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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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17th May 2022, 1:28 pm | #1 |
Dekatron
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X 1 Y2 Capacitor , Dual Purpose??
Have seen capacitors with X1 Y2 on the same cap, how can this be right when one fails open and the other is meant to fail short ?
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17th May 2022, 1:50 pm | #2 |
Hexode
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Re: X 1 Y2 Capacitor , Dual Purpose??
Have a look at this, should answer your question.
https://www.allaboutcircuits.com/tec...-y-capacitors/
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17th May 2022, 3:46 pm | #3 | |
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
" When a Class-X capacitor, also referred to as an "across the line capacitor"—the capacitor placed between line and neutral—fails because of an overvoltage event, it is likely to fail short. This failure, in turn, would cause an overcurrent protective device, like a fuse or circuit breaker, to open. Therefore, a capacitor failing in this fashion would not cause any electrical shock hazards. If a Class-Y capacitor, also known as the "line to ground capacitor" or "the line bypass capacitor"—the capacitor placed between line and ground—fails short, this could lead to a fatal electric shock due to the loss of the ground connection. Class-Y safety capacitors are designed to fail open. A failure will cause your electronic device to be subjected to the noise and interference that the capacitor would normally filter out, but at least there will be no fatal electric shock hazard. " |
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17th May 2022, 4:04 pm | #4 |
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Re: X 1 Y2 Capacitor , Dual Purpose??
I always thought that both X and Y caps were supposed to fail open. The specs are different in other respects of course.
The fact that lots of Xs fail short circuit wasn't a design objective, it's just that there are lots of lousy Xs out there! |
17th May 2022, 4:07 pm | #5 |
Dekatron
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Re: X 1 Y2 Capacitor , Dual Purpose??
My point was, there are caps being sold as rated at both (X 1 Y2). This is written on them. So I cannot see how one cap can be for two purposes. reading above Vishay do one that do both jobs, surely cannot be safe.
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17th May 2022, 4:12 pm | #6 |
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Re: X 1 Y2 Capacitor , Dual Purpose??
From the point of view of peak voltages the caps can withstand, the Y specs are more demanding than the X specs, so it's not a surprise that something Y2 rated is also X1 rated. There is still the issue of failing short or open by design. I found it quite surprising that I couldn't find clear information on this, even though most manufacturers show a typical application sketch with an X cap across the line and an Y cap between line and ground, and the used arguments do imply that Xs fail short and Ys fail open. I really have no clue.
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17th May 2022, 4:15 pm | #7 |
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Re: X 1 Y2 Capacitor , Dual Purpose??
I think you mean X2 Y1.
If I'm right that failing short circuit isn't part of the class X spec, then there's no reason why a manufacturer can't make a cap that exceeds both specs. Class X are normally much higher in capacity than class Y, so are physically bigger with a different construction, but the specs aren't contradictory. |
17th May 2022, 4:19 pm | #8 | |
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
https://www.powerelectronictips.com/...isolation-faq/ I agree that the voltage specs are not contradictory, but the failure mode is, and again this is mentioned in this page (X fails short; Y fails open). - helder |
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17th May 2022, 4:20 pm | #9 |
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Re: X 1 Y2 Capacitor , Dual Purpose??
You live and learn.
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17th May 2022, 4:22 pm | #10 |
Dekatron
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Re: X 1 Y2 Capacitor , Dual Purpose??
It is the failure mode that bothers me, in my case I better buy a Y only as it isolates ac on an Eddystone. It is on an EB35 I think the model and uses the mains as an aerial, I will check again before I change the wax cap that is in that position now.
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17th May 2022, 4:29 pm | #11 | |
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
What had me think about this was the fact that Panrock used a Y cap in the Bush TV22 restoration detailed in his excellent website. - Helder |
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17th May 2022, 4:39 pm | #12 |
Dekatron
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Re: X 1 Y2 Capacitor , Dual Purpose??
Hi Folks, Y caps are normally in values up to about 4n7 may and must not fail s/c . I don't think there is a mention in the srecs of them failing open
X caps can be had in values up to 2uF, and in failing short, the dielectric at the short melts, isolating the fault section of the cap. This reduces the total capacitance but allows the device to keep working in a reduced manner. Ed |
17th May 2022, 5:24 pm | #13 | |
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
I wrote 'more or less guaranteed', because sometimes even Y capacitors are known to fail short or leaky, especially paper capacitors. Somehow those are allowed to sport the Y marking. Last edited by Maarten; 17th May 2022 at 5:32 pm. |
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17th May 2022, 6:34 pm | #14 |
Hexode
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Re: X 1 Y2 Capacitor , Dual Purpose??
Repairing brown goods, (VCR, TV, HI FI etc) for longer than I care to remember, I have always found a Class X to fail short circuit, however, I cannot speak for Class Y but assumed they usually fail open circuit allowing SMPSU noise to return to the mains supply.
There were not many but Grundig VCRs spring to mind for more failures than most others. Maybe I had more Grundig devices brought to my bench than other makes ... who knows. When they do fail, a Class X capacitor mutates into a charcoal looking blob as during the "self healing" process, little bits blow and build up under the epoxy skin awaiting the 'Frosted eyebrow feature', as I called it, for the poor engineer who was looking at it, at the point of failure.
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17th May 2022, 7:44 pm | #15 |
Hexode
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Re: X 1 Y2 Capacitor , Dual Purpose??
Ok, time for a bad joke. The X-Y is a quantum capacitor. If fails both open and short. It's only when you look at it that its state collapses into one or another.
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17th May 2022, 10:26 pm | #16 |
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Re: X 1 Y2 Capacitor , Dual Purpose??
I think the smoke and sizzling noises are a bit of a giveaway.
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18th May 2022, 2:21 am | #17 | |
Dekatron
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
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18th May 2022, 7:49 am | #18 |
Dekatron
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Re: X 1 Y2 Capacitor , Dual Purpose??
Y class are built in a way that makes them kind of like two capacitors in series. This is how the "fails open" works but what I do not like is that with checking for a rise in value you won't know it has "gone".
X class are just robust enough to live a life on the mains So no reason that a Y built cap could not also meet the X spec. They both have an element of self repair. |
18th May 2022, 9:38 pm | #19 |
Heptode
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Re: X 1 Y2 Capacitor , Dual Purpose??
I would assume that most desktop computers use X-Y configuration on their power supplies. This is because alternative earth leakage protection (other than RCD) has to be considered when multiple computers are plugged into the same electrical sub circuit.
It would be interesting to know how much earth leakage current one computer spec. capacitor will create when connected across a mains supply. Then again if both elements of the Y component are also connected across the phase & neutral I would expect that to null out any current via the earth connection (unless of course the two Y caps elements are not identical value i.e. inbalance) ? Rog |
19th May 2022, 10:02 am | #20 | |
Hexode
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Re: X 1 Y2 Capacitor , Dual Purpose??
Quote:
If I recall correctly total earth leakage current <=9mA is recommended for domestic circuits for each 30mA RCD. On an (outdated) split load board, this may mean swapping circuits between RCDs to prevent unwanted tripping. Nowadays with modern electronics the earth leakage currents will soon add up.
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Eddie BVWS Member. Friend of the BVWTM Last edited by Station X; 19th May 2022 at 10:32 am. Reason: Quote attributed. |
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