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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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Old 18th Oct 2021, 11:38 am   #1
murphy512
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Default 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
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Old 18th Oct 2021, 12:06 pm   #2
kalee20
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Default 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.
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Old 18th Oct 2021, 12:15 pm   #3
paulsherwin
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Default 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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Old 18th Oct 2021, 1:31 pm   #4
merlinmaxwell
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Default Re: Paper capacitors substitution

Quote:
Polypropylene is better than polyester (lower losses) but the capacitors are larger.
And much better than the old wax paper types.
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Old 20th Oct 2021, 6:09 pm   #5
Maarten
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Default Re: Paper capacitors substitution

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Originally Posted by murphy512 View Post
What type of capacitors can be used to substitude paper capacitors?
I have a choice of disc ceramic, metallised polyester and axial polypropylene film.
It really depends on the application.

- 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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