Strange electrical sensation from my laptop - Page 1
Forum section: electronics / projects

author: Stonent
author_rank: Super Contributor
timestamp: May 04, 2015, 04:41:54 am
content: I've had my Toshiba S55-B5289 for about 6 months now and it wasn't until today that I realized something strange.Since I've had it, I've noticed if I take a finger and drag it across the aluminum finish, I feel a strange sensation in my finger.At first I thought it was electrical in nature but then thought I was feeling the grain.A few weeks ago I looked it up again to see how much it cost and was reading the reviews here:http://www.microcenter.com/product/434555/Satellite_S55-B5289_156_Laptop_Computer_-_Brushed_Aluminum_Finish_in_Satin_GoldAnd read this:QuoteThat was the exact thing I noticed. Today I realized you don't get that sensation if it isn't plugged in. So now I'm wondering what it is.It has an ungrounded powersupply so I'm assuming it's electrically isolated via a transformer. I tried taking some measurements from the case with a multimeter but found nothing noticeably different than if I just held the leads.I tried: (on 200mV scale)Voltage from me to the case - anywhere from 10 to 40mVVoltage from case to negative on the power supply while it's plugged in - keeps alternating between 1mV and -2mV (at a rate about as fast as you can say one two one two one two)Voltage on multimeter sitting on the table with nothing connected - +/- .4mV depending on the direction it is facing.The other strange thing is it doesn't have to be charging to do this. If I pull out the plug where it stops charging but is still making some electrical contact, I will feel the buzzing on my finger when I slide it on the case, but when completely unplugged, I feel nothing.I'm certainly not grounded when doing this, I'm just sitting down not touching anything metallic other than the laptop.Any ideas?http://www.toshiba.com/us/computers/laptops/satellite/s50

author: Stonent
author_rank: Super Contributor
timestamp: May 04, 2015, 04:52:47 am
content: Apparently more people have seen it:http://slickdeals.net/f/6240374-toshiba-satellite-laptops-a-widespread-electrical-or-grounding-issueHowever I just noticed that when unplugged, I can't feel the sensation on the palm rest but if I slide my fingers across the lid, I feel it.Something related to the backlight maybe? I would assume this laptop uses an LED back-lit display so there shouldn't be any high voltages.If I touch a wire from the case to the lid it doesn't seem to bring the feeling back to the palm rest when not on AC power.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 04, 2015, 05:28:18 am
content: Did you measure AC voltage between the laptop casing and mains earth?This is a typical non-earthed chassis issue you'll also have on desktops.

author: Stonent
author_rank: Super Contributor
timestamp: May 04, 2015, 05:40:57 am
content: Quote from: Jeroen3 on May 04, 2015, 05:28:18 amWell I didn't but then since it also does it on the lid when AC is removed I'm not thinking it is power supply related.

author: aargee
author_rank: Frequent Contributor
timestamp: May 04, 2015, 06:19:01 am
content: I gather the case is that 'brushed' aluminium material? I'm assuming you measured DC rather than AC voltage?I get this same buzz like feeling from my son's Macbook aluminium shell. It is the capacitive grounding effect of a double insulated power supply. There will be a very, very low current at 100 or more volts AC running through your finger tips. Only when the power brick is connected (charging or not, on or not) remove the power lead and the buzzing stops.Quite normal for consumer devices with double insulated power supplies. Nothing to worry about, just an odd feeling.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 04, 2015, 06:20:04 am
content: Probably resonances from the fans or hard drive. Try turning it off or to sleep mode and try again.

author: ElektroQuark
author_rank: Unknown
timestamp: May 04, 2015, 06:27:34 am
content: Same here with a Satellite P70. But this has a grounded power supply. When using a grounded wall socket (the recommended in the manual) there are no "feelings". They only appear in ungrounded sockets.

author: LektroiD
author_rank: Frequent Contributor
timestamp: May 04, 2015, 06:36:01 am
content: I noticed the same sensation with my macbook pro. I put it down to the matt texture of the aluminium used, since it is not evident if my hand is stationary. Just checked it for AC, nothing spurious...

