<q> It was like testing fuses <q> Exactly! Most smart-batteries have non-resettable fuses designed to be tripped by over-temp. Originally thought to protect the chemistry from reaching ignition temps. But as Ed found, also a very good one-time RF detector!
// Patrick -----Original Message----- From: Ed Price [mailto:edpr...@cox.net] Sent: Thursday, August 23, 2012 1:21 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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:oconne...@tamuracorp.com] Sent: Wednesday, August 22, 2012 1:47 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Wednesday, August 22, 2012 10:55 AM To: emc-p...@ieee.org 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: <rehel...@mmm.com> Date: Wed, 22 Aug 2012 11:43:03 -0500 To: <emc-p...@ieee.org> 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. 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