W520 requires 170W AC adapter

[jcvjcvjcvjcv]

That's easy. 170 Watts in 12 Volts gives over 14 Amps; in 20 V it's just 8.5

Higher amperage means more energy lost and bigger wires / connectors needed.

Also keep in mind that there were also 4, 7 and 8 cell batteries for some models. I have a 7-cell battery (42T5229) for my T61 that has two series in it. On the casing it says 10.8 AND 14.4 Volt:
see:
http://www.computerrecyclingllc.com/eBa ... 2-9266.JPG

To top that off at 16.8 (4.2 per cell)... you need more than 12 Volt. Keep a little margin, round it to a nice number, etc. and you get to 20 Volts.

Don't know where you would need 12 Volt in a laptop either... as far as I know the SATA-power connectors lack 12 V in notebooks.

[hellosailor]

"That's easy. 170 Watts in 12 Volts gives over 14 Amps; in 20 V it's just 8.5"
Which is meaningless, since that's a measure of power that cannot be used. The computer requires a set maximum voltage, anything above that is NOT delivered as extra power, it is simply dumped as heat, or left unused, depending on the circuitry in the computer.

"Higher amperage means more energy lost and bigger wires / connectors needed. "
Nope. That's the theory but only for a device capable of using "power" without specific lower limits of voltage or amperage. You can deliver "more power" to the power cord, but it doesn't get accepted into the computer, so it is simply wasted or rejected. Net result? You're talking about wire loss, which just doesn't have any role here. In this context, it is meaningless.

Let's see, I have a 9-cell battery for my T61P. It says...10.8 volts. Only.
Those "more" cells are still typically only multiple strings of 3 or 4 cells, nominal voltage of 3.5-4 volts per cell. A "6 cell" is two strings of 3 cells, same voltage as 3 cells in one string. "8 cell" is two strings of 4 cells, same voltage as 4 cells. 9-cell, is simply three strings of 3 cells.

So they all come back to a similar voltage, and even for a 4-cell string, that's nowhere near 20 volts. If you apply just a little higher voltage than what LiOn batteries need, they overheat, dry out, and then rapidly explode. Which tends to upset the owner.

If there are legacy batteries with 4-cell strings (as you seem to have, although I've never met one) from different models, they'd need a 16-volt charger. If there's a regulator inside the computer (good safety) with a 10% overhead loss, that would still only need 17.6 volts and some engineer might say, OK, let's supply 18 volts. But 20?? Would be overly generous for a 4-cell battery, and a total waste for a 3-cell battery, such as my T61P or W530. Both use 3-cell strings, 10.8 volts.

20 just doesn't make sense, even for legacy chargers, since there's so much money to be made by providing "just enough" instead of 20. And the main reason we have "power bricks" is because it is so simple to have a new brick certified (UL, CE) and then used across a whole family of products.

[jcvjcvjcvjcv]

"That's easy. 170 Watts in 12 Volts gives over 14 Amps; in 20 V it's just 8.5"
Which is meaningless, since that's a measure of power that cannot be used. The computer requires a set maximum voltage, anything above that is NOT delivered as extra power, it is simply dumped as heat, or left unused, depending on the circuitry in the computer.

You always design something around the maximum it must be able to accept. Somehow Lenovo deemed that the W520 could exceed 135W and picked a 170W Power Supply for it. If one assumes a certain amount of required energy, transporting that with a higher voltage will result in a lower amperage trough the DC cord and the connector. Keep in mind that the circuit breakers in a normal house (at least in my part of continental Europe) are 16 A.

"Higher amperage means more energy lost and bigger wires / connectors needed. "
Nope. That's the theory but only for a device capable of using "power" without specific lower limits of voltage or amperage. You can deliver "more power" to the power cord, but it doesn't get accepted into the computer, so it is simply wasted or rejected. Net result? You're talking about wire loss, which just doesn't have any role here. In this context, it is meaningless.

Yes, wire resistance will be pretty small, but so what? It will be even smaller with a higher voltage. It would be higher if they used 12 Volt. The bigger win is probably in the connector.

