I have two questions to which I could not find the answers.

1. Why does Lenovo intentionally prevents plugging the 170W adapter to other machines? If they plan to start making the connectors like keys, so that they would not be interchangeable between machines to give Lenovo more profit, it's disgusting. Anyone who understand basic law of physics knows that the argument that "170W is too powerful for other machines" makes no sense - 170W is the maximum rating. In addition, those who bought Mini Dock Series 3 with 90W power supply, cannot use it with the 170W power supply as the connector does not match. Powering w520 in the dock with a 135W adapter would work perfrectly.

2. Why would not they allow topping up the battery of a 90W adapter when the computer is ON? I can see in the Power Manager that W520 consumes about 20W in idle, so it would work normally for light loads even with 65W adapter. The argument that 90W might not be enough also does not make sense: how can getting some power from the wall, even if it is not enough, be worse than just discharging the battery. This is a very important concern for every one who travels with their machine.

Did Lenovo give any explanation?

#2. Just one scenario I came up with.... Let's presume that the battery can either be discharging or charging, but not both simultaneously. That makes sense, right? So, maybe you can power the W520 from 65W/90W most of the time, but occasionally something kicks in and the current draw spikes. Suddenly it has to switch from AC power to battery power. Okay, fine let it. But let's say you have different settings in the power manager for AC/battery screen brightness -- as it does by default. Maybe also for WiFi power. USB standby. GPU settings. And maybe the threshold is crossed every couple of seconds (even several times a second).

I could see a situation where a computer was reduced to a beeping, flickering hysterical mess by trying to switch back and forth too often. Yeah, you could "fix" this with a custom power scheme, but the out-of-the-box experience on an Energy-Star-labeled machine could be pretty nasty. (I wonder how the Mac PowerBooks with their 85W power supplies handle this. MikeM, you still here?)

I think there's an similarity to uninterruptible power supplies. Most are "standby" systems where only one power source (battery+inverter or line) is connected to the load. A more expensive "online" (or "double-conversion") always has the load connected to the battery+inverter and available line power can run the inverter and/or charge the battery as appropriate.

If this idea is remotely connected to reality, then perhaps what we need is for Lenovo to come up with a power handling circuit more like the online UPS... but responding to load rather than line.

#1. Could it have anything to do with whatever mechanism is used to sense the current rating of the power supply being incompatible with older machines? I really have no idea. Indeed, it seems like what they needed to do was prevent connecting a too-small adapter, but the plug redesign does not achieve this. But if they really wanted to gouge on adapters, they'd follow Apple's example. (How many different video ports have they come up with over the years? Round serial ports, too.)

#2. I am not an expert, but I do not believe laptop battery is similar to cheap UPS as there is no AC inside of the laptop and according to wikipedia
(http://en.wikipedia.org/wiki/Uninterrup ... wer_supply) the whole idea of standby UPS is to save costs on AC/DC conversion. Besides, they could
force the CPU and GPU into the most power efficient mode instead of just refusing to boot: if I travel with the laptop and intend to use it lightly, why should I lag a 2-pound adapter? Again, for light use it consumes just 20w of power.

#1. The knob in the connector (http://msinetpub.vo.llnwd.net/d1/keithc ... onnect.jpg) has nothing to do with how the laptop senses adapter's power: the connectors of 90W and 130W are identical, yet the computer would not boot with the former if the battery is disconnected.

I have a really strong feeling that they just want to gouge customers on accessories: they want users who already have a 90W Mini Dock Series 3 to buy a 170W version for $200+, while the only difference between the two is the connector. [As well as they would love users to buy more of 130W-170W adapters instead of reusing the old 65W-90W ones, even at cost of inconvenience to the customer]

Anyone willing to shim the connectors?

Yes, you can shim the connector. I've done it myself. Works perfect.
The Series 3 Plus docks all have the same board, only difference is the connector.
This is done as a cheap way to force W510 owners to buy new Docks. For a 5 cent connector change, Lenovo makes 250 bucks.
All you need a fine razor, some balls of steal, and a filing unit. Once you shim the teeth down on the 170 AC you're good to go.
Save yourself $250 on a brand new dock.

The only difference between the 135 AC connector and the 170 AC connector is the two protruding keys, file those down and they are the same.

I'm typing a old series 3 dock with a modded connector right now.

Nice forum by the way. I hope my post will save people some money. Spread the word.

So can you confirm that if you file away the yellow teeth of the 170W adapter for the W520, you can still use it to run and charge the computer itself (without the dock)? You don't get any nasty messages saying it's the wrong adapter? Also, as well as using it to power the W510 dock for use with the W520. can the filed-down adapter tip also be used to run/charge any other 20V Thinkpad (e.g. a T61) without problems?

Yes, yes and yes.
The filed down 170w works on all Thinkpads and charges lightning fast.
Used it on X301, T61, X220T and etc. Its just plastic man, how is your W520 supposed to know that its gone? Just a little trick used to sell more accessories.
As for using it on series 3 docks, it works on both the 90w and 135w version with no errors. Been using it for a long time now.

The internal board on the 90/135/170 docks are the same Lenovo just changes the connector on the 170w model.

Also if you remove the alignment blocker like I mentioned in my other post, you will
open the dock up for better airflow and X220T support, another cheap trick used to sell you an Ultrabase.

The small tricks Lenovo uses to get you to buy new docks is astounding. Nothing a little logic won't solve.
http://img690.imageshack.us/img690/8803/593f.jpg

Just wanted to add my 2 cents to this thread. (Actually I only registered to reply to this thread - I don't know Kaze22 though, by coincidence I also live in Vancouver).
I have a W500 sitting next to me that is being powered by the 170Watt brick. As far as power management is concerned it believes it is attached to a 135W supply. Everything works fine.

I used a small x-acto knife to chop away at the tabs. I was wondering how difficult it would be to trim them all the way down the barrel of the connector but it turns out that the outer metal contact wasn't split at the tabs but was a continuous ring and instead the tabs merely lay on top of the metal. Once I had whittled the tabs down to where the outer conductor started they just fell off. I used small needle nosed pliers to get the lose bits out of the hole and now everything is good.

So a 90W car charger for the T61 should also work on my w530 - atleast when it is powered down?