CR-Cells Can Go BANG!

There we were, four of us, a small family gathering this evening, when...

Bang!

A bit like a gun-shot at a moderate distance.

Everyone looked at me as the apparent source.

I was the source.

I was wearing my keys and a small l.e.d. torch on a lanyard tucked down inside my shirt. Dismantling the torch revealed one of its 4 CR44 button-cells, in a loose column inside the aluminium case, had burst.

Its spun-in cover has not detached completely, but is open at a shallow angle. None of the other cells are damaged though all are a bit low, at only 1.2V. The lamp seems unhurt but I can't test it until I buy some new cells. The explosion was entirely within the torch and I was not damaged either.

It may be salient that the cells are a sloppy fit inside the opened torch so you need be careful they don't overturn when installing them; but once in, the contact spring on the screwed base cap should keep them all in order.

Can anyone suggest why this cell may have burst?

IF the cells are in a column and not in a insulated sleeve (plastic tube) 1 or more can short circuit if the torch body is metal. Noel

Chemical energy can do weird stuff, could be a bit of contaminant got in during some stage of production

A lot of batteries can have the potential to explode, that is discharge rapidly and violently, Lithium cells are prone to catch fire spontaneously, hence the Air Carriage regs concerning their exclusion from enclosed baggage holds on aircraft. Royal Mail will not carry any batteries in mail, any equipment containing batteries or just batteries on their own must be consigned through a carrier who will handle packages that are correctly packaged with all relevant labelling. My wife has a cochlear implant which uses small rechargeable batteries, previously sent via Royal Mail Special Delivery now have to be sent via DPD. Dave W

Samsaranda said " Royal Mail will not carry any batteries in mail, any equipment containing batteries or just batteries on their own must be consigned through a carrier "

This is NOT correct. there are restrictions but you cna send many batteries through the post within the UK. Details are here: https://personal.help.royalmail.com/app/answers/detail/a_id/96/~/prohibited-and-restricted-items---advice-for-personal-customers

You must "drill down" through the links (in red) to find the exact item and situation. For example most batteries IN or with equipment are allowed as are most new cells in retail packaging. Even small sealed lead acid batteries are allowed.

Robert.

Two guesses:

1. An internal short circuit due to faulty mechanical construction. Although the chemicals inside the cell are quite energetic, they don't react unless the cathode and anode are connected allowing electrons to flow. The cells are made from a conductive metal pot crimped to a conductive lid and separated by an insulator. The metal parts are stampings, prone to whiskers, and the conductive lid might be faulty, and the whole come together in a press, maybe squeezing in a metal shaving or other dirt. Once the conditions needed to allow local corrosion start, you could get thermal runaway. OR
2. The environment is significant. The device is owned by a Model Engineer who makes loads of conductive swarf in all sizes from micro-particles to 10 metre ribbons! Maybe swarf got inside the torch when Nigel last changed the cells, where it rattled around inside until it shorted out a cell.

The longest I've seen swarf travel from my workshop is nearly 10 miles as the crow flies. Visiting mother one day, I noticed an Aluminium chip embedded deep into her best Persian Rug!

Dave

Royal Mail will deliver batteries in certain circumstances. I have sold two cameras which included their removable batteries. I was asked what was in the box, and replied "a camera with its battery fitted". That was ok because the battery was in its intended place. I have had batteries delivered via Royal Mail several times and strongly suspect that the senders had not been honest when posting them.

If you accidentally incinerate an alkaline button cell the contents boil and the case opens with a crack.

If you short a new one out, it heats up and does the same.

If you accidentally incinerate a box full it can be quite exciting

I hesitate to ask how you have such deep knowledge of this subject

In respect of Royal Mail and the carriage of batteries I bet you couldn’t get a package containing batteries past our local village postmaster, he refuses point blank to accept any batteries no matter what they are contained in, having witnessed how volatile batteries can be I am with him all the way.

in respect of the batteries that my wife uses in her cochlear implant, they are very expensive, costing into three figures each, and until the Royal Mail refused to carry them they always included a postage paid envelope to return the old batteries, apparently there was some value in recycling them for some purpose, but now the patient is asked to dispose of them and any recycling value is lost. (This is a private contractor who supplies the NHS with spares and repairs for the cochlear implants so there is an impact indirectly on public funds in that this now increases the overall contract costs). Dave W

Here are the official Royal Mail requirements for sending batteries.

**LINK**

Edited By old mart on 20/02/2023 19:02:04

Noel -

I suppose it's possible the cap had loosened enough for one cell to twist and short out on something, but not very likely and the cap seemed fully home when I examined it.

Although the cells are a loose fit by diameter, once all assembled in the torch they've nowhere to go.

.

Dave -

Interesting possibility, my having accidentally dropped swarf into it from my clothes.

I have had a spiral of bronze take advantage of most of the swarf falling safely in front of the lathe to sneak round the back and into the motor to cause a short-circuit that broke the electronics (3ph conversion on a Myford lathe).

A tiny particle though... maybe.

.

Robin -

Since the torch was inside my shirt, nestled against my chest, I am reasonably certain fire was not the cause. Body heat sufficient? I'd not have thought so.

.

Overall - I think Dave's idea, of a fault within the cell, the most likely cause.

If you throw handfuls into a waste paper basket you can expect a few bangs as they short each other out. Makes you jump.

The contents swell as the cell is used up. Eventually, they leak horrible fumes that denature nearby lead-free solder and stop everything from working. Replace it with good old 60:40 and it all bursts back into life.

I used to get through about 4000 a year and have never known one to detonate without some kind of abuse.

However, as we have ruled out the impossible and everything that did not happen, we must go with whatever is left. I think you are probably right

Old Mart,

I was aware of the Royal Mail regulations but they are at best confusing and in some places seem to contradict themselves by saying certain items are prohibited but in another area the same items appear permitted. I think our local Post Office person has the right interpretation of the regs, he refuses point blank to accept any batteries or equipment with them fitted. Dave W