Author Topic: Voltage on ground of powersupplies, normal or not?  (Read 1439 times)

0 Members and 1 Guest are viewing this topic.

Offline v81Topic starter

  • Regular Contributor
  • *
  • Posts: 89
  • Country: au
Voltage on ground of powersupplies, normal or not?
« on: February 04, 2020, 08:05:28 am »
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?
 

Offline Siwastaja

  • Super Contributor
  • ***
  • Posts: 9336
  • Country: fi
Re: Voltage on ground of powersupplies, normal or not?
« Reply #1 on: February 04, 2020, 08:24:27 am »
1) Completely normal,
2) Yes, it's possible.
 

Offline GeorgeOfTheJungle

  • Super Contributor
  • ***
  • !
  • Posts: 2699
  • Country: tr
Re: Voltage on ground of powersupplies, normal or not?
« Reply #2 on: February 04, 2020, 09:38:41 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.

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.
« Last Edit: February 04, 2020, 06:07:27 pm by GeorgeOfTheJungle »
The further a society drifts from truth, the more it will hate those who speak it.
 

Offline v81Topic starter

  • Regular Contributor
  • *
  • Posts: 89
  • Country: au
Re: Voltage on ground of powersupplies, normal or not?
« Reply #3 on: February 05, 2020, 04:44:43 am »
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.
 

Online magic

  • Super Contributor
  • ***
  • Posts: 7453
  • Country: pl
Re: Voltage on ground of powersupplies, normal or not?
« Reply #4 on: February 05, 2020, 07:16:05 am »
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.
 

Offline mikerj

  • Super Contributor
  • ***
  • Posts: 3382
  • Country: gb
Re: Voltage on ground of powersupplies, normal or not?
« Reply #5 on: February 05, 2020, 01:37:10 pm »
So Siwastaja says completely normal.
I wonder if you mean completely normal or that it is common?

It'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.
 

Offline Siwastaja

  • Super Contributor
  • ***
  • Posts: 9336
  • Country: fi
Re: Voltage on ground of powersupplies, normal or not?
« Reply #6 on: February 05, 2020, 01:53:32 pm »
Normal as in, allowed by regulations and extremely usual, everyone has seen/felt it, although not everyone has noticed or understood what 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.
« Last Edit: February 05, 2020, 01:55:07 pm by Siwastaja »
 

Offline v81Topic starter

  • Regular Contributor
  • *
  • Posts: 89
  • Country: au
Re: Voltage on ground of powersupplies, normal or not?
« Reply #7 on: February 06, 2020, 10:06:19 am »
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.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf