What temperature indicates the start of thermal runaway in a lithium ion battery?

[guerney]

While charging my battery last night, the case felt a little warm to the touch after about 15 minutes, it was cool again after 40 minutes, as it continued charging... therefore I was wondering what temperature would indicate the beginning of thermal runaway - if known, would a thermal alarm with the sensor inside the battery pack possibly provide a useful timeframe of advance warning? This "pulse" charger from ebikebatteries.co.uk starts charging at a low voltage, which may reduce the initial temperature spike? I wish they didn't insist on bank transfer as payment method, which is basically a donation with zero buyer protection.

eBike Batteries 36v 2A Lithium-ion charger (CE & ROHS Certified) – eBike Batteries

ebikebatteries.co.uk

 

[StuartsProjects]

I wish they didn't insist on bank transfer as payment method, which is basically a donation with zero buyer protection.

I dont do online banking, I spent too long working in data security and know what the 'experts' get up to. If you make a mistake with on-line then your money can be gone for ever. And because I dont use on-line banking, if there was a hacking attempt, then I have good evidence it was unliklely to be me.

Same with contactless payments, dont use them, so if my card is lost\stolen the bank would not find it easy to claim I had been making subsequent payments.

ebikebatteries.co.uk accept cheques, remember them ?

 

[guerney]

I dont do online banking, if you make a mistake then your money can be gone for ever. And because I dont use on-line banking, if there was a hacking attempt, then I have good evidence it was unliklely to be me.

Same with contactless payments, dont use them, so if my card is lost\stolen the bank would not find it easy to claim I had been making subsequent payments.

You could use a prepaid credit card, limiting damage in the event of horrible happenings. The Post Office offers a multi-currency Mastercard, which you can top-up as needed. Foil over your card would stop contactless card sniffing pocket thieves.

ebikebatteries.co.uk accept cheques, remember them ?

Do they? But then someone also has your signature, as well as address, sort code and account number:

Clarkson stung by fraud stunt
The charity is one of many organisations that do not need a signature to set up a direct debit.

https://www.theguardian.com/money/2008/jan/07/personalfinancenews.scamsandfraud

 

[StuartsProjects]

Do they? But then someone also has your signature, as well as sort code and account number:

Sure, but its the lesser of the evils.

I would much prefer to pay by Paypal etc.

 

[StuartsProjects]

would a thermal alarm with the sensor inside the battery pack possibly provide a useful timeframe of advance warning?

Maybe, but where to put it ?

Do all the cells do thermal runaway at the same time ?

 

[guerney]

Maybe, but where to put it ?

Perhaps a set of far-infrared sensors? They wouldn't need to be inside the battery pack.

Do all the cells do thermal runaway at the same time ?

Like people, it's always the quiet ones who suffer in silence and explode when you least expect, inflaming anyone nearby.

 

[StuartsProjects]

You would think that someone somewhere sells a temperature alarm in the style of a smoke alarm that you could plonk on top of the batttery whilst its charging.

 

[guerney]

You would think that someone somewhere sells a temperature alarm in the style of a smoke alarm that you could plonk on top of the batttery whilst its charging.

With user-assignable temperature control triggering the alarm, set to sound before lithium ion battery thermal runaway temperature, at whatever point that hapens.

 

[guerney]

I already have one of these, of which I could attach the probe to the battery case using gaffa tape, to switch off the charger if temperature of say 80 degrees C (?) is detected, which could also switch off a desk lamp... I could buy a second unit to switch on a more suitably alarming siren and bright strobe at 79 degrees.

https://www.amazon.co.uk/Lotvic-Temperature-Controller-Thermostat-Greenhouse/dp/B0BL7CHS1F/

 

[Woosh]

I was wondering what temperature would indicate the beginning of thermal runaway

The internal resistance of a cell drops when the temperature rises.
the mechanism of thermal runaway is that something, a mechanical or electrical or chemical event triggers that positive feedback loop. When it's a fault, it raises the temperature past the point of no return. The positive feedback causes the temperature to rise which causes the current (usually charging current) to rise which increases the temperature even further until the cell starts a fire. It can happen to more than one cell at the same time depending on the cause of the trigger.

Do all the cells do thermal runaway at the same time ?

It's usually just one cell which then catches fire and sets off neighbouring cells.

 

[Nealh]

Are you sure it is cell heat and not the BMS being the heat source.

 

[guerney]

Are you sure it is cell heat and not the BMS being the heat source.

I suppose I could charge the battery with thermometers attached to the cell pack and BMS to find out. Thermal imaging cameras are getting cheaper, which could possibly show hotspots without needing to open the battery case - this phone has one:

 

[guerney]

Are you sure it is cell heat and not the BMS being the heat source.

I was wondering whether some sort of contraption to detect heat spikes inside battery packs, would provide a useful length of time to serve as advance warning of impending doom by lithium ion battery fire. But to answer your very good question, I am charging the battery now, monitoring using a LCD room thermometer strip, and the temperature is a tad higher on the side over where the BMS is located: 21 degrees on top, 24 on the side. I don't usually charge the battery on it's side, but did so while in a hurry last night. I wasn't imagining this slight warming after all, having got jittery after a lithium pouch battery puffed up like a ball yesterday, blowing the bloody printer door off with a bang. Using my newfound soldering superpowers, I soldered two battery contacts on the printer together, so it works using the power supply without the unobtanium-ion battery.

 

[AndyBike]

I dont do online banking, I spent too long working in data security and know what the 'experts' get up to. If you make a mistake with on-line then your money can be gone for ever. And because I dont use on-line banking, if there was a hacking attempt, then I have good evidence it was unlikely to be me.

Same with contactless payments, dont use them

likewise, as in online banking with the high st banks, though I do use paypal(and have done for 15 years)
Problem as I see it with the online banking is soon as you do and theres a prob or a fraud, its going to be near impossible convincing a bank that the breach was their end and not something you've failed to do, and I am seeing banks almost using this as an excuse to avoid paying any compensation, even though many breaches are at their end due to a rogue employee.
Contactless is ok, in places like a big supermarket, but no way in god i would use it in a local store or newsagent.

 

[guerney]

After the charger LED goes green, indicating the start of the balancing phase, the battery case, over the area above the BMS, heats up a couple of degrees beyond 24C... If I were to rig an alarm siren, I'd set it to sound at 40 degrees. My latest plan for a home free of battery fire, is to charge the battery in a metal box suspended by chains, held high from my sturdy new Aldi bike stand's clamp (extends to about 1.8m), next to an open window - if I hear the siren, I'd simply kick the bike stand over so that the box hangs out of the window, then throw it and the battery out the window into a water butt outside, lifting it by the legs, kindof like a pole toss at the Highland Games. There may even be time to don a kilt and cue my favourite bagpipe LP, but unlikely enough time to eat a bowl of porridge. Throw it out early I say (battery fire, not porridge).