Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

What is the DC voltage rating of this Y2 capacitor?

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
14,712
Helped
4,808
Reputation
9,633
Reaction score
4,590
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
125,319
If it says 250V RMS I think its safe to say it is at least the peak of that ~360V but that component is intended to be used in an AC circuit.

Brian.
 
  • Like
Reactions: treez

    treez

    points: 2
    Helpful Answer Positive Rating

c_mitra

Advanced Member level 5
Joined
Nov 13, 2012
Messages
3,548
Helped
885
Reputation
1,772
Reaction score
854
Trophy points
1,393
Activity points
27,600
....datasheet doesnt say.
Many of the exotic dielectrics do not provide a DC rating; they are expected to be used only in an AC circuit.

However, you can take the RMS value to be the equivalent DC voltage.

But if the device is going to see a const DC for extended period, please derate the RMS (equivalent DC) by 20-40% and use judiciously.

I do not have any idea about the exact nature of the dielectric but they are often titanates ot niobates or mixtures and they are often ferroelectric or piezoelectric and most often belong spinel class (crystals). The dielectric experiences high stress under const DC voltage and may crack.

Good engineers derate all specs generously.
 

    treez

    points: 2
    Helpful Answer Positive Rating

JohnBG

Junior Member level 3
Joined
Feb 23, 2021
Messages
27
Helped
3
Reputation
6
Reaction score
2
Trophy points
3
Activity points
238
Y capacitors adhere to EN 60384-14

[/URL]

As VICOR white paper explains

.

Y caps subcategories have to do with voltage ranges.

It seems you are either
1. trying to use Y capacitors ‘out of specs’ hence the ‘poor’ performance you mention in your question,
2. or your design has something that causes the system to perform poorly, and you have apparently traced the cause to the type of capacitor you initially chose.

So either you choose better capacitors or you change your design.

Attempting to find an extensive table that relates the dielectric used in the unspecified Y1 Y2 capacitors you choose seems as if you would like capacitor manufacturers to reveal details that most likely they’d tag as ‘proprietary’, usually the best one can get is a telegraphy note like ‘metalized paper’, example PZB300 specs



So why don’t you try replacing the unknown choice of capacitors?

Also, the term ‘poor’ requires elaboration, because it may be that the low performance does not really originate from such components, or that the system is subject to excessive humidity, vibration, dust, unfiltered input, poor grounding, temperature out oc specs ..
 

c_mitra

Advanced Member level 5
Joined
Nov 13, 2012
Messages
3,548
Helped
885
Reputation
1,772
Reaction score
854
Trophy points
1,393
Activity points
27,600
As VICOR white paper explains...
The document is confusing at best. Some samples:

a. It says "If this is allowed to flow back on to the mains supply line, it can disturb other equipment also connected to the same line." Also soon after, it says "The reliability of these capacitors is critical to the safety of the equipment’s users." But soon after they say "Y-capacitors are designed to filter out common-mode noise, and are connected between line and chassis; if they short-circuit, they create a risk of shock to the user." I am confused. In a SMPS, the Y cap is not connected to the chassis.

b. They say "Capacitance values are also limited to reduce the current passing through the capacitor when AC voltage is applied, and reduce the energy stored to a safe limit when DC voltage is applied." I find that strange.

In my opinion, the correct answer is given in https://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do

"Switched mode power supplies use what is known as a "flyback converter" to provide voltage conversion and galvanic isolation. A core component of this converter is a high frequency transformer.

Practical transformers have some stray capacitance between primary and secondary windings. This capacitance interacts with the switching operation of the converter. If there is no other connection between input and output this will result in a high frequency voltage between the output and input.

This is really bad from an EMC perspective. The cables from the power brick are now essentially acting as an antenna transmitting the high frequency generated by the switching process."
 

JohnBG

Junior Member level 3
Joined
Feb 23, 2021
Messages
27
Helped
3
Reputation
6
Reaction score
2
Trophy points
3
Activity points
238
Hi this is JohnBG2021. I’d like to refine my answer to this question with the following lines:

1. I agree with c_mitra , Vicor’s note I mentioned earlier on apparently shows capacitors XY safety rating, but only includes some figures for Y type, and is an application note more focussed on how to use Vicor products than to explain XY Cap ratings.

2. Found


with more detail and accuracy about XY Cap safety ratings.

3. The so called XY safety ratings standard is just a half-way job because Voltages alone do not overheat or burn things: It’s a combination of enough Voltage and enough current, Amperes burn things.

4. In the muRata Cap specs attached to question one observes that all graphs in page 2 include a clear DC0V.

But neither manufacturers nor IEC related standard supply DC tests, with currents, just a few orienting vague AC Voltages out of barely specified tests, and there’s a good reason: The manufacturer doesn’t know the currents you plan to use through this capacitor, after all it’s your design, it’s your job to know whether currents flowing through your circuit are ok or not.

5. The capacitor you have inquired about is a cheap 2.2nF +-20% rated by manufactured with 250Vac(rms) meaning

this 250V is the recommended top Vdc you asked for provided you limit AC current that may flow through this capacitor, down to safe levels, safe for the capacitor to not overheat and end up with through hole.