Let's see, I have a 9-cell battery for my T61P. It says...10.8 volts. Only.
Those "more" cells are still typically only multiple strings of 3 or 4 cells, nominal voltage of 3.5-4 volts per cell. A "6 cell" is two strings of 3 cells, same voltage as 3 cells in one string. "8 cell" is two strings of 4 cells, same voltage as 4 cells. 9-cell, is simply three strings of 3 cells.

So they all come back to a similar voltage, and even for a 4-cell string, that's nowhere near 20 volts. If you apply just a little higher voltage than what LiOn batteries need, they overheat, dry out, and then rapidly explode. Which tends to upset the owner.

If there are legacy batteries with 4-cell strings (as you seem to have, although I've never met one) from different models, they'd need a 16-volt charger. If there's a regulator inside the computer (good safety) with a 10% overhead loss, that would still only need 17.6 volts and some engineer might say, OK, let's supply 18 volts. But 20?? Would be overly generous for a 4-cell battery, and a total waste for a 3-cell battery, such as my T61P or W530. Both use 3-cell strings, 10.8 volts.

It's not a waste to transform the voltage to a lower level. Also; for the sake of using the same components over and over again across the board; no, they aren't going to use a lower voltage for the current W series just because they only have the 10.8 Volt batteries. Everyone would be even more pee'd if they did.

Also; if you output 16V at the brick, you're never gonna get to 16 V with 4 Li-ion batteries, leave alone topping them off at 16.8. For small stuff it's a lot easier to reduce the voltage than to increase it.

20 just doesn't make sense, even for legacy chargers, since there's so much money to be made by providing "just enough" instead of 20. And the main reason we have "power bricks" is because it is so simple to have a new brick certified (UL, CE) and then used across a whole family of products.

Yeah, and they picked 20V

I'm not saying it ultimately came down to something I mentioned. Perhaps it was easier for the CCFL's, or they wanted to scare everyone in thinking that using an other brand 19V supply won't work, or ..., or ..

[hellosailor]

"Yes, wire resistance will be pretty small, but so what? It will be even smaller with a higher voltage. It would be higher if they used 12 Volt. "
Again, irrelevant. You don't rate a power supply by the voltage at the brick, you rate it by the voltage delivered at the connector, under load. The wire size and drop is taken into account either way, so it is irrelevant.

"The bigger win is probably in the connector."
I have no idea how the connector can be a factor in that. The connector must be chosen depending on the amperage it can carry, and all things being equal, it will be a cheaper connector for lower voltage.

"It's not a waste to transform the voltage to a lower level. "
Yes, it is. Every time you transform or regulate voltage, there are overhead losses. For a DC-to-DC change, you need electronics. Every part costs money and takes up real estate, that's expensive.

"Also; for the sake of using the same components over and over again across the board; no, they aren't going to use a lower voltage for the current W series just because they only have the 10.8 Volt batteries. "
You've got it backwards, I think. First find one technical reason that any machine is using higher voltage. Assuming you really have a 14.4 volt battery pack and that there isn't a misunderstanding there, just how many modern machines are using it? Other than desktop hard drives, there's been darn little that uses a computer's "12 volt" bus even in desktops for the last decade. You're saying the tail should wag the dog?

"Also; if you output 16V at the brick, you're never gonna get to 16 V with 4 Li-ion batteries,"
Right, but as I've said, 4-cell battery strings are the exception, not the rule. And 18 volts is enough to charge them, there's still no need for 20. There are, fwiw, also 17 volt power supplies so again, there's no need for 20 and no magic to 20.

"Yeah, and they picked 20V"
Soo Lin Chun's nephew owns the patent rights to the 20V plug design, that's why Mr. Soo chose it for a standard. (Hey, nepotism makes better sense than any unexplained poor design choice, doesn't it?)

