Use of 65W or 90W power adapter with T520 QM that needs 135W

[wwcanoer]

I will buy a T520 and am considering the four-core 2720QM model but this brings the disadvantage of requiring the larger & heavier 135W power adapter.

Q: Can a 65W and/or 90W power adapter still be used when traveling?
i) Simply for charging.
ii) When in operation.
(The Lenovo documentation online simply says that 65W and 90W are not compatible.)

Certainly, one could not use the 4-cores at full strength with a smaller adapter, but when performing basic office tasks (MS office, web browsing), will one be able to use a 65W or 90W adapter in order to keep working longer than the battery alone could provide?

FYI: I did find an old post for the W510 where a fellow was able to use the 90W in place of a 135W but I am wondering if the same holds true for the T520 and if a 65W adapter can be used. (I have many normal 65W bricks and two 90W slim ones, but the slim ones make an annoying buzzing sound.)

Thanks in advance!

[wwcanoer]

Another post confirmed that a 90W adapter can be used with the T520 4-core. http://forum.thinkpads.com/viewtopic.ph ... 19&start=0

Has anyone tried a 65W?

[TuuS]

You may find that it drains the battery faster then it can charge, but I also wonder how the circuitry will react when it senses AC power, but needs to use the battery to put the amps it requires. In other words, what if it trys to force your 90w charger to supply it 120w... have you seen one of these catch on fire? I have. I had a generic p/s that worked fine on my A31, but when I charged it with two batteries installed, the charger was laying on my bed under the bedspread and I smelled something burning. I got a nasty 2nd degree burn trying to pick it up, the plastic housing was literally melted and was beginning to flame. I had to grab the wires and pull them apart to get it unplugged.

Obviously this wouldn't be the same risk using a genuine adapter, but the question is, will the laptop pull current from the battery and let the charger put back as much as it can, or will the system expect to have 135w available to it and draw upto that much direct from the charger.

Some testing could tell, an amp meter running on it while the system is under heavy load, but bottom line is, use the 90w under careful supervision, and Don't try the 65. I can't imagine why you'd want to, it's not that much smaller, so no real reason to prefer it.

If used only when the system is powered off, then I think you'll be fine with either, but check to make sure it doesn't overheat.

[chairsky]

Have tried 65w on intel GPU model and 90w on Nvidia GPU model.

Both works, but the CPU performance is much affected (GPU seems fine, affected to some extent any way, but not that much)

[Colonel O'Neill]

The W520 just got a BIOS update involving "improved performance on a 65W adapter" and something about an "airplane inseat power mode". Sounds like with the second feature, you'll be able to run on 65W or less but with reduced performance.

[wwcanoer]

@Thinkpadder. That is very interesting. Thanks!