6. Just in case

working with single phase then Vac(peak)/sqrt(2)=Vac(rms) supplied
working with 3 phase then Vac(peak)/sqrt(3)=Vac(rms) supplied

7. I found the Vac(rms) in muRata specs confusing so I looked for same cap type value in Radio Spares and it turns out that Vishay has quite the same capacitor, but clearly stating 250Vac only, have a look:


8. muRata specs included in question shouldn’t mix AC and RMS.
V values, in this context, are either
AC amplitudes, or
DC flat really 0Hz, or
rms: equivalent DC to an AC signal would carry same power.

9. Vishay specs for equivalent cap,


again, as abridged as specs can be for mass production cheap components, but at least including:

9.1. Leakage currents graph: all caps have a parallel resistance, for
2.2nF and 500Vac I_leak expected below approx. 300uA.
9.2. Duration and DC voltage of endurance test carried out.
Tested sample :
9.2.1. Survived, held 2 seconds on 2.5kVac
9.2.2. Destroyed (stopped functioning as cap) after 60s on 1.5kVac
9.2.3. Destroyed (cap kaput and coating melted) after 60s on 2kVac

Note that in equivalent Vishay cap specs you chose, there’s no ‘Vac(rms)’ that as I said is at best confusing.

Hope it helps

JohnBG2021
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,960
Helped
14,147
Reputation
28,553
Reaction score
12,833
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,233
Regarding 9.2.2 and 9.2.3. Destructive test does not mean that the DUT is allowed to fail under the given test conditions. It means that the test can be only performed once because DUT is expected to deteriorate. Thus the test is only feasible for type but not routine (production) testing.
--- Updated ---

Regarding the original question, X and Y capacitors have no DC rating as such. Manufaturers often (but not necessarily) give an additional DC rating, usually with the amendment that DC voltage operation is beyond the IEC 60384 qualification.
 
Last edited:

JohnBG

Junior Member level 3
Joined
Feb 23, 2021
Messages
27
Helped
3
Reputation
6
Reaction score
2
Trophy points
3
Activity points
238
thanks FvM for pointing out these 2 corrections. If my question I'd buy samples from different manufacturers and test. Experimental results are more reliable than any assurance on paper that a certain component can do this or can go that far.
 

c_mitra

Advanced Member level 5
Joined
Nov 13, 2012
Messages
3,548
Helped
885
Reputation
1,772
Reaction score
854
Trophy points
1,393
Activity points
27,600
If my question I'd buy samples from different manufacturers and test.
I don't recommend such a test.

If my understanding is any good, the manufacturer selects by random sampling a reasonable number of devices for testing. It is not desirable nor feasible to test all the components in any given batch. The devices that are being tested are not returned to the batch (some might have experienced excessive stress). These tests are statistically sound although they do not present confidence limits.

One comment on leakage current:

Leakage currents graph: all caps have a parallel resistance, for
2.2nF and 500Vac I_leak expected below approx. 300uA.
I presume what is called leakage current is actually the reactive current; else we should see a linear part in the curve.

The reactive current does not increase with voltage: it saturates. That is because the capacitance value decreases with applied voltage.

I cannot use the impedance vs freq graph because it is incomplete; you need to see both mag(Z) and phase(Z) but I do not know what is being presented.

Perhaps someone may enlighten me.
--- Updated ---

The so called XY safety ratings standard is just a half-way job because Voltages alone do not overheat or burn things: It’s a combination of enough Voltage and enough current, Amperes burn things.
It is entirely possible that a high voltage (very little current) can crack the dielectric and can cause the capacitor to fail; the capacitor can fail without being overheated or any symptom of burning. A crack can severely reduce the effective voltage rating of the capacitor. In fact, most of the exotic dielectrics used in these capacitors experience considerable stress while under a DC voltage.
 
Last edited:

JohnBG

Junior Member level 3
Joined
Feb 23, 2021
Messages
27
Helped
3
Reputation
6
Reaction score
2
Trophy points
3
Activity points
238
Hi c_mitra, when I mentioned that I'd test it, I implied: if time, money, space, if at work only when line manager requested so.

I agree that these 'endurance tests' should be the exception rather that the rule, even in product design/development. After all the manufacturer has already carried out such tests, wide enough sample assumed, and on purchasing certified products, complying manufacturers legally declare their production deviation (sigma) is thin enough for most of the items to meet compliance.

I recomend treez to take the muRata specs 250Vac(rms) as actually 250Vac, therefore the single phase equivalent DC value that treez asks for (reasonably safe, for 'low' AC currents, device at reasonable temperature and acceptable cooling) being 250/sqrt(2).

The value of the capacitor itself, in [Farad], for 230Vac, if part of the power supply, I'd recommend to either replace the 2200pF for a cap values in the order of micro, or treez could use both in parallel, if space on the PCB board, or leave enough space on the PCB board to replace the 2200pF with a potentially slightly larger in [Farad] and size capacitor.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,960
Helped
14,147
Reputation
28,553
Reaction score
12,833
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,233
Treez managed to kick of this discussion without ever mentioning the capacitor application. It's almost useless to procede without knowing the actual AC and DC rating requirements. Is it misusing an AC capacitor for pure DC (shouldn't be much of a problem) or is it AC capacitor, possibly in X or Y function, with superimposed DC?
 

JohnBG

Junior Member level 3
Joined
Feb 23, 2021
Messages
27
Helped
3
Reputation
6
Reaction score
2
Trophy points
3
Activity points
238
that would be good to know .. along with a circuit diagram
 

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top