From: liz@poppyrecords.invalid.invalid   
      
   Bill Sloman  wrote:   
      
   > On 21/12/2025 1:39 am, Liz Tuddenham wrote:   
   > > Bill Sloman  wrote:   
   > >   
   > >> On 20/12/2025 10:02 pm, Liz Tuddenham wrote:   
   > >>> Bill Sloman  wrote:   
   > >>>   
   > >>>> On 19/12/2025 6:49 am, Liz Tuddenham wrote:   
   > >>>   
   > >>> [...]   
   > >>>>> Warning the user isn't much good, the battery technology needs to be   
   > >>>>> fail-safe not impending-fail-evident to the user.   
   > >>>>   
   > >>>> Fail safe would involve a big resistor into which you could start   
   > >>>> discharging the battery if you detected worrying warming. You'd have to   
   > >>>> design the system to cope with that, and it would  make the designers   
   > >>>> job more difficult.   
   > >>>   
   > >>> Let's do some sums:   
   > >>   
   > >> First show where you got your numbers from.   
   > >>   
   > >> I've snipped out that bit of bizarre speculation.   
   > >   
   > > In more detail: the delamination of the seperator occurs at 25 metres   
   > > per second but the thermal runaway reaches a peak of 600 mm/sec and then   
   > > falls to 80 mm/sec according to Franson, Pfaff et al. "Exploring thermal   
   > > runaway propagation in Li-ion batteries through high-speed X-ray imaging   
   > > and thermal analysis".   
   > >   
   > > For their experiment, they initiated the failure by penetration with a   
   > > nail, but the same propagation could equally well be started by failure   
   > > of a very small area of a separator.  The nail penetration was near the   
   > > casing and this sometimes resulted in a hole melting in the casing and   
   > > relieving the excess internal pressure.  A separator failure  away from   
   > > the casing could well result in much higher pressures and greater   
   > > spreading of incandescent materials   
      
      
   > This wasn't just an experiment, but rather a piece of fossil carbon   
   > industry propaganda generated by simulating a remarkably improbable   
   > incident.   
      
   Do you have any evidence for that?  ...or should all experiments that   
   don't give the results you agree with be dismissed as propaganda?   
      
   A wise man adapts his ideas to take account of reality   
      
      
   > > They measured the propagation time between the initially-failed cell and   
   > > an adjacent cell to be about 4 minutes but various videos of lithium   
   > > battery fires show cells exploding at a faster rate than this, once the   
   > > fire has taken hold.   
   > >   
   > > If we take the 4-minute figure as a reasonable approximation, this is   
   > > the time in which a 70 kWh battery must be discharged to prevent a   
   > > failed cell from setting off the others.  That is more than 1 megawatt   
   > > to be dissipated in something the size of a car.   
   >   
   > This is roughly equivalent to insisting that petrol-engined car won't   
   > catch fire if you shoot a bullet into the petrol tank.   
      
   Your analogy is completely false.   
      
   They initiated the fire with a nail, so that they could be certain of   
   the starting time.  They could equally well have initiated it by   
   over-charging the battery but the exact start of the process would have   
   been uncertain.   If you wanted to study the spread of fire from a   
   petrol tank, you would need to initiate the reaction by some   
   intervention that rarely occurred in practice - but it wouldn't mean   
   that measurements taken on the subsequent events weren't valid.   
      
      
   --   
   ~ Liz Tuddenham ~   
   (Remove the ".invalid"s and add ".co.uk" to reply)   
   www.poppyrecords.co.uk   
      
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