Unfused 13A "wall-warts"

We have a number of chargers for mobile phones and ipods in our house, they are all of the type that have the electronics incorporated in the plug. They are all sealed, and none of them have a fuse, at least not one that can be changed. Are these allowed? I thought that all devices that plug into a 13 Amp socket had to have a readily accessible and replacable fuse?

They will probably be fused internally. They are designed that if anything goes wrong, they are not reapirable, and should be thrown away.

They need in the design some safety system often this is a spring soldered and over temperature will cause it to disconnect plus many other methods but the thickness of the cable will often be smaller than a 1A fuse so it will fail safe. Often there is some automatic method to restrict the output and if this fails then replacement will be required so although a fusible link may be included in the design there are no user serviceable parts so no point in a user changeable fuse.

Mobile phone chargers are often switch mode and these are not repairable at a price less than replacement so no option given.

Thanks for the replies.

It was the safety aspect I was concerned about. My teenage kids have a habit of yanking the cables of these and on a couple of the chargers the cable support has fractured where it enters the charger, exposing the inner insulation of the wires. I was concerned that if the inner insulation broke or wore, and the wires touched, that if there was no fuse then the unit may overheat. I guess the output stage may be current limited anyway, but you have put my mind at rest, thanks.

Of course, I replace them if I notice they are like this, but they could go unnoticed as the chargers lurk in the darker recesses of the kids bedrooms and I tend not to venture in there too often!!

How long will it be before we have to PAT everything in order to get houshold insurance?

have you seen the price of phone chargers?

As everyone said, they have several safety features built in. Dont forget though, these aren't transformers, they are SMPSs, their electronic equivalent. All thats in there is a voltage stepping circuit. No windings or anything (unless i weighs a bit, then it probably has an iron core and windings, but most stuff comes with SMPSs nowadays, as they run on any voltage and are cheaper).

Steve said:

...No windings or anything...

Click to expand...

They'll always have a transformer in them for isolation, as they are always flyback or tapped inductor types for consumer 'wall-warts'.

The transformer used can be much lighter though, since it's running at a much higher frequency. As frequency goes down, you need a larger transformer for the same amount of power. Even the difference between 50Hz power distribution in Europe and 60Hz in North America results in a significant size difference at higher powers.

The switched-mode power supply generates a much higher frequency (in the kilohertz range), which can then feed a small transformer to provide isolation to the final output.

Reputable brand "wall warts" will contain either an internal fuse or equivalent for protection, but there are some cheap imported units which are not properly protected.