Consultancies are mis-designing offline SMPS's? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: May 01, 2023, 01:57:45 pm
content: Hi,It is accepted that any offline SMPS >75W which is in a totally sealed plastic case needs to have metal mesh, or metal foil, or metal plate lining within that plastic enclosure, in order for it to pass Radiated EMC to EN55032.However, consultancies, are not adding the metal lining, because they know that they will be payed off long before the customer ever gets round to Radiated EMC compliance testing.By that time they will have cut and run.As you know, the metal lining is most effective if connected to earth ground, and this earth ground connection should stem from the incoming mains cable.However, having an earthed metal lining round the SMPS , will , of course, worsen Conducted Common mode emissions, and means that the common mode filtration will then need to be larger.....hence one of the reasons why consultancies are not bothering to do the "earth metal lining" thing.(As well as the obvious extra cost of the earthed metal lining).How can you stop consultancies from doing this? The customer companies won't listen to your crys of getting the metal lining added....they just see it as an extra expense, and have no idea that avoiding it will result in Radiated EMC compliance failure.....the consultancies tell them it is not necessary.

author: MK14
author_rank: Super Contributor
timestamp: May 01, 2023, 02:41:45 pm
content: We had exactly the same problem, with our consultancies. It was not only breaking the EMC regulations, but was probably illegal as well. We were extremely disappointed. Our boss got so angry at this, that we ended up hiring a private detective agency, to get to the bottom of this situation.To our complete surprise and amazement. It turned out that our consultant, when they had too much free time on their hands, such as UK national bank holidays, like today is. Was actually cheekily going onto a popular electronics forum, and spending all day writing out useless troll stories and things, instead of working on our SMPS. At times, they were even multi-accounting. For the life of me, I can't remember their user name. Typical of me, I can't see the wood for the treez's.

author: Faringdon
author_rank: Super Contributor
timestamp: May 01, 2023, 03:04:47 pm
content: Thanks, and i would hazard that you agree with the fact that.....It is accepted that any offline SMPS >75W which is in a totally sealed plastic case needs to have metal mesh, or metal foil, or metal plate lining within that plastic enclosure, in order for it to pass Radiated EMC to EN55032.

author: MK14
author_rank: Super Contributor
timestamp: May 01, 2023, 03:15:08 pm
content: Quote from: Faringdon on May 01, 2023, 03:04:47 pmAfter much research (), I found this:https://www.power.com/community/forum/ac-dc-conversion-forum/2023/offline-smps-plastic-enclosure-needs-metal-foil-liningQuoteEDIT:So the answer is:Yes (or no, or even something else), because every story/cloud has a silver lining.QuoteEdit2:QuotePlease tell me more about the boss?

author: mzzj
author_rank: Super Contributor
timestamp: May 01, 2023, 03:28:49 pm
content: You can fail the test even with the metal lining or pass it without lining.For the smps consultant I’d suggest metal lining: better change to pass the requlations as the consultant typically wont be able to afford the standards, let alone the actual testing. And the design is ”verified” on online forum where other users give half-assed answers or just plain troll to consultants questions.Here is a advance seal of approval to the design and any questions related with it:

author: MK14
author_rank: Super Contributor
timestamp: May 01, 2023, 03:55:24 pm
content: The following link, seems to show the development of the OP's question(s).https://www.edaboard.com/search/2983411/Where I suspect user (on the linked to forum) cupoftea = Treez = FaringdonRecent example:https://www.edaboard.com/threads/offline-smps-needs-metal-enclosure-to-pass-radiated-emissions.406663/#post-1753116Quote

author: Gyro
author_rank: Super Contributor
timestamp: May 01, 2023, 03:57:38 pm
content: Maybe these disreputable consultancies could make use of this (they must manage customer availability expectations carefully though!)...

author: Faringdon
author_rank: Super Contributor
timestamp: May 01, 2023, 05:28:33 pm
content: QuoteThanks, but it woudl be irresponsible not to add the metal lining, or at least to leave room for it.Point 8 of the following states why the metal foil lining is needed.https://www.eetimes.com/safety-concerns-for-practical-emi-line-filters/..This is wrtten by one of the greatest Power electronics engineers that ever lived...Sanjaya Maniktala....Principal Engineer at Power Management Group of National Semiconductor.I think we all pretty much agree that we are going to be planning to use a metal lining in our plastic enclosed offline SMPS?Certainly in my experience, if you even suggest to doing offline SMPS without metal enclosuring, you are viewed as semi-insane......but ive added units to smps's in metal enclosures....and the cables i brought out of the metal box's had to be shielded otherwise radiated EMI played havoc.

