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eetcowie
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Blogger
Re: Exploding batteries
eetcowie   5/13/2014 10:00:33 AM
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Some batteries need discharge balancing for series-connected cells, to prevent the weekest cell from taking full-load current into a very high internal resistance. This is one reason why balancing chips, such as S-8209BAA-T8T1y from Seiko Instruments Inc, have included that function. Sometimes, even at the beginning of the depth of discharge, a high-rate, fast-switching load demands dynamic currents faster than the battery chemistry can respond, which can overheat a given cell. To compensate for heating as well as low pulse-current ratings, companies like Tadiran put a parallel capacitor inside their Lithium Thionyl Chloride cells. However, everyone enjoys a good, safe poof/bang, now and then.

Thanks for sharing!

elizabethsimon
User Rank
CEO
Exploding batteries
elizabethsimon   5/12/2014 12:15:11 PM
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The mention of Lithiium Thionyl Chloride and expolsive reminds me of the following...


Many years ago, I was working for a company that made postage meters. In those days, you had to take the postage meter to the post office to add postage. The old postage meter had a power supply in the case but that required that there be an outlet available. We decided that we could make the postage meter operate off battery power for adding postage. Since the battery would not be user replacable, it had to have a long life so we made a pack of AA size Lithiium Thionyl Chloride batteries with a key operated switch so the battery woul donly be active when it was in the post office.

This was all very well until one day we got a report that one of our postage meters made a loud noise and emmitted smoke while in transit to a customer. The meter was returned to us for analysis where we found that the batteries had exploded and done an impressive amount of dammage to the inside of the postage meter, which included burning a hole most of the way though the metal case.

As part of our analysis, we decided we needed to determine what caused the explosion. Having seen the damage caused, we put the batteries under test in a sand filled metal trash can outside next to the back door and ran the wires and thrremocouples out. Our precautions were justified when we finally triggered an explosion. The trash can lid (which was tied down) was bent in half and the rest of the trash can was decidedly battered.

We decided to redesign the battery pack using the Duracell lithium camera batteries which were much safer since they had built-in thermal fuses.

 

Max The Magnificent
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Blogger
Re: And people wonder...
Max The Magnificent   5/8/2014 11:00:11 AM
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@David: That should sort him out.....  :-)

As should the cattle prod I have on order from Amazon.com LOL

eetcowie
User Rank
Blogger
Re: Fusing
eetcowie   5/8/2014 10:57:54 AM
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Good points. Shipping poses special circumstances, since it has the highest likelyhood of damage that could cause a short -- which is why the shipping regulations ask for protection specifically for shorts and accidental activation. What I do is give consideration to all issues, including shipping, when designing enclosures. For example, sometimes the batteries already have massive protection from over-temperature, over-pressure, and shorts -- so I ONLY have to meet shipping regulations that are above the design criteria. In some cases because of this, the enclosure needs no extra protection, shipping or otherwise.

I also like your point to add messages and warnings.

Good stuff.

antedeluvian
User Rank
Blogger
Fusing
antedeluvian   5/8/2014 8:58:16 AM
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Ivan

In you hint about designing enclosures you said

For shipping, protection from shorts or accidental device activation (providing disconnection for example)

I would propose that you remove the proviso for shipping. A short can happen at any time during installation or servicing and I think that a fuse or circuit breaker right at the battery is the ideal place for it.

I might also add a point that there should be a place for an instruction/warning label to try and prevent misconnection of the battery and other such messages.

David Ashton
User Rank
Blogger
Re: And people wonder...
David Ashton   5/8/2014 8:27:54 AM
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You need to work on your comebacks, Max.

When he asks you "What is the difference between a duck?"

You say  "About this colour" indicating the dimension with your two hands.

That should sort him out.....  :-)

Max The Magnificent
User Rank
Blogger
And people wonder...
Max The Magnificent   5/7/2014 6:07:33 PM
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@Ivan: "Perhaps it's the fact that he keeps putting up with my bad jokes."

And people wonder why I have a nervous tic LOL



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