A little more information to help "right-size" and inverter. I hooked up an ammeter to the W520's power supply for a little while. During idle, it read around 0.25A. When I had it refresh the Windows Experience Index score, it peaked at around 1.25A (DirectX 10 tests, using the Quadro 2000 locked on in BIOS... same 6.9 score as with it set to automatic, BTW). When doing normal office-type work, it was around 0.5A.

The same same test when docked was not much higher.

One thing that was interesting was how rapidly the power draw would change and how fine-grained the jumps were. At one point during a CPU test, it was alternating about 5x/second between about 0.62A and 0.64A. (The numbers are not actually that accurate because this is an analog ammeter... it was twitching/flickering just a little somewhere a bit above the 0.6 mark, but shy of 0.65.) Somehow I'd expected that the power consumption changes would be slower and more dramatic.

Oh, I had two hard drives plus mSATA installed during the tests. A fair number of USB devices when docked.

Anyway, standard US household current is nominally 120VAC; today my digital true RMS meter is calling it 122.8. So with V*A=W, it sounds like an auto inverter that can *honestly* deliver 200W continuous power ought to be able to power this brick. (Unfortunately, it seems that inverter manufacturers are worse than used car salesmen.)

Has anyone tried running the W520 (i7-2820QM, 1920x1080, 8GB, 1000M, SSD primary) on the slim 90W adapter plugged into a wall socket? Does it run:

• at full speed (if so, does it drain the battery, or charge it a tiny bit, or do nothing with it?)
• not at all
• at lower speed (if so, does it drain the battery, or charge it a tiny bit, or do nothing with it?)

Personally, I never use the battery, so don't care about it charging, but do travel a lot so don't want the extra 0.5kg of the 170W beast.

W520 and 90W will discharge battery while running. You can charge battery while laptop is off.

Or standby. The battery life is good enough, that if you work in the morning, charge at lunch, you'd be able to easily make it through a day with the 90w in your bag. Not ideal, but it's a cheaper way to go than buying another brick.

I thought people are paranoid, but I got my lenovo today. This thing IS a monster! OMG, what were they thinking while engineering this module?

They were probably thinking: How big does it have to be so that it can supply enough power when the W520 is running at full throttle.

If you want a quad-core that discharges the battery when running at full speed, get yourself a mac

The W520 170W is the only adapter that can fully function the laptop. The 170W adapter doesn't fit into other lenovo laptops, but the 90W does fit and does charge the battery while the computer is in sleep mode only(or if it's off). During use the laptop does not function as 'plugged in'. It functions as if it's on battery with the message that the ac adapter can't provide enough power. I've got an i7-2720 model with 8GB Ram and 1920x1080 screen with the 1GB Nvidia optimus graphics. The battery seems to drain at the normal rate with the 90W adapter plugged in when the laptop is in use.

I have similar experience to pkincy and davidhrown

Mine is also a ThinkPad W520, and since the mains adapter is a brick 17cm x 8cm x 3.5cm weighing 750g (6.7"x 3.2" x 1.3" weighing 1.64 lbs) I figured from suggestions above
that I can equally use a smaller mains Adapter also available from Lenovo.
As you know, the "Brick" has an output of 170W, 20V charging at 8.5A
The smaller versions have an output 90W and charge at 4.5A
so accordingly I bought a Lenovo 41R4494 Ultraslim Adapter which is 11.5 cm x 7cm x 1.7cm and weighs 377g (4.5" x 2.75" x 0.67" weighing under 12 ounces). I felt very pleased.

