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 Posted: Aug 07, 2009 - 07:47 PM |
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Joined: Apr 25, 2006
Posts: 2304
Location: Germany
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Posted: Aug 07, 2009 - 08:33 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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IIRC Class Y caps are guaranteed/required not to fail into a dead short.
Isn't the capacitor required to shunt HF noise to somewhere? One PCB designed had an isolated area with DC/DC converters and optocouplers. I used one single capacitor between the grounds and that reduced noise on the isolated side enormously. |
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Posted: Aug 07, 2009 - 09:45 PM |
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Joined: Nov 01, 2005
Posts: 6357
Location: Hilversum - the Netherlands
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Quote:
I used one single capacitor between the grounds and that reduced noise on the isolated side enormously.
Aha, I snap it (Dutch joke)
Without that Ycap, the capacitive coupling between primary and secundary winding, at the high frequency as used in SMPS's, is large enough to make the secondary circuit to jump up and down at the switching frequency, resulting in noise.
Hmmm, pretty odd sentence, but the intention is good.
Tomorrow I will give it a try ... live !
Thanks Jeroen.
Ossi, very interesting piece of documentation. I will keep it with other treasures. It explains very well and clear the construction for SMPS's with a SafetyGround connection. And from there it's a small step to SMPS's without a SG connection.
In the live test I will use a radio to get an impression of the effect.
You guys rock 
Nard |
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Posted: Aug 07, 2009 - 09:50 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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| Google for 'stitching cap'. |
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Posted: Aug 08, 2009 - 03:22 AM |
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Joined: Jun 18, 2001
Posts: 1085
Location: Brisbane Queensland Australia
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Posted: Aug 08, 2009 - 03:44 AM |
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Joined: Sep 07, 2004
Posts: 2564
Location: New York State
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Posted: Aug 08, 2009 - 02:24 PM |
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Joined: Nov 01, 2005
Posts: 6357
Location: Hilversum - the Netherlands
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I did the radio-test on one of the SMPS's: There is an audible difference with the Y-cap in versus open. I have no equipment to quantify the difference ... 
Video: http://www.aplomb.nl/SMPS_leakage/Doc_ie.html , in the top of the page is the .mpg
Edit: added a second video with effect visible on oscilloscope |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
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Posted: Aug 10, 2009 - 02:47 PM |
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Joined: Jun 17, 2002
Posts: 300
Location: Melbourne, Australia
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Greetings Nard, and A/all
Nard wrote:
Quote:
What is the purpose of that Y-class capacitor ? EMI regulations have been mentioned, but what is the explanation .... what does it do ?
And what are the risks of removing it ?
This link is most informative:
http://www.powerint.com/sites/default/files/product-docs/an15.pdf
Nard, Thanks to you and others for putting in the time and effort on this subject, and for publishing your results. It has been enlightening to many AVRfreaks, created good discussion and has opened up the benifits and pitfalls of using SMPS plug packs for our AVR projects.
One thing I have to ask is why not make 3 pin SMPS plugpacks? i.e. ones with a ground to return the HF noise to?
Surely a third pin on a plug would be a better solution for both EMC and Safety?
Ron. |
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Posted: Aug 10, 2009 - 04:25 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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Because not every socket in the world has an safety earth so it would be completely impractical  And as most, if not all, chargers are completely plastic and are double insulated they are class B and don't require a safety earth.
edit:
In NL since 2003 or so are new home electrical installations required to provide safety earth on every socket; before 2003 it was only required in the kitchen and bathrooms. Old installations don't need to be upgraded, so in most homes you only find sockets with safety earth in the kitchen and bathroom, the latter usually not there either. Washing machines in the bathroom need a hard wired connection. |
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Posted: Aug 10, 2009 - 05:28 PM |
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Joined: Sep 07, 2004
Posts: 2564
Location: New York State
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That's a good point. I guess the ubiquitous cheap switching power supplies will have two pins for a long time.
