Operating a CE marked power supply out of spec - Page 1
Forum section: electronics / projects

author: Mark
author_rank: Frequent Contributor
timestamp: February 26, 2019, 02:56:41 pm
content: Hello,If we purchase a CE marked power supply that has a DC input voltage range Vmin to Vmax but we intend to operate it outside that range (lower than Vmin) will it invalidate the CE mark?.Thank you.

author: grifftech
author_rank: Frequent Contributor
timestamp: February 26, 2019, 03:00:35 pm
content: Will it even work?

author: Mark
author_rank: Frequent Contributor
timestamp: February 26, 2019, 03:09:00 pm
content: Quote from: grifftech on February 26, 2019, 03:00:35 pmSuppose the manufacturer specifies a DC-DC power supply for 120VDC minimum. If we want to use the PS at 90VDC, and we test it down to 80VDC and "it works"....I am thinking that is a Bad Idea because we need to treat the PS as a black box. The lower voltage will result in a higher input current and could cause components or traces to overheat, maybe the transformer winding will get too hot and damage the insulation so that it fails sometime in the future when used at a higher voltage...

author: Gyro
author_rank: Super Contributor
timestamp: February 26, 2019, 03:19:44 pm
content: It depends how it is specified - for instance a universal input SMPS that is specified for 120 - 240V [EDIT: AC] mains with actually be designed to operate over a 90 - 264V input range to cope with mains voltage tolerances. Of course operating at 90V gives you no further negative tolerance allowance. 80V sounds too low.QuoteExactly so (although transformer insulation damage is probably less of a concern). The switching devices etc will certainly be under higher current stress though. EMC emissions could also possibly go outside limits.EDIT: Of course, in a production environment, using any component, be it a resistor or a 'black box', outside its specifications is very bad (unacceptable) practice that will usually end in tears.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 26, 2019, 03:58:58 pm
content: Who is "we", and what's the intended purpose? Are you designing a product or is it as an end-user?If you're designing a product, want to use a power supply for it (that you'd buy as a CE-marked end-product), and this power supply would be an integral part of your product, the CE mark of the power supply, which would then just be a component of your product, doesn't really matter. The CE mark of a product is not a simple addition of already CE-marked parts. So if this is your question, you're probably asking it wrong.Whatever you do, you'd have to CE-mark your product as a whole. Power supply included. The fact that you'd be using it out of spec is a clear indicator, IMO, that you'd be using it as a component of your product and not just as an off-the-shelf accessory, so again its own CE mark is not the question. Its compliance to some standards (UL for instance) would certainly help in your CE mark process, but if you're using it out of spec, obviously you can't claim the standards it's compliant with. So not only will you have to prove your whole product is compliant, including the power supply and all testing concerned, but you would also lose any warranty or ability to get back to the manufacturer of this PS in case of any fault (even if not related to your using it out of spec...)Overall, this all sounds like a very bad idea, because you'd take full responsibility for the PS and would have to have it re-tested with your own specs, which could be costly, but also you'd probably never be able to get complete compliance without having the technical documentation, include the schematics...If, OTOH, you're asking this as an end-user, then this is a different question and yes that would invalidate any claimed compliance, thus ultimately the CE mark, and also any warranty. Possibly if that ever caused a fire, you could also get into nasty troubles with your insurance company.

author: Mark
author_rank: Frequent Contributor
timestamp: February 26, 2019, 04:51:14 pm
content: Hi SiliconWizard,We are designing a product which will be CE marked and using a CE marked power supply module internally to our unit.My worry is that this power supply is not just a component of our product, but a safety critical component.It is my understanding thatsafety critical componentsMUST be CE marked on their own, by their manufacturer.http://www.tracglobal.com/sites/tracglobal.com/files/pdfs/componentacceptabilityforceproductsafety.pdfThe above PDF "Guidelines for selection of safety critical components " says:Quote from: tracglobalSo my question would be, if the PSU needs to be CE marked, but it has only been rated for use at 120VDC, wouldn't it invalidate the CE mark if we use it outside the ratings? In other words, what's the point of requiring a CE marked safety critical component if it is allowable to use it way out of spec?Is there a definitive (legal) answer on whether safety critical components can be used out-of-spec in normal operation?

author: ogden
author_rank: Super Contributor
timestamp: February 26, 2019, 04:56:55 pm
content: Quote from: Mark on February 26, 2019, 04:51:14 pmIt would not invalidate CE marking if you operate supply *below* it's input voltage specs. Anyway you are advised to ask manufacturer, not public forum where anybody can say anything. If current supplier/manufacturer do not talk to you - better find one who does.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2019, 05:17:34 pm
content: There's a lot of myth on "safety critical components", like they come from the Heaven as-is, and your product magically becomes compliant by installing them.In reality, someone makes these "safety critical components" from non-safety critical components! You can be this party. And, if you use a product outside of it's intended parameters, you already are in this position: you need to make a compliant product to whatever requirements are relevant to your product segment; including the internals of this power supply. If you cant't find a more suitable one, then you do what you need to do. The options are, do thorough evaluation and testing (including documentation) for the product to actually prove it works with the reduced voltage; or design your own ground-up. It's hard to say which one is harder - both require a lot of work and understanding about SMPS design.You say this is a "safety critical component". Why do you think so, are you sure it is? Is a 80VDC system such? (Asking because I don't know.)

author: Gyro
author_rank: Super Contributor
timestamp: February 26, 2019, 05:20:21 pm
content: That document you linked is a pretty good summary, but as it states normally refers to discrete safety critical components - X and Y caps, Optos, detailed construction and insulation used in the transformer, etc. If you are the power supply manufacturer, to obtain the safety approval documentation for all of these all these from the component manufacturer and include them in your Technical Construction file - the test house... and anyone challenging your CE certification will want to see them. BTW as the customer of the PSU manufacturer you are entitled to ask for copies of them.It is for you to determine whether the PSU is a safety critical component in your system - I note that you indicatedDCinput. This implies that it is not directly mains connected and that you may have other safety components in place to mitigate the effects of its failure.Quote from: Mark on February 26, 2019, 04:51:14 pmThat's the killer. The definitive legally responsible entity for the safety of your product is YOU, in association with your overall 'Design Authority' (but individual engineers can still be held liable). It is you (collectively) who decide what components you put in your product and how you use them. It doesn't matter whether you use a CE marked PSU or not. The only thing the Law is concerned about is who puts thefinalproduct on the market, which is you (or the importer if bringing in from abroad).You might have a secondary case against the PSU manufacturer if your product kills someone (though not likely if you used it out of spec) but that is entirely a separate matter. All the law is interested in is the final product and whether you acted wilfully or negligently, in its design and manufacture, including your choice, sourcing, and usage of components.

author: Eric_the_EE
author_rank: Contributor
timestamp: March 01, 2019, 03:13:08 am
content: With which EU directives and standards are you trying to declare conformity regarding your unit? I assume you want to conform with EMC and LVD directives. If so, there isn't anything in the EMC directive to my knowledge that would cause a conformity issue with your scenario. But the LVD probably will. You first should identify which applicable standards in the LVD you want to evaluate your unit against. I've only tested against EN61010. IIRC there were some sections in the EN61010 that addressed this very topic. Essentially, improperly use of certain components inside a product would not allow you to pass evaluation against EN61010 (thus rendering your unit non conformal to CE marking requirements). But this was just my experience with a specific product.But this CE marking process all begins with identifying which EU directives are applicable to your device, then choosing which standards you want to be tested/evaluated against. Those standards will explicitly answer these types of questions.