But now my ThinkPad is nagging me each time I switch on or close down:
"Ïncorrect AC adapter is attached.
This AC adapter may not provide enough power to your Thinkpad. Please reconnect the proper AC adapter." - also reported by davidhbrown
i.e they mean I am ündercharging the battery, right?
Most warnings about batteries are about insufficient discharge, constantly running at 100%, or overcharging.
I am not doing any of those things.
It is true that, if I leave the UltraSlim attached while I work, the battery runs down.
Question: But is that bad? Maybe it runs down more slowly, than if the UltraSlim Adapter is *not* attached?
If I am out in the field, visiting a plant, without the UltraSlim Mains Adapter attached I get at least 6 or 7 hours - maybe using the Adapter I can extend it to last 10 hours?
Can it damage the control circuits in the battery or the mains adapter?
skrasher says that "During use the laptop does not function as 'plugged in'. It functions as if it's on battery with the message that the ac adapter can't provide enough power."
Provided I have enough battery for a day's work, the smaller charging unit serves the pupose, right?

So now I have adopted the compromise work routine suggested by pkincy, which uses the Li-battery during the working day, and charge the battery overnight.
1. I hibernate the computer - with remaining charge ca. 30% - leaving it plugged in to the UltraSlim charger overnight.

2. In the morning I unplug the mains adapter, before waking up the computer (thereby avoiding the nag).
It's back to 98% - 100% - showing 8 or 9 hours work available in the battery (the 9-cell battery)
During the day, I use the computer entirely on battery, in sporadic intervals of half to 1½ hours.
Between each work interval I close the lid to hibernate.
I rarely finish the day with less than 30% charge in the battery.

So now to my main questions:

A. is this routine harmful for the life of a Li-Battery?
B. is it better to oscillate between 90% - 100% for a life permanently connected to the mains power?
C. if there's no harm done, why does Lenovo nag me for using the 4.5A mains adapter?
(it charges OK when I am not using the computer).

Many thanks for any insight or 'light' the Team can shed on this subject.
Any ideas?

Cheers = John

I fly a lot and rely on the on-board power to get my W500 through a transcon or international flight. I got the W500 instead of the W510 solely because of the availability of the travel adapter. I actually bought a W700 and returned it immediately, it was like the clown shoes of laptops, ridiculously over-sized: both the laptop (absurdly larger than the apple 17") and the power cinder block (several times the volume of the compact 90W adapter, too big to be a "brick").

I'm very curious if run time can be extended meaningfully by using the 90W adapter in combination with batteries in the W520. It would be extremely helpful if someone would undertake the following experiment:

Run the W520 on battery alone for normal laptop tasks and report runtime.
Run the W520 on battery plus 90W for similar tasks and report runtime.
(bonus points for running it down with some standardized test suite to improve the accuracy of the results)
extra bonus points for running the same experiment with the 135 W adapter
Double extra bonus points for testing on plane power.

My experience so far:
Older KID DC-DC systems (still in use on many planes) can drive 120W power adapters. This is sufficient to run the W500. I don't have a 510/520 to test. The batteries charge normally. It will also run the compact 90 AC/DC adapter through the DC cable.

Newer Astronics systems (AC plugs, labelled "Empower") will sometimes drive the 90W AC compact travel adapter (41R4538), but not always. I fly United so my tests are on their planes. I've learned that UE/UB/UF classes may have different power limits, but the maximum is 75W per seat pair if both people are using the power, or 90W if the person in the seat next to you isn't using power.

Different planes seem to be configured differently. This is possible - there are several Astronics units: the 1215 which puts out 150VA per outlet and the 1191 which can supply 200VA per outlet. This may explain why some planes barely run the W500 on AC (generally the batteries charge fine in sleep mode, the computer can sometimes run at minimum power draw, but will trip the breaker reliably if the batteries are discharged and the computer is running in "performance mode.")

However, in most first class cabins on transatlantic flights, on the one continental domestic first 737 I've flown recently and most UAL PS flight business cabins (but not all) the plug-in power works fine and will charge the laptop while running.

It would be awesome if Lenovo would add a "plane mode" and travel charger for the W520 which would use as much power as available, with a software controlled throttle to allow setting the maximum wattage drawn through the adapter before tripping a breaker, so those of us who fly AND need a powerful computer can get as much work done as possible.

If you do not use the battery, you can never achieve full speed, even if you have 170w adapter attached.
90W should make the laptop work at lower speed, and if you run resource-demanding program, it would put the adapter into danger.

