[SystemSafety] E-bike battery fires in NY

[Bruce Hunter]

Good and useful discussions!

Product Safety standards do have strong requirements for safety of  primary
and secondary batteries in equipment. These standards (IEC 60950, IEC
62133, UL 1642, UL 2054 etc.) include proof of safety in fault conditions
including short circuit, thermal abuse, crush, overcharge vibration etc.
Compliance is required BEFORE Regulatory Compliance Marking and sale.

It still surprises and disappoints me that products are released that
still do not meet the requirements of these standards we have been around
for some time.

I have had experience 20 years ago assessing a Bus Drivers Console that
exploded after some time in use, hurting the driver and smashing the
windscreen. This was a small button lithium cell for memory backup, so the
explosive force was impressive for its size. The product did have
Compliance Marking but we found that the isolating diode for the battery
was reversed so that the battery was unintentionally receiving a continuous
high current charge. This manufacturing error should have been picked up in
testing.

This has since made me suspicious of product safety labelling and
statements of compliance to standards. Dormant failures are the bane of
safety.

Best regards,
Bruce Hunter





On Wed, 16 Nov 2022 at 03:21, M Ellims <mike at ellims.xyz> wrote:

> Inserted below...
>
> -----Original Message-----
> From: systemsafety [mailto:
> systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of Peter
> Bernard Ladkin
> Sent: 15 November 2022 09:34
> To: systemsafety at lists.techfak.uni-bielefeld.de
> Subject: Re: [SystemSafety] E-bike battery fires in NY
>
>
>
> On 2022-11-15 10:13 , M Ellims wrote:
> >> For some perspective - it's not just batteries...
>
> > I would distinguish battery safety from electrical safety in general.
> The causes of battery fires > are physico-chemical and very different from
> the causes of electrical-circuitry fires.
>
> The primary cause of most battery fires is not usually the underlying
> chemistry or physical manufacture, failure rates are quoted between 10E-8
> and 10E-11 for individual cells HOWEVER take with a grain of salt as
> getting good information is difficult!
>
> The primary cause is usually some sort of abuse while in use e.g.
> Attempting to charge cells below zero deg. C which can lead to dendrite
> formation (spikes of lithium metal), vehicles will warm cells up to above
> zero degrees before allowing charging to start (discharge is OK though).
> Other things that can cause cell damage are
> - discharge below some specified cell voltage
> - overcharging i.e. raising cell voltage about some threshold
> - charging or discharging about temperature threshold
> - failure to re-balance cells (as they age)
> - Using mismatched cells in a battery pack i.e. cells with for example
> different internal resistances.
>
> Precise nature of issues is somewhat dependant on cell chemistry but the
> above is a reasonable catalogue.
>
> But a poor pack design coupled with a low cost charger...
>
> >> However the risk of a single cell failing can simply be mitigated in
> >> many cases, research from NASA and NREL suggests that by simply
> separating cells from
> >> each other by 1-2mm almost removes the risk of a chain reaction
> occurring.
>
> > It depends how big the cell is; it depends how the separation is
> achieved. Safety also depends upon > the design of the containment
> structure. When Tesla started out, they claimed their battery design, >
> following these principles, was such that thermal runaway on a cell was
> contained. Part of the
> > solution to the Boeing 787 problem was a heavy containment structure
> that more or less undid all of > the claimed weight advantages of
> lithium-ion main batteries.
>
> Tesla vehicles have actually performed fairly well as far as containment
> is concerned. It can of course fail when you ram the car into something
> immovable at high speed.
>
> I think with the 787 is one of the problems is that they didn't allow
> sufficient space between cells, so there was a clear path for heat transfer
> between them. It's also possible that the pack designers didn't appreciate
> how much a cell will expand when it fails. For example a  18650 cylindrical
> cell will produce something like 25 litters (at STP) of gas if it ignites.
>
> >> It would also probably be better if lithium iron phosphate chemistries
> >> were used
>
> > What are those? Linden's 4th edition (2011) has lithium iron disulphide
> but
> > no lithium iron phosphate amongst the combinations.
>
> Probably the most widely used battery chemistry for electric vehicles
> (i.e. just about everything built in China).
>
> https://en.wikipedia.org/wiki/Lithium_iron_phosphate
>
> >> nickel-magnesium-cobalt (LFP vs NMC)
>
> > What are those? Again, Linden's 4th doesn't have them.
>
> They and NMA (Nickel-Magnesium-Aluminium) batteries have all but replaced
> an older generation of cells based on LiCoO2 (Lithium-Cobalt-Oxygen)
> chemistries as they are far less likely ignite and use much less cobalt.
>
>
> https://en.wikipedia.org/wiki/Lithium_nickel_manganese_cobalt_oxides#Use_of_NMC_electrodes
>
>
>
> PBL
>
> Prof. i.R. Dr. Peter Bernard Ladkin, Bielefeld, Germany
> Tel+msg +49 (0)521 880 7319  www.rvs-bi.de
>
>
>
>
>
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