But there might be a market for three pin supplies also. Computer power supplies around here use a 3 pin power cord, and in fact have a switching supply.
One problem with 3 conductor cords is they are thick, stiff and clumsy. It hasn't helped the situation that in the U.S., apparently many power cords must have thicker wires than in previous times. I've given up trying to find an extension cord using 18 gauge wire. They are all 16 gauge. |
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Posted: Aug 10, 2009 - 08:45 PM |
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Joined: Nov 01, 2005
Posts: 6357
Location: Hilversum - the Netherlands
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Posted: Aug 11, 2009 - 02:24 AM |
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Joined: Dec 11, 2007
Posts: 6982
Location: Cleveland, OH
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Nard,
Thanks for the testing, results, documentation, and work put forth!
Thanks to several for the explaination and links on Y caps!
I am certainly much more knowlegable about the subject now, but I'm not sure I like what I found out! 
JC |
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Posted: Aug 11, 2009 - 01:47 PM |
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Joined: Jun 17, 2002
Posts: 300
Location: Melbourne, Australia
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jayjay1974wrote:
Quote:
In NL since 2003 or so are new home electrical installations required to provide safety earth on every socket; before 2003 it was only required in the kitchen and bathrooms. Old installations don't need to be upgraded, so in most homes you only find sockets with safety earth in the kitchen and bathroom, the latter usually not there either.
When I was 12 and in Blerick/Venlo Holand, 1969, I seem to recall many large round plugs that had an earth conection.
Perhaps my memory has faded over the last 40 Yrs.
Ron. |
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Posted: Aug 11, 2009 - 01:54 PM |
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Joined: Jun 17, 2002
Posts: 300
Location: Melbourne, Australia
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Quote:
Ron, there is hope...This was a usefull exercise and a pleasant thread.
Many thanks Nard.
At this point in time it has pointed out the basic limiting parameters of un earthed SMPS based Plug Packs/Wall Warts.
Kind Regards,
Ron. |
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Posted: Aug 12, 2009 - 12:49 PM |
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Joined: Nov 01, 2005
Posts: 6357
Location: Hilversum - the Netherlands
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Posted: Aug 12, 2009 - 01:50 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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Nice that the PS comes with a earthed plug, probably a Shuko, but in NL that does not guarantee any connection to safety earth because it still fits a non-earthed socket a well-known problem with Dutch sockets.
So I guess 99% of all PCs in NL are not earthed at all  |
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Posted: Aug 12, 2009 - 02:16 PM |
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Joined: Nov 01, 2005
Posts: 6357
Location: Hilversum - the Netherlands
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Quote:
probably a Shuko
?? I call it a "schuif-AMPje"
True. It's a shame that a plug with SG can be inserted into a 2 pin nonSG wall-socket. So the NEN1010-change of 2003 improves the situation.
My house is older than I am
Therefor I added some sockets with SG to the livingroom, shack, previous shack and attick.
PC's are grounded here All of them.
Quote:
So I guess 99% of all PCs in NL are not earthed at all
I hope it's not that bad, Jeroen. But you're close I think.
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
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Posted: Aug 12, 2009 - 02:18 PM |
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Joined: Apr 25, 2006
Posts: 2304
Location: Germany
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At my workplace every device with the 3-wire mains
connector is checked every 3 years or so, that the
connection between the PE-pin (Protective earth) and
every metallic part that may be touched is low ohmic.
That costs a lot of money, but its required by law. |
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Posted: Aug 12, 2009 - 02:20 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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| You call these schuif-ampje? |
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Posted: Aug 12, 2009 - 02:25 PM |
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Joined: Sep 07, 2004
Posts: 2564
Location: New York State
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jayjay1974 wrote:
So I guess 99% of all PCs in NL are not earthed at all
As long as you are not surfing the web while you have a finger in a hole in a dike, you should be okay. |
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