Offline isolated SMPS must be in metal enclosure. (to pass radiated emissions) - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 13, 2021, 08:26:25 pm
content: Hi ,Do you agree, that an isolated offline SMPS cannot pass EU/UK USA radiated emissions compliance testing unless it is in a metal enclosure? (this might just be a plastic enclosure with a complete metal foil lining.The following document by Meanwell, referenced in their IRM-15 power supply datasheet, basically confirms that no offline SMPS above say 5w can ever pass radiated emissions without being in a metal enclosure...https://www.meanwell.com/EMI_statement_en.pdf...Meanwell confess here that they actually EMC test their offline power supplies (for radiated emissions) in metal cabinets, like what they say the customer uses.

author: Gyro
author_rank: Super Contributor
timestamp: July 13, 2021, 09:14:46 pm
content: FFS treez. How many times are you going to ask the same question?Same answer as last time, I do not agree, and you are making gross generalisations.It comes down to how well you design your product to accommodate the OEM PSU module. Just because Meanwell test their module under certain circumstances (they obviously can't accommodate and test in every situation that the customer will use it in!) doesn't mean that you can't use it in other situations if you put the work (and testing) in. I don't think confessions come into it!

author: Faringdon
author_rank: Super Contributor
timestamp: July 14, 2021, 04:22:54 am
content: QuoteThanks, I agree, so why bother to put the OEM PSU module in a metal enclosure when testing it for radiated emissions? (as they have done)I believe we would agree, that the main reason the following offline PSU's are in metal cases is so they pass radiated emissions testinghttps://www.meanwell.com/productSeries.aspx?i=16&c=6#tag-6-16(the holes designed to allow ventilation but small enough to block below a certain wavelength of radiated emission)In this , i am speaking of hard switched offline SMPS, not resonant ones.....(as you know, all offline SMPS > 75W have a hard switching boost pfc in, which even if quasi resonant, hard switches at turn off time....and isnt completely soft at turn on.)I once worked for a company who had designed a world beating product, powered by an offline PSU in a plastic case, bought from China…..but couldn’t pass radiated EMC with it. They never realised that they only had to metal foil line the plastic case to pass radiated EMC……….they ended up selling the company off……..when I got there , I could see the signs of their desperation to pass radiated emc…they had purchased a super expensive near-field radiated emissions test apparatus….and they had a large device bolted to a bench, which they had been using to crack open other peoples offline plastic PSUs…so they could see what they weren’t doing to pass. But they never realised in time…and so came the sell off……all for the sake of a bit of metal foil lining!...............................-------------Hi,...Its quite a situation with radiated emissions for offline SMPS. If your company's product is powered by an offline SMPS...then go onto your co's hard drive and fish out the offline SMPS's radiated emissions scan graphs........Thats right....you wont be able to find them.These radiated scans are one of the deepest secrets of the company...only the owner and his most trusted staff will be allowed access to these scans.The cost of a radiated emissions test is enormous...the cost of buying the test kit yourself (chamber etc) is totally unaffordable to most companys.Ever offered to go along to the radiated emissions lab and carry out radiated emissions pre-compliance or compliance testing of your company's offline SMPS?.....you wouldnt have been allowed to go and do it.Only the owner , or most trusted few, will be allowed to go and do it. If they dont know how to do it, then i find they call you up on the phone from the lab and ask for circuit mod ideas ....if it still fails, they just keep asking you for more ideas. I remember once recomending an "across the isol barrier" Y cap for an offline SMPS that didnt have one......the answer came back....."made it much worse!"..this was obviously a fib...when they returned, this "cross the barrier" cap had been included in the next build.So i believe most agree that an offline SMPS for EU/UK radiated emissions testing needs to be in a metal case of some description.

author: Gyro
author_rank: Super Contributor
timestamp: July 14, 2021, 08:30:34 am
content: Treez,Again you chose to pick stuff out of context to justify your wild assumptions!The statement in the Meanwell PDF that you linked reads quite clearly and honestly to me. I detect no deception or 'confession' in any way!QuoteMost buyers of these OEM moduleswillbe bought by industrial customers and stuck in industrial metal enclosures. They know their customer base for that range of products. Customers wanting to put them in atypical plastic enclosures will of course need to take additional precautions to ensure compliance of the end product.Quote from: Faringdon on July 13, 2021, 08:26:25 pmAgain you make wild assumptions based on the odd out of context references and anecdotes from one of the many companies that you have been a 'hired hand' for.You just need to look around you to see that your assertion that "no offline SMPS above say 5w can ever pass radiated emissions without being in a metal enclosure" is complete rubbish.If you look on the Mean Well (UK!) website, you will seeplastic enclosedpower supplies - the GE and GST ranges, intended for the consumer products, which have a power rating ranges of 12 - 280W! Just look down at you own or somebody else's laptop brick.I really don't know why you continue to switch forum identities while continuing to spout this sort of rubbish.

