Correct capacitor size for short-circuiting high(er) frequencies - Page 1
Forum section: electronics / beginners

author: gcl
author_rank: Newbie
timestamp: June 18, 2023, 09:02:03 am
content: Hello!a ham operator recommended lowering inhouse high frequency disturbances on the power lines by wiring a capacitor 50-100 nF/1000 V between live conductor and protective earth and the same between neutral and protective earth, and to plug a schuko (european plug) wired like that in several sockets in the house. He wrote he could lower interfering signals significantly, short-circuiting high frequency signals.Several dealers offer 100 nF and 1000VDC (400 VAC). I could not find a 1000VAC capacitor. So i am wondering if in fact a 1000VDC could be meant.I asked the ham operator by mail, but so far no answer.What do you mean? Yes, i am real newbie...Thank you!

author: Siwastaja
author_rank: Super Contributor
timestamp: June 18, 2023, 09:06:48 am
content: What you are attempting to do is extremely dangerous with the skill level you have, as evident from the fact you are seriously looking dangerously wrong types of capacitors.There is no need to do anything.

author: Zero999
author_rank: Super Contributor
timestamp: June 18, 2023, 09:14:16 am
content: A capacitor has an impedance equal to the following formula:Z = 1/(2π*FC)Where:Z = impedanceF = FrequencyC = CapacitanceThe idea is the capacitor has a very low impedance to high frequencies and a high impedance to low frequencies, so RF is shunted to earth, but not low mains frequencies.Don't bother trying to build it. Ready made RF filters can be purchased for this. They include inductors as well has capacitors and resistors.

author: srb1954
author_rank: Super Contributor
timestamp: June 18, 2023, 09:18:03 am
content: Several capacitors of this size between the live conductor and protective earth would immediately trip a GFCI breaker.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 18, 2023, 10:35:06 am
content: Here is a typical RF power line filter. The values of the capacitance are marked.These are used on all sorts of equipment.

author: tggzzz
author_rank: Super Contributor
timestamp: June 18, 2023, 11:03:38 am
content: Quote from: gcl on June 18, 2023, 09:02:03 amDo not attempt to do this. It would be dangerous.Do use a proper mains filter; they are safe and easy to use.If you really want to do this yourself:make sure you understand the reasons X and Y class capacitors existmake sure you understand how they are correctly used in mains filtersget the ham to tell you why you have a problemmake sure you do have the problem the ham definedmake sure you don't have a simllar problem with a different causeget the ham to define the relevant frequenciesget the ham to tell you why his "design" will solve the problemThen go and buy a proper mains filter

author: gcl
author_rank: Newbie
timestamp: June 19, 2023, 11:12:31 am
content: Thank you, and all of the other people who answered!Ok - i will not try the "solution" i described. Probably i get a line filter as in your picture. There are several ones i found ready to use, cause already built in a case with sockets. Price 60-90 EUR with different filter characteristics.Kind regards - gcl

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 21, 2023, 12:18:38 am
content: The one in the picture is from e bay and a lot less than 60 euros..You can also pick them up at flea markets like Hamfests for maybe a few bucks. Buy a few and use them on whatever you build.