The 170W adapter can drive the W520 without the battery.

When I get home (that's months yet) I will post a pic of the power adapter of the T221 monitor. That will teach you younglings to appreciate modern technology it's 16V 10A larger footprint than a CD and several kilograms .

So, I don't mean to re-kindle a dead thread.

However, I left my 170 Watt power brick at the office today, and I have a problem set I'm working on at home, so I'm kind of screwed.

The BIOS release notes for my BIOS (v. 1.34) state that there should be a mode in ThinkVantage Power Manager for a 90 watt auto/air adapter. I can't find that option, and my battery slowly discharges, regardless of whether it's plugged into my 120 watt Kensington or my 90 watt Targus Universal adapter.

However, I can charge the W520 in standby using either adapter. (For the Targus, I use tip L112, and for the Kensington, I forced tip N29B onto my adapter.)

I fried my N19 tip on my old Kensington with my Dell M4400...can't find one anywhere to replace it. I guess I have to be happy with tip L109 on the Targus for my Dell, unless I happen to stumble on the right eBay item.

Lenovo, could you please, please, please figure out a way to power this wonderful Lenovo W520 beast of a machine on 90 watts, even if I can only run notepad? It would make my life much easier, and all I really want is to be able to "DO" regardless of my power situation. Nvidia Optimus gets me most of the way there, so thank you for that.

And to CHX who points out that he has a massive adapter for an ancient piece of tech: we shouldn't need power adapters in this day and age. Wouldn't it be wonderful if any AC or DC signal above 5 volts could power your lappie in some manner? Even if the battery had to discharge slightly? Cell phones are moving in that direction. Laptops should catch up. Sadly I had to type this on my M4400. I'm saving the juice on my W520 for Eclipse a bit later.

I'm starting to wish I had gotten a T520 and sacrificed just the extra GPU speed on the W520. NVS 4200 wouldn't be that much slower than a Quadro 1000M. Also, $110 is way too much for a second 170 W AC adapter. I think I'll take the smaller 135 W one for $88. I think an EliteBook will be my next purchase, assuming I can afford it.

I found a pretty simple solution. I unsoldered the cable from my 170W power adapter and soldered it to my 90W adapter. Voilà! The W520 runs and charges at the same time.

The adapter does get slightly warm sometimes, but so far I never managed to get it warmer than when it ran with my T60p. I just wished somebody would sell the cables or tips separately from the 170W power adapter, so one doesn't need to destroy that. But I'm so happy I can leave the huge 170W power brick on the attic, and have only the small adapter in my backpack.

Please be sure to let us know when either your laptop or AC adaptor melt down or catch fire.

Will do. But don't put your hopes high. I'm not a heavy gamer who, at the same time, formats his HD, writes DVDs, and uses the docking station and all ports.

Can you provide some closeup pictures of exactly what did you cut down and how did you connect it? If it's just a cable then there is no electronics / chip in the authentication mechanism it seems. This way we can make a 120W adapter from a Cooler Master USNA 120 (only 268 gramm) and the tip of the 170W adapter!

Very easy: I cut the one cable, took the two cables inside, and soldered them to the two cables from the other cable. Just make sure +/- matches. Voilà.

The 90W adapter does it fine so far, 120W would surely work, too, even under higher loads. I don't know if the trick would work by taking the connector cable from the 135W adapter. The only visible difference from the 170W to 90W (and 135W) are the two little plastic notches inside of the otherwise round plug. If it's not them who tell the W520 it has the right power supply, the cable from the 135W power supply could work.

***Does anybody know if the Lenovo 135W power supply charges and supplies the W520 when on?***

If it's the two plastic notches, one could try to add them manually.

AFAIK there is a place in Power Manager where it tells you what adapter is connected, so there must be something else other than a simple plastic for identifying the adapters. The good news is that if it's not a chip but just a resistance or something easy then we can make an adapter cable.

For overheating the adapters, AFAIK these all output max the given current rating, so no matter what you do they can never give more than the rated current, thus cannot overheat!

