Battery Ooops!

[TelePlay]

Sometimes a workshop project can result in a coincidental catastrophe, sort of.

Was building a device powered by two AA batteries. Put them in a holder for breadboard testing. Removed the holder and placed it into a plastic tub.

When I tried to remove it from the tub today, the ends of the leads were stuck to the plastic tub. This is the holder hanging from the tub with the tub in a vertical position.



I thought it was glued somehow to the inside of the tub, but I wasn't using glue in the project.



Then I discovered the stranded wire was passing through the tub with about 1/16th of an inch outside the tub.



Turns out, I wasn't careful, didn't take precautions, when I tossed the holder into the tub and when it came to rest, the bare conductors were touching and pressed, by gravity, against the side of the tub. The 2 batteries were shorted out and the bare conductors got hot enough to "bore" through the side of the plastic tub. After the batteries died, the plastic cooled "welding" the conductors into the plastic.

Oh, well. Other than loosing 2 batteries and a plastic tub needing a JB Weld patch, nothing lost but lesson learned.

   

[countryman]

I would have thought that the wires quickly weld together to a full short, heating up only the batteries. Chances to reproduce this outcome must be pretty small.
In fact nothing too bad happened here, standard batteries are safe. Be careful with Lithium cells...

As a kid I knew the battery boxes for Lego trains but was not sure what happens inside them. I had read in a book about magnetism, that horseshoe magnets should be stored with a keeper across the poles. When I wanted to try out an experiment from another book, I needed a 9 Volt block battery. It did cost me some begging before mum bought one in the local hardware store, they weren't cheap back then. I quickly had to learn that the "keeper" idea does not work for batteries...

[TelePlay]

I would have thought that the wires quickly weld together to a full short, . . .

It took some strong pulling to free the conductors from the plastic. The wires themselves were not welded together. The probability of the bare ends touching together pushing against the plastic wall when dropped into the plastic tub is quite low.

The melting point of "poly" tub plastics is between 240 and 300 degrees F so those 2 AA shorted out had significant current.


Thinking I placed the battery holder into the center of the tub and it slid to a corner when moving the tub. Just chance the bare ends touched together while pressing against the plastic - a variation of the hot pin test for bakelite.

Checked the 1.5 VDC batteries, both were dead generating about 0.65 VDC each with almost no current.

As for 9 volt batteries, never put one in a pants (trousers) pocket having loose change, metal coins. Did that once, another hot learning moment in life.

[TelePlay]

Looking more closely at the tub since pulling the conductors out, the touching bare ends did not "drill" there way through the polypropylene tub wall, the sliced their way through.

That makes more sense. After moving the tub which slid the battery case into the corner, the conductors ended up touching while being bent against the wall. After getting hot, that bend or spring force caused the bare wires to cut a slit about 3/8 inch long.

In this image, the cutting started at the top moving downward ending with a short "ear" of melted plastic extending outward from where to conductors came to rest.

[19and41]

Good thing it didn't cause the batteries to leak.  less of a discharge than a short can cause leakage.