170 W 8.5 A is not enough

[damusto]

Hi, recently I was able to buy the maximally equipped W520, I have a problem with it though.
It's about power supply when working with a docking station, the laptop claims that the power supply is too weak and suggests switching to the one purchased with it.
Of course it works with the original power supply, I wonder is it too weak to power a laptop and several peripherals connected to the station at the same time or is something wrong with it ?
Other W520s a bit less equipped works fine here.
My spec is:
8 GB RAM, i7-2960XM, 128 SSD, NVIDIA Quadro 2000M

help me here please.

[RealBlackStuff]

Are you sure yours is a genuine Lenovo 170W power supply, and not a Chinese knock-off?

[TheForgottenKing]

No way that's legit. It's probably either a knockoff or broken. I'd return it.

[FryPpy]

I need some more info.
First of all - what is your docking station?
If i understand right: this ThinkPad starts without any warnings if connected to this power supply without docking station. If you can install Windows and Lenovo Power Manager please start it and go to battery tab. And write there what "AC adapter is attached" shown here when this ThinkPad is connected to AC adapter and when it is sitting in Docking Station.

PS
I have one 170W adapter and W530 treat it as normal 170W. But after some modification (removing internal plastic tabs) i have connected it to X61... and it show that it is 120W;)

[Jake.Werecat]

I'd also say that the AC adapter has to be fake or damaged. It would help to actually measure the current flowing into the laptop with amp meter. But it will require at least a spare plug, multimeter, a piece of wire and some DIY skills.
As for checking in Lenovo Power Manager the type of adapter it might now bring the most accurate results. The way that ThinkPad determines the wattage is simply measuring the resistance between ground and plug center pin. You can fake any kind of adapter with it and I'm sure if it's a Chinese "compatible" thing it will imitate being a 170W.

PS. I've always wondered what are those plastic tabs inside the 170W plug for... Just to make life less comfortable? XD

[jcvjcvjcvjcv]

Yes. You can remove the tabs with security Torx 30. Someone apparently quote me on that into the Thinkwiki

[Jake.Werecat]

Yea, I know you can hack those plugs, but the very fact that they exists is awkward. If there should be any incompatibility at all it should be the other way - so you cannot plug in an under-powered AC adapter to more power demanding machines - as this way it will not work. But the way it is? Crazy and stupid.

[FryPpy]

If there should be any incompatibility at all it should be the other way - so you cannot plug in an under-powered AC adapter to more power demanding machines - as this way it will not work. But the way it is? Crazy and stupid.

If this thesis seems stupid, so we can rephrase it... With this tabs you can't connect overpowered power brick to weak ThinkPad. (if i remember right X301 even haven't power sense signal wire in power socket). ThinkPads have tons of fuses. Each have its own amperage and each protects very own circuit in case of troubles. But who protects input circuit in case of troubles??? Power brick have it's own protection against overcurrent, but 170W brick can do 8.5Amp without troubles (65W is only 3.25Amp and 45W - 2.25Amp).
Each power brick have maximum power signal - central pin (it's very dumb - resistance denotes the the maximum power). Controllers can read this signal and protect ThinkPad or power brick from bad behavior, but this only happens when controller is working. In case of malfunction only fuses and other hardware protections can help.

Some words to this thread. May be the docking station somehow lost maximum power signal on path from power brick to ThinkPad. I know that infinity resistance denotes 90W maximum power. For example: if wire from power socket in docking station have broken ThinkPad will think that it connected to 90W power brick and show boot up warning. But when it connected to power brick directly it can read resistance of 170W power brick and don't show warning messages.

[Jake.Werecat]

If this thesis seems stupid, so we can rephrase it... With this tabs you can't connect overpowered power brick to weak ThinkPad. (if i remember right X301 even haven't power sense signal wire in power socket). ThinkPads have tons of fuses. Each have its own amperage and each protects very own circuit in case of troubles. But who protects input circuit in case of troubles??? Power brick have it's own protection against overcurrent, but 170W brick can do 8.5Amp without troubles (65W is only 3.25Amp and 45W - 2.25Amp).
Each power brick have maximum power signal - central pin (it's very dumb - resistance denotes the the maximum power). Controllers can read this signal and protect ThinkPad or power brick from bad behavior, but this only happens when controller is working. In case of malfunction only fuses and other hardware protections can help.

I am afraid I cannot agree with the theory of yours. There is nothing wrong in connecting more powerful adapter to a weaker machine (it's the opposite, you shouldn't connect an under powered adapter, as it won't work). You can run X60s on 170W, but cannot run W530 on 65W. Wattage has nothing to do with security (or lack of it), it's the measure of power efficiency, in other words the maximum amount of power that one can get from that particular supply, it doesn't mean in any case that you will always get that. Connecting even 500W power adapter to a weak laptop won't do any harm, the laptop will still drain 30,40,60, 90 or whatever power it demands. What is important is the correct voltage, as voltage determines the current, not wattage.
You are absolutely right about the center pin, though it's function is the opposite, it tells the machine (and only the machine, as it's a one way information), how much power can a machine drain from the supply, not to get to an UNDERpowered situation, some models can adapt to run e.g. on 90W full power and 65W but underclocking the CPU or in airplane mode only, others will display information about insufficient power and will refuse to operate.
As for no sense signal wire in the plug = no resistance = the adapter is treated as 90W.
Here's the table: