Thanks for the response. It's hard to say. I wasn't there for the hipot test. I just saw the aftermath.
A little background: The unit under test had a power supply which we designed from off the shelf building blocks. The first building block is a rectifier/doubler, which takes the AC input and rectifies it. The rectifier also has some "smarts" which kick in a doubler for input voltages under 180VAC. The output of the rectifier is always about 320VDC. This 320VDC is split into two rails of 160VDC each so that 200V, low profile capacitors can be used. Each of these split rails is protected by a 230V gas tube. The 320VDC is then used by high voltage DC/DC converters (purchased modules) which make 5V and 12V. The hipot test burned out the rectifier. My guess is that the gas tubes on the output fired. Since they have such a high instantaneous current draw, the recitifier could be momentarily overloaded. Even the fuse in front of the rectifier (it did blow) could not protect the rectifier from the hard blow characteristic of the gas tubes. We could populate the circuitboard without the gas tubes, assemble the unit, hipot test it and then install the gas tubes. However, to me, this would seem to make the hipot test superfluous. The amount of re-assembly required to re-install the gas tubes would make the initial hipot test a waste of time. There would be all sorts of chances for somebody to drop a screw into the unit, or leave one out. Is there a way that the subassemblies could be hipot tested, then the main assembly could have a low voltage hipot just to check for the ubiquitous "dropped screw"? Chris Maxwell | Design Engineer - Instruments Group 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: Rich Nute [SMTP:[email protected]] > Sent: Thursday, August 28, 2003 1:31 PM > To: Chris Maxwell > Cc: [email protected] > Subject: Re: Hi-Pot testing > > > > > Hi Chris: > > > > During safety testing at the lab, the unit passes HiPot > > testing. However, the unit is broken by the testing. > > > > Rigorously, the unit "passes" its type testing because > > it doesn't become unsafe by the Hipot. However, it isn't > > functional after the test; and it requires repair. > > I have two questions: > > 1. Is the functional failure due to over-voltage > of a component? > > Or > > 2. Is the functional failure due to the hi-pot > "leakage" current between primary and secondary? > > If 1, then you should be able to disconnect that > component during the test. Or, you could use the > solution for 2. > > If 2, then the problem becomes much more complex. > We test the board before it goes into the product > using a "bed of nails" that equalizes the potential > on throughout the primary and throughout the > secondary. This prevents current through the > components, yet tests the isolation between primary > and secondary. > > Of course, such a test does not test the board in > the end-product, which is a problem if the enclosure > is metal. > > Without more details of your circuit and the parts > which are broken, I cannot give you further advice. > > > Best regards, > Rich > > > 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
