x7r vs z5u capacitor for transformer in power supply? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: September 21, 2022, 05:23:40 am
content: I have a power supply with singing transformers. The original part is a Z5U 100nF disk 500V.I see the same thing is available in X7R.Naturally I would imagine X7R is better for signal reasons, but for a transformer decoupling cap, is there any reliability issue with X7R vs Z5U? To me X7R = higher temp, so its better. is there anything else about them that makes it for some reason desirable to put in a Z5U?I need the same form factor because its HP so they bend it right under the chassis, so it has to be a little disk. They use it on the secondary of a transformer that supplies the 35V rail.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 21, 2022, 06:02:05 pm
content: 35 VDC rail, so 27 VAC? You may try X7R there, but I would try film cap. 100 nF is not much capacitance, so film cap can be small (100-160 VDC rated).

author: wraper
author_rank: Unknown
timestamp: September 21, 2022, 06:32:42 pm
content: There is no reason to use Z5U other than cost, size and unless you want to make a capacitive temperature sensor.

author: ConKbot
author_rank: Super Contributor
timestamp: September 21, 2022, 07:03:58 pm
content: Z5U is so bad I've seen a video of a presentation where the Kemet rep was shitting on them in front of people. No reason to even consider them unless you're trying to shave every fraction of a cent and have determined that it being at some abysmal fraction of the rated capacitance at 25 percent of the rated voltage is ok. Then maybe consider.

author: coppercone2
author_rank: Super Contributor
timestamp: September 21, 2022, 10:00:31 pm
content: I just wondered if they maybe had higher robustness or surge handling or something like that.... the Z5U part is alot bigger then theX7R replacement I ordered. I know technology is moving forward, and prices of components decrease.. but I wanted to be informed (its not critical, just interest).When I try to research this, people mostly talk about temp stability, drift and capacitance/voltage effect... but I am not sure how much this has to do with toughness/survivability/overload. It's in a non-critical electrical spec location for the circuit.I would imagine the materials properties which I assume would be the key factors in this would be pretty consistent between ceramics, but I can't find any information.i.e. the comparison you might draw is a material like choosing resistors, you can imagine most of the time a wire wound resistor is way tougher then a thin film resistor that could be made to higher precision.So, is there any significant difference in the mechanical properties of the different ceramics/construction methods between the different ceramic families? Like if you had to choose between boron nitride and glass, maybe glass would be better for some things but the BN is wayyyyy tougher.But from what you are all saying in the topic, it seems that its splitting hairs, right? I know it sounds silly but you still can get pretty specific with parts like resistors.And that brings to another question, are ceramic parts with a higher temperature rating generally mechanically stronger then ones with a lower rating?... is there any relationship there? From what I understand I have a hunch that the more expensive part is better manufactured anyway (X7R), in terms of pressure control, temperature control, etc (I researched porcelain manufacturing on the forum a while back and there is something to be said about poorly made ceramics... where process might end up being more important then material in many cases).I know for sure that there at least was, and maybe is, a problem with certain ceramic SMD capacitor type reliability (usually in tiny form factor with poor mechanical design), but this is a leaded part so that can be brushed aside.I also see a roughly factor 50x price increase for the 200C rated ceramic capacitors for borehole applications.

author: wraper
author_rank: Unknown
timestamp: September 22, 2022, 10:20:36 am
content: Quote from: coppercone2 on September 21, 2022, 10:00:31 pmOriginal part likely is a single layer disc capacitor but replacement is MLCC.

author: coppercone2
author_rank: Super Contributor
timestamp: September 22, 2022, 01:51:23 pm
content: IS that even available anymore?I can only find 'poor' materials capacitors (similar to the original) for 100nF through hole disk form as a single layer capacitor. Is this the catch, that z5u is the only material available for single layer capacitors?

