Allowed leakage current and current harmonics - Page 1
Forum section: electronics / projects

author: prasimix
author_rank: Unknown
timestamp: August 20, 2020, 08:51:11 am
content: I am in the process of certification to obtain CE (EMC and LVD). Two new requests regarding AC input arose:1) Leakage current has to be below 3.5 mA (for sinusoidal currents)2) Current harmonics will be measured (because total power is above 75 W)Any idea where and how to measure the required params is welcome!Thank you in advance.

author: Alti
author_rank: Frequent Contributor
timestamp: August 20, 2020, 10:55:17 am
content: Interesting question.I do not know the answer but I am guessing the leakage only applies to Iappliance class. Can you quote specific regulation/norm that limits the leakage to 3.5mA? Considering that typical residential RCDs are set to trip over 15mA, this 3.5mA sounds quite high..

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 20, 2020, 01:17:32 pm
content: Leakage current mostly depends on Y2 capacitors value (for AC/DC).

author: prasimix
author_rank: Unknown
timestamp: August 20, 2020, 03:43:14 pm
content: I have just 2 x 2.2 nF Y capacitors between AC and PE, and 2 x 10 nF between DC and PE. Therefore the leakage current should be well below 3.5 mA limit.

author: TimNJ
author_rank: Super Contributor
timestamp: August 20, 2020, 05:09:26 pm
content: Two types of leakage current:1. Earth conductor current (mainly driven by Y-caps to earth)2. Touch current (mainly driven by capacitance across transformer)The latter is more directly related to user safety since it's the current which flows through an equipment-human-earth loop. The first is also limited per safety standards but usually only becomes a safety issue in particular cases/environments. The "measurement device" is specified in the standard. All it is is a current measuring shunt resistor with an RC filter. Usually 1K shunt resistor (1mV = 1uA) with RC = 10K + 0.015uF (-3dB @ 1KHz). But, the measurement device can vary.If you want to measure touch current, put this network between an output conductor, say V+, and the input earth connection. Use a true RMS multimeter with decent bandwidth to measure the voltage across the resistor.If you want to measure earth conductor current, put the network in line with the input earth conductor to your power supply.Typically a normal condition (NC) and single fault condition (SFC) limit is specified for each. Single fault condition for touch current is either open neutral or open earth. I'm not too familiar with LVD, so I'm not sure. This should be tested at worst case line voltage (240 * 1.1 = 264V)----Regarding harmonics measurement...usually this is done with a dedicated piece of equipment (AC power analyzer). May be a way to do it with a current probe and FFT, but I am not sure the accuracy. If the main power supply is >75W rated, it has PFC and most likely will be okay. If you're running a few non-PFC converters side-by-side, may be an issue.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 20, 2020, 05:14:03 pm
content: Quote from: Alti on August 20, 2020, 10:55:17 amI'm not sure to what country/region this applies but it should be noted at least this is not universally true. I'll refrain from generalising but at least here a main 300mA unit is regular, supplemented by a 30mA unit in humid areas.

author: prasimix
author_rank: Unknown
timestamp: August 21, 2020, 08:55:47 am
content: Thanks everyone for more inputs and ideas. I measured "Earth conductor current" as @TimNJ noted and it seems that I'm within limits.The real challenge will be to pass the test for the current harmonics since used Mean Well LRS-150F-48 do not come with PFC, and I don’t have room in the current enclosure for a model that has PFC.I made a preliminary measurement for half the power of one module and the current has characteristic shape for such a converter without PFC. Rigol's FFT analysis is not very helpful I will have to analyze the data elsewhere, preferably in an application that recognizes/detects harmonics and their values in percentages.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 21, 2020, 09:28:48 am
content: Harmonics are just multiples of 50, which regulations take up to the 50th (2.5khz).You are looking at 500 Hz/div, so only the 4 left divs are useful. You will get 3,5,7,9...Try changing the Hz/div and increase the vertical scale. You also have a linear scale Vrms.

author: jbb
author_rank: Super Contributor
timestamp: August 21, 2020, 09:35:35 am
content: Yeah, that doesn’t look promising re harmonic currents.If your current probe has OK bandwidth, a scope FFT is a good start. You’ll need to adjust the FFT settings to get reasonable results, then read off using the cursors. Then calculateIt’s probably good to dig into the standard a little for details on harmonic limits. Is it Total Demand Distortion (TDD) or THD? TDD is a win because it (basically) means you use thefull loadfundamental current. It’s a huge help at partial load.

author: David Hess
author_rank: Super Contributor
timestamp: August 22, 2020, 04:18:42 pm
content: As other have posted, Rigol's FFT is not the best but I can see everything you need there. Adjusting the sampling parameters will help somewhat; it looks like a lower time/div will help.

author: prasimix
author_rank: Unknown
timestamp: August 23, 2020, 12:22:06 pm
content: Hm, this doesn't look good at all. Another measurement on Rigol with 50 Hz/div:FFT performed in EEZ Studio with the same load:It looks to me that 3rd harmonic alone (150 Hz) is enough to not pass this test.This is what one can find in the Mean Well report. Interestingly, for current harmonics there is no mention that the test was done in a certified lab.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 23, 2020, 03:40:55 pm
content: Hi,The harmonics should be measured over 200ms. 10 cycles of 50 Hz or 12 cycles of 60Hz.I found this reference:https://www.emcstandards.co.uk/files/61000-3-2_mains_harmonics.pdfI believe that you need to pass class A.The class A limits are not a percentage but absolute limits:Mean Well are self-certifying based on the measurements from their Chroma Power Meter Harmonic Measurement.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: August 23, 2020, 03:57:55 pm
content: Thanks a lot. Don't have currently idea how to proceed before visiting the lab once again and that they make measurements. If we failed it seems that I don't have many options then to try to deploy another model that includes PFC, or to build my own PFC that has to be installed before existing Mean well modules (up to three of them).

author: prasimix
author_rank: Unknown
timestamp: August 23, 2020, 04:19:19 pm
content: Another presentation of the similar results (output power is the same, about half of the total load for a single module or 77 W, Vin=115 Vac via isolation transformer):

author: prasimix
author_rank: Unknown
timestamp: August 23, 2020, 04:28:30 pm
content: Another measurement, the same setup but with Vin=230 Vac:

author: jbb
author_rank: Super Contributor
timestamp: August 23, 2020, 06:40:08 pm
content: Well, I’m not too well versed on the standards side, but there are a couple of things that could be attempted on the power side.If you’re close to a pass, it might be feasible to add some filtering with a larger differential mode capacitance. Industrial settings may use LC filters on specific harmonics, but that would be bulky and heavy.Cooking up a PFC rectifier and feeding the modules with DC might work, but could land you in trouble with EMC emissions again.The most academically interesting solution would be an active power filter: essentially a small mains inverter with special control so that it spits out currents to cancel the lumpy stuff from the Mean Wells. (Typically one would measure either the total line current or the current branching off to the Mean Wells and use frequency selected control loops to force the odd-numbered harmonic currents to zero.). Would be a custom design with microprocessor control.

author: TimNJ
author_rank: Super Contributor
timestamp: August 23, 2020, 09:21:05 pm
content: I would not bother trying to roll your own PFC module. While you don’t have to worry about primary-secondary isolation safety, since the PFC deals directly with mains, it will need some level of 3rd party safety testing and validation. In my opinion, much more straightforward to use an off the shelf converter with integrated PFC.But does your configuration even fail?Regardless, I’d take a guess that the $25USD pricetag is somewhat related to the lack of PFC. How about Cosel PJA150F-48? You have to be careful with some of these old school type power supplies. Their days may be numbered.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 23, 2020, 10:06:58 pm
content: Quote from: prasimix on August 23, 2020, 04:19:19 pmHi,I think that this looks like a pass to me.at 150Hz you have 524mA this is the third harmonic.If you are class A the limit for the third harmonic is 2.3A you are 1/4 of the limit.Because of the symmetry in the waveform all the even harmonics should be zero.at 250 Hz (N=5) you are 200mA the limit is 1.14Aetc..I believe that you can justify class A.This why you have to transition to PFC at around 200 - 300W for class AOther classes need a PFC at lower power levelsRegards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: August 24, 2020, 06:42:33 am
content: Quote from: jbb on August 23, 2020, 06:40:08 pmYou're right, especially if we can expect change in both radiated and conducted emissions. I would definitely like to skip another round of the radiated emission testing.Quote from: jbb on August 23, 2020, 06:40:08 pmHuh, I'm completely lost here, but even if I decided to build a "trivial" PFC it would surely take me a few extra months, not to mention an academically interesting solution.

author: prasimix
author_rank: Unknown
timestamp: August 24, 2020, 06:49:20 am
content: Quote from: TimNJ on August 23, 2020, 09:21:05 pmPrice tag is more like 25-35 USD, but you have to multiply that by 2 or 3 for multichannel configuration. Cosel PJA150F-48 is way above my budget (my margin on the BB3 is simply miserable). I can see on the Mouser that is about 47 EUR (25+ pcs). I would rather choose Mean Well EPP-200-48 that I can get for about half of the Cosel price but is twice as expensive as the currently used LRS-150F-48!

author: prasimix
author_rank: Unknown
timestamp: August 24, 2020, 06:58:36 am
content: Quote from: Jay_Diddy_B on August 23, 2020, 10:06:58 pmPrevious measurements was for half the output power of one converter. I made another measurement for full output power for two converters (300 W, Vin=230 Vac) and it seems that I'm still within the budget. Now we need to wait and see how it goes in the lab.

author: TimNJ
author_rank: Super Contributor
timestamp: August 24, 2020, 03:23:16 pm
content: Quote from: prasimix on August 24, 2020, 06:49:20 amI figured as much about the cost. Cosel not exactly cheap. I've tested Meanwell EPP-200 at work to check its conducted/radiated emissions profile. It's okay. The competitors (XP, Murata, Bel) were generally better, but Meanwell not too bad. (Remember that EPP-200 140-144W power supply with 200W forced air rating.) It is a much newer design so you won't have to worry about obsolescence, although designs like LRS-150F have the cost advantage, so Meanwell may not be so inclined to obsolete it.Make sure to look at the other harmonics too. I don't think it's as much of a problem for IEC61000-3-2 Class A, but for Class C, sometimes issues at the higher harmonics, like 9, 11, and 13. But the Class A limits are defined differently than Class C, so you'll probably be okay.

author: prasimix
author_rank: Unknown
timestamp: August 24, 2020, 03:33:28 pm
content: Quote from: TimNJ on August 24, 2020, 03:23:16 pmI believe that EEZ BB3 belongs to Class A since it does not belongs to other: B is for portable tools; arc welding equipment which is not professional equipment, C is for lighting equipment and D is personal computers and personal computer monitors and television receivers.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 24, 2020, 04:33:00 pm
content: Hi,A believe that the classes are based on population and usage factors.The more popular an item is and the more frequently it used the tougher the regulations.Power tools are intermittent use, so the harmonics that they generate are not really important. so they have higher limits.TVs have very strict requirements, everybody has one and they are on multiple hours a day.I noticed that Mean Well tested at 80% max output. You might be able to do this if you are close to the limit. I am not sure what the IEC61000-3-2 says. It may say 'typical usage' or it may say 'worst case'.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: August 24, 2020, 04:38:02 pm
content: It says:C.15 Test conditions for other equipmentTest conditions for other equipment will be given as required.

author: prasimix
author_rank: Unknown
timestamp: October 15, 2020, 09:59:42 am
content: I got a report this morning from the lab regarding current harmonics. Mean Well LRS-150F-48 (i.e. two of them max. load) failed miserably and now I have to find a way how to pass this testing. One possibility is to add PFC on the AUX-PS module, another one is to try Mean Well with built-in PFC. Your suggestions are welcome. This is a summary of report, a whole report can be found in attachment.

author: jbb
author_rank: Super Contributor
timestamp: October 15, 2020, 10:21:15 am
content: Well, are you sure you’re texting against the appropriate requirements? It’s not consumer equipment so there may be exemptions.It looks like you’re fairly close to a pass. While adding a switch mode PFC would be challenging, a good old fashioned LC line filter might actually do the trick here. Do you have any power factor requirements to meet, or just the harmonic limits?

author: prasimix
author_rank: Unknown
timestamp: October 15, 2020, 10:23:55 am
content: Yes, just current harmonics (there was no mention of PF). I already added filtering to pass conducted emission (seehere), do you think that passive filtering could improve situation?

author: prasimix
author_rank: Unknown
timestamp: October 15, 2020, 10:36:31 am
content: I got additional clarifications: if each power module is measured individually (i.e. DCP or DCM only) with the corresponding Mean well then I pass the tests. In combination, they break the limit.

author: prasimix
author_rank: Unknown
timestamp: October 17, 2020, 03:44:05 pm
content: I continued to study current harmonics. The thing that is worrying is the big discrepancy in the distribution of harmonics between what I can measure on Rsense and the results from the lab.However, I managed to make a difference. This time I measured the voltage (cyan) and current (yellow) at the input at the same time. Without any correction for two almost max. loaded channels I have this:If I add a 10 uF capacitor to the AC input in parallel I get the following correction:FFT analysis gives the following results and shows a significant attenuation of higher harmonics where several of them break the limit:The question is whether it makes sense to further complicate this with making a single pole filter, or a high-pass filter, or staying just on the capacitor and believing that I will pass the tests.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 18, 2020, 03:59:22 pm
content: Adding quite some capacitance to mains also adds demand on the discharge circuit. The other alternative would be a choke - likely one with a heavy iron core, e.g. like the old PFC chokes found in PC supplies in the 1990s. AFIAK they are no longer sufficient to easily meet the limit for the PCs. So PCs switched to active PFC as part of the circuit.

author: prasimix
author_rank: Unknown
timestamp: October 18, 2020, 05:18:05 pm
content: Yes, 10 uF on the AC input is massive. It'll require a massive bleeder. I opened one old PC PSU. Could this be the kind of choke they put for similar purpose? Don't know why it has 4 wires, possibly it is CM choke? Perhaps something smaller could be used in future production instead of adding PFC.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 18, 2020, 06:47:16 pm
content: I also don't know why they have 4 wires. It could be an additional use for common mode filtering. I am afraid a PFC choke would need about that size. The old PC supplies where in the 200-300 W range and thus comparable or even lower power than a full equipped BB3. Chances are they already build the chokes to a price.No sure if one can still get them, as they are more like technology of the past. There are a few PFC chokes still available, but not sure they are sufficient. The filter inside the meanwell supplies may also hinder the function somewhat.

author: nightfire
author_rank: Frequent Contributor
timestamp: October 18, 2020, 08:16:08 pm
content: A bit late to the party, but I also throw my 2 Cents (or 0.02 EUR) into the hat: In my experience as a user of equipment (and designer of electric distribution throughout a house etc.) and person that does Appliance testing, Leakage currents are nowadays quite important.I have in mind that EN60950 (and the successor EN62368) mandates those rules. In the national VDE 0701-0702 (germany) I have to use for checking appliances after they have been bought and are in use, leakage current on the PE is allowed to be at 3.5 mA, touch current 0.5mA.As a RCD with 30 mA is mandatory in newly built electric installations, the combined leakage of poorly designed devices/appliances can impose some problem, because they are pre-loading the circuit. As a RCD with 30 mA rated differential current is able to act between 15 mA and 30 mA, it can be "blown" by several poorly working stuff that add up a bit.Probably a ready-made PSU with PFC would be the easier way to go. Also, if commercial buyers are the target, in due to regulations they are required to ensure that the total power factor towards the energy network provider is within a certain tolerance- and every device that causes unwanted network feedback is no good.Question: How are the 3.5 mA determined/to measure? "Only" TrueRMS, or with the so-called 50Hz filter according to EN 61010 table A1? Here the body sensitivity is taken into account (DC and high-frequency AC are less harmful to the human body as AC 50Hz) and with the described circuit filter the measured trueRMS value is somewhat normalized.A PAT tester from the big manufacturers as Gossen Metrawatt, Metrel, Megger, Fluke etc. has this built-in, so the values those testers will show are somewhat lower that if a leakage current is measured by multimeter.

author: prasimix
author_rank: Unknown
timestamp: October 27, 2020, 07:54:34 am
content: Yesterday, I got two Mean Well EPP-150-48 that has built-in PFC. With the same declared max. power, they are surprisingly small compared to LRS modules:It wasn't a problem to install them, and 4 pieces easily fit into the existing space. This means that if they were used for a future 4-quadrant power module (symmetrical power is needed), as many as two 4-quadrant modules could be placed in the chassis, or two more 1-quadrant (DCP or DCM) modules could be placed next to one 4-quadrant module.As expected the current harmonics are far below the allowable limits:

author: jonpaul
author_rank: Super Contributor
timestamp: October 27, 2020, 08:26:47 pm
content: You are trying to fix a compliance issue with a bandaidSuggest to nix the chinese Meanwell and get a good quality PSU with builtin PFC and leakage spec.Jon

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 29, 2020, 01:37:38 am
content: Quote from: prasimix on October 27, 2020, 07:54:34 amHave you looked at the conducted emissions of the EPP modules with PFC?I don't know if they will be better or worse. I know that they will be different than the modules that you were using.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: October 29, 2020, 06:22:33 am
content: Yes I checked, and with the filter I added for the LRS-150F-48 it looks maybe a bit better.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 29, 2020, 08:05:30 am
content: The EPP 150-48 supplies look like they have no PE at the input and thus have the class y caps to both L and N. This can be a problem with the touch current if multiply supplies are combined.

author: prasimix
author_rank: Unknown
timestamp: October 29, 2020, 08:25:18 am
content: How I can test or measure that with the current setup?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 29, 2020, 11:25:59 am
content: Hi,There is a PE connection, it is doubling as a mounting hole:(I am not sure I like the idea of relying on a mounting hole for PE)Jay_Diddy_B

author: Kleinstein
author_rank: Super Contributor
timestamp: October 29, 2020, 11:57:51 am
content: Ground just at the mounting hole must be a thing of cost cutting. Anyway it looks like PW would be mainly used for RF filtering, not as protection for electrical safety.One can directly measure the leakage current from the isolated output to ground. I am not sure about the limits with respect to the frequencies. There would be some 50Hz part and likely something in the 100 kHz range. The higher frequency part can be additionally reduced from an common mode choke at the regulating modules. So ideally one would measure the leakage current with a complete setup, not just the SMPS module.

author: prasimix
author_rank: Unknown
timestamp: October 29, 2020, 01:05:00 pm
content: It should be better now:

author: TimNJ
author_rank: Super Contributor
timestamp: October 29, 2020, 03:26:29 pm
content: The "touch current" should be measured from user accessible parts (system output terminals) to earth. Use the setup and procedure defined in IEC60990:2016.You insert the below measurement device between the output terminal and earth.Depends what standard you are going for, but for IEC62368, you declare the "energy class" of your equipment. I'm not sure entirely how you classify, but you should go for ES1 if possible. So, 500uA RMS for touch current. This is the approximate current that might flow through a human body if touched.For earth leakage current ("protective conductor current"), the measurement is performed in line with the input earth conductor. This is the current the power supply dumps back into the earth conductor, usually as a result of Y-cap leakage. I believe this should be 3.5mA max.

author: TimNJ
author_rank: Super Contributor
timestamp: October 29, 2020, 04:49:05 pm
content: By the way, above may be somewhat confusing. You insert the pair of terminals with 'V1' between them in line with the current path, and make a measurement at 'V2'. The 'V1' terminals are equivalent to points A and B on the second image.

author: prasimix
author_rank: Unknown
timestamp: November 04, 2020, 10:12:06 am
content: Yesterday I passed the test for current harmonics but with the new Mean Well EPP-150-48. My attempt to do this with the LRS-150F-48 by adding a large capacitor failed because the harmonics 5, 7, 9 and 11 are still above the limit.

author: Kean
author_rank: Unknown
timestamp: November 04, 2020, 02:02:20 pm
content: Well that is some progress at least. Congrats!