"Perhaps it was easier for the CCFL's, or they wanted to scare everyone "
No, the CCFL in my old Canon scanner was quite happy with the five volts from a USB bus. They don't need anything near 20, not even 12.Now "scare" I could easily believe. Or rather, marketing. You know, this MUST be a powerful computer, it needs a TWENTY volt supply and a HUGE brick.
In America we sell cars that way. 140mph speedometers, 55mph speed limits. But it must be a fast car, the speedometer goes to 140. (Sigh)

"Keep in mind that the circuit breakers in a normal house (at least in my part of continental Europe) are 16 A."
Irrelevant. The issues concerning variable loads and voltage drops just don't apply to computer power supplies the same way, because the computer is a closed situation. The supply is fixed, the cords are fixed, the load is fixed. The standard in every electronics industry is that you rate the supply according to what it will deliver under the maximum load. A plain analog "wall wart" power supply often puts out 17 volts under no load, but it will be labeled and rated as a 12 volt supply, if that is what it drops to, when it is plugged into the device it was sold with. With the cost of copper wire and transformers being so high, most of the new ones are digital and a digital regulator will hold the nominal voltage, load or no load, till it fails.

If you are using 220VAC and 16A breakers, that's twice the normal power of a home circuit in the US. Here they are a nominal 117V (often called 110 or 120) with either 15A or 20A limits on each circuit, normally 15.

I've designed and built power supplies up to the kilowatt range, and multiple hundred amp twelve volt mobile systems. I can tell you for a fact that the voltage drop in the cable which is an integral fixed part of a power brick is NOT an issue, the designer designs and rates the entire system based on including that drop. If I want to deliver "20" volts, I factor in the cable needed. If I only need "12" at the business end, it is still called a "12" volt supply, even if it needs more voltage at the other internal end of the cable.

[jcvjcvjcvjcv]

"Yes, wire resistance will be pretty small, but so what? It will be even smaller with a higher voltage. It would be higher if they used 12 Volt. "
Again, irrelevant. You don't rate a power supply by the voltage at the brick, you rate it by the voltage delivered at the connector, under load. The wire size and drop is taken into account either way, so it is irrelevant.

"The bigger win is probably in the connector."
I have no idea how the connector can be a factor in that. The connector must be chosen depending on the amperage it can carry, and all things being equal, it will be a cheaper connector for lower voltage.

You say it yourself: "The connector must be chosen depending on the amperage it can carry". If your notebook consumes 170 Watt, it will take 8.5 A if you use 20V and 14 A if you use 12V.

"It's not a waste to transform the voltage to a lower level. "
Yes, it is. Every time you transform or regulate voltage, there are overhead losses. For a DC-to-DC change, you need electronics. Every part costs money and takes up real estate, that's expensive.

Yes, you loose some, but definitely not "all" or 'total'.

"Also; for the sake of using the same components over and over again across the board; no, they aren't going to use a lower voltage for the current W series just because they only have the 10.8 Volt batteries. "
You've got it backwards, I think. First find one technical reason that any machine is using higher voltage. Assuming you really have a 14.4 volt battery pack and that there isn't a misunderstanding there, just how many modern machines are using it? Other than desktop hard drives, there's been *****Expletives removed by Moderator***** little that uses a computer's "12 volt" bus even in desktops for the last decade. You're saying the tail should wag the dog?

You want to transport 3.3V at 50A to a graphics card in a desktop PC? Funny...
Yes, I do have a 14.4 pack; the same as is in the picture that I linked.

"Also; if you output 16V at the brick, you're never gonna get to 16 V with 4 Li-ion batteries,"
Right, but as I've said, 4-cell battery strings are the exception, not the rule. And 18 volts is enough to charge them, there's still no need for 20. There are, fwiw, also 17 volt power supplies so again, there's no need for 20 and no magic to 20.

"Yeah, and they picked 20V"
Soo Lin Chun's nephew owns the patent rights to the 20V plug design, that's why Mr. Soo chose it for a standard. (Hey, nepotism makes better sense than any unexplained poor design choice, doesn't it?)

Lol, yeah, that might be a reason too.

"Perhaps it was easier for the CCFL's, or they wanted to scare everyone "
No, the CCFL in my old Canon scanner was quite happy with the five volts from a USB bus.

So? Perhaps they transform it to a higher voltage in that scanner. It might have been cheaper compared to providing a brick (the old HP scanner here does have a powerbrick and works fine from an unpowered USB port). If your scanner runs just on the power of a single USB port, it uses quite a bit (times 10) less energy than a full 15" notebook CCFL backlight.

They don't need anything near 20, not even 12.Now "scare" I could easily believe. Or rather, marketing. You know, this MUST be a powerful computer, it needs a TWENTY volt supply and a HUGE brick.
In America we sell cars that way. 140mph speedometers, 55mph speed limits. But it must be a fast car, the speedometer goes to 140. (Sigh)

Visit Germany one day If you drive 90 mph you'll have to move a lane to the right quite often.

"Keep in mind that the circuit breakers in a normal house (at least in my part of continental Europe) are 16 A."
Irrelevant. The issues concerning variable loads and voltage drops just don't apply to computer power supplies the same way, because the computer is a closed situation. The supply is fixed, the cords are fixed, the load is fixed. The standard in every electronics industry is that you rate the supply according to what it will deliver under the maximum load.

No, not really. You don't want it to deliver a lot more under normal load.

If you are using 220VAC and 16A breakers, that's twice the normal power of a home circuit in the US. Here they are a nominal 117V (often called 110 or 120) with either 15A or 20A limits on each circuit, normally 15.

No, not 220. Here it's 230 nominally, but 220 and 240 are both within the EU's margins. Usually it reads 234 on the multimeter. In the area of the country were there are a lot of greenhouses there are complaints from those with solar panels that their transformers shut off (because they sense a net voltage of ~255).

Yes, twice the power, but the same amperage Funny thing is that most things run more efficiently on 230 compared to 110, computer power supplies included.

Standard mains connection here for new houses is 3-phase 25A. Apartments usually have 1-phase 40A. The only thing a "normal" household might have that doesn't run off a normal outlet is an electric cooktop; for that we have either a double-phase or 3-phase Perilex outlet in the kitchen. A 11.1 KW cooktop can be easily connected. How does one connect such a thing in the US? Do you guys have a 3-phase mains connection for normal houses? Or is it all split-phase?

I can't imagine how irritating 117V at 15-20 A must be. At least here combining a 2.2 KW router with a 1.2 Kw vacuum cleaner won't give any problems...

[hellosailor]

"A 11.1 KW cooktop can be easily connected. How does one connect such a thing in the US? "
Apartments, older "prewar" meaning WW2 apartments, might have 50A service. But 75-100A is more likely as most have been renovated. The typical circuits are 15A but there are normally 20A circuits for specific purposes, including the kitchen, a laundry room, or an air-conditioning run.

"Do you guys have a 3-phase mains connection for normal houses? Or is it all split-phase?"
Usually 220V "from the pole" split into two 110V sides in the house or apartment. There is still a patchwork quilt of different systems, some genuine 240 rather than 220, sometimes split, not always. But typically, split "220".

"I can't imagine how irritating 117V at 15-20 A must be. "
Usually it is painless, although for some reason the hand-held hairdryers escalated into a wattage war. Most are now 1600 or 1700 watt rated, which is enough to blow the circuit in a normal bathroom, or at least to dim the bathroom light when they are used. In modern construction the bathroom would be on a 15A circuit (rarely 20) of its own. One morning I found out that my bathroom and kitchen (~1939) were sharing one 15A fuse, when the toaster and coffeepot were both running and I went in to use a dryer. Which of course didn't exist in 1939.

[jcvjcvjcvjcv]

So you had half a cup of coffee and lukewarm toast?

What about the Vacuum cleaner? Just like hairdryers they too have ballooned in Wattage in the last decade. Most of them are 2200 W here.

But a 11.1 Kw cooktop... does one take three times 220 with 20 A fuses in the same way we use two 16 A fuses for the more common 7.4 KW cooktops?

[hellosailor]

I have no idea what the cooktops are here. Many of us use gas (piped natural gas) ranges in the cities and electric cooktops are considered a deprivation that folks in worse buildings have to put up with.

Whatever the amperage draw of vacuum cleaners is, they generally work without problems too. High power vacuums are usually also a con on consumers, since drawing "more" power has little or nothing to do with how well they do their job.

