Voltage on ground of powersupplies, normal or not? - Page 1
Forum section: electronics / projects

author: v81
author_rank: Regular Contributor
timestamp: February 04, 2020, 08:05:28 am
content: 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?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2020, 08:24:27 am
content: 1) Completely normal,2) Yes, it's possible.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: February 04, 2020, 09:38:41 am
content: Quote from: v81 on February 04, 2020, 08:05:28 amThere'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.

author: v81
author_rank: Regular Contributor
timestamp: February 05, 2020, 04:44:43 am
content: 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.

author: magic
author_rank: Super Contributor
timestamp: February 05, 2020, 07:16:05 am
content: 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.

author: mikerj
author_rank: Super Contributor
timestamp: February 05, 2020, 01:37:10 pm
content: Quote from: v81 on February 05, 2020, 04:44:43 amIt's extremely common, and "normal" in the sense that it's an unfortunate side effect of a device engineered to meet conducted emissions compliance. Perversely it's the nasty, electrically noisy power supplies that don't tend to have this leakage.I'm not sure if I'm more susceptible than others, but I don't like it at all. Touching with fingers isn't so bad, but inadvertently lightly touching e.g. my forearm onto the leaky device really makes me jump.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 05, 2020, 01:53:32 pm
content: Normal as in, allowed by regulations and extremely usual, everyone has seen/felt it, although not everyone hasnoticedorunderstoodwhat it is (prompting these recurring question threads).Devices with earth terminal avoid this leakage voltage, but two-prong devices have the problem, and even many with the earth connection can be - fully legally - connected to a socket without earth connection. It sucks, and it can cause damage, but is considered normal and acceptable, like it or not.Switch mode supplies have been able to reduce the leakage current, though. Some of the best leak so little it's very difficult to feel it.

author: v81
author_rank: Regular Contributor
timestamp: February 06, 2020, 10:06:19 am
content: So common, normal and legal, but not necessarily nice or desirable kinda covers it?Was crudely aware of it for years, but never thought about it critically or in detail until now.Seeing the AC voltage on the raspberry pi ground got me to thinking (internal dialogue)'what happens if i connect the pi to something that is earth grounded?? ' .I guess I can't be sure this caused the death of the Pi4, I'll make a warranty claim and see how i go.They're getting a little more expensive these days with ram options and lousy exchange rate.To all whom replied, thank you for the info, diagrams, discussion and data.Your time is very much appreciated.