IEC 61000-4-5 compliance testing and potentially another issue with Mean Well - Page 1
Forum section: electronics / projects

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 06:05:52 pm
content: Today BB3 was tested for CE according to the IEC 61000-4-5 standard. The lab operator informed me that we failed the -1kV (L - N) test. What happened? The display froze and a BB3 restart was required to return to normal. According to them, this is not an acceptable scenario. This attitude surprised me because it turns out that the BB3 is at least in the class of life support or mission critical devices while IEC 61000-4-5 defines four performance criterion as described in Section 9. BB3 currently passes test according to performance criterion C.In addition, Section 10, which defines what the test report should contain, states that I, as a manufacturer, can define the performance criterion, but also that the product-family standard should be taken into account.The question is where to look for the “product-family standard” to which BB3 would belong?Another thing, assuming the lab insists on a higher performance criterion (currently A and eventually B) the question is how did the -1 kV shock get through to the MCU to get it stuck? The first thing that comes to mind are (again) Mean Well AC/DC converters, this time the IRM-10 models (TR1, TR2) I use in the AUX PS that powers the MCU module. The currently used version looks like this:On the MCU side I have 4n7/1 kV ceramic cap from GND to PE.I was also forced to remove ZD1 and ZD2 because one of them shorted (they are for 400 V) and blown the fuse, which of course according to criterion A is not allowed behavior and it rather belongs to criterion D because once the TVS breaks, only its replacement remains. Your comments and suggestions are welcome!

author: Yansi
author_rank: Super Contributor
timestamp: November 04, 2020, 06:20:29 pm
content: I do NOT think that placing a TVS from L or N against PE is even allowed to do.

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 06:37:50 pm
content: Yes, it is, an example from TDK/Epcos:

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 06:41:53 pm
content: To continue I will probably need some DIY version of the test generator that can inject 1 and 2 kV.

author: The Soulman
author_rank: Super Contributor
timestamp: November 04, 2020, 06:55:45 pm
content: Quote from: Yansi on November 04, 2020, 06:20:29 pmI'm not an expert but that would make perfect sense, or at least it should be behind a fuse and only between L and N.

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 07:32:57 pm
content: There is one more thing I forgot to mention and it is possible that it is related to the fact that only negative surge of -1 kV leads to blocking. At the input to the MCU module there is also a 5 VunidirectionalTVS. Is it possible for the negative pulse to somehow pass to +5 V from Mean Well and that TVS immediately shorts and which results in a brownout and an undefined state of the MCU? PerhapsbidirectionalTVS should behave better?

author: Yansi
author_rank: Super Contributor
timestamp: November 04, 2020, 07:47:22 pm
content: Quote from: The Soulman on November 04, 2020, 06:55:45 pmIt is more than likely violation of basic safety rules, as it prevents the function of the safety isolation from the live/neutral to the chassis/ground. Anything placed between L/N and PE should be rated I think at least 2000V. 400V TVS is certainly not it.That's also why you always use Y2 rated capacitors from L to PE and N to PE.//Also, I think small pissend TVS is going to do nothing against mains surges. If you want surge protection, use varistor. And only between L-N.

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 07:51:03 pm
content: Ok, thanks, so we covered the issue of TVS that are not present anymore. The main topic still remains unaddressed.

author: Niklas
author_rank: Frequent Contributor
timestamp: November 04, 2020, 10:39:26 pm
content: I am not sure of exactly which of the standards that is applicable for your product, but 10 years ago we had a similar problem that required user intervention to recover. In that case it was ESD discharge och the package that caused an LCD to reset. The product was covered by the 60335 household equipment standard and the equipment was required to recover without user intervention.Have you looked at how the wire harnesses are routed inside the enclosure? With fast edge rate, you can get coupling between wires that are located close to each other. Loop size and distance matters, so twist wires that belongs together and separate the input/output bundles.

author: TimNJ
author_rank: Super Contributor
timestamp: November 05, 2020, 04:07:12 am
content: I too am a little surprised that the lab is recommending such a high classification.A few ideas:1. Does the IRM-10 module powering the MCU temporarily lose output voltage during the surge? The IRM-10 datasheet says it passes 1KV surge with Critereon A, which is promising, but you never know.2. BB3 appears to have good protection against common-mode line surges by VAR1, VAR2, but I do not see any MOV for differential mode surges. Most (decent) AC/DC power supplies usually include a MOV from line to neutral, but with small bricks like IRM-10...maybe not. As long as IRM-10 can survive the surge, IRM-10 is IEC61000-4-5 compliant, but that doesn't mean it will protect anything connected to it. Try a 430/470V MOV across line/neutral.3. IRM-10 has a (presumably) unidirectional zener/TVS across it's output. If the surge is passing through IRM-10 as a differential-mode voltage, this may help to limit it in one direction, but not the other. Kind of in line with your thought about the zener at the MCU.

author: prasimix
author_rank: Unknown
timestamp: November 05, 2020, 07:23:07 am
content: Quote from: TimNJ on November 05, 2020, 04:07:12 amGood question, but I hadn’t gone to a lab equipped with an oscilloscope to be able to track something like that. I don’t know if they would even allow me to have anything externally plugged in during the test, because that could theoretically affect the results. This is one more reason why you should have a "DIY test generator" (professional cost several thousand USD / EUR).Quote from: TimNJ on November 05, 2020, 04:07:12 amThanks for this suggestion! It seems to me like a simple remedy for the problem, if MOV would do its job. I guess it shouldn’t explode, and preferably it won’t blow the fuse, because if that happens again we won’t pass by their criteria.

author: prasimix
author_rank: Unknown
timestamp: November 05, 2020, 07:40:07 am
content: Quote from: Niklas on November 04, 2020, 10:39:26 pmWiring is pretty simple since I tried to simplified it by using PCBs for that as much as possible. Therefore that is only one short low voltage power/data cable (16-pin IDC) that connected AUX PS with MCU module that is positioned perpendicular to the AC lines going along the AUX PS PCB.But there is perhaps another way in which something could have arrived at the MCU and bypassing the Mean Well converter: on the AC side I have 2n2 Y-capacitors connected to PE, and on the MCU module I have 4n7 between GND and PE.

author: Yansi
author_rank: Super Contributor
timestamp: November 05, 2020, 08:45:21 am
content: That should not care much, as long as the PE impedance is low enough.Why is the Y2 cap near the MCU, and not in the power supply?

author: prasimix
author_rank: Unknown
timestamp: November 05, 2020, 08:48:10 am
content: Quote from: Yansi on November 05, 2020, 08:45:21 amPerhaps my inexperience with such matter?Thanks for asking that, I can try to move it as close as possible to Mean Well IRM-10-5 if that could improve current situation.

author: TimNJ
author_rank: Super Contributor
timestamp: November 05, 2020, 02:51:47 pm
content: Quote from: prasimix on November 05, 2020, 07:23:07 amThere are lots and lots of products with MOVs across the line. In general, it's safe. However, there are thermally protected MOVs (thermal fuse in series with the MOV) which can prevent MOV from catastrophic failure (fire). Bourns makes TMOV.Whether a MOV will help or fix your issue, hard to say. A standard 430/470V MOV has a clamping voltage of around 750/775V during the surge waveform. So, for 1KV, you can expect a 25% reduction in peak voltage.

author: jbb
author_rank: Super Contributor
timestamp: November 05, 2020, 05:59:57 pm
content: If you’re going to get into the Protective Earth weeds, I suggest you take a detour into the safety arena. You might need to make safety changes to the earthing and that could change EMC behaviour.

author: prasimix
author_rank: Unknown
timestamp: November 05, 2020, 06:21:37 pm
content: Quote from: TimNJ on November 05, 2020, 02:51:47 pmWhy not use 275 V MOV instead for better reduction in peak voltage?

author: TimNJ
author_rank: Super Contributor
timestamp: November 05, 2020, 06:49:59 pm
content: Quote from: prasimix on November 05, 2020, 06:21:37 pmI think we are talking about the same MOV. I believe you are talking about a MOV with maximum withstand/recommended AC line voltage of 275VAC. This "275V MOV" is the same as a MOV with a varistor voltage of 430V. The varistor voltage is usually defined as the voltage which causes 1mA of current to flow.

author: prasimix
author_rank: Unknown
timestamp: November 05, 2020, 06:53:08 pm
content: That's right. Sorry for confusion.

author: uer166
author_rank: Super Contributor
timestamp: November 05, 2020, 06:54:28 pm
content: Quote from: Yansi on November 04, 2020, 07:47:22 pmYou are certainly allowed to place MOVs and other clamping devices between Lines and PE. I've seen many products certified that way with no issues. The only complication is, when you do the hipot test from input lines to PE in production and regulatory testing, you need to disconnect the clamping devices one way or another. If you couldn't clamp to PE, how would you ever reasonably pass a 6kV common mode surge test and such?Safety/regulation is not somewhere you can make blanket statements like that without referring to a specific clause of a specific standard, this stuff varies a lot..

author: jonpaul
author_rank: Super Contributor
timestamp: November 06, 2020, 10:32:04 am
content: Hello all: Used to design SMPS PSU, EMI and transient filters for cinema projectors and professional arc lighting, medical and avionics.Use of gas spark gap protectors usually reserved for telecom lines.MOVs deteriorate over time, have high capacitance and can catch fire or explode if overloaded.TAZ are NEVER used across line.The "meanwell" Chinese supplies may have marginal EMI and transient compliance.Adding all the filtering and protection is the worst approach. Just get a high quality compliant designed PSU with built in compliance.Best way to prevent CPU upset in transient test is careful layout of PCB, bypass caps on LV lines and TAZ eg on +5V.Finally is your transient generator compliant to the specs being met?The good ones cost 10s of K$.Many good texts on EMI and transient compliance design. Humbly suggest to lear about what you are designing.Just the ramblings of an old retired EE,Enjoy and bon chance,Jon

author: prasimix
author_rank: Unknown
timestamp: November 06, 2020, 10:50:57 am
content: I learn along the way, as do many others. I naively started with the assumption that Mean Well certifications mean something. Turns out they're pretty much what you said: marginal. Using the better brands is not an option at the moment because it would raise a price that will be difficult to justify (maybe once the EEZ becomes a brand itself).I don’t have a test generator and that’s a serious problem, I can just keep going to a test lab that will charge me for new arrivals and believe that it won’t ultimately cost me more than buying my own tester, even a used one. So I also asked if anyone knows of any “DIY” version of the hipot generator that could be used to get an idea of what’s going on.There seems to be room for improvement: I will move the TVS on the MCU module right after the output of the Mean Well module. Between L-N there will be additional MOV, we will try to catch a "brownout" in fw and initiate a restart, etc. I will continue to report here about progress.

author: jonpaul
author_rank: Super Contributor
timestamp: November 06, 2020, 11:45:03 am
content: Bonjour encore prasimix, BRAVO for your efforts.Been an EE since 1968 in audio, analog, power, cinema, lighting, designed up to 55 kV and 12 kW. So guess I am an "old hand" having made all the mistakes......My general feeling is your input protect is overkill and copying mfg app notes is not a best strategy.Check out MOV life and MOV fires.NOT recommended anymore.The IEEE/CISPR, IEC compliance is a fine topic for study, but EMI and transient suseptibility.Notice that the compliance affects both mains line INPUT and ALL outputs and connections!Your project is reminiscent of 1970s.1980s Tektronix modular TM500 and its higher power HPIB brother, TM5000, both classics!https://w140.com/tekwiki/wiki/List_of_TM500_and_TM5000_equipmentThe transient tests can be approximated with an ESD gun especially to debug CPU crashes.We built some pulse line injectors with arc lamp ignitor series injection HV Tesla coils!Used on Furman Sound transient protector / power distribution and Welsch Allyn medical illuminator.After lash up tests still needed lab for final approvals.TAZ use across LV lines nearest CPU and sensitive cks NOT across line.Finally if it shall be used worldwide, BEWARE very high line V in UK (Ring Bus) and VERY bad line fluctuations and transients in South America and much of Asia outside of Japan and South Korea.Can discuss further via PM if you like.Where are you located? Am in ParisBon chance,Jon

author: jonpaul
author_rank: Super Contributor
timestamp: November 06, 2020, 01:12:50 pm
content: Hello again to prasimix: You wrote:"lab .. performance criterion (.. A .. B)... how did the -1 kV shock get through to the MCU to get it stuck?"Common mode noise coupling via pri..sec transformer capacitance (no faraday shields in MeanWell!) and PCB, wiring. The transients have fast rise and very wide bandwidth!See the excellent texts like Ott Noise reduction and Electromagnetic Compatibility, etc. Note also CM to DM noise conversion.All of these issues solved decades ago!Enjoy,Jon

author: bjbb
author_rank: Contributor
timestamp: November 08, 2020, 12:08:58 am
content: As some have replied, this particular TVS is not necessarily rated for Class I construction where protection from hazardous voltage is required; e.g., where a Y-rated capacitor would be required. For Class II construction, the component would be ok, because failure of component puts the hazardous energy 'behind' double or reinforced insulation. This assumes an end-use safety standard such as 60950, 62368, etc.Please reference the UL recognition for this component in file E230531 per CCN QVGQ2, in particular the conditions of acceptability per the file.

author: prasimix
author_rank: Unknown
timestamp: December 03, 2020, 04:34:52 pm
content: I continued to work on preparations for next visit to the test lab. The idea is to pass the surge immunity test I failed last time as the BB3 is expected to recover on its own after all sorts of surges.For this I have now prepared an external supervisor (reset/watchdog) chip that will get a “heartbeat” from the MCU. When the “heartbeat” skips or is late the supervisor will generate a reset. The selected supervisor isSTM6824SWY6F. The tests I did in-house look promising. We’ll see how the supervisor behaves in the lab.

author: prasimix
author_rank: Unknown
timestamp: December 03, 2020, 04:58:26 pm
content: Oh, I forgot to mention: TVS on AC inputs are removed, new MOV across N-L are introduced, and bidirectional TVS were added across +5 V and +12 V outputs..

author: prasimix
author_rank: Unknown
timestamp: December 11, 2020, 06:25:40 pm
content: The last modifications were fruitful. Today we passed IEC 61000-4-5 test.

author: jbb
author_rank: Super Contributor
timestamp: December 11, 2020, 08:33:43 pm
content: Congratulations

author: prasimix
author_rank: Unknown
timestamp: December 11, 2020, 08:40:11 pm
content: Thanks, We are slowly approaching the end. We will have to repeat some tests because we changed the Mean Well LRS with the EPP model. However, I believe that new problems should not arise because of that. The remaining new tests are less demanding, although there is still the possibility that we will not pass some of them. I'll keep you informed here of by opening a new topic related to newly found issue.