just be a generic charger made to supply newer generations of siemans laptops ie that use more power, higher cap batteries etc.

The Laptop gets fairly warm and the charger does get quite hot on max load (ie doing folding at home, charging a flat battery with LCD Screen on full brighness doing some work in PS CS.) but not as hot as the stats would say it should at max load :rolleyes:

Finally does that mean there will be roughly a 12 AMP draw through the cigarette socket/car altenator?

Here's a pic showing the underside of the charger.

charger7dm.jpg
 
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Im leaning towards the theory that the 6A current rating is for peak loads for when the battery is charging + the laptop is under full load.

DC transformers are always over rated in power output so that they dont melt, i think it says 6A just as like saying "it can pump out 6A if needed"

I look at it in the same way normal desktop power supplies are, you buy a 600W supply but in reality your PC is probably only using 300-400 Watts max at full load.

That all probably doesnt make any logical sense but oh well :p
 
I'm leaning in the way of your thought too, as i would have never thought a 2Ghz Laptop even with a 17inch screen and a graphics card could draw that much but i guess it has to be fairly beefy. I'll a 150 Watt version but get one with thermal and current overload protection just to be safe :D

Till i looked i never thought laptops would take a 20V input... :(

Cheers for the advice guys!
 
Just looking at the power supply for my external HDD, it says a DC output of 12V and 2A........which is 24W.....since when do HDD's need 24W :p
 
why not just get a cigarette charger like i have? i paid about £15 for mine from ebay and used it for sat nav on my lappy on what turned out to be a 12 hour trip down south and an 8 hour trip back up with no problems. It has different voltagte settings from 12v upto about 28v and i've had no probs with it.
 
Whent for a DC / DC power source in the end. Trust Car/Plane Notebook Power Adapter 250NCP (20V 6A/120W). So hopefully that will suffice.

Thanks for the help!
 
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