Use of Class X2 Capacitors as Droppers.

[ukcol]

I had not been aware of the fact that Class X2 capacitors lose capacitance when they self heal after a mains spike. As a result of this (new to me) information I revisited a problem I had with a mains powered remote doorbell.

The receiver unit is powered via a Class X2 capacitor being used effectively as a dropper. The symptom was that the sound from the bell was extremely distorted, my Wife would say that it sounded as if it had a sore throat.

I had not measured the capacitance of the Class X2 because I had assumed X2s had similar modes of failure to all modern plastic capacitors. So, when I did measured its capacitance I found it was less than 10% of its original value and a replacement solved the problem.

It seems that an X2 is vunerable in this application because it is connected to the mains supply 24 hours per day, something that is not the case with a radio dropper capacitor.

Colin M

[Herald1360]

Sounds like a case for some judicious use of VDRs with a bit of series resistance.

[ukcol]

But the customer won't buy new doorbell then. (He said Cynically).

Colin M

[Herald1360]

Good theory there. A little bit of built in obsolescence. If it lasts a few years, the customer isn't too unhappy and it's easier to replace like with like than fit something else. It's only the likes of us who will bother to fix it!