Saturday, 4 August 2012

Apple laptop charging vibration effect

If I brush my hand across the top of my shiny Aluminium case of my Apple laptop I feel a strange vibration effect.

Turns out I am not going mad - James has felt it too. Interestingly the new MacBook pro is lower frequency than the Air. But both are very noticeable.

If you hold your hand still, you don't feel vibration. lightly brush your hand or fingers over any of the metal surfaces and you feel it.

What is interesting is that this effect is only present if connected to the power (charging).

It is mostly noticeable if you move you hand/fingers over the surface. However, on the Pro just having my arm lightly touching the corner of the case can create quite a noticeable stinging pain. It has bugged me quite a lot while trying to use it today.

WTF is this?

33 comments:

  1. I have felt the same vibration on my 2003 Powerbook, but also on HiFi amplifiers. Turn the amp off and it doesn't happen.

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  2. I've come across this with all sorts of devices. There was a discussion on some newsgroup or other, where we concluded that:

    The un-earthed power supply design was causing the conductive case to float to half of mains voltage. This bit's easily verifiable with a meter.

    Some sort of nerve or muscular effect as a result of moving fingers over a surface with an AC voltage applied makes it feel 'rough' or 'sticky'.

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  3. I used to work for an AASP (Apple Authorised Service Provider), and we had many people querying this ever since Apple did 'metal' cased Powerbooks. The line from Apple was it's perfectly normal, and not at all harmful in any way. Like Kimble has said, with a voltmeter, you can see that there is normally voltage on the case (stick one probe into an earth socket, and the other onto the MacBook case) and you'll see it. Voltage leakage doesn't really matter, as long as the Ampage is low.

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  4. Well, it hurts when using it - that is starting to count as a problem to me.,

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  5. I've noticed exactly the same thing with the 8 series samsung tv's, their metal casing has exactly the same weird vibration that goes away when you stop moving your finger.

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    1. Yes, same thing on my Pana plasma

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  6. I find that it only happens if I am earthed or if I am touching another apple product, e.g. using my MacBook Pro and then my other brushes my Air.

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  7. On my Air, I found it happens only when using the mains wall-wart attachment for the adapter, or when using a bog standard figure eight cable. This is because the Apple mains->adapter cable passes an earth via that big shiny stud on the adapter

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    1. Ditto. This is exactly the same for me.

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  8. I'm glad you posted this, I've noticed similar a couple of times on my Air and thought I was going mad.

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  9. You sure, it actually just isn't still on? Mountain Lion and with later MBAs and the new MBP have PowerNap [1].

    This might explain why it only felt when it's plugged in, as PN by default will only work when connected to power?

    [1] http://support.apple.com/kb/HT5394

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    1. It is on - what has that to do with it?

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  10. Myself, a friend and one of my customers have noticed this effect with Dell XPS metal wrist rest style laptops!

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  11. I'd felt it on both the laptops here and assumed it was earth leakage. Just measured it between two if them and get a nice healthy 80v ac :P it's good to surprise someone with on the end if a USB cable!

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  12. I get this with any metal covered device plugged into a charger, including HTC phones and the metal covers on the underside of my old Thinkpad. I will sure it is a fairly recent effect, but it is a useful way of checking a device is powered from the mains - a useful 6th sense!

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  13. There seems to be a thread about this here: https://discussions.apple.com/thread/2663087?start=0&tstart=0
    You can get rid of it by using a different cable, apparently.

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  14. In the past I've heard this effect referred to as 'earth finger'. You are likely to feel it on many un-earthed powered metal devices. My Sony laptop does it just like much MBP.

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  15. https://discussions.apple.com/thread/4087798?start=0&tstart=0

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  16. Having spent nearly a quarter of my life servicing brown goods both domestic and professional. i can tell you that this is standard practice on unearthed devices to connect them loosely via a 5 meg resistor to half mains potential. Of course in the USA this is 55v and is hardly going to cause any problems.

    The practice was started with CRT TV's where the chassis was actually hard connected to halve mains potential, these sets used antenna isolators . Later on when sets started using video in / out connections it was easier to isolate the psu with a transformer rather than all the video IO, though I have seen the odd set with video isolation achieved through transformers. The whole point of all this is to stop the chassis rising or rather falling to half EHT potential (around -12KV depending on screen size).

    On AV equipment something that you plug into is usually earthed, A TV antenna (if you are using a distribution amplifier for example or some HIFI amplifiers.

    On a laptop I can see this being more of a problem as Ethernet is isolated via a transformer there is not much you can plug into to earth. The only thing I'd suggest is maybe using a powered USB3 hub run from an earthed psu. This may well require you to modify the PSU in some way IE adding a connection from 0V to earth. Or make sure you have a brother printer connected to the hub, they are earthed.

    Alternatively ring up apple and ask them if you are supposed to be getting electric shocks from your new macbook, ask them why is it that you see sparks as you connect some USB devices explain that you have never seen this before and your windows laptop doesn't do it :)

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  17. My original Intel MacBook Pro had the same issue. As others have said, it's caused by voltage in the metal casing and poor grounding.

    Back then, the PSU came with two plugs - one allowed you to plug the PSU almost directly into the socket, and the other had a trailing lead. One of those was grounded, and the other wasn't - I forget which was which, but plug in the right one and the weird vibration effect will go away.

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  18. I have had the same on pretty much all my apple stuff, due to those being metal cased. if you use the trailing lead on the PSU you do not get this.

