Laptop Adaptor Third Ground Pin connected To Earth Reference Through 1 Mega Ohm  - Page 1
Forum section: electronics / testgear

author: suryaputhra
author_rank: Regular Contributor
timestamp: September 30, 2017, 03:36:29 pm
content: Laptop adaptor third ground pin connected to earth reference(utility earth ground) through 1 Mega Ohm so in this case are they really isolated from mains?

author: suryaputhra
author_rank: Regular Contributor
timestamp: September 30, 2017, 05:53:15 pm
content: Can someone put light on my above topic

author: jpc
author_rank: Unknown
timestamp: September 30, 2017, 06:11:36 pm
content: Some, like Dell, use it as a means to signal the type of power brick attached. E.G. recently my Dell XPS 130W power brick died so temporarily I swapped it for one of my Dell 90 Watt bricks and it immediately warned me that I had the wrong 90W brick inserted and that I might not be able to get full performance. It will still work, just doesn't have the power to spare so if pushing the laptop and charging the battery, one has to suffer in the meantime.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 06:32:49 pm
content: Can you clarify the situation please? Where is the 1M resistor? Inside the adapter of is it something that you are trying to wire externally?If it is a three pin adapter, then the ground pin should be connected directly to utility ground. The ground connection isnormallycarried through to so that the DC output is grounded too.

author: suryaputhra
author_rank: Regular Contributor
timestamp: September 30, 2017, 07:41:46 pm
content: Quote from: Gyro on September 30, 2017, 06:32:49 pmIt is inside the adaptor, I have measured resistance between earth pin to output ground of adaptor.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 07:55:35 pm
content: Thanks for the clarification. Well I did say "normallycarried through".It may be that the all primary side EMC filter component leakage currents are returned to the mains connector ground pin, with just a resistor (more likely an EMC capacitor and 1M discharge resistor in parallel) between mains ground pin and output ground.The easiest way to confirm this is to power the adapter and measure the AC voltage beween the mains (utility) ground and DC output ground. You should hopefully find this to be very near zero.

author: suryaputhra
author_rank: Regular Contributor
timestamp: September 30, 2017, 08:25:01 pm
content: Quote from: Gyro on September 30, 2017, 07:55:35 pmThanks for the reply, you mean let me measure voltage between neutral or ground(earth reference utility) and adaptor ground, if so I will check, so in this scenario the adaptor is not technically isolated but practically it is isolated what is your opinion. Thanks in advance.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 08:47:57 pm
content: Ground (Earth) ONLY! Please don't even attempt to connect your meter to either Live or Neutral - It is not safe for you!.Please do not attempt this sort of test if you don't feel competent to do so. Just measure the voltage between ground - Earth reference (maybe use even a conduit or water pipe?) and the outer barrel of the DC connector.If you don't see a voltage then the output is 'effectively' isolated for practical purposes (eg. floating a low voltage DC supply).

author: suryaputhra
author_rank: Regular Contributor
timestamp: September 30, 2017, 09:01:50 pm
content: Quote from: Gyro on September 30, 2017, 08:47:57 pmExcellent technical info, I will check and post reply, but how to"maybe use even a conduit or water pipe"pls look into my other thread. Thankshttps://www.eevblog.com/forum/testgear/oscilloscope-and-isolation-transformer/

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2017, 09:10:23 pm
content: QuoteI was just looking for metal objects that would be connected to Earth that didn't involve you sticking your meter probe into a mains socket (even if only the Earth pin).QuoteI have done.