[jcvjcvjcvjcv]

The same here (The Netherlands has a very complete gas network), but with induction it's not so bad (it works nicer really). Except for the wok.

Yes, my 1.2 KW industrial vacuum cleaner outperforms most 2 KW consumer vacuum cleaners

[automobus]

previous summary
previous chart



170 watt rectangle

I just received my W540. The power connector is rectangular, and the resistance from the center pin to outer shell is 1.9K OHMS. This resistance tells the computer it's a 170W power adapter, as opposed to a 90W power adapter.

http://forum.thinkpads.com/viewtopic.ph ... 14#p725514

Code: Select all

resistance signal chart
0 Ω              = 135 W barrel
(0 Ω, 120 Ω)     = uncertain
120 Ω            = 45 W rectangle
(120 Ω, 550 Ω)   = uncertain
550 Ω            = 90 W rectangle
(550 Ω, 1.5 kΩ)  = uncertain
1.5 kΩ           = 170 W barrel
(1.5 kΩ, 1.9 kΩ) = uncertain
1.9 kΩ           = 170 W rectangle
(1.9 kΩ, 2.5 kΩ) = uncertain
[2.5 kΩ, 6 kΩ]   = reserved for 50 W, not used in any released products?
(6 kΩ, 6.5 kΩ)   = uncertain
[6.5 kΩ, 10 kΩ]  = 65 W barrel
(10 kΩ, ?)       = uncertain
∞ Ω              = 90 W barrel

Does anybody have a opportunity to check a rectangle slim tip 65W or 135W supply signal?

[jdrou]

Does anybody have a opportunity to check a rectangle slim tip 65W or 135W supply signal?

135W from my T440p appears to be 1 kΩ.

[taxilof]

I measured 280Ω on 65W rectangle (both ADLX65NLC3A and ADLX65SDC2A).

Also this square to rectangle power adapter from china has 550Ω. So regardless what power adapter is used, my T440s reports a 90W adapter.

[automobus]

previous chart



Thank you very much, jdrou and taxilof. I sincerely appreciate everyone's help.

Code: Select all

resistance signal chart
0 Ω              = 135 W barrel
(0 Ω, 120 Ω)     = uncertain
120 Ω            = 45 W rectangle
(120 Ω, 280 Ω)   = uncertain
280 Ω            = 65 W rectangle
(280 Ω, 550 Ω)   = uncertain
[550 Ω, 555 Ω]   = 90 W rectangle
(555 Ω, 1 kΩ)    = uncertain
1 kΩ             = 135 W rectangle
(1 kΩ, 1.5 kΩ)   = uncertain
1.5 kΩ           = 170 W barrel
(1.5 kΩ, 1.9 kΩ) = uncertain
1.9 kΩ           = 170 W rectangle
(1.9 kΩ, 2.5 kΩ) = uncertain
[2.5 kΩ, 6 kΩ]   = reserved for 50 W, not used in any released products?
(6 kΩ, 6.5 kΩ)   = uncertain
[6.5 kΩ, 10 kΩ]  = 65 W barrel
(10 kΩ, ?)       = uncertain
∞ Ω              = 90 W barrel

minor edit 2014-07-18: add 555Ω

Would anybody happen know, what exactly is does number 43X6713 refer to? I found it in a picture, related to 0B47046.

[hellosailor]

"what exactly is does number 43X6713 refer to?"

It is does refers to the much longer PART'S SERIAL NUMBER that you found it in.

Really? You've never seen a SERIAL NUMBER or production code on a part before?

[Coriander]

I have W520 that I have had for almost three years now. As a university student, I take it with me every day in a backpack, use badly positioned outlets, and just generally put a lot of wear on my ac adapter. It recently developed a fray in the cord near enough to the tip that a splice was impractical.

Despite reading this forum I decided to try a repair anyway. I purchased a tip for the z series off ebay <$9 with shipping and spliced it in. A bit tricky, since my cord is a center wire-connects to outer barrel and shield-connects to inner barrel and the replacement is two thinner copper wires the whole way. The resistance in the new tip is much lower than the old but the output still reads 20v. Plugged it in and it does charge my battery when the computer is off but refuses to work when it's on. Pop up on start asks me to plug in adapter that came with the unit.

