Four-wire capacitors

[Morgan Jones]

As some of you know, I favour four-wire polypropylene capacitors for HT supplies because the four-wire connection moves lead inductance to a position where it doesn't degrade high frequency filtering. Plus, any plastic capacitor has much lower ESR than an electrolytic capacitor. The combination of low ESR and four-wire connection means that you get better high frequency filtering. But having them made was expensive (not as expensive as you might think, but not cheap).

However...

You can now buy 14uF 900V four-wire polypropylene capacitors as standard parts from Farnell: # 376-0199 £7.41 + VAT one off. They are intended for PCB mounting, and because they're quite big and heavy, the manufacturer fitted two wires at each end to make the mounting mechanically strong. I sacrificed one to science on the mill and it's a genuine four-wire connection with both wires going directly to the sprayed metallisation that connects to the (metallised) polypropylene. What more could you want? Specified ESR is 6mΩ and inductance is 10nH.

Polypropylene is a far less lossy dielectric than polyethylene terephthalate, and it is self-healing whereas polyethylene terephthalate fails short circuit (and creates an awful stink). Also, I can pronounce polypropylene without having to take a run-up at it.

[Paul Barker]

Thanks and lol to last comment

I like sound of polyprops.