author: mzzj
author_rank: Super Contributor
timestamp: May 01, 2023, 05:33:24 pm
content: Quote from: Gyro on May 01, 2023, 03:57:38 pmIt says it protects from slugs but how about EMI?Would you agree that the copper tape has to be actually specified for EMI suppression instead of garden use and of slug suppression?How do you test the attenuation of slug infestation? My boss told me we need 100% slug-proof shielding. I think gardening consultants are scamming us as there is no way to fit 1 million slugs over 1 meter of copper tape to verify a minimum of 120db slug reduction. Would you agree?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2023, 05:58:13 pm
content: Quote from: mzzj on May 01, 2023, 05:33:24 pmVideo game reference: telepathic alien slugs. I bet copper makes an excellent tinfoil hat against them! Bonus if it keeps their slimy pseudopods off my back too.Tim

author: Gyro
author_rank: Super Contributor
timestamp: May 01, 2023, 06:04:33 pm
content: Quote from: mzzj on May 01, 2023, 05:33:24 pmMaybe the copper mesh would be more applicable because it is specified for general pest control in an indoor and outdoor setting. On the face of it, this would give it a better chance of capturing those pesky emmisions, and indeed the dodgy consultants themselves! Would you agree?P.S. Lidl have excellent aftersales service, so may be able to advise (on optimal deployment).

author: dmills
author_rank: Super Contributor
timestamp: May 01, 2023, 07:23:40 pm
content: The slug is a unit of mass (Yes really), but quite how to apply that to a rather "Hard of thinking" EMC design question?I mean copper is a slug repellent, I will grant you, but lowering emissions usually means more copper and hence more slugs of mass, checkmate EMC guys!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 02, 2023, 04:58:04 am
content: Quote from: dmills on May 01, 2023, 07:23:40 pmAs with applying a snubber to reduce transistor switching losses -- perhaps there is a global minima between the two extremes: no copper, maximum gastropoda slugs; maximum copper, maximum slugs of metal. Can we perhaps design a slug snubber? A slubber? Or would it be a slugger?Tim

author: 5U4GB
author_rank: Super Contributor
timestamp: May 02, 2023, 06:35:20 am
content: Quote from: mzzj on May 01, 2023, 05:33:24 pmSo your company builds power substations for the US market?

author: f4eru
author_rank: Super Contributor
timestamp: May 02, 2023, 11:45:50 pm
content: Better get a tungsten, or depleted uranium mesh instead of copperhttps://www.forbes.com/sites/davidaxe/2023/01/27/the-tungsten-m-1-how-ukraines-tanks-will-differ-from-americas/?sh=1c2a930326b3Sure, you can never build a PSU into a plastic case ! It's utterly ImpossibolHow would you even dream to pass EMC with a plastic case only

author: Gregg
author_rank: Super Contributor
timestamp: May 03, 2023, 12:32:55 am
content: We’ve all heard of Faraday cages, but what is really needed here is a Faringdon cage!

author: coppice
author_rank: Super Contributor
timestamp: May 03, 2023, 12:41:55 am
content: Quote from: mzzj on May 01, 2023, 05:33:24 pmPeople have always expected me to produce bullet proof designs.

author: jonpaul
author_rank: Super Contributor
timestamp: May 06, 2023, 07:21:50 am
content: Could our friend FTTS (Farrington/Treeze Time Sink ) be a very advanced chatbot, perhaps promilgated by the Russians or Chinese to waste our time and energy?Jon

author: mzzj
author_rank: Super Contributor
timestamp: May 06, 2023, 10:12:03 am
content: Quote from: jonpaul on May 06, 2023, 07:21:50 amHas crossed my mind couple of times that we are attempting to coach chatGPT to build power supplies.If I bother to answer it’s usually because the question might be worthwhile to answer providing some info for some other beginner even if it seems like wasted effort with OP.