This supports the idea that the tip is the key, but I admit I have only a basic understanding of electronics. I read somewhere in here there is a way to trick the bios with a resistor? Or did I do something wrong that will give my computer trouble when it tries to pull 170 w through the repaired cord?

Also I would try to open up the 170w tip but I have no idea how to go about that.

Does anyone know if generic adapters are any good? Some advertise that they are compatible with W520s but the ALL list 90w as the output .

[jcvjcvjcvjcv]

It was already discovered long ago that it's the tip...

Instead of messing around with the tip you could alternately mess with the connector inside the W520.

See here:
http://forums.lenovo.com/t5/W-Series-Th ... 845#M12703

http://sunhongyi.outuo.net/w510/2.jpg
http://sunhongyi.outuo.net/w510/1.jpg

As is already posted before in this thread.

There is too much crap on the market with generic adapters, that's why the easiest thing to do is avoiding them all. Try at your own risk.

[SkiBunny]

Can anyone definitively say whether you can use the 135w adapter for the W520, without getting the "wrong adapter" nag like with the 90w adapter??

I hate the big heavy 170w adapter and doubt I'll ever consume 135w even.

[hellosailor]

Since the nag presumably comes from the power management software, and that gets updated and changed from time to time (not always for the better) I doubt anyone can say it definitively.

I used a 90(?)W supply with my W530 for a while, it only complained on startup and didn't nag at all the rest of the time.

Quite possibly if you actively run software that's using all the CPU cores, spin up all the motors, and try to charge a flat battery at the same it might be smart enough to nag every time the load exceeds the charger's power.

[jcvjcvjcvjcv]

And did your W530 actually use that 90W adapter when turned on?

I can connect a 90W adapter to my W520 and after the initial warning it won't say anything, but it will discharge the battery while connected to that 90W adapter. Only when not turned on does it use the 90W.

But since some local private seller had next-to-new advanced docks and 170W power supplies I bought myself two of each for 105 euro's.

So actually I don't lug around the 170W that much anymore.

[hellosailor]

Yes, it showed as running on AC not battery.

"but it will discharge the battery while connected to that 90W adapter."
I'm sure that if I was drawing more than 90 watts, mine would have sucked on the battery as well. However, since all LiOn batteries have a limited charge cycle life (500-1000 cycles, maximum) it would be poor engineering for the computer to draw ANY power from the battery at all, until the AC adapter's power was exceeded or absent. Under all circumstances, all the time, and regardless of the adapter's power rating.

"Only when not turned on does it use the 90W."
I have no idea. As I said, every different version of power management software may do things differently. I would not be surprised to learn that the bugs I have previously seen in "real basic" power management software from Lenovo and others, are not the only real basic flaws they have had. It could just mean that your basic "idle" configuration, your CPU with whatever background tasks and default hardware (spinning hard drive, screen backlight, etc.) require more than 90W to simply run.

Sometimes there is no one answer that fits all. Sometimes the answer is "it depends".

As in, "How long is piece of string?"
It depends.

[mpcook]

Can anyone definitively say whether you can use the 135w adapter for the W520, without getting the "wrong adapter" nag like with the 90w adapter??

I hate the big heavy 170w adapter and doubt I'll ever consume 135w even.

My W520 works fine with a 135W adapter. No messages, no nags. It runs, it charges. I keep my 170W on the dock, and the 135W for everywhere else. My W520 has all latest updates, drivers, BIOS.

[SkiBunny]

My W520 works fine with a 135W adapter. No messages, no nags. It runs, it charges. I keep my 170W on the dock, and the 135W for everywhere else. My W520 has all latest updates, drivers, BIOS.

Thanks for sharing your experience. That's with the thinkpad Power Manager software too?

Change of topic... I see you own a W520 and W530... Is your W530 panel less "purplish" than the 520?
Cuz I've had purplish panels on the W510 and W520 as per here (tho my T420 panel has been fine even with factory settings).

