I think this happened to me many years ago with old devices but at least the last 10 years this never happened to me again.
So can anybody else “Test” this?
I was playing a game with high load, turned hibernate on and pulled the plug and accidentally touched the plug pins. It wasn’t a very nice experience and I was surprised how strong it was.
From what I know, power supplies with power factor correction (PFC) are more likely to give you an electric shock if you touch the plug pins right after unplugging as power supplies without PFC have their rectifier diodes before the capacitors. I got shocked last year from a portable 1200W charger
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Might not be a long line of testers to sign up for this one…
The inductors in the power supply were likely fully charged, unfortunately you touching the prongs of the plug created a nice place for the current to dump instantaneously instead of decaying away. I would have to believe the power supply was tested against numerous standards for safety.
That specific application (yanking the plug and accidentally bridging the prongs immediately afterwards) is probably not in the battery of tests because it is not a regular function of using a power supply.
Not that I want to experiment with this, I suspect doing the same thing to most computer power supplies will result in the same effect.
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I tried with mine and a Voltmeter instead of fingers. Highest out of 5ish tries was 3.5V
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As luck would have it, I accidentally “tested” this issue as well just now when my finger touched both metal prongs of the plug right after I plugged it out, while the USB-C side was not connected to the laptop. It was quite a strong shock. My guess is if it isn’t connected to the laptop, it doesn’t get to discharge whatever was left in the capacitors to the laptop.
I can’t find my multimeter right now, but will test with it later.
Measure the current, not just the volts.
If the PSU has an LED, look to see when it goes out, as this means it’s drained, which will be faster if the laptop is connected.
Same here. Mine wasn’t plugged in into the laptop.
And I’m sure it wasn’t 3.5V as the other user posted.
With 3.5V you wouldn’t feel much.
I tested with a multimeter and for a very short moment, it shows anywhere from 30 to 35v DC through the plug prongs. If it weren’t for the fact that I had myself felt the shock through them just a few hours ago, I could have chalked up the momentary voltage as error of the meter as it is auto sensing and immediately then shows mV scale.
Any electrical engineers willing to chime in here?
If there is a capacitor in front of the rectifier, for noise suppression or something it would depend on when in the 50/60hz cycle you unplug the thing. Not sure they do that on power supplies though.
There is normally a pair of capacitors, one from the line side and one from the neutral side, with the common connected to earth. There is normally a pair of high value resistors (typically around 1Meg ohm) fitted as well to discharge any residual voltage on the capacitors to minimise this sort of problem.
The capaitors are there to minimise the amount of EMC noise that gets fed back up the mains from the power supply.
That would mean if you unplug it at the right time you can have full line voltage on those for a moment?
The current is not a concern. The capacitors have very little, capacity, they are very small, but they can have 230V or 110V across them.
The volts have to be well in excess of 20v and depending upon how dry the hands are even 40v will not be felt.
But hands are sweaty and from one finger to another, or the palm that can be felt as the fingers have a lot more nerve ends than say the arm in general.
Back in the 60’s I accidentally put my hand across 400V DC which blew some fuses. Had it not the magnetic field would have held me to the busbar and fried my hand. Luckily Small holes in the hand and a bruise as I fell is all I had, oh! and the embarrassment which really hurt.
Former Navy Radio Electrician.
Don’t pull the plug for a minute or two after powering off, and the PSU isn’t off unless you switch it’s supply.