Designing battery current limiters for childrens' activities

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Designing battery current limiters for childrens' activities

Postby crlMidi » Sat May 12, 2018 8:36 pm

Some though not all young children (aged 5-11) are remarkably fascinated by experiments involving electricity. Non-elektorist adults may be discouraged from supervising such out-of-school activities because of worries about overloading or short-circuiting batteries and blowing electronic components, however inexpensive they may be. Current-limiting resistors are not usually an ideal solution.

I generally use batteries or cells in cell-holders ranging from 3 to 9 volts. Despite their expense, non-rechargeable batteries seem to be the safest, at least in the absence of suitable protection.

Currents through LEDs need to be limited to 20mA, though I usually do that by soldering a resistor to them. Filament lamps often run at 300mA. Solenoids and motors probably need at least 1 amp, at least momentarily. We make our own remarkably inefficient motors, and in any case motors tend to