Alan B. Pearce wrote:
>
> >Why is this? The test procedure indicates kilovolts. This is more likely
> >due to high-voltage spikes on the line rather than the triac switching.
>
> >If this is expected, as I said, the proper solution would seem to be a
> >varistor to limit the voltage excursions rather than try to find a
> >capacitor which could survive them.
>
> I am not familiar with type X capacitors as I have not had to get involved with
> this sort of network for a long time, but the capacitor type can be important as
> the dV/dt rating can be important, even with the resistor in circuit. This is
> affected by the type of dielectric used in the capacitor.
>
> An example of this was about 25 years ago I was involved in developing a
> capacitor discharge ignition system along with some work colleagues. We punched
> through several of the Philips "lollipop" polycarbonate capacitors because the
> losses in the capacitor generated hot spots that caused the capacitor to short
> through. we replaced these with a capacitor designed for TV Line Output stages
> that had an infinite dV/dt rating and had no more failures.

I have buckets of HV polyester caps from TVs.
They are cool. I also like the 2kv and 6kv blue
coated ceramics, these are just about indestructable.
Anytime I need a bulletproof cap under 2nF I go for
one of those. They are about $1 each but you get
a few in every TV, and it's good for the apprentices
to strip dead TVs!! Good soldering and finger burning
practice.:o)
-Roman

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