Shocking laptops ?

Question

just google and you will know what i mean.

just one of the posts,

http://crave.cnet.com/8301-1_105-9852716-1.html

> It's caused by the two-pronged connection between the mains lead and the power adaptor, which isn't earthed properly because of its lack of a third pin.

btw, i have read of ample cases with 3 pronged plugs too

laptop metal to ground measurements vary between 20 volts to 120 volts ac

the laptop receives 15 to 20 volts dc from the power adapter

>> can somebody please explain, how the heck does this even happen ?

Answer 1

Actually, the lack of a 3rd pin has nothing to do with it if there are only two wires from the adaptor to the computer.  

  Any two prong plug is supposed to have one prong at neutral and that is supposed to be connected to ground at the box.  2 prong items are supposed to be double insulated.

  With unpolarized 2 prong plugs, it is possible to have the case end up at a high voltage - see toaster in 50's with stainless steel counter tops.

  It looks like in this case there is a wiring mistake so that something designed for a plastic case got put in a metal case without enough thinking.  The ground for the 12 volt power supply is floating above the household ground so you get a net voltage that people can feel - not good.

Answer 2

problem lies in power adapter: it is switching type and not galvanically isolated, so output can 'float' in regard to ground on about half of power supply (55V) which will schock you. The problem with said models is probably that aluminium casing is connected to 'ground' on motherboard.

The solution: connect power adapter via isolating transformer (110V->110V) or ground the case

Answer 3

It is just floating and the voltage depends on the insulation in your transformer. It behaves like a capacitor and holds the charge until U get across it.

Answer 4

very shocking! since i am on a xps m1530 as i answer this. imagine that, i feel a recall coming on the adapter! i do use anti static cleaner, hope that helps until then!