no-one has confirmed yet if and there is really a signal chip in the 170w adapter's connector tip and what it does - the Dell article points to an example of such a chip being in the logical place - inside the adapter housing

It looks to me like the two notches break the contact between the two sides of the inner circle, unlike on the 90W where the circle is a complete piece of metal. Notice that there are *two* electrodes on the *inner core* of the W520's socket. If only one side or the other is powered, the laptop would be able to detect internally that it is connected to the 170W tip as opposed to the 90W. Alternatively, it might check to see if there is an open circuit between the two electrodes. Just a guess. Could be tested by someone with an amp-meter. Or, with a 90W adapter, by a strategically positioned bit of paper to try to cut current to one or other electrode on the inner core of the W520 socket.

This is probably completely wrong, but worth a shot?

Yes you could break the circuit, may not prove anything as you either

a) Simply interrupt the power to the W520
b) Disconnect something that's not connected to anything anyway.

I'd be a bit careful not to short anything too.

The logic puzzle is that the tip can be rotated 180 deg and plugged in, reversing the contacts....

Thinkbigger is in the best position to check out the tip as he has already disconnected the cable.

I tried covering half of the inner surface of a 90W adapter with sellotape, and then inserting it so that the sellotape breaks the electical contact with one of the two inner electrodes but not the other. Unfortunately no luck, the W520 still recognizes the adapter as 90W and fails to charge while working. There must be more complex electronics at work, or possibly a precise resistance rather than a complete circuit break.

Funny thing, though, I have a damaged 90W adapter (my son broke the tip), which I resoldered back to a new tip from one of those universal adapters. I could have sworn it was the central pin rather than the inner ring across which I measured a potential difference when I was fixing it. It's just a bog-standard replacement tip and seems to work fine with all the Thinkpads in the house. So nothing special in the 90W tip as far as I can tell (I hacked back a lot of the plastic it to find a good anchor for the wires, and no evidence of internal electronics). NB the test with the W520 above was done with an original unmodified 90W adapter from Lenovo.

So according to Kaze22 in this thread, you can just file off the yellow teeth and the 170W adapter can still be used with no problems for the W520 and can also be used to charge/run any other 20V Thinkpad or docking station. If so, it means that the yellow teeth are just a marketing ploy to lock you into a specific line of adapters and/or to make you think you need to buy a W520-specific docking station. It doesn't seem to make much sense that they would try to prevent you using the 170W adapter for charging other 20V Thinkpads, though, unless the BIOS on those Thinkpads can't recognize the 170W.

Still doesn't explain the mystery of how, simply by swapping the tip of a 170W charger into a 90W charger it becomes possible to run and charge the W520 from the 90W.

I don't think that'll work. I think the firmware on the 170W ac is whats actually sending the signal to the W520 thats its a 170W.
So unless you manage to flash the firmware on a 90w ac to the same firmware on the 170w version, I doubt you can get the W520 to run off of it.



It doesn't, unless they can make money. It's all about selling new docks. It's always been about selling new docks. Any small change that doesn't cost much to apply, will be used to make incompabitbility an issue. The 170W AC can charge and run any Thinkpad with ease, its also the fastest charging AC in the Thinkpad line.

Here's a picture of my X220T running off the 170w AC. It's actually docked to my Modded Series 3 Dock too. So, a laptop attached to a dock that it's not supposed to, and a dock plugged into a AC thats its not supposed to. Lenovo would not approve.


Uploaded with ImageShack.us

Let's assume thinkbigger's fix really did work: Once some entrepreneur has decoded what's going on electrically, maybe tip adapters so 90W can power W520 will start appearing on Ebay. There must be shedloads of legacy 90w power supplies lying around! I for sure would be first in line.

I don't think there's really that big a market for a 90W W520 AC to tell you the truth.
This site is the first that I've ever seen anyone interested in one.

I have 90W Lenovo Slim Travel AC with interchangeable tips. I might get myself a W520 tip off Ebay and see if I can mod the tip to my 90w slim attachment.
I highly doubt it'll work, since I'm sure the AC is the one sending the signal not the tip.

I think that 20% of W520 owners who who travel, and who already own a couple of 90w power units due to previous Lenovo ownership will be interested in a cheap tip adapter - if it works, of course.

I don't really travel with my W520 anywhere, since I consider it a desktop replacement. Most of the times it just sits on the dock.
When I do travel with it, I usually just carry my old 135W AC from my Series 3 Dock.
I keep my 170W AC permantly plugged to the dock nowadays.

The difference in size from the regular 90W and the 135W is not that big.

Most of the times I just travel with my X220T or X301 running off of the Slim 90W AC. It would be cool to have a 170w tip that fits on the slim AC for the W520 though.
But I highly doubt its the tip doing the signalling. Even if you manage to get a 90W ac to run a W520, it's going to be very glitchy, since the system uses so much power.
It'll throttle the system down to the point where it's the same as an X220.

Why do you doubt? It has been proven that with the tip the W520 believes the adapter ok.

The difference between a Cooler Master USNA 120 and the Lenovo 170W adapter is almost 0.5 kg! That is quite a difference.

I didn't read the earlier post by Think bigger, I didn't see any proof of this either but I'll take his word for it.
If think bigger is right, then both the 135w and the w170w connectors are id tagged on the pin level. Which means anyone with some basic soldering skills can merge a 170w connector to a 20v slim AC tip and have a working 90w w520 charger.
I don't know why Lenovo doesn't sell w520 power tips for the slim AC.

The difference between the non slim 90 and the 135 is negligible. I may give the power tip mod a try assuming I can find a cheap 135 or 170 tip. Although the mod seems pointless to me since a 90w W520 would be throttled down to my X220 level, which negates the point of even carrying a w520 with me. I'd much rather just carry the 135w AC.

