Is this dangerous?

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Again with odd or bad electric on reddit. Yawn. Boring.
Until you read this:

It's not dangerous. Many consumer electronics use ungrounded, unisolated power supplies and leak AC current on the DC output. It is very low current, and won't harm you beyond feeling it on some devices. You can actually measure it if you have a multimeter. You'll see something like 60-80V AC, which sounds high, but then if you measure the current you'll see a few dozen microamps.
For reference, a dangerous level of AC current starts around 1mA, so you'll be about 20-1000 times smaller than that.
If you're the DIY type, you can make a little filter adapter for your power supply. Plug the power supply in, the filter uses a capacitor and resistor to connect to ground, which will remove most of the AC voltage, and then you just output to your laptop. You won't be dealing with AC mains, so it is pretty safe. Alternatively, just buy a new plug online. However, be warned that even some 3-pronged adapters leak AC current, so just being 3-pronged isn't a guarantee. Your best bet would be buying from a good manufacturer.
You won't have any recourse with contacting the manufacturer of your laptop. There's noting actually wrong with the power supply.
I don't understand how this can be correct.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
The 55V is being coupled through a very high impedance, and then being measured with a high impedance multimeter.

If you place a load across the meter terminals ( say a 10K resistor) then the voltage would drop tremendously. So the current that can pass from this '55V' source through a person is very small.

But if the person reports being shocked, that current isn't negligible. It isn't an immediate shock harm hazard, but perhaps there is a health effect from chronic exposure to this low lever shock.

-Jon
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I had that on a laptop for years (Toshiba), it was a "shock" in the sense of what felt like a static electricity discharge when I touched the case. Turned out I had a bad power supply. Yes, the switch mode power supplies used for PCs create a lot of Common Mode current based on how they work, but it is generally taken to ground right away, usually through a capacitor (Common Mode Capacitor) on the DC side. If there is some sort of surge in the system and that CM cap gets fried, then YOU can become the capacitor when you touch the frame and it stings.
 

kwired

Electron manager
Location
NE Nebraska
What is voltage if measured with a low impedance meter? If still about same it probably is dangerous, if it doesn't read any voltage might not be much of a danger.
 
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