author: dmills
author_rank: Super Contributor
timestamp: July 14, 2021, 05:05:04 pm
content: At this point I cannot decide if Treez is a psychology student running an experiment on engineers, a performance artist, or an unusually long lived troll.I mean nobody can have been in the engineering game for as long as he has without figuring out that the answer is almost always, "it depends on your specific systems design" surely.

author: Faringdon
author_rank: Super Contributor
timestamp: July 14, 2021, 06:19:58 pm
content: QuoteThanks, ive taken many of these apart with the kit mentioned in #2...as you know, they have totally enclosing inner metal foil lining

author: Faringdon
author_rank: Super Contributor
timestamp: July 14, 2021, 06:21:45 pm
content: QuoteThanks yes..often used in metal enclosures that they are fitted in to.....if not inner metal foil lined anyway.And of course, many products dont see a radiated emissions test....for whatever the reason......--....So yes, but its interesting, ....Please add your thoughts to this....just imagine a company's product didnt comply with radiated EMC regs....then the standards bodys would take samples of the company's product, do radiated EMC tests on them...and ban their product, right?....As you know, this never happens. A Radiated EMC test on an apparatus containing an offline SMPS takes ages to do and costs utterly shed loads of money...and can only be done in super-expensive chambers which are pretty rare to find......the EMC antenna has to be moved all over the place to re-scan the product from different angles and elevations...then any failure peaks have to be re-scanned to see if they really are fails....takes ages and ages. So no standards bodies have organised radiated EMC testing for company products.So many company's products simply dont comply with radiated EMC.....but what a small startup has to bear in mind, is that a big competitor may well sneak their product into a radiated EMC test...so that they can proove it fails....then they would put the small startup out of business by using their highly payed lawyers to do this...But even that rarely happens....because if you bomb your enemies...then your enemies may bomb you too. So in fact, in radiated emissions, as well as many other electrical standards areas....companys in a particular sector tend to have "amnestys", whereby neither criticises the radiated EMC (and other) failures of each other....and they live and let live. This often also happens with PFC (EN610000-3-2)...companys simply avoid using PFC on SMPS >75W...because all their competitors dont use it either....and neither criticises the other.I believe we all know that the standards bodies (who answer ultimately to the governments), dont actually test samples of company products in order to see if they comply with radiated EMC regulations...as discussed...its just too expensive, and takes too long....there is a reliance on the goodwill of companys to oversee it themselves. I mean, Western Governments have suffered such a "dereliction of duty" such that the vast majority of the Western general electronics sector has been outsourced to companies in the Far East.....leaving gaping holes in Western capability.....i'm sure we all realise that Governments that behave like that, are far from having the "upright-ness" towards implementing measures to check and ensure products have the necessary radiated EMC compliance.

author: Faringdon
author_rank: Super Contributor
timestamp: July 17, 2021, 08:35:40 pm
content: Hi,Here is another Question on the same kind of subject , if i may...Supposing we have an offline 20W Flyback SMPS on a PCB. We want to house it in an earthed metal enclosure so that we can pass radiated EMC testing to EN55032. (30MHz to 1GHz).Example of offline SMPS in earthed metal enclosure...https://www.meanwell.com/webapp/product/search.aspx?prod=RS-15The earthed metal enclosure is needed for radiated emissions reduction. However, as you know it brings problems at lower frequencies as conducted common mode emissions...eg around 20 to 30MHz. -These problems can however be solved by using a more attenuative common mode filter.Anyway, we want the enclosure to be totally surrounding the SMPS for obvious reasons. Also, the further away from the SMPS it is, the better.....however, we have space limitations so it'll have to "hug" quite closely up to the SMPS.What do you think is the closest we can have the earthed metal shield to the SMPS without causing too much extra common mode emissions?.... I mean, you see switching FETs screwed directly to earthed metal enclosures, so i guesss if it has be very close, then its do-able without too much common mode emissions penalty.Also, the earthed shield can have holes as long as they are less in diameter than lambda/20 (15mm).Would you agree that the more "holey" the shield is, then the less common mode emissions we will get? (whilst still stopping the high frequency radiated emissions)