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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: lithium explosion
Date: Sun, 14 Apr 2024 15:35:10 +1000
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On 14/04/2024 2:35 am, John Larkin wrote:
> On Sat, 13 Apr 2024 16:14:07 +0100, liz@poppyrecords.invalid.invalid
> (Liz Tuddenham) wrote:
> 
>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>
>>> On 13/04/2024 3:39 am, Liz Tuddenham wrote:
>>>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>>>
>>>>> On 12/04/2024 6:55 pm, Liz Tuddenham wrote:
>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>>>>>
>>>>>>> ... if
>>>>>>> it had a safe place to dissipate the stored energy.
>>>>>>
>>>>>> What if it didn't?
>>>>>
>>>>> Then it probably needs to include a louder hooter and brilliant flashing
>>>>> lights to serve the same purpose, if more slowly than a purpose designed
>>>>> dissipator.
>>>>>
>>>>>>> ..was being looked
>>>>>>> after by somebody who ignored the early warnings.
>>>>>>
>>>>>> That includes 99% of battery users who wouldn't know what to do it they
>>>>>> noticed the warnings or wouldn't be able to do it anyway.
>>>>>
>>>>> A voice message could be pretty explicit. All the message needs to say
>>>>> is to move the battery outside to where it can't do much damage if it
>>>>> bursts into flames. EV car batteries are big enough that that's quite a
>>>>> way, but cars are designed to move appreciable distances.
>>>>
>>>> It's not really a very good selling point.  "Oh, by the way, this model
>>>> has the latest upgrade and tells you when it is going to explode, so you
>>>> can get out of the way".
>>>
>>> You don't seem to have been paying attention. If you deal with the
>>> warning by discharging the battery, and making it safe, it won't explode.
>>
>>
>> Who it the 'you' in that sentence?  Do you mean the average user,  in
>> which case this is a hopeless scenario as most users of batteries
>> wouldn't have a clue.
>>
>> Until recently batteries have been inherently safe: unless you did
>> something stupid they were unlikely to give any trouble.  You are now
>> supporting a type of battery that is inherently unsafe and will catch
>> fire or explode unless the user takes some positive action.  Even if the
>> user delegates this action to an automated system there is no guarantee
>> that the action will be taken every time it is needed.
>>
>> 'Safety' that depends on taking a positive action to prevent a disaster
>> is not safe at all.
> 
> References say that a tiny separator defect spreads radially at
> centimeters per second. 

But you can't provide a link to any such reference.

Google threw up a paper on using airflow to test test battery separators 
before they were assembled into a battery, so your defect is going to be 
present in new cells, and detectable before they are into assembled 
batteries of cells.

> Any somehow-sensed defect will explode in
> flames in well under a minute, from the bad cell into the whole pack.
> See Youtube examples... smoke to explosion in seconds.

Youtube is full of half-baked rubbish, and you are sucker for that.
> If I heard an alarm from a lithium battery pack, I wouldn't try to fix
> it, I'd run in the opposite direction. What automated system could
> discharge an 80 KWH battery pack in a few seconds? Or even 1 KWH?

It doesn't have to discharge it in a few seconds. An increased 
self-discharge rate is detectable long before a cell gets to the point 
of thermal runaway - the local temperature has to get up to  between 
130C and 160C - depending on battery type - before it can move into 
thermal run-away, so you have plenty of time to make it safe.
> And a defect sensor would have to constantly snoop every cell of a
> pack. A typical Tesla might have 7000 cells.

It doesn't. It has to snoop the battery core temperature and compare it 
with battery surface temperature. A few sensors spread around the core 
would let you pick up the existence of hot spots - you wouldn't need to 
work out exactly where they were.

The Telsa battery monitors it own core temperature and has built in 
resistive heaters to warm it up when outside temperatures are too low to 
let it deliver full power at start-up.

-- 
Bill Sloman, Sydney