Smallest t6x power adapter?

[fefrie]

I just bought a t60 and it came with a smaller power adapter.

Yes this is nice. However, it comes with a wall cable that is of the three prong variety which makes the carrying around a bit bulkier.

The smaller power source is 65w/20v while the larger one is 90w/20v.

Just wondering if anyone has seen the smaller powersource that comes with a two prong outlet....

[fefrie]

Looks like the smaller power source is just for laptops with integrated graphics.

I read some reviews that they burn out a lot.

Probably from people who use them in laptops with discrete graphics.

[rumbero]

However, it comes with a wall cable that is of the three prong variety which makes the carrying around a bit bulkier.

I solved this issue by replacing that cable with just the plug: ebay.com/itm/140481666953.

If the image link fails, try the picture linked here to get an idea how this looks like.
Here is another image showing that plug in action: images.klinger-photography.com/image-stecker_ku9i74.html

[Saucey]

Woah, that is pretty neat! Might pick one up.

[fefrie]

Make sure you get a two prong one. The three prong one is bulky.

[dr_st]

If you are staying in North America it's probably OK, but otherwise I would never get a two-prong one. From my experience they cause severe interference if you use them with a 220-240V grid (the chassis and laptop LCD might become slightly electrified giving you mild shocks/ripples when you touch it)

I never had a T60 PSU burn out, 65W or 90W, integrated or discrete graphics.

[TuuS]

The three prong cord is used to comply with grounding regulations in some countries but it's redundant because the adapters are double insulated making it unnecessary to have the separate ground. Generally for this reason the 3prong cords are less desireable. The two prong unit is rated for 220vac so I don't think there is any problem using them in other countries but could be wrong. One thing there may be a problem with is finding international cords for the 2prong part because the 3prong uses the universal (mickymouse) type cord.

The 65w will work with discrete graphics but you won't get full performance and I'd only use it for brief periods with a charged battery. Integrated graphics will be fine but the 90w will charge the battery faster while using the laptop.

In my opinion, if I was going to use a 65w, I'd get a 2prong because the cords are easier to stow and won't negate the advantage of it being smaller.

[Ash]

The Output - is connected to the computer's enclosure (any outer metal surfaces/hinges/screw heads, shields of USB, Ethernet, VGA etc connectors etc). The Output + is at +20v vs the Output -. The laptop's circuitry is all connected between the + and - so sees 20v anyways

The issues are all about what voltage is present between the laptop and the outer world. The outer world is mostly at Earth potential, ie 0v. If the laptop is at 0v too, no stray voltages appear between the laptop and outer world, and no weird effects are experienced

When you use a 3 contact plug, the Output - is connected together with the Earth from the wall, therefore the Output - is firmly held at 0v towards Earth

When you use a 2 contact plug, the Output - WOULD BE floating, which means that the voltage between it and Earth is undefined, but no voltage source is present to cause any voltage to appear in there. If you touch the laptop, by doing so you are setting it at 0v towards Earth. There is no voltage source present, with 1 terminal in Earth and 1 in the laptop, which would cause any other voltage to appear there : The 20v are set between 2 points inside the laptop, they dont define its voltage vs. the Earth. The mains voltage in the power supply is isolated by a transformer, so it has no effect either

The culprit is, that it is NOT exactly true that "no voltage source is present to cause any voltage to appear in there". The power supply contains usually 3 EMI suppression capacitors, which have small capacitance so dont get much current, but there is some tingle they let through. They are present :
- From internal -170v or -340v DC point (on high voltage part) to Output -
- From Input Live(Hot) to Output -
- From Input Neutral to Output -

With an Earth connection (3 contact plug), the Earth holds the laptop at 0v to Earth anyway. Without the Earth connection, the laptop is "floating" on the voltage it gets through those capacitors, which is derived from the mains voltage, often being at about 1/2 of the mains voltage (60v for 120v, 120v for 240v) but it can be anything up to full voltage. The current let through by those capacitors is tiny so the laptop does not pose a shock hazard (the voltage present on its metal parts has enough power just to give that tingle), but it is there.....

