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?
I just experienced the same problem with my Framework 180W power adapter (model FRANCNCH00), connected to a German power socket (230 VAC). I used my Brymen BM789 multimeter to measure the voltage across the plug pins in crest mode immediately after pulling the plug several times; the highest voltage I measured was 119,3 V:
That’s the side effect of power factor correction. I got shocked by another power supply (not related to framework) a year ago and it felt like my finger was hit hard by a hammer.
Most power supplies have X and Y capacitors attached to the main power plug pins.
There is then a bridge rectifier that will prevent any other charge in the PSU from reaching the main power plug pins.
If it is a 240V AC supply (same in EU and UK, US is 110V AC), that puts a peak of about 340V on the X capacitors (between Live and Neutral) but less so on the Y capacitors between Neutral and Earth.
The X capacitors are not large, but whatever energy they do have will discharge very quickly to eventually nothing through your fingers. The X capacitors will also discharge themselves quite quickly if a resistor is also in the PSU for that purpose.
I am based in the UK, and it is very difficult to get a shock with a UK plug.
- When pulling a UK plug it is not normally possible to accidentally touch the power pins while doing it.
- When the UK plug is only half pushed into the socket on the wall, one can still not get your fingers round it and get a shock, because half the length of the Live/Neutral pins are insulated, so you would only be touching the insulated part of the pin.
- UK wall sockets have on/off switches so you can switch off at the wall before pulling the plug.
- All UK plugs also have safety fuses in them.
- UK wall sockets have safety shutters on the live holes, so that it is impossible to push a screwdriver into the live pins. So nice and very child safe. Bizarrely, some so called child safe blanking plates for UK plugs actually make it less safe, because it disables the safety shutters!!!
I guess the EU plug is not such a safe plug.
If you have wall socket switches, turn the switch off before removing the plug. It at least gives the X/Y capacitors a little time to discharge before unplugging.
Actually the modern EU plugs are just as safe as the UK ones, as they have a plastic sleeve which goes around half way down the pins, just like the modern UK plugs do. But the problem he is referring to is voltage on the pins some seconds after unplugging from the wall. UK plugs will have the same problem if you are quick enough at grabbing the pins after unplugging.
The best idea is to leave the charger connected to the laptop while switching the power off at the wall. This then means the charger has a load to dissipate any charge in the X and Y capacitors into. If the charger is disconnected from the laptop before being switched off the capacitors will discharge quite slowly, and still leave some voltage on the pins to give an electric shock.
UK plugs are a bit safer (e.g. with integrated fuse), but oh well. EU plugs are much smaller and safe enough.
Anyway I don’t believe there’s enough charge left in the adapter for it to be able to kill you.
Most definitely not.
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