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My 6-year-old son has shown some interest in electronics, and I thought I'd get him some basic components (motors, LEDs, buzzers, etc) and let him experiment (using alligator clips and the like -- no soldering at his age!).

The one worry I have is that he'll accidentally short-circuit the battery, which could be dangerous. Are there battery cases (for standard AA, etc) available for purchase somewhere with built-in overload protection?

Failing that, I thought of soldering fuses to the battery holders. What would be an appropriate current rating for the fuse? I was thinking 1-2A, but my electronics expertise is pretty rudimentary.

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I would suggest a 1A polyfuse. Or a wall-wart with short-circuit protection.

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I think you're more in danger of exploding components like reverse-biased caps venting. I managed to popcorn the front off a TIP31 in my industrial technologies class in highschool with a lot less power than I thought it would take (pieces were bouncing off the back wall).

Nothing he's doing should require more than 250ma at his age, so I'd suggest a large series resistor on the battery pack.

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The AA (assuming alkaline) batteries are not capable of sourcing dangerous currents. A direct short across a AA battery will produce at most a warm battery. I wouldn't worry about fusing in this particular scenario.

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    \$\begingroup\$ The battery may be warm, but in some cases, the wires used to short the battery can get very hot, particularly if they're very thin. During prolonged shorts, this can cause in some cases melting of insulation. \$\endgroup\$
    – AndrejaKo
    Commented Jul 10, 2012 at 18:01
  • \$\begingroup\$ Is 10A a dangerous current? 20A? A NiMh rechargeable battery may have an internal resistance as low as tens of milliohms and is able to source up to 40-50 Amperes. Even with the added resistance of the shorting wire, that'd still be a lot of current flowing. \$\endgroup\$
    – DimKo
    Commented Jul 10, 2012 at 18:17
  • \$\begingroup\$ In this context, a dangerous current would be any current which would result in a burn or electrical fire. Though, I do see your point on the chemistry. \$\endgroup\$
    – Jason
    Commented Jul 10, 2012 at 18:26
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I would recommend getting an old used benchtop power supply that has a current limit function. That way you can limit what the power supply will do, and it will give you a bit more flexibility than just some batteries. An added benefit is that it's easier to use clip leads with a standard supply.

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