Shock from a laptop

[sandyf]

Just seen the thread on shocks from a PC which has been closed. I had a similar problem with my old laptop, would get a shock from the CD drive virtually every time I changed a disc. Happened both here and the UK.

I would never have changed a disc when on battery so I wouldn't know about that. I didn't think that there was any high voltages within a laptop so it has always been a bit of a puzzle.

[Crossy]

I had a Dell lappie that would bite, but only when connected to a 'pattern' (non-genuine) power block.

Although the lead was 2-core (so shouldn't need a ground) I suspect the power block had the usual mains filter connected to the internal ground (usually the -ve supply).

[RichCor]

Even though the power-brick is supposed to rectify AC into DC, the added filters can allow AC to travel on the Ground side of a DC Voltage connection to the laptop.

Normally this isn't an issue. But it can become an issue either by causing 'noise' interference in Audio or Video circuits or annoying 'biting' when YOU become the final necessary 'leg' of the circuit allowing electricity to flow through you to actual-Ground. My laptop is PLASTIC but my earphones are metallic-plastic and will not-so-nicely annoy my ears when I press my bare feet to the tile floor.

Luckily it's only a small amount of electricity.

The cure is to make sure the device 'Ground' and actual-Ground are tied together so there is no differential of potential.

This is why it's nice having a actual working grounded socket and a laptop power-brick that supports the third-wire Ground so then the Laptop and 'floor' will be tied together and be at the same voltage level (no real voltage flow between the laptop, you, and the floor).

[sandyf]

I wondered if it may be down to the power supply. I don't know if they use isolating or auto transformers in these units. It was the original power unit and the problem did not appear until the laptop was several years old. I still have it and it still works but it must be over ten years old now. The laptop was assembled in Germany but the power unit is from China and I wonder now if the insulation inside the power unit has broken down through overheating. It is a bit warmer over here than in Europe.

Thanks for the suggestions.

[Tywais]

I wondered if it may be down to the power supply. I don't know if they use isolating or auto transformers in these units.

Most of these are SMPS (switch mode power supplies) rather than conventional transformer based. However, SMPS do have a transformer, often in the form of a toroid wound with primary and secondary windings, and age could cause leakage through it as the insulation and associated chemical drys and breaks down.

[bankruatsteve]

If you have a 10 year old laptop that still functions for what you want to do, use it with clothes on and you won't have any issues.