author: amyk
author_rank: Super Contributor
timestamp: May 04, 2015, 06:42:40 am
content: It's basically mains voltage at a constant current of several tens of uA through the EMI reduction capacitors.http://www.aplomb.nl/SMPS_leakage/Doc_ie.html

author: electr_peter
author_rank: Unknown
timestamp: May 04, 2015, 06:59:46 am
content: Another definite case of various parasitic capacitances and resistances (in the form of EMC Y caps (hopefully) from mains to GND in SMPS). It was clear from first few sentences.I have experienced it myself with many laptops and other electronic devices. Slide one your fingers along metal part - slight roughness is felt even on flat surface. At the same time, touch few other fingers - if this sensation vanishes, cause is confirmed.Once you know what to expect, you will find it easier to detect by senses. You will find that tingling sensation ceases to exist if you touch with your full palm/hand, not just one part of the finger. It is not about power delivery, it is about connection to mains (even with single wire).It is not dangerous. Effect varies greatly by the environment conditions, overall house wiring and person sensitivity. It is not possible to get rid of it completely, unless you a) run from batteries all the time, b) buy a grounded PS and have proper grounding in the house (or ground laptop externally - not recommended) , c) get another power supply with lower leakage.EDIT:You can set your DMM to AC uA range, grab one lead with a hand and stick other lead to metal laptop part while SMPS is connected (or to SMPS GND or VCC). uA reading will appear, I can guarantee that.

author: MatthewEveritt
author_rank: Unknown
timestamp: May 04, 2015, 11:37:41 am
content: I've had the same thing with a metal shelled toughbook, as electr_peter says it's capacitive coupling - n9thing to worry about but annoying. Some chargers try to suppress it but adding a capacitor across one side of the transformer to alter the ratio (it acts like like a capacitive voltage divider so if you make one sidelarger than the other you can make the observed voltage higher or lower.) If the cap is on the right side it will pull the thing closer to neutral, which is hopefully tied to earth somewhere nearby, but if it's on the wrong side it actually pulls closer to live, giving more buzz.If the charger has a two pin mains cable (either in to the wall or into the charger) it's possible that turning the plug 180degrees will lesson the effect.

author: Stonent
author_rank: Super Contributor
timestamp: May 04, 2015, 11:41:35 am
content: Quote from: Stonent

author: wraper
author_rank: Unknown
timestamp: May 04, 2015, 11:41:42 am
content: Actually there is something to worry about. That means there is no ground connection in your mains socket. Edit: I see the power supply is without ground pin.The same thing with my Acer laptop when connected to some crap sockets.

author: electr_peter
author_rank: Unknown
timestamp: May 04, 2015, 01:15:25 pm
content: If youreallyfeel something when AC cord isdisconnected(I have serious doubts), something in laptop may be generating high AC/DC voltages, weird ground loop exists or static charge builds up. Try debugging things one by one - try turning laptop off, screen light on/off, set various brightness levels for screen LEDs (if it LEDs at all) (this sets up high frequency PWM -> shard edges, possible problem), touch and measure various parts of laptop, etc.Please do more tests and write your findings, it can be really interesting

author: Jeroen3
author_rank: Super Contributor
timestamp: May 04, 2015, 02:01:45 pm
content: Quote from: StonentAre there any other peripheral devices attached? Such as printers, monitors or speakers?

author: rsjsouza
author_rank: Super Contributor
timestamp: May 04, 2015, 02:46:48 pm
content: Quote from: electr_peter on May 04, 2015, 01:15:25 pmThe subsystem that generates high voltage on any laptop is the screen backlight (hundreds of volts on the CFL).I've felt this sensation through the case of some prototype units (never on production units); I have also felt this by touching the LCD of some older development kits.I was able to "see" this by using my old trusty screwdriver test light with a neon lamp - something similar tothis.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2015, 07:10:18 pm
content: Quote from: rsjsouza on May 04, 2015, 02:46:48 pmNewer devices use LEDs rather than a CCFL backlight and the OP said it's the Toshiba S55-B5289 which is too new for a CCFL backlight - it'll probably have LEDs.

author: Tinkerer
author_rank: Frequent Contributor
timestamp: May 05, 2015, 12:18:48 am
content: This has everything to do with grounding. I use an ungrounded outlet where I plug my computer in and already noticed this effect a while back. Get the exact same effect with a product where I work. Easy to measure between the case and ground to see a couple volts. Interestingly, if I hold my feet up off the floor(im sitting on a plastic chair) I feel mush less and effect. Harder path to ground of course.

author: Stonent
author_rank: Super Contributor
timestamp: May 05, 2015, 12:27:34 am
content: Quote from: Hero999 on May 04, 2015, 07:10:18 pmYes, I just confirmed it on their website:QuoteOdd wording. I'm not so sure what is unique about an LED backlit display in 2015.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2015, 12:40:16 am
content: Yes, real effect. Well, I don't know if the effect is well known or understood, but it's definitely caused by an electric potential; feels like vibration, or a rubbery, stick-slip surface; and goes away when the chassis is grounded. I have a few pieces of equipment around here that do the same thing.Tim

author: amyk
author_rank: Super Contributor
timestamp: May 05, 2015, 01:49:42 am
content: Quote from: Hero999 on May 04, 2015, 07:10:18 pmLED backlights are comprised of long series strings which can have a total forward voltage near 100V, and the high drive frequency makes capacitive coupling more effective.