If it's not the notches that push something that then tells the W520 it's the right AC (I agree that seems unlikely), then the 135W adapter may also have that invisible little something in the tip (I wouldn't think it's in the middle of the cable), and may work just as fine.

My assumption is that the first thing that gets shut off when using the 90W power supply is the battery charging function. So far, I didn't feel like the battery charges slower. The reason may be that on the road I'm using mostly office programs. The W520 has two graphic cards, and for less demanding tasks it uses the lesser, saving power, which is also nice to the battery.

Obviously, the W520 would use between 15 to say 50 W during everyday use, that why I really don't understand why don't let us use a smaller adapter. Of course when the load gets bigger, throttling would occur, but it could be our choice if we want to go that way (to make it function like a Macbook Pro with 85W adapters).

Typical Apple paternalism. Hold on, it's not Apple but Lenovo who is paternalistic? Well, it doesn't surprise me anymore; each new ThinkPad I got since 2001 had some stupid or cheap new flaw that wasn't there in the previous generation. They also don't offer the adapter cable as a spare part, so if you want to do the soldering trick, you have to take it from your 170W AC and thereby make it unusable, or buy another one.

A maxed out W520 running everything from Extreme Quad, 2000m, msata SSD, RAID 0 HDD, 32gb ram will need 170w guaranteed.

Extreme Quad 55w, Quadro 2000m 45w = 100w + LED, mobo, msata, two HDDs and 32gb of Ram = 160w easy.

You build a AC for worst case scenario, very few W520 owners will ever see the above maxed out system running in full capacity, but some will, I've come pretty close.

I wonder why they don't give you the option. For example, when configuring my new T420, if I picked discrete graphics I had the option of a 65 watt or 90 watt power supply. Why not give W520 customers the option of choosing between the 170 watt and the 135 watt? Since they weigh about the same, but the 135 watt takes up less space in a bag (which is important as I have both the 170 watt for my work W520 and the 135 watt for my personal docking station - the 135 watt works better in my bag for travel).

Seems like folks could read a couple sentences in the "help" on the order page and make as good a decision for them as they can about any other configurable part.

thinkbigger's solution looks great - swap the tip so the 90W power supply supports the 170W supply's plug tip.
This is elegant and can save us bucks and weight as well as the highly desired 'have 1 laptop but a power supply in every port' model!

I almost thought I could do a physical hack here, and glue 2 small inserts into a standard 90W plug tip to fool the W520.

BUT

looking into the socket, there's no reason it would work.

Looks like there are 3 contacts in the tip - the inner pin, the inner surface of the plug and the outer surface. They all have a function?

@thinkbigger, could you let us know, when you took your 170W supply's cable off, did you resolder with 2 or 3 wires? Are there really 3 active connections, I wonder?

I'm pretty sure I had to resolder only two wires.

Even if there was a third, that should not make a difference, since the 90W adapter is accepted fine. The difference must be in the plug.

Measuring with a voltmeter reveals that the outer surface is the minus, the inner the plus pole. They are 20V on the 90W and on the 170W adapter, as printed on the AC. The inner pin does not seem to be connected differently either, at least it's not shortened on either cable.

So unless the difference is something like a different resistance of the inner pole within the plug itself, the physical (glue inserts) solution should work. I would be very interested if it does. Maybe those two notches push something in the socket?

Look at the label of the 170W watt adapter, it explains it: the inner one is called "signal"! I'm sure there must be a very small chip in the plug, which provides this "signal".

Ideally, we should find someone who is willing to "decode" this signal and manufacture an adapter cable! Any ideas?

In Dell AC adapters, there are three wires, with the ID chip in the adapter housing. You all might like to read the articles by Nomad.

about Dell Power Plug, by Nomad at The Laptop Junction.

So it's still a bit of a mystery how thinkbigger got his 90w adapter to work using a 2 wire connection to the 170w tip

Why? It's clear: the signal chip is inside the plug, not in the adapter, so there is only 2 wires going from the adapter.