PC charger causes socket to flash when plugged in?

[mattylad]

Hi guys, when my wife plugs her HP laptop charger into the 4 way extension lead (from Ikea) it causes a flash at the socket.
I can see pitting on the plug pins.

I have changed the extension lead and it still does it.

This is only in the bedroom, which is on a different ring to downstairs where it does not do this.

The bedroom is on a separate ring that is on an RCD, yet downstairs is on the old CU which is not.

Any suggestions on what may be causing the sparking?

Cheers,
Matt.

 

[Monkeh]

Any suggestions on what may be causing the sparking?

A capacitor.

Don't switch the socket on until it's inserted.

 

[mattylad]

The problem is its an unswitched extension, the switched socket is behind the cupboard.

Ah well, she will just have to get a switched extension block.

I'd like one of those myself but I cannot find one with a 7m cable or that I can rewire.

Cheers.

 

[bernardgreen]

Switching the socket ON after the plug is in moves the problem to the switch contacts in the socket and after time these contacts can fail.

Using an extension lead as a sacrificial item ( destroy and bin when it starts to fail ) is a way to protect the socket on the wall and the mains lead for the lap top power module.


Minimal cost means the units do not have current limiting on the mains input.

 

[mattylad]

OK, so why does this not happen when plugged in downstairs?
Same type of extension, unswitched.

 

[bernardgreen]

The inductive impedance of the circuit to the instant rise in current will affect the way the contacts arc together.

The amount of inter conductor capacity in the wiring which will be shorted circuited by the power unit until its own capacitor is charged will affect the size of the arc.

The sense coil of the RCD puts an inductive impedance into the circuit and this will slow the rate of rise of current when the plug is inserted. This will prolong the duration of any arc. This rate of change of current is a high frequency change and thus the RCD's impedance for this change is many times more than the impedance at 50 Hz for normal currents.

 

[Monkeh]

Switching the socket ON after the plug is in moves the problem to the switch contacts in the socket and after time these contacts can fail.

Except they're designed to handle it.

 

[bernardgreen]

Except they're designed to handle it.

Actually they are designed to switch 13 amps. When switching ON a typical lap top power supply they could be switching well over 20 amps, As much as 120 amps for 5 milliseconds has been measured in the laboratory, not long enough to trip an MCB but more than enough to partially de-plate the switch contacts.

 

[Monkeh]

Except they're designed to handle it.

Actually they are designed to switch 13 amps. When switching ON a typical lap top power supply they could be switching well over 20 amps, As much as 120 amps for 5 milliseconds has been measured in the laboratory, not long enough to trip an MCB but more than enough to partially de-plate the switch contacts.

They're much more appropriate for it than the plug contacts, at any rate.

 

[mattylad]

Cheers guys.

 

[SimonH2]

When you work in IT ... you learn to ignore it

 

[mattylad]

I do, she on the other hand refuses to charge her laptop upstairs lol

 

[ban-all-sheds]

I cannot find one with a 7m cable or that I can rewire.

Why do you want to rewire it?

Cut the plug off, and replace it with an IEC 60320 C14. Then you can extend it with an BS 1363 to ICE 60620 C13 cord.

But the real beauty of that solution is you can now get different power cords to use in different countries

and have a much better way of using electrical items on holiday than those plug-in adapters.

If you want to travel light you can buy the local power cord when you're there, or borrow one from the hotel, or use the one from the kettle, or if you're on business there's bound to be one somewhere in the office.

 

[Monkeh]

I do, she on the other hand refuses to charge her laptop upstairs lol

Tell her to stop being such a wuss, then. She sets off a whole lot more sparks every time she starts the car.

 

[ban-all-sheds]

She also initiates thousands of fuel/air explosions per second, but that's not necessarily something you'd want to try at home.