Wich Suppression Capacitor to block Mains emi? - diyAudio
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Old 29th January 2009, 03:39 PM   #1
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Default Wich Suppression Capacitor to block Mains emi?

Hi guys, i want to know if need to have some special care when choice an capacitor to use between AC Mains to Block some EMI.

i want to know if need to have some special care about brands or sizes, for example any small value will be OK?

Material? Polyester? Polypropilene?

Value?

0.1uf
0.068uf
0.047uf
0.022uf
0.015uf
0.01uf
0,0068uf
0,0047uf
0,0022uf
0,0001uf

Any will works?
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Old 29th January 2009, 03:48 PM   #2
00940 is online now 00940  Belgium
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You cannot use any capacitors on the mains, read this first:

http://www.evox-rifa.com/technote_pdf/rfi_fact.pdf
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Old 10th November 2010, 04:31 PM   #3
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Sorry for the long delay....

I understand, i need to use it after the transformer

im using this design

Click the image to open in full size.

What about values?

0.1uf
0.068uf
0.047uf
0.022uf
0.015uf
0.01uf
0,0068uf
0,0047uf
0,0022uf
0,0001uf
Any will works?

Wich is the best material of these caps?

Im talking abt C3 C4 and C5. These schematic say 100nf, but maybe other value will be better (or cheaper).

Thanks in advance,
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Old 10th November 2010, 04:47 PM   #4
Atilla is offline Atilla  Norway
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If you want to block EMI, get an EMI filter, or a socket with integrated filter. Tthat's the easiest way and they're not expensive. Or salvage one from an old PC power-supply, they often come as a separate small board.

Generally, it's 1 X-rated cap between Live and Neutral, 2 Y-rated caps between Live-Ground and Neutral-Ground (sometimes those aren't used, like in the case of double-insulated equipment) and a Common-mode choke.

Something like this is your safest bet, especially because it comes encased in a metal, grounded enclosure:

Click the image to open in full size.

A simple cap after the trafo won't do you way too much good in that regard.
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Old 10th November 2010, 05:10 PM   #5
jtwrace is offline jtwrace  United States
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or build one of these:


Common Diff. DCR Volt. Amp.
Mode L Mode L
P3717-AL 25.0 1000 0.30 1500 3
Q4007-AL 4.5 150 0.06 1500 5
Q4018-AL 1.5 35 0.02 1500 10" Logged

Coilcraft - RF chip inductor, power inductor, power magnetics, and other inductors

I'm getting read to build mine. I have the PCB already. Just waiting on some parts.

BC1587-NDCAP FILM MKP .01UF 440VAC X1 20%

220BC1588-NDCAP FILM MKP .1UF 440VAC X1 20%

320BC1589-NDCAP FILM MKP 1UF 440VAC X1 20%

Thread I learned it from is here: Felix project
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File Type: jpg felixschematic.jpg (21.8 KB, 244 views)
File Type: jpg felixpcb.jpg (22.4 KB, 230 views)
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Old 10th November 2010, 05:17 PM   #6
jtwrace is offline jtwrace  United States
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Thought I would add this Vishay Cap PDF as too.
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Old 10th November 2010, 06:16 PM   #7
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Quote:
Originally Posted by samsagaz View Post
Sorry for the long delay....

I understand, i need to use it after the transformer

im using this design

TNT design pic

What about values?

Wich is the best material of these caps?

Im talking abt C3 C4 and C5. These schematic say 100nf, but maybe other value will be better (or cheaper).

Thanks in advance,
You may as well use what they show, as the only way you will improve is to use proper EMI measuring equipment.
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Old 10th November 2010, 06:25 PM   #8
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Quote:
Originally Posted by 00940 View Post
You cannot use any capacitors on the mains, read this first:

http://www.evox-rifa.com/technote_pdf/rfi_fact.pdf
404 error.

Ehh? X2 caps are specifically rated for across-the-line duty. You sure as heck can put caps across the mains.

Value depends on frequency and current being filtered. This only matters for SMPS supplies, to prevent conducted noise into the mains. Noise going from line to load is negligible because it's well filtered by design. In your case, the transformer and filter capacitors take out any RFI you could ever worry about.

Tim
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Old 10th November 2010, 06:58 PM   #9
WuYit is offline WuYit  Sweden
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Hi,
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Old 10th November 2010, 07:02 PM   #10
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wich will be the diference between Felix project and the one that WyYit Post it?

using components in the mains or just in the secundary, or in both places!

Last edited by samsagaz; 10th November 2010 at 07:04 PM.
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