One problem possible with it is, damage to equipment. Imagine you plug your laptop, with a 2 pin power supply, to a VGA cable of an external monitor, which have proper Earth connection

The VGA connector is designed so that the outer shield makes contact first, and the moment it makes contact it holds the laptop at 0v using the Earth from the monitor. As you insert the plug further in, the actual data/analog pins of the VGA are at the correct voltages as they make contact

But imagine the connector is a bit worn out, not making too good connection, or the cable is defective and the shield from the cable (which is pretty stressed when pulling on the cable) detached from the shield of the VGA connector (it may or may not be visible on the outside that the cable is pulled out of the connector) - There are many ways how a connector may become "bad". Now, you insert the plug, the shield did not do its task, and by the time the data/analog pins are coming in contact together, the laptop is still at 60 or 120v towards Earth (and towards the monitor's circuitry, which expects 1v on the analog pins for example....) - And here comes the chance to blow the GPU in the laptop or the monitor....... Which is rare occurence but possible and here is 1 way how it happens

When plugging/unplugging laptops to external monitors - especially when you are somewhere else where you dont exactly trust the wiring and correctness of installation - i use a precaution : Unplug the power supply from the laptop. Plug in the VGA while the laptop is on battery. And then plug in back the power supply. This way, the "last connection" closing the circuit on the stray 60 or 120v is being made in the power connector. Since the current draw of the laptop is >>>> the current going through EMI capacitors, the effect of the stray voltage there is negligible. In contrast to the VGA, where the stray current is pretty significant compared to the tiny signal currents... And when unplugging the VGA, unplug the power supply for the moment as well



There is one drawback (electrical drawback, not in adapter/plug size) to having an Earth connection, and it is when the laptop is used in a setup with remote Earth connection. Say you make some huge outdoors party, with the laptop. You connected to a 20M Ethernet extension cable from building A, and plug in the laptop for power from a 20M extenion cable from building B, or from a nearby outdoors panel, or a generator etc

The Earth connections of buildings A and B may be at some voltage difference between them (for example : not really open but "bad" main Neutral connection - which can go for years without being detected, or just the buildings being supplied from 2 different grids), and this time, there is plenty (few A or more) current available, not the tiny current that was with the EMI capacitors. When plugging the laptop, it becomes an only link between those 2 buildings.... And if few A are flowing through there, the conductors carrying them (Ethernet cable shield, Ethernet plug, PCB traces in laptop, power supply plug, power supply cable, mains cable....) may not be up to the task - And then you can get really haunted occurences like Ethernet plug melting into the laptop's Ethernet connector..... Which would NOT happen with a 2 contact power supply, as it does not close the Earth circuit

Again, rare occurence, but be cautious when connecting wired electronics to 2 buildings at the same time, and better avoid it. Same for any other IT equipment, Same for PA audio, Same for remote mixing panels.....



I'd take 3 contact over 2 contact power supply

[dr_st]

The three prong cord is used to comply with grounding regulations in some countries but it's redundant because the adapters are double insulated making it unnecessary to have the separate ground. Generally for this reason the 3prong cords are less desireable. The two prong unit is rated for 220vac so I don't think there is any problem using them in other countries but could be wrong.

Theory and practice do not always coincide. Ash's explanation is very thorough and far deeper than anything I could have come up with, and seems to address those points where the theory fails, and explains why in most cases a properly grounded adapter is better. Although he also mentions cases where it would be the other way around.

So, thank you, Ash, for your wonderful lecture.

What I told you is simply my personal experience from using the 2-prong and the 3-prong adapters. I had a few of them and were using them on different Thinkpads too, so I would rule out the fact that I simply had a faulty adapter.

With 2-prongs, I would often experience those mild tingles touching the screen and/or laptop chassis. Nothing like this ever happens to me with a 3-prong.

Now, it may be due to the 110V vs 220V difference. If as Ash says, the voltage often floats around 1/2 of the mains, it would explain why US/Canada users generally don't feel it.

But for me, this makes the 3-prong far more desirable than a 2-prong. Even if it poses no hazard, and even if the chance of damage to equipment, as in the example Ash gave, is very small - I have to ask myself - "why would I want something like this when I can get a properly grounded 3-prong adapter?"

The only advantage I see for the 2-prong is that the power cord itself (the part between the adapter and the wall) is a bit thinner and therefore lighter. But it is also less sturdy and more prone to being pulled out of the wall accidentally.

I've been to the US quite a few times, and have never seen an outlet where I couldn't plug a ground pin. Maybe they are more common in Canada (I haven't been), so it makes sense. Also perhaps Japan?

One thing there may be a problem with is finding international cords for the 2prong part because the 3prong uses the universal (mickymouse) type cord.

Actually the 2-prong cord (8-shape) is also standard. But may be less common, depending on country. In Israel we actually have some appliances using that cord. But I understand that in some countries in Europe everything is grounded.

The 65w will work with discrete graphics but you won't get full performance and I'd only use it for brief periods with a charged battery.

I am not familiar with any performance limitations when a discrete graphics Thinkpad is used with a 65W. But maybe there is something?

