Why number 5?

       

Nowadays it is always advisable to operate electronic devices with some sort of unit which provides isolation from the mains. A multiple flexible socket equipped with a switch will do. Special devices with lovely sounding names like »power manager« are smarter solutions and offer the opportunity to switch connected appliances jointly or individually. The reason for the need of such solutions is that most electronic devices, also computers and their peripherals, do no longer have a real power switch. When out of operation, they continue to use some power and are prone to damages caused by any surges and overvoltages arising from the mains. The on / off position of these external switches is usually indicated by a glow lamp. In one case, as in the picture, premature ageing of the glow lamp was observed. The question is why this happened.

The operating modes are a follows:

Switch No. 1 switches the keyboard lighting (incandescent lamps 23 V with conventional transformer).

Switch No. 2 switches the switch-mode power supply for a notebook PC (without active electronic power factor correction – PFC).

Switch No. 3 is empty and switched on only for illustrative purposes here.

Switch No. 4 switches the printer (is rarely ever switched, just a few hours of operation).

Switch No. 5 switches the PC and the adjacent flat screen (modern PC power unit with PFC, screen with usual SMPS without PFC).

Switch No. 6 switches a WLAN router (with conventional transformer – can be seen on the right behind the foot of the screen).

Now in total the router connected to switch No. 6 is operated a lot longer than the PC because it also has to serve another 3 notebook PCs in the home. Yet, the lamp in switch No. 5 has already aged a lot more than the one in switch No. 6. The question is whether this has anything to do with the HF disturbances arising from the active front end in the PFC unit, so that it has hardly any more luminous output at all after only 2000 to 3000 hours of operation.