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Flashlight gets really hot

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  • Flashlight gets really hot

    I put two new AA batteries into one of my small LED flashlights last night.
    I was about to put the flashlight away in a cabinet when I noticed the flashlight barrel getting very hot. I removed the two batteries, and they were too hot to even hold . The plastic coating on the batteries was even melting. Something apparently was causing a dead short. I looked down the barrel of the flashlight, and saw the problem. At the head end of the flashlight where the positive end of the first battery made contact, they had used a rather large conical spring . The spring had bent over, and made contact with the negative strap that runs from the other end of the flashight. The heat generated from those two batteries dead shorted was amazing, and I do believe the plastic flashlight barrel would have melted down if I had not noticed the heat. I then removed the batteries from several other flashlights, and found that the overheated one was the only flashlight I had that used a conical spring large enough to bend over and short out at the positive end. All others used a small contact tab. This flashlight went into the trash can (as soon as it cooled off !).

  • #2
    Such a simple thing as a flashlight can involve a lot of design work and engineering to optimize it. The cheaper ones are a crap-shoot since they are often a copy of someone else's engineering. They might or might not copy the features that make it a good light.

    The other common error is a sharp edge that cuts through the wrap of the first cell, shorting out the second one.

    Can you imagine what would have happened if you had used a hi energy battery like a lithium? Those get interesting when shorted.

    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.