What I do know is that the 65W will lock your CPU to the lowest speed if you use it without the battery, and also it won't power a mini-dock.

In my opinion, if I was going to use a 65w, I'd get a 2prong because the cords are easier to stow and won't negate the advantage of it being smaller.

You do have a point here, so I understand where you and fefrie are coming from.

Still, I would prefer a 3-prong one any day. To me, the 2-prongs are just defective by design, and given the choice I refuse to use them.

[pianowizard]

I've been to the US quite a few times, and have never seen an outlet where I couldn't plug a ground pin.

Strangely, many of my extension cords (all purchased in the U.S.) only have 2 slots. There have been times when I needed to extend a 3-pin laptop charger but only had 2-slot extension cords around.

[rsutoratosu]

I use this 90w ultra slim. Its half the thickness of the 65w one and it charges a 2nd usb device also

http://support.lenovo.com/en_US/product ... MIGR-72900

[precip9]

The culprit is, that it is NOT exactly true that "no voltage source is present to cause any voltage to appear in there". The power supply contains usually 3 EMI suppression capacitors, which have small capacitance so dont get much current, but there is some tingle they let through. They are present :
- From internal -170v or -340v DC point (on high voltage part) to Output -
- From Input Live(Hot) to Output -
- From Input Neutral to Output -

This is not correct. The capacitors are not present in double-insulated power supplies. All supplies that use a two-wire line cord, and comply with UL regulations, are double-insulated. It is impossible to manufacture a capacitor that has double insulation, so they are omitted.

Although the "capacitors" are not present, they exist as functional circuit elements. Each capacitor is represented by a mathematical value called a "lumped constant." But they are not really there; they represent captive coupling through the transformer, which is very carefully constructed to comply with UL double insulation requirements.

Unfortunately, a 3 wire wall wart may provide no more security than a 2 wire. If you are hoping for a low resistance connection between the ground prong of the plug, and the barrel of the power plug, it isn't there. In the samples I have measured, the resistance between these two points is about a megohm. This means that the three wire ground cord provides no added safety. It does remove the "tingle" caused by capacitive coupling through the transformer. And many users of laptops with metal cases, including Apple and Dell, have complained bitterly about that tingle.

Ash is completely correct about typical stationary computer supplies, where the ground prong provides a true chassis ground.

[dr_st]

So now I'm confused.

If, as you say, the double-insulated power supplies has none of these capacitors, why do they still cause the tingle effect which is "caused by capacitive coupling through the transformer". Is that a different effect?

[precip9]

It would be nice if a transformer could be just a transformer, but it has what's called stray capacitance. Likewise, there is no perfect capacitor. Capacitors have stray inductance.

To model the circuit precisely, the stray capacitance of the transformer appears in the model diagram as imaginary capacitors connecting each node of the transformer.

And yes, the imaginary capacitors are what cause the tingle. Electrically speaking, they are very real.

[Ash]

This is not correct. The capacitors are not present in double-insulated power supplies. All supplies that use a two-wire line cord, and comply with UL regulations, are double-insulated. It is impossible to manufacture a capacitor that has double insulation, so they are omitted

The capacitors used for the task are made specifically for it, and are generally classified as Y capacitors. Those capacitors (for the correct voltage rating) allthough dont have really 2 layers of isolation, are considered as being double isolated between the 2 terminals and are ok to connect directly from mains to SELV

I did not yet see a 2 contact Thinkpad power supply, but in most others i opened at least the one capacitor from DC - on mains side to Output - is there



The capacity between the winding layers of the transformer..... Good point but lets have a look at how much it really is....

Capacitors
Typically something like "102" or "222" so 1000-2200pF

Transformer
I have no data but lets try to evaluate..... Think something you'd find in a laptop power supply - area of interface between coils about 20mm * 100mm, and they are isolated with polyimide or polyester tape of about 60um thickness according to here, and lets assume its in 1 layer. Ignore the thickness of the wire's enamel isolation (so our calculation will give higher capacitance than really is). The material's relative dielectric constant varies according to different sources but the max i found (from few google results) is polyimide ϵ = 3.5 and polyester ϵ = 5, so lets assume max ϵ for max capacitance

C = ϵ0 ϵ A / 4pi D = 8.854*10^−12 F/m * 5 * 0.02 m * 0.1 m / (4 * pi * 60 *10^-6 m) = 1.17*10^-10 F = 117 pF

Apparently not too much compared to the actual capacitor.....

