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LAPTOP POWER MEASUREMENTS
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Using the above setup, I measured the draw of my laptop both with and without an inverter.
Laptop: IBM/Lenovo T60. Input: 20V. Rated at 90W on the back of the laptop.
Power Supply: AC/DC Combo Adapter P/N: 40Y7656; supplies 20V power to the laptop from either AC or 10.5-18V DC sources. Sweet.
Usage conditions: Screen brightest, volume up all the way, Wifi on, bluetooth off, DVD in playing movie.
Inverter: small 150W (peak) cig socket inverter from Radio Shack.
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RESULTS:
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Inverter alone (nothing plugged in): 3.6-4W (avg ~3.8W)
Computer plugged into inverter using AC: 38-40W
No inverter, computer plugged directly into DC: 30-31W
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COMMENTARY:
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A. Nice low power draws regardless. I love the Thinkpads. Your mileage may vary, laptop dependant. Especially with a Sony Powerhog.
B. Inverter alone doesn't draw TOO much power. My guess is larger inverters would draw MORE standby power due to larger fans and electronics. However, they may be more efficient at converting larger loads to AC.
C. Assuming a constant inverter overhead of ~4W, then the extra conversion inefficiencies between the inverter and laptop power supply are ~5W over a baseline of 30W. This may be slightly flawed thinking though.
D. Overall inefficiency of moving from DC to AC is a almost a 30% overhead in extra energy cost.
E. Summary: GET A DC POWER SUPPLY FOR YOUR LAPTOP ALREADY!