Ed nails it again! I used a homebrew parallel plate and illuminated the batteries in all three orientations relative to the vertical electric field.
And it's not terribly surprising that battery manufacturers don't have a lot of EMC experience. They never needed to consider it previously. Ken Javor Phone: (256) 650-5261 > From: Ed Price <[email protected]> > Organization: ESP Labs > Reply-To: <[email protected]> > Date: Thu, 23 Aug 2012 12:20:37 -0700 > To: <[email protected]> > Subject: RE: [PSES] "Smart" Batteries > > At my previous employer, we began using "smart" batteries around 6 years > ago. These batteries were mounted into a soldier-worn fabric harness, and > were the power source for both the optical detectors & signal processing > equipment, plus the pulsed 20 Watt peak RF data transceiver. Batteries were > charged in a shop environment, then plugged into the soldier harnesses and > used in the operational environment for a few days (either before the > training scenario ended or a fresh battery was installed). Thus, MIL-STD-461 > dictated testing in two environments; the stringent operational environment > (imagine a squad hopping on a helicopter, with all transceivers chirping > away and subject to the airborne RF environment) and the much less stringent > charging environment (imagine the corner of a storage shed, with a few dozen > batteries sitting in charging trays). > > The first time I encountered these batteries, I didn't realize that they had > built-in microprocessors that never turned off. In addition to the normal > "user" noise problems, I now had what had always been considered to be a > passive device contributing its own EMC problems. > > One interesting thing was that these "smart" batteries had a rather > long-period, short duration mode in which the battery brains would call for > a capacity test that created a quick noise burst. Another problem was that > the battery manufacturers were (initially) very EMC naive; no shielding, > long internal sensor leads that acted like little antennas and fed directly > into microprocessor inputs, apparently no history of ever doing any previous > component-level EMC investigation. > > So these batteries had emission and immunity problems all by themselves, and > we had to adopt several less-than perfect fixes in order to use them. We > went through powerline filtering, discrete harness pouch shields, wrapping > foil around the batteries, and even to conductive fabric harness pouches. > > And then, after we got happy with our fixes, we suddenly began having many > field failures, dead batteries everywhere! It seems that we had changed > battery vendors, and the new vendor had an internal design that was an > extremely good RF detector. Batteries could be killed with only a few V/M > (you could get 10 V/M from a cell phone at 6-foot separation, and anyway, > 461 defined a 50 V/M requirement)! Investigation revealed that the batteries > were also very position and polarization sensitive; they might survive 50 > V/M from the front, but roll them 90 degrees and expose the back, and the > microprocessor goes to silicon heaven in microseconds. The culprit turned > out to be the wiring for inter-cell temperature sensors; these fed the RF > directly into the microprocessor. During the course of one investigation, I > was directed to expose 25 batteries to varying positional and RF level > exposures; not one battery was alive by the time I was up to 20 V/M. It was > like testing fuses. We got that problem under control by going back to the > old vendor, and fortunately, since the batteries were designed to be easily > replaceable, there was no major field-fix problem. > > Since that was over 5 years ago, I would hope that smart battery vendors > would have become much more familiar with RF techniques and have hardened > their designs to withstand the commercial and military environments. OK, > this turned into a war story, but the lesson is that a smart battery now has > every EMC vulnerability itself, and has to be tested in every operational > and support mode associated with your product. > > > Ed Price > El Cajon, CA > USA > > > -----Original Message----- > From: Brian Oconnell [mailto:[email protected]] > Sent: Wednesday, August 22, 2012 1:47 PM > To: [email protected] > Subject: Re: [PSES] "Smart" Batteries > > Ken, > > For MS461, did you test the batteries as a seperate item, or as part of a > charger or the end-use unit? > > Brian > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of Ken Javor > Sent: Wednesday, August 22, 2012 10:55 AM > To: [email protected] > Subject: Re: "Smart" Batteries > > Not what you personally are looking for, but in the military world > MIL-STD-461 applies to such batteries just as to any other item that > contains electronics. I have tested them and found them susceptible, albeit > at field intensities much higher than required in the commercial world. > > Ken Javor > Phone: (256) 650-5261 > > > > From: <[email protected]> > Date: Wed, 22 Aug 2012 11:43:03 -0500 > To: <[email protected]> > Subject: "Smart" Batteries > > Can someone tell me if there are any EMC standards for the so-called "smart" > batteries? These are batteries that communication with the charger or EUT > for charge rates, time left, overheating, etc. > > Thanks, > Bob Heller > St. Paul, MN 55107-1208 > Tel: 651-778-6336 > Fax: 651-778-6252 > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used > formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