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2015, 12:06:58 pm
content: Quote from: amyk on May 05, 2015, 01:49:42 amThat still seems doubtful. I would've thought the current through the LEDs would be DC and if it does have an AC component, it'll be way over 20kHz so you wouldn't feel a buzz anyway. 100V would only shock you if it was directly connected to the case (there's no way it could capacitive coupling could be sufficient) and without an earth connection, two parts of the case would have to be at different potentials in order to shock.

author: TerraHertz
author_rank: Super Contributor
timestamp: May 05, 2015, 12:58:24 pm
content: This effect is nothing new. It's been around as long as ungrounded mains appliances. It's the tiny AC current coupled to exterior conductive surfaces via whatever internal capacitances there are to the live side of the mains.You'll find the effect is much more noticeable if you make very light contact with the backs of your fingers, or inside wrist. Thinner, more sensitive skin. I'd presume it's nerves being stimulated to fire by the current. Also with a very light touch, the metal surface probably rises up to some large portion of mains AC voltage then discharges across the insulating air+skin layer to your more conductive inner layers. Hence, small spike of energy to trigger nerves each half cycle.If you don't like it, you have a choice. Either wire the metal case to ground somehow, or wire yourself to mains Active. Ha ha, just kidding about that last one. It would only work in 'limited circumstances'. Like, if you never touched anything else. Or were already dead.

author: wraper
author_rank: Unknown
timestamp: May 05, 2015, 01:05:58 pm
content: Quote from: Hero999 on May 05, 2015, 12:06:58 pmDoubtful yes, however backlight usually is PWMed at a few hundred HZ to adjust brightness.

author: electr_peter
author_rank: Unknown
timestamp: May 05, 2015, 02:25:33 pm
content: Quote from: wraper on May 05, 2015, 01:05:58 pmI can see PWM effect on LED backlighted LCD under specific conditions. There are at least two frequencies involved in typical LED LCD - high frequency for constant current drive and low frequency for PWM brightness regulation. Could low frequency account for strange feelings in above posts (without AC cord)?I still do not see how one can feel something with power cord disconnected.

author: Wilksey
author_rank: Super Contributor
timestamp: May 05, 2015, 03:03:31 pm
content: I had something similar, I have a Dell XPS with brushed aluminium casing, whilst the laptop itself is fine when running etc, I was transferring some videos last year and had the VCR (yes, the old tape player) on my lap and the laptop on the arm of the chair, I got the "humming" across the brushed aluminium when I touched it, I figured it was to do with ground issues with me having contact with the VCR, didn't think much more of it as usually it is fine.

author: LektroiD
author_rank: Frequent Contributor
timestamp: May 05, 2015, 06:54:51 pm
content: Just noticed it on my iPad while I was charging it. Unplugged the charger; sensation gone!

author: Andlier
author_rank: Contributor
timestamp: May 05, 2015, 11:43:26 pm
content: http://en.wikipedia.org/wiki/Electrovibration

author: Jeroen3
author_rank: Super Contributor
timestamp: May 06, 2015, 05:30:46 am
content: Quote from: LektroiD on May 05, 2015, 06:54:51 pmDo you have a genuine charger? I also noticed this with non-apple chargers.

author: LektroiD
author_rank: Frequent Contributor
timestamp: May 07, 2015, 03:34:23 am
content: All my Apple chargers are genuine, I wouldn't touch knock off Apple gear - I run a recording studio and found fake Apple chargers introduce audible noise when recording.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 07, 2015, 06:15:55 am
content: I had this on some apple kit. There's a capacitor of sorts between the two halves of your average switch mode. I think it leaks some current through AC coupling as there was about 70v between the chassis and earth. If you lift your feet up off the floor it stopped for me.Chinese cack laptop chargers tend to do this as well. Probably due to minimal parts count side effects!