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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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18th Oct 2021, 12:38 pm | #1 |
Pentode
Join Date: Mar 2008
Location: London, UK.
Posts: 122
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Paper capacitors substitution
What type of capacitors can be used to substitude paper capacitors?
I have a choice of disc ceramic, metallised polyester and axial polypropylene film. Thanks |
18th Oct 2021, 1:06 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,081
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Re: Paper capacitors substitution
Metallised polyester in most cases.
Disc ceramics for low capacitance or high voltage, though watch the tolerance and temperature coefficient, there's all sorts of ceramic! Polypropylene is better than polyester (lower losses) but the capacitors are larger. |
18th Oct 2021, 1:15 pm | #3 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,942
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Re: Paper capacitors substitution
It doesn't really matter in most cases. The important things are the value and voltage rating.
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18th Oct 2021, 2:31 pm | #4 | |
Guest
Posts: n/a
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Re: Paper capacitors substitution
Quote:
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20th Oct 2021, 7:09 pm | #5 | |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,199
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Re: Paper capacitors substitution
Quote:
- For general purpose (couping and decoupling) up to 630V polyester is a good and affordable substitute. - For pulse applications (anything near an inductive component really) and voltage ratings >630V, polypropylene is the dielectricum of choice. - For pulse applications, isolation, decoupling with higher voltage ratings and/or smaller values, ceramics might be used. - If the paper capacitor is across the mains, use an X rated capacitor of any type (polypropylene preferred), if the paper capacitor is between mains and ground or external parts or inputs, use a Y rated capacitor of any type (polypropylene or ceramic preferred). The reasoning behind this, is that polyester has more dielectric losses and tolerates a lower dV/dt than the original paper caps so it cannot be used in all cases while polypropylene is superior to both paper and polyester, but harder to metallise so a relatively new technology and in case of non-metallised foil is larger so might be harder to fit. Philips/Mullard knew this when they introduced the polyester foil (mustard) caps, and still made paper caps and mixed dielectric caps for pulse- and across the mains applications. Only by the 1980's, polypropylene technology was sufficiently advanced to replace all paper applications in consumer electronics. |
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