[mpcook]

Thanks for sharing your experience. That's with the thinkpad Power Manager software too?

Change of topic... I see you own a W520 and W530... Is your W530 panel less "purplish" than the 520?
Cuz I've had purplish panels on the W510 and W520 as per here (tho my T420 panel has been fine even with factory settings).

I haven't noticed purple panel on the W520. I have the 1920x1080 LCD. Although I am on the external LCD 95% of the time.

Yes, I am using all stock Lenovo software, including the Power Manager.

[jcvjcvjcvjcv]

I've used the 135W as well with my W520, but I don't own one. It just happens that often I had a lot of T530 (quadcore) owners around me and thus an abundant supply of 135W adapters to leech. Works perfectly fine. I haven't used any 135W on the dock though.

Yes, it showed as running on AC not battery.

"but it will discharge the battery while connected to that 90W adapter."
I'm sure that if I was drawing more than 90 watts, mine would have sucked on the battery as well. However, since all LiOn batteries have a limited charge cycle life (500-1000 cycles, maximum) it would be poor engineering for the computer to draw ANY power from the battery at all, until the AC adapter's power was exceeded or absent. Under all circumstances, all the time, and regardless of the adapter's power rating.

I doubt they have internal power management that would allow limiting adapter power intake or draw from two sources. At best it will pause charing the battery during peak demand.

"Only when not turned on does it use the 90W."
I have no idea. As I said, every different version of power management software may do things differently. I would not be surprised to learn that the bugs I have previously seen in "real basic" power management software from Lenovo and others, are not the only real basic flaws they have had. It could just mean that your basic "idle" configuration, your CPU with whatever background tasks and default hardware (spinning hard drive, screen backlight, etc.) require more than 90W to simply run.

Lol no, it easily stays below 20W

[hellosailor]

"I doubt they have internal power management that would allow limiting adapter power intake or draw from two sources."
Actually the power management would be the same as it is in any UPS or constant power source. Probably one commodity-grade power management chip that serves the same purpose in all cases.

It isn't a matter of limits and sources, but rather lumping the sources together (constant charge by a simple charge monitor or limiter) and a simple measure of how fast the power is being drawn--which is already how you get the "power gauge" on screen predicting time left on the battery.

The engineering could be done in many ways, all trivial. Remember this is digital electronics. If there's one special-purpose power management/measurement IC (and many vendors make dozens of them) it becomes trivial to put two or four or eight inputs on the same chip and measure multiple sources at once. Which is also done inside every battery pack, where the charge management computer (full blown computer) measures the voltage on each battery, or each set of batteries, in a LiOn stack. They're controlled as three in series, or two in parallel times three of those in series, etc. to ensure that no one battery gets too high a charge voltage if any one cell fails. This is old, mature, commonplace technology by now. Battery pack management has been quite sophisticated for 20 years now.

[automobus]

Hi all. I learned that Lenovo's fondleslabs use slimtangle, too, but they get twelve volt instead of twenty. Does anybody have a ThinkPad Tablet 36W DC Charger (model 4X20E75080; FRU 03X6283) to check its signal pin?

[jedisurfer1]

been using the 135w as my travel adapter for a few years. It works perfectly and the bonus is it works on my other laptops also.

[KMantas]

I have W520 and original adapter. I've changed cable for it and after some time PC started showing that adapter is not original and there is not enough power. It charges when PC is switched off.
Does anyone have an idea what measures I have to check? My friend checked amperage and said it is ok ~8 or smth.

update:
from my adapter only 2 cables comes, not 3. First time I changed cable I got one with 3 so I connected 2 of them into 1. And it was working fine. After some time cable which goes to the pin broke and laptop was showing that there is not enough power from adapter.So I got new cable, this time with 2 cables inside. I got it replaced but it still shows that there is not enough power. Is it possible that I just got wrong cable?

[axur-delmeria]

The power adapters are identified through the resistance between the center pin and the outer metal cylinder. It seems that there's a resistor somewhere inside the power connector.

[KMantas]

does anyone know where from to get correct cable?