Because then it would need to implement some throttling for those chargers, like Apple does it with it's 85W adapters.

Personally the mod is pointless to me, since like I said I only use my w520 for power and throttling it down would render it useless, might as well just carry my x220.
If you want to why don't you just do it? Think bigger has proven it, so just get a tip and start soldering.

My problem is that the only way to get a tip is to buy an adapter (lot of money) and pretty much destroy it for the $0.02 tip.

Plus, how safe is tricking a W520 into thinking its got 170w of power to draw on when it doesn't. That's just asking for bsod.

No, it will use the battery, but yes, in extreme cases it could be dangerous to the battery!

This seems to be the case, but how would "id tagged on the pin level" work? You've proven that it's not the yellow plastic teeth that do anything, and thinkbigger has proven that it's the tip which tells the computer which adapter is plugged in. If it's not the yellow teeth, then what else in the tip could be doing this? A different resistance on the "signal" line (the little pin in the middle)? Yet thinkbigger says he soldered only two wires, so where is the "signal" coming from? Just tapped through a resistor off the + wire?

The reason why some of us want to carry the 90W around instead of the 170W is because we don't have spare X220s or X301s to use as travel computers instead! Mostly when travelling I'm not doing gaming or anything graphic intensive -- I'll just be doing general Office stuff (and please don't say I got the wrong computer for that -- I wanted a computer that could do everything!). So having a 90W adapter for these kinds of situations would be ideal, and I really don't see why Lenovo didn't allow it.

OK, getting closer. According to this old post:

So if the signal pin had varying resistance, the ThinkPad could measure that. A small resistor could easily be embedded in the plastic under the pin.

And here is some more interesting info from a recent post over at the Lenovo forum:

There's also an internal mod mentioned (earlier in the same thread) to make the W510 think that all adapters attached are the 135W -- it involves shorting two pins on the power-supply connector under the keyboard. A few people tested it. However no-one has tried it on a W520, and I suspect the mod, if it doesn't blow a vital circuit, might end up making the W520 think it's connected to the 135W even with the 170W plugged in. That could limit functionality (as well as void warranty, etc.). But it's clear now that the resistance of the central pin in the power tip is the key.

PS I'm not an electrician and don't really understand what the "mass" referred to is. Also an SMD? And how a "circuit board" could fit inside the tip. Finally the plastic is pretty solid, and there are no obvious ways to "open" it!

Probably:
"mass" is what we normally refer to as "ground" in the USA.
SMD is surface-mount device

I think I found the trick! The resistance between the pin and the outside metal is 10K on a normal TP adapter.
It is 1.5K on the W520 adapter!!! That's it! That's the only difference (+the plastic).

Also, since there are only two cables going out from the power brick, it must mean that the resistor is inside the plug!

Great find!

The 135 W adapter (DCWP CM-2) also officially works with W520, but the plug is a completely standard one as per say the T61, no extra plastic. So it looks like the plastic is complete red herring and the resistor is all.

So, one could presumably shunt another resister in parallel via an extension plug + socket, to spoof the 1.5k resistance?
'There's a formula for that'.

No need to make it parallel, just connect the new one to the outside with a 1.5K. But the problem is that all of them seems to be integrated in the grey plastic. Look at some tips:
universal
lenovo
All these tips must have a 10K resistor inside, as there is only 2 cables going in.

Our only solution might be this cable: 3 wire generic or this one

I don't think the resistor is telling the laptop the type of power adapter. If the power adapter is powered up when it is plugged into the laptop, the laptop would have no way of reading the resistor value. I think there is an AC code riding on top of the 20V DC, that the laptop is reading.

Any proofs? Why do you think: no way? 2 pins are supplying 0 and +20V, the third is connected to 0 with a resistor. Couldn't be more simple!

And please don't forget thinkbigger's experiment of cutting the 170W tip and soldering it to a 90W adapter, which makes the W520 run and charge at the same time, basically tricking it into thinking it's connected to the 170W. This, for me, proves that there is no signal coming from the adapter, and that it's all in the tip. Copy of thinkbigger's post below (also available on page 2 of this thread):

Someone over here:
http://forums.lenovo.com/t5/W-Series-Th ... 485/page/4

confirms that the mod of the 90 W tip works

Meaning; this mod;

Hello

I would very much like to solve this mystery of the PSU identification thing.

Mostly because I am cheap, and I bought a third-party 150W PSU for a W510 and found out that it will only see it as a 90W. So I can either go purchase a new $150 Lenovo 135W PSU or I can muck about with these three $3 power connector tips I have here.

I surmise that the laptop identifies the PSU on the resistance of the center pin. Could we make a collective effort in unraveling the mystery and decoding that scheme?

I am not skilled in electronics, so I am uncertain what to do. I have a 65W 20V Lenovo PSU here with my x61p. What do I measure? Is ground the outer metal surface of the tip and +20V on the inner? Should the PSU be unplugged from the wall and allowed to rest to discharge capacitors or something? Can I destroy it by being an idiot?

I will get my hands on the "real" 135W PSU in a week or so. I forgot it in another city, hence the purchase of the cheap third-party unit.

The quoted link in the post above this one suggests that at least one option is to connect the center pin to ground. Thus, zero ohm means... what? 135W PSU? 170W PSU?

zsero suggests 1500 ohm for one PSU and 10k for another. Should we make a table with which corresponds to what?

Another option is to watch the outlet. I paid about $129 for a Thinkpad Mini Dock Plus series 3 for mobile workstations which came with a 135 watt power adapter. It was new, not a refurb. Definitely a better deal than the power adapter alone. I even considered flipping my power adapter for a cheaper 90 watt and pocketing the difference, but I'm glad I didn't as I now have a W520 from work that I can dock if I want as it'll run fine off the 135 watt.