Macbook: Weird Electrical Vibration When Charging
November 16, 2018 5:20 PM   Subscribe

I just bought a new Macbook Pro, and have spent the day setting it up. I just started charging it, and have noticed a weird, tingly sensation when I brush my fingers across the top of the lid and on the metal surrounding the keyboard. Sort of like static electricity?

The sensation stops when I unplug it. A cursory Google search has many users reporting the same thing, and suggesting that it is some type of electrical leakage and nothing to be worried about and that it is not a health or safety hazard. I'm kinda worried. Should I be? Is this normal or is this defective?
posted by nanook to Computers & Internet (16 answers total) 4 users marked this as a favorite
I had this happen with a phone; it happened more with some outlets/chargers than others and the battery life really went to hell around the same time but I don’t know if it was related.

If it’s new and it happens with all outlets I’d start a service request with Apple.
posted by mskyle at 5:24 PM on November 16, 2018

I’ve experienced this with many electrical items over the years. I’ve been led to believe that it’s a grounding issue.
posted by Thorzdad at 5:34 PM on November 16, 2018

I've had that happen with my Mac laptop. I think it's either due to the case developing a voltage relative to ground if your charging cable doesn't have a grounding pin, or if the case is properly grounded, you developing a charge on your body and then discharging through the case (happens a lot in winter here because it's so dry).
posted by heatherlogan at 5:35 PM on November 16, 2018 [1 favorite]

This frequently happened to me while I lived in the UK for a couple years and it freaked me out at first. It was usually felt in the palms of my hands as I typed or used the trackpad.

I was using an older MacBook Pro I brought over from the US (the late 2008 model). I remember reading at the time - this was around 2014 - that it was due to improper grounding, because instead of getting a proper UK plug for the computer's AC adapter I plugged it into a wall adapter bought off Amazon. I can't find my online sources for that information anymore.

As disconcerting as the sensation was, the computer didn't suffer any ill effects and the folks I spoke with at Apple didn't think it was anything to be concerned about.
posted by theory at 5:47 PM on November 16, 2018 [1 favorite]

This is a slight bit of mains leakage -- microamps, really -- and is harmless but annoying. Try reversing the adapter in the outlet; just turn it 180 degrees. If it's a polarization issue this may fix it. Try other outlets, also. A UPS (battery backup system, a cheap one will do) may also provide relief if it does 100% circuit isolation.
posted by seanmpuckett at 6:00 PM on November 16, 2018 [5 favorites]

I would send it back immediately. The electrical issues alone. Like how can you trust the computer, the charger? I wouldn't have it in my house if it did that.

I would not accept that "this is a standard thing". No it's not.

I was a forensic fire investigator for a lot of years though, so grain of salt and all.
posted by sanka at 7:18 PM on November 16, 2018 [3 favorites]

I've had this happen at times with every metal-cased PowerBook and MacBook I've owned since I got a PowerBook G4 in 2003, in various places and on different mains, and it does indeed have to do with a very slight amount of current leakage when the machine is not grounded.

Mac laptops have historically been shipped with both an ungrounded two prong plug and a grounded three prong extension cable for the power adapter, and "the tingle" was something that was usually resolved by using the grounded (three prong) extension cable with the power adapter. However, I understand that Apple is no longer shipping the three prong extension cable with some machines, which is bizarre and churlish, but there it is. You can buy a grounded plug off of Amazon, although if you're plugging into an ungrounded outlet or one with a "fake" ground, it won't make any difference.

Based on my experience, I think it's unlikely that if you exchange the machine you will get one that does not demonstrate this unfortunate artifact of a metal case with an ungrounded power supply. I'd try the grounded extension cable first if you haven't already.
posted by eschatfische at 8:00 PM on November 16, 2018 [1 favorite]

This is likely AC leakage through a capacitor. This is common in cheap power supplies (no isolation transformer to buy). The grounded cord should solve the problem, but I wouldn't use the computer in the bathtub.
posted by H21 at 8:08 PM on November 16, 2018 [1 favorite]

It happens with my iPad Pro. It’s pretty normal, according to Apple.
posted by Andrhia at 8:15 PM on November 16, 2018 [1 favorite]

This is a normal consequence of how the power adapter is designed. There is no direct electrical connection between the power mains and the low voltage laptop side of the adapter. They are completely isolated from each other by isolated power inductors operating like an isolation transformer. That means there is no direct electrical connection between the AC outlet ground and the laptop chassis ground. They are separated.

