In message <[email protected]>, dated Mon, 13 Aug 2007, "MacArthur, Don" <[email protected]> writes:
>1. Why is the above statement a requirement? Worded another way... It's probably pragmatic, to accommodate a particular product that has or had two cells in parallel and did not cause any safety problem for many years. This might well be so if the cells in question are/were zinc-ammonium (Leclanché), which have a fairly high internal resistance relative to more modern types. >2. What is the safety issue when cells are connected in series with >some in parallel when the cells are used in an explosive gas >atmosphere? In general, cells in parallel are a safety hazard wherever they are, especially with modern high energy-density cells. This is obviously because if one cell develops a fault, or is inserted incorrectly, a very large circulating current is likely to flow, with consequent heating and expansion, perhaps violent. If there are cells in series as well as in parallel, the total energy stored is greater, so the risk of heating to high temperatures is greater. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