Which one will give a tingle ?
(im taking frequency to be 60 KHz as this is typical for many current mode IC's used in those power supplies, and since we only want an evaluation maybe we can ignore the harmonics too.... dont know)

Capacitor :
Xc = 1 / (2pi F C) = 1 / (2 * pi * 60000 Hz * 1*10^-6 F) = 2652 ohm

Transformer :
Xc = 1 / (2pi F C) = 1 / (2 * pi * 60000 Hz switching frequency * 1.17*10^-10 F) = 22588 ohm

I dont know what is the ripple voltage seen on the primary side so can't apply Ohm to get mA figures though......

[precip9]

See
http://www.nxp.com/documents/user_manual/UM10391.pdf figure 20.

I think we are both half right/wrong. There is a single Y cap, CY1, connecting mains neutral to low side ground. This is why polarized two prong plugs are used. If that Y cap fails, it will not connect high-hot to the low side. So there are two levels of protection:
1. properly polarized mains connection
2. Y capacitor standard

In a stationary supply, with a 3 prong mains/safety ground, it is possible to use two y-caps, because the safety ground provides the second protection. In the 3 prong laptop adapters I examined, it is not possible, because the mains ground is connected through a high value resistor.

[Ash]

CY1 on the high side is connected to the HV DC negative, after the diode bridge BD1. It is not the Neutral. Anything before BD1 is symmetrical, either one of the AC wires is at the same "distance" from the DC negative (the "distance" being 1 diode out of 4 identical ones within BD1)

(They draw the HV DC as "Earth" but in fact it is not connected to Earth. There is up to -170v or -340v between this point and Earth during 1/2 of the mains cycle)



Just for curiosity :

1.
It looks like mains polarity is treated differently in US and Europe :

In US it is sometimes being depended on as a safety step (for example polarized plugs on lamps to ensure that the screw shell of the socket is Neutral) and i see that many appliances with 2 pin plugs have wider Neutral blade)

In Europe, same lamps with 2 pin plugs have the standard "Europlug", a non polarized plug with 2 round pins that goes in any direction into the socket. The safety in those lamps is built in another spot : The screw shell of the socket is not a current carrying connection. The contact with the lamp's screw shell is made by a small contact at the side deep in the socket. While the lamp is screwed in there is 1/2 chance that the screw shell is at 240v to Earth, but it is completely protected by the socket plastic. As soon as you screw the lamp out enough to expose the screw base, it is allready disconnected from both the center and side contacts in the socket

Even some Earthed plug standards in Europe (German CEE 7/4 which is used in most of east/central Europe, and Italian CEI 23-16 which is used in Italy only) are non polarized at all i.e. there does not exist a polarized plug for those sockets

The mains poarity (Live and Neutral) is followed strictly throughout the grid, panel and house wiring (breakers, light switches must be on the Live and so on), but from the wall socket and downstream in some countries is regarded as unimportant, in some is not controlled strictly, and in some is kept uniform and the 3 pin plugs are polarized (like here in Israel), but still appliances never depend on the plug polarity, not even as a secondary safety measure

2.
A while back i tested a few IEC320 C13 cables (just ordinary desktop computer power cables, Earthed, with polarized plug) and the polarity between the wall plug and IEC plug was pretty much random (each manufacturer adhered to what he wants)

3.
I have somewhere a DVD player which was imported 10 years ago from US (for DVD regional lockdown considerations...) which is rated for 120v only (not 100-240v as most are today) and it does come with polarized 2 pin US plug. You now intrigued me to open it, and check if in there is any inequal treatment of Live and Neutral.....



BTW, at least in some of the power bricks i opened, the Input Earth was connected to the Output Negative, usually thorough the EMI shield foil - The copper foil is soldered to a wire coming from the Earth terminal of the input connector and to one of the output electrolitic capacitors Negative side (which was intentionally not cut short after soldering)

[precip9]

Ash,
In the US, the two main connectors are not symmetrical. Neutral is actually bonded to earth at the house power panel. So, if the author of the schematic happened to be in the US, he would not be implying a hot-high-->low capacitor connection. But in most other regions, this is not true. So you are correct.

I think you are winning this one, but it is disturbing to me that a single point failure could cause a lethal fault. To me, "double insulation" really means double, not a part like a Y1 cap that has regulatory approval as double. I see a fuse in series with Y1. If the fuse is fast enough, perhaps it works like a GFCI.

For those who think that a 3 wire adapter provides more safety, measure the resistance between the ground prong of the line cord and the barrel of the DC plug. I measure very high, in which case it provides no added safety.

