From: bill.sloman@ieee.org   
      
   On 19/12/2025 7:16 am, john larkin wrote:   
   > On Thu, 18 Dec 2025 19:49:36 +0000, liz@poppyrecords.invalid.invalid   
   > (Liz Tuddenham) wrote:   
   >   
   >> Bill Sloman  wrote:   
   >>   
   >>   
   >> [Lithium batteries    ....again!!]   
   >>   
   >>> More technically, they can go into thermal runaway - they have to get   
   >>> above 120C before they can do it,   
   >>   
   >> How does the sensor monitor every part of the battery?  A small defect   
   >> in a separator could easily heat up to 120C before the temperature of   
   >> the mass of the cell rose noticeably.   
   >   
   > A microscopic dendrite defect can start an ignition that propagates in   
   > all directions at centimers per second.   
      
   The dendrite has to grow before it can initiate an ignition.   
      
   You've got to abuse a battery for quite a while before you can get it to   
   ignition, and presumably the area around the dentrite will be warm for   
   quite a while before it gets hot enough to initiate thermal runaway.   
      
   Hot spots in batteries warm up the whole battery. The component cells   
   have a much higher thermal conductivity than the outside air.   
      
   >>> so any sensible battery condition   
   >>> monitoring scheme can warn the user long before there much of a risk.   
   >>   
   >> Warning the user isn't much good, the battery technology needs to be   
   >> fail-safe not impending-fail-evident to the user.   
   >   
   >   I once worked with a fire alarm company in Freehold, New Jersey.   
   >   
   > They had a sign on the wall   
   >   
   >    IN CASE OF FIRE RUN, YELL "FIRE"   
      
   People who design fire alarms are more aware than most that they can fail.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)