Hello Guys, Apologies for getting into many IF's. Yes, our discussion is based on assumption and description provided. There are many unknown for us on his unit.
I believe the fundamental of the safety concept, which have been discussed should be look in depth by Raymond. Maybe it is time for Raymond to give us some input over the different area we discussed. Best Regards, Chengwee From: Peter L. Tarver [mailto:peter.tar...@sanmina-sci.com] Sent: Wednesday, November 05, 2003 7:40 AM To: emc-p...@ieee.org Cc: raymond...@omnisourceasia.com.hk; c...@netscreen.com; 'Rich Nute' Subject: RE: Class 1 AC/DC adapter Let's look at these what ifs. > From: ChengWee Lai > Sent: Tuesday, November 04, 2003 4:38 PM > > Raymond might be able to convince Safety agency > to accept PE continuity test > with 1500Vac Hipot at the production line. > However in the Scenerio with end > customer, it could mean business or no business. > > Question regarding: > > Whether customer can accept his adaptor with only > 1500Vac hipot tested where > other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. > Would that affect his customer Safety testing, > because his customer unit > with his power supply only meet 1500Vac hipot > after heating test? Only Raymond and his customers can answer this. > Or what if Safety agency require his customer > unit to do grounding test to > accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. > Regards, > Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must bite the bullet to get into the market or meet a customer's time constraint. Regards, Peter L. Tarver, PE ptar...@ieee.org This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