    I started off thinking the wrist area on the laptop was sharp or something, but nope, it's a weird earthing thing as already discussed.

    bit annoying, but only happens if you are earthing yourself via seat/shoes.

    My parents hot-tub does similar and is actually quite scary if someone outside the tub hands you a drink or touches you whilst in it, a bit of a shock! you could say... :-)

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  19. OK, clearly some electrical effect. What is very very odd is that today we had a couple of power cuts. Now, after those, almost no vibration effect and no shock at all, but is still charging. That is well odd.

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  20. OO.

    Thanks for this.

    It's been driving me bonkers for a couple of years :D

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  21. This is a frustration with all sorts of electrical equipment powered in this way. Switch-mode power-supplies are the worst - the small tightly-would transformers that isolate the mains from the equipment couple the two together by the parasitic capacitance between the windings. As Oryn says, there's also the sensible precaution in some power supplies to include an intentional leakage path between the equipment and the mains to avoid any huge voltage build-up (the risk is partly that a big voltage from, say, static from clothing will eventually discharge across the transformer, damaging its insulation and creating a more hazardous leak). The quest for nicer aesthetics and smaller size just make the leakage harder to minimise.
    The currents involved are way too small to cause you any harm but I agree they are uncomfortable. The quandary for the PSU manufacturers is whether to use just a 2-pole connection which is easiest for travelers or add an earth connection which complicates use in some countries and arguably adds the additional risk of the earth getting connected to something it shouldn't. There are more 3-pin earthed PSUs around now than before.
    The capacitance part of the leakage is not perfectly symmetrical so, sometimes, if you swap the mains plug around you can achieve greater or less 'tingle' as more or less capacitance is associated with the 'hot' side of the mains. This is probably the main reason for apparent inconsistencies. Your own contact with earth (probably which shoes you're wearing) also has a significant effect.
    With enough of a groundswell we could get this taken more seriously and might also be an opportunity for some enterprising third-party PSU manufacturers. The big OEMs probably won't be too interested - it's not a big problem in the US or Japan at 110V or 100V. For the rest of us, transformers with less capacitance would solve much of the problem - perhaps a little bulkier and maybe very slightly less efficient but much less uncomfortable.
    An earth connection as an option is good and solves the problem completely (as well as removing the irritating hum that can be introduced in head-set microphones using internal sound-cards on lap-tops). It's also possible to add a screen between the windings of a transformer which can be earthed to eliminate the coupling but can still keep the equipment safely isolated (but this might be difficult to apply in a nice small high-frequency switch-mode supply).
    As an aside I'm concerned at how seriously OEMs take the qualification and supervision of their PSU vendors. These components should not be not be treated as commodities in my opinion. They are critical to the safety of users (fire and electric shock) as well as the reliability of the equipment they power. (How does this work with FireBricks, by the way?)

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  22. I'm intrigued to know whether this effect is detectable by all users, or whether it depends on the user's internal body resistance. I noticed it first on a Psion 5. Subtle but repeatable effect when moving your finger across the casing - but only when plugged in to the power adapter (not when running from battery).

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  23. Not the only one - I have had this effect for years so much so that I no longer use apple devices!

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  24. As mentioned by several posters, i you use the trailing lead on the PSU this goes away. On closer inspection, if you look at where the "trailing" lead attaches to the PSU, it connects an earth to a metal stub on the PSU, so obviously this is why it fixes the problem.

    Thanks for all the info folks.

    Cheers,
    Con

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  25. I know this is nearly half a year late, but swapping the figure 8 cable round may solve that issue, often the PSU uses a high voltage, low value cap to link the DC and AC sides for RFI immunity (so far as RF is concerned, the entire AC power system is a ground reference). If it's merely grounding to one side of the input plug, reversing polarity on the AC input side would work.

    It's not a new effect, I noticed it on a vintage (circa 1950s) unearthed metal cased communications receiver, very odd, like people have said, almost like the surface is ridged. I connected the chassis to earth, that solved it :)

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    Replies
    1. Agreed. Same for our apple mac book pro, turn around the magnetic cable connection

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  26. Sound good... My MBPro charger has been intermittent...and only works if i have it in certain positions. i saw someone on YT gently flex the cable and 'push' the cable towards the flimsy part of the magnetic connector part. it works. for sure! i figured that i yank the magnet when im done charging so...its got loose wired probably or even out a weeny bit...and can be fixed by doing the above.. thanks all :)

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  27. Nope.. You're all out to lunch on the plugged in thing... I just got it - very strong - with the laptop unplugged.. Very strong. And, while trying to demonstrate the phenomenon to my wife we discovered that she felt it more strongly when I touched the back of her hand while she was wiping it across the metal -- also, when the second hand is touching the laptop and remaining motionless the phenomenon almost disappears in the hand which is wiping. there's something else going on here.. would love to know what. My guess is that not everyone can feel this.

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  28. RevK's point is interesting - it may be that some fault in the mains supply could be raising the voltage relative to earth and so making the sensation more apparent. It will depend on how well you are earthed - sitting on a leather or metal seat on a wooden floor will earth you better than a plastic chair on a laminate floor. Touching a grounded object such as a radiator will increase the effect (one hand on the radiator and one lightly brushing the electrical item). Here in the UK we have a live and neutral that returns to the power source but I believe the US has live and earth, relying on the ground to take the return current - this may contribute to differences in various countries.

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  29. i lick my MBP 2015 and it got me retarded.

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