[Ash]

Its the same here. Neutral is bonded to Earth, and there are 240v between Live and Earth (and 415v between 2 Live wires in a 3 phase system, from which houses are supplied). Its not like US 240v between 2 Live wires where each wire is at 120v to Earth

I seen some device (i think it was a CRT monitor but im unsure) that employed 2 of those capacitors in series, therefore making real double isolation. But most only use one cap, which is like you say just "regulatory approved". I seen one case where such capacitor shorted out, that was in a desktop power supply which was Earthed, therefore tripped the GFCI when it happened. And yep, i'd take the Earthed adapters, allthough if as you say there is no connection between the Input Earth and Output - then there is still not so much protection....

[blackgul]

When you use a 3 contact plug, the Output - is connected together with the Earth from the wall, therefore the Output - is firmly held at 0v towards Earth

When you use a 2 contact plug, the Output - WOULD BE floating, which means that the voltage between it and Earth is undefined, but no voltage source is present to cause any voltage to appear in there. If you touch the laptop, by doing so you are setting it at 0v towards Earth. There is no voltage source present, with 1 terminal in Earth and 1 in the laptop, which would cause any other voltage to appear there : The 20v are set between 2 points inside the laptop, they dont define its voltage vs. the Earth. The mains voltage in the power supply is isolated by a transformer, so it has no effect either

The culprit is, that it is NOT exactly true that "no voltage source is present to cause any voltage to appear in there". The power supply contains usually 3 EMI suppression capacitors, which have small capacitance so dont get much current, but there is some tingle they let through. They are present :
- From internal -170v or -340v DC point (on high voltage part) to Output -
- From Input Live(Hot) to Output -
- From Input Neutral to Output -

With an Earth connection (3 contact plug), the Earth holds the laptop at 0v to Earth anyway. Without the Earth connection, the laptop is "floating" on the voltage it gets through those capacitors, which is derived from the mains voltage, often being at about 1/2 of the mains voltage (60v for 120v, 120v for 240v) but it can be anything up to full voltage. The current let through by those capacitors is tiny so the laptop does not pose a shock hazard (the voltage present on its metal parts has enough power just to give that tingle), but it is there.....

[precip9]

When you use a 3 contact plug, the Output - is connected together with the Earth from the wall, therefore the Output - is firmly held at 0v towards Earth

I wish that were generally true, but it is not. It might be true for some adapters, and not others. I have just measured an HP brand 90watt supply. The resistance between the neutral prong and the outer barrel of the DC plug is 1.050 megohms.

Everybody, get your meters out and measure. This is no time to play Aristotle.

[Ash]

I have quite a bunch of various supplies here, i'll go and test them to find out how common it really is

When you measured the 1Mohm, was that with a HV isolation testing tool (megger) or just plain multimeter ? - If with a multimeter, i'd say its weird if not alarming. What exactly can give 1Mohm result ? The board material and isolation of Y capacitors are normally excellent isolators, i'd expect them to be way above the range a common multimeter can measure..... I'm gonna check that out as well

[precip9]

I used two multimeters, not meggers. The one I consider most accurate measured 1.050M. A Radio Shack autoranger gave 994K.

I think it's an ordinary 1 megohm resistor, between safety ground and the DC barrel. I'm no lawyer, so I can't see why it would be either permitted or prohibited.

My guesses as to why it's there:
1. It's enough to drain off the leakage from Y1, getting rid of the tingle.
2. It's not enough to make the laptop a high amperage ground path for attached equipment, possibly defective,
that is self-powered. Perhaps it was found that attaching equipment could cause surges in the laptop they didn't want to deal with.
3. Or maybe it's just to protect against defective outlets. You travel around with a laptop. Eventually you might hit an outlet where the ground is lit up. Then the 1meg would be a safety device.

[Ash]

I tested some adapters :
http://s7.postimg.org/4hedn1mzv/ycap_all.jpg

As for the resistor - You are right :
http://s9.postimg.org/bm2rdvr5r/ycap_ibm.jpg

It does not make any functional Earthing of the output (in case of the Y capacitor failure) either. The current it will pass through (0.24mA for 240v) is not enough to trip GFCI and by far not enough to blow a fuse, so if the Y capacitor shorts the output will stay at line voltage. Pretty much the same as with a non Earthed power supply

Then only the tingle elimination option remains untill we overlooked something...

And some more :
http://s23.postimg.org/3urylwku3/ycap_dell.jpg
http://s23.postimg.org/nhuyp9egr/ycap_lien.jpg
http://s10.postimg.org/rg31l36ax/ycap_ls.jpg
http://s22.postimg.org/xufvpk8pd/ycap_lc.jpg
http://s24.postimg.org/apxwsyph1/ycap_hp.jpg

[BKthink]

I have only one thing to say:

BK