author: floobydust
author_rank: Super Contributor
timestamp: September 22, 2022, 05:28:08 pm
content: What year and model is the power supply? 0.1uF 500V disc is basically huge and rare until I think the late 1980's, but the circuit is not critical so they might have used whatever was in stock. The part has mega safety margin with 70Vp-p? yet a 500V rating. Usually it's much smaller value 0.01-0.047uFI would not worry so much about the part's construction, Z5U is a basic ghetto dielectric. A cap plopped right across a transformer's secondary can cause problems. Normally the part shunts RF/HF mains noise and transients, protects the rectifier diodes against the leakage inductance spikes. But it also creates a tank circuit with the transformer's secondary which resonates with every diode switching, causing ringing. This is OK if at a low frequency, depends on how slow the rectifier diodes are but normally you'd have lower Q and use an RC there, this is what I do and scope it to make sure the EMI is low.I don't see the part aggravating acoustic noise unless you have a power quality issue, dirty power with lots of higher harmonics. The cap's piezoelectric noise should be very little at 60Hz its big size, it's not a MLCC.

author: TimFox
author_rank: Super Contributor
timestamp: September 22, 2022, 06:48:15 pm
content: Back when ceramic capacitors were normally in disc form, the single-dielectric layer was a serious limit on the available capacitance for a reasonable disc diameter.With simpler internal construction, disc capacitors may be more reliable than MLCCs but with much larger physical size.High-voltage disc capacitors usually used the mediocre Class II or crappy Class III dielectrics (X7R and Y5U are class II, Z5U is class III) to achieve the required capacitance.Besides the good "Class I" dielectrics (NP0/C0G), there are higher dielectric constant Class I materials such as N750 that have a large negative temperature co-efficient, but decent loss, available in disc capacitors.They are also useful for temperature compensation of LC networks.Another reasonably linear capacitor, not strictly Class I, is "SL"; at present, they seem to be available only up to about 1 nF at several hundred volts.In high-voltage disc units from AVX, Y5U is available up to 100 nF at 500 VDC and X5V is available up to 33 nF at 500 VDC.On the other hand, MLCC construction is limited in the available voltage due to its smaller size.MLCC examples: AVX/Kyocera has 1812 SMT X7R capacitors up to 220 nF at 630 VDC.

author: wraper
author_rank: Unknown
timestamp: September 22, 2022, 07:27:13 pm
content: Quote from: TimFox on September 22, 2022, 06:48:15 pmDon't you mean Y5V which is class II, while Y5U does exist, it's rare enough to not be worth mentioning. Z5U is class II, not III.

author: TimFox
author_rank: Super Contributor
timestamp: September 22, 2022, 07:50:21 pm
content: Quote from: wraper on September 22, 2022, 07:27:13 pmThe AVX disc ceramic capacitor catalog lists Y5U as common indisc capacitors.https://www.mouser.com/datasheet/2/40/cerdisc-23539.pdfI stand corrected on Z5U: it is Class II. Apparently Class III dielectrics are now very rare.I was confusing the better Class II dielectrics with the worse Class II dielectrics.

author: coppercone2
author_rank: Super Contributor
timestamp: September 22, 2022, 10:40:24 pm
content: Quote from: floobydust on September 22, 2022, 05:28:08 pmThe ceramic and sometimes foil capacitors make a strong whine when they get old. There was 2x 1uF foil and 1x 100nF ceramic there in the noise area, so I am replacing all of them. The foil caps I got are a bit bigger but the same specification. I would not expect the Y5V part to make noise either when its new. I noticed this is a way to solve the noise problem in alot of HP power supplies that use capacitors near the transformers.Its a supply amplifier, I will get the number later because I don't remember it and its in my repair area. Right now I want to desolder the wires going to the transformer with some heat sink clips and then get rid of the old wires from the cut capacitors and also insulate them with heat shrink.Don't ask me WHY the caps make noise, but they do, and i have replaced them in some supplies with foil (when they are on the PCB) and also other ceramics like 100nF 50V cap that was on a 10V rail or whatever, all my replacement parts don't make noise. I got down to the bottom of this when I varnished a transformer and it did nothing, so I went hunting around until I found that the disk capacitors were just loud for some reason. I am not worried that the new part will make noise, I just go through alot of effort to restore them like lubricating pots, replacing caps, cleaning muck, heat shrinking some wires, replacing binding post/BNC, replacing or cleaning nasty screws and stuff like that.In this case (unlike prior cases), I am not sure that the ceramic cap was making noise, when I removed it from the circuit there was still noise (hard to quantify if it was partially responsible), and it was the foil capacitor that is also soldered right up against the transformer. I did unroll the foil capacitor and everything seemed OK with it (no missing metalization).. so it must be some kind of glue issue or something. It's very loud, I would say 10x louder then the transformer hum, I have to stick my ear near the open chassis to hear the transformer but I could hear the caps across the room with the chassis closed up. The capacitors just sound downright annoying compared to the transformer, which can be a pleasing hum IMO. The noise is shrill from the caps.I did power the supply with no capacitors and nothing bad happened, but I might as well replace them when I am working on it.

author: coppercone2
author_rank: Super Contributor
timestamp: September 22, 2022, 10:55:25 pm
content: Do you think that maybe X7R could form a resonator that is too good with the transformer if its left in there, maybe its doing more harm then good?I think I should get both types and scope them to see if there is any problems rather then just dropping random stuff in there..Its a CeraMite-Z5U 0.1M 500V

author: TimFox
author_rank: Super Contributor
timestamp: September 23, 2022, 04:13:31 am
content: To test that hypothesis, you could try adding a resistor in series with the capacitor, perhaps 22 or 100 ohms.

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2022, 04:52:09 am
content: and I think it might be a good idea to put something to power on the supply too

author: wraper
author_rank: Unknown
timestamp: September 23, 2022, 06:46:33 am
content: Quote from: coppercone2 on September 22, 2022, 10:55:25 pmYou're way overthinking that.

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2022, 01:01:26 pm
content: I mean its part of whatever EMI tests they did back in the day, since that stuff had some... exotic designers I would imagine compared to most stuff of the era. HP might have actually measured something that most designer don't bother to measure. But yeah its hard to take seriously a specification with the tolerance of the Z5U dielectric, its kind of like putting a specification of what you can burn in a camp fire... no tires I suppose. ... so I can understand everyone says that basically anything will work here. (700000 PPM), thats like political science specs not engineering math lolPlus there is a quite a bit of literature about SLCC and MLCC differences.. glad someone caught that, I forgot you can even have SLCC. Seems to be oriented around frequency ranges too high to be near a transformer, but its still good education..I got both parts anyway and I will find out soon enough if you can measure any difference with one or the other.And just keep in mind its a supply amplifier (amplifier or power supply, switch selectable), so the EMI might be a little bit more important, I feel like its a more complex device then just a linear power supply.https://www.keysight.com/us/en/product/6825A/power-supplyamplifier.htmljust buyer beware, the spec on noise is 10mv rms, compared to the uV specs of the linear supplies. its not a substitute for a good supply

author: TimNJ
author_rank: Super Contributor
timestamp: September 23, 2022, 03:40:37 pm
content: I think just about all Y-class caps are "SLCC". I've seen maybe(?) a handful of MLCC types, but I think they only went up to Y2, not Y1. (Check Vishay VJ, for example.) I'm not sure if there is something inherent about X7R which makes it unsuitable for single-layer application, but I don't think I've ever seen it?

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2022, 03:54:34 pm
content: it exists for chip rf devices but not through hole disks (they use them for ultrawide band, its like 100GHz)

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 23, 2022, 04:15:25 pm
content: High K ceramic dielectrics are piezoelectric. Some make great little loudspeakers for high frequencies!

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2022, 04:26:31 pm
content: so its an interesting choice to leave that cap flapping in the breeze on top of a transformer (its soldered where the wires are soldered, at least the other two are foil, to the transformer terminals that come out of the paper wrapping. I guess the rest of the circuit regulation takes care of it, but.. that is kind of amusing to think about the microphone essentially connected to the transformer.

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2022, 09:41:26 pm
content: of course, it now looks like the main caps are buzzing a little. I should have listened to it longer then 2 seconds after removing the main noisy capacitors before ordering parts, but I don't like running this stuff with missing parts.