Small PSUs breaking all the time

[akis]

In the past year I have had 4-5 PSUs breaking/blowing/melting. The first was supposed to deliver 2.5 Amps at 5 VDC to power the wireless access point in the loft. I appreciate the loft is quite inhospitable, but the designer of the PSU should have included heat/cold in the parameters. That was a USRobotics5450. I made my own PSU, it is 3 times the size, not switched you see, but works cool.

Then we got another 3 or 4 PSUs blowing, the all-in-one-with-plug types. Sure they were plugged in all day, but why get so hot and why melt? The latest one made some loud cracking noises, which I thought was the cat, instead it was the PSU of my cable modem, been in service for more than 4-5 years and always on. The plastic outside has melted, no idea what the inside looks like.

In general, those PSUs all run quite hot, at 22-25 C ambient, excepting the one in the loft, and I cannot understand why they break after a few years (or months). These are PSUs that we leave plugged in permanently - they power the routers, the modems, the answer phones etc.

I am thinking this is serious fire hazard (since it managed to melt the plastic) and as they run hot and can blow at any time then you are never safe.

Any thoughts?

[star882]

They're undersized for the load.

[Frank Berry]

Most of these "Wall Warts" are not rated for continuous duty.
The transformers get too warm. The heat dries out the electrolytic and it eventually shorts ... taking the rectifiers and transformer with it.
They can be a fire hazard.
A good rule of thumb is never to draw more than 50% of the Wall Wart current rating.

[akis]

Manufacturers trying to cut down on costs... Nothing the consumer can do. It is appalling and should be authorities action on this.

Test: buy brand new device. Plug in for 1 hour. Touch PSU - if more than 40 C (in a 25 C ambient ) then there is an issue (it will be hotter inside).