But there is a problem with common-mode noise that can radiate out the power cable in violation of electromagnetic interference standards. To reduce this noise, there is a special capacitor called a Y-capacitor that connects the laptop ground to the input power side. The capacitor is high voltage rated and a small value, typically just a couple of nanofarads. But this means that there is some small amount of AC current that passes through this capacitor to the laptop chassis.

Depending on the design standard, this leakage current is limited to two or three hundred microamps. This is not enough to be dangerous, most people can't even feel it, but it can cause slight tingling in certain circumstances, especially if you body has a good connection to earth ground.

This is particularly common complaint for MacBooks because of their metal case. Other laptops with a plastic case usually don't have the problem.

So what it boils down to is a design trade off between leakage current and EMI noise suppression. In order to reduce the amount of EMI, there exists a tiny amount of leakage current through the filter capacitor. Verifying that the leakage current is a safe level is part of the certification testing for the power adapter.

It is not dangerous.
posted by JackFlash at 8:41 PM on November 16, 2018 [20 favorites]

Just another voice chipping in to say that I've had the same exact thing with a couple of aluminium body phones. Neither of them killed me and neither of them exploded. Seems to be pretty common with metal body electronics.
posted by Dext at 9:35 PM on November 16, 2018 [1 favorite]

All my metal laptops have done this.
posted by DarlingBri at 12:23 AM on November 17, 2018 [1 favorite]

Nthing that it’s metal cases and common. I can “transfer” the buzz to my partners skin with a light touch, or pick it up from her if she’s using the iPad. Sighed any benefit to choosing non-metal laptops etc you think?
posted by Iteki at 3:00 AM on November 17, 2018 [1 favorite]

Thanks to JackFlash for saving me typing up the correct explanation.

As you will see from this article, it's typical for Y capacitors to be installed between only one of the input mains conductors and ground. They will perform their intended noise reduction function regardless of whether they're connected to the live input wire or the neutral input wire, but since the AC voltage on the neutral input wire will be very close to ground in most cases, the Y capacitor will couple much less leakage signal to the equipment ground if it ends up connected to neutral instead of live.

So if your power supply is indeed connected to the mains outlet via an ungrounded two-pin plug, you should find that you can substantially reduce your tingles just by plugging it into the outlet with the pins the other way around as seanmpuckett suggests.
posted by flabdablet at 6:33 AM on November 17, 2018 [1 favorite]

You have a grounding issue. this is something you should generally get fixed as it is not good for either you or the laptop.
posted by evilmonk at 10:12 AM on November 17, 2018

For those who would like a mathematical explanation, the Y-capacitor forms a connection between the high voltage AC mains side of the adapter and the low voltage DC side that connects to your laptop. A small leakage current flows across that capacitor from the AC plug to the laptop and your fingers.

The AC impedance of the capacitor ( you can think of this as the resistance to AC current) is given as:

X = 1/(2*pi*f*C) where

X is the AC impedance, f is the 60 Hz frequency and C is typically 2 nanofarads (2 *10^-9).

If we plug in the numbers the impedance comes out to 1.3 megaohms (1.3*10^6). So the Y-capacitor acts like a 1.3 megaohm resistor connecting the AC plug to your laptop and your fingers.

The leakage is given by Ohm's Law:
I = V/X
where I is the AC current, V is 120 AC volts, and X is the impedance we calculated above.

So the leakage current is 120/1.3*10^6 = 90 microamps.

There are other stray capacitance leakage paths as well, but the Y-capacitor is the big one. So total leakage current is typically less than 200 microamps -- nothing that is going to hurt you, although you might be able to feel it if you are connected to a good ground.

From those formulas you can see that the larger the capacitor, the greater the leakage current, so for safety you want the Y-capacitor to have a small farad value. But the Y-capacitor is also the EMI shorting path.

The Y-capacitor shorts the EMI that passes from the noisy, low voltage switching side of the transformer to the quieter AC mains side of the transformer. There is a very small stray capacitance inherent to the transformer that passes this noise. So the Y-capacitor shorts that noise right back from the quiet side to the noisy side before it can travel down the AC power cord and which radiates like an antenna. So to effectively short-circuit the noise, the Y-capacitor must be significantly larger value than the stray capacitance inherent in the transformer.

This is the trade off between safety and EMI noise suppression. The capacitor must be large enough to short-circuit the noise, but not so large that the leakage current is dangerous.
posted by JackFlash at 12:28 PM on November 17, 2018 [3 favorites]

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