Chris, Your story sounds exactly like what happened to us about 3 years ago. Our company bought a design from another company that used a Vicor power system consisting of a Vicor Line Filter module, AC-DC module, and several DC-DC modules (note the isolation is in the DC-DC modules, not the AC-DC module so any caps to ground between these modules will cause your leakage to go high). When we tested it for Surge we started blowing up the AC-DC modules. Vicor was no help. They insisted that it passes when they test it. So, we had no choice but to design out the Vicor power system. About a year later, two guys from Vicor shows up at my door with sheepish looks on their faces. They admitted to the Surge problem with their product and insured me it had been corrected. But it was too late. We had already designed it out. We are considering a Vicor power system in future designs. They have a very nice flexible power system and I am hopeful that they are getting their act together regarding Surge. To be fair I must say that we fail a lot of power supplies during our regulatory evaluation. Many of them fail Surge or one of the other Immunities required for CE. The most common problem we see is during the Surge test many power supplies will shut down and restart. I bet we fail 2 out of 3 power supplies we have tested over the last 3 years. And you are correct, line filters will often make the Surge Pulse larger than 2KV, so PSU manufacturers should be designing for something higher, like maybe 3KV.
When power supplies fail Surge in our products we usually have to find an alternative power supply. Sometimes this can be difficult. I found a Surge Suppressor I thought might work, but have never tried it. Look at the OKAYA RAV-BWZ and RAV-BXZ series of parts. They are line to ground surge suppressor modules that has gas tubes to protect against high leakage. It says in their literature that these parts can be used on devices that require the CE mark. It has TUV to EN60099-1 and UL 1449. If parts like this can be used I'm sure there are others. It would be nice to know for sure if there are acceptable line to ground surge suppression devises out there. Maybe some of the safety authorities out there can give us their latest position on this subject. Several years ago I received the following text from this IEEE email group. Maybe it will be helpful to you. Transient Suppressors according to EN60950 CCA doc section 1.5 ACROSS THE MAINS Transient suppressors can be connected across the mains if it is separately approved to IEC 1051-1 and IEC 1051-2 (or CECC 42200). If it is not separately approved, then a short-circuit protective device (such as a fuse) is required. BETWEEN LINE AND GROUND (PE) It is NOT recommended that Transient suppressor are used between Line and Ground due to the many safety issue it generates: varistors has the tendency to generate excessive leakage current within a few years of use, and a varistor >from line to ground will cause a false production High Pot test failure. Transient suppressors can only be connected from Line to Ground (Protective Earth) on pluggable equipment if a gas tube and fuse is in series with the varistor (transient suppressing device). To solve the High Pot problem, some companies install a special screw in the back on the unit that opens the ground connection to the transient suppressing device when the screw is removed. If this approach is taken, it must be well documented in the User's documentation. Surge Suppressors are allowed from line to ground on Permanently connected equipment. Hope this was helpful. Brian Kunde LECO ____________________Reply Separator____________________ Subject: Vicor Power Supply Surge Immunity--- More testing... Author: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: 5/05/03 12:02 PM All, It seems that I could possibly pass the testing with a suppression device between Line and Chassis (probably from Neutral to chassis as well). Some experiments with TVS diodes that I have on hand have been promising. However, the diodes can't stand up to the multiple surges. i.e. I get passing test results until the TVS diodes are reduced to a broken pile piece of Silicon with all of its smoke let out. I'm also concerned with leakage current. My design already has a MOV from Line to Neutral; but I have heard that such components are taboo from Line to Chassis or Neutral to Chassis. Is there a "Y rated" TVS, MOV, Sidactor... out there? I'm tempted to try some 4700pF Y caps that I have around to see if they'll soak up the surge a little bit. Chris Maxwell | Design Engineer - Optical Division email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: Chris Maxwell > Sent: Friday, May 02, 2003 8:33 AM > To: 'EMC-PSTC Internet Forum' > Subject: Vicor Power Supply Surge Immunity > > Colleagues, > > Has anyone out there designed power supplies based on the Vicor 2nd generation converters? I have a design based on the Vicor "FARM" (Filter And Rectification Module) with two Vicor V300 series DC-DC converters behind it. > > I can't get this design through surge testing at 500V/250V, even though the data sheets for all of the modules claim immunity to 2KV/1KV. I'm not taking issue with the data sheets, Vicor makes good stuff. I just can't figure out what's up with this design. > > I have followed the spec sheet protection recommendations to the letter. I have suspected the Corcom 6ED8 filter in front could be causing "ringing" of the surge; but found that the failure occurs with or without the filter. > > The failure is very strange in that it: > -Is load dependent. It seems that a higher load makes failure more likely > -It happens at a random time, up to 17seconds after the surge. > -Is characterized by the FARM's enable signal (which controls the V300s behind it) going low. > -I can get some improvment (pass 500/250 but fail 1000/500) if I remove chassis ground from the FARM heatsink. > > It almost seems as though the surge is passing through the FARM to its grounded heatsink, along the way, maybe it is heating up some components, perhaps this heat takes a little while to get to the FARM's thermal shutdown circuit, which then dumps the enable signal (I know, really far fetched.) > > Maybe a layout problem? > > I'd appreciate any experience that others could share with this. > > Thanks, > > Chris Maxwell | Design Engineer - Optical Division > email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 > > NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA > web www.nettest.com | tel +1 315 797 4449 | > > > > 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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
