Electronics > Projects, Designs, and Technical Stuff
Voltage on ground of powersupplies, normal or not?
v81:
Have recently received a NexDock2 (A rare kickstarter that follows through with a reasonable product with minimal delays, seriously, this is unicorn s*it!).
I felt a 'vibration' when passing fingers lightly over the case.
I've had this before on iPhones, Macbooks and a Google Nexus 6P, where following up i've found AC voltage on the outside of these devices.
So on testing the NexDock i find ~90VAC on the ground (against mains earth, green terminal on Rigol DP832 PSU).
I had used this nexdock with a Raspberry Pi 4, but now the Pi is dead.
2 questions..
1) Is it OK for there to be voltage on the enclosure/ground of a product?
2) Any chance this could have killed my Pi?
Siwastaja:
1) Completely normal,
2) Yes, it's possible.
GeorgeOfTheJungle:
--- Quote from: v81 on February 04, 2020, 08:05:28 am ---I felt a 'vibration' when passing fingers lightly over the case.
I've had this before on iPhones, Macbooks and a Google Nexus 6P, where following up i've found AC voltage on the outside of these devices.
--- End quote ---
There's a line filter in the power "brick" that looks like this:
See C2 and C3? When you plug it in to a wall socket w/o a proper earth, the laptop case is connected to live and neutral through those caps (*).
I have no idea why the MacBook power adapter comes with that two prongs only/no earth plug adapter, because with a case that's 100% metallic you're guaranteed to close the circuit, especially if you're barefoot then get ready for a nasty shock and surprise. The underside of the forearm is extra sensitive too.
(*) 1nF, 1nF plus 1kΩ in series.
v81:
Thanks for the info.
Mild electric shock was also a concern, but measuring current i got about 100 µA or so.
As is happens the NexDock2 housing is aluminum, as is the Nexus 6P, don't own any Apple products but have had hands on others Macbooks and iPhones where i encountered same.
So Siwastaja says completely normal.
I wonder if you mean completely normal or that it is common?
The unpleasant sting that occurs on occasion when certain parts of wrist or forearm com in contact suggests that it really shouldn't be happening at all.
magic:
This can kill electronics if there are signal connections between two devices but no corresponding ground connection. It's enough that ground is lost only for a short moment. I have once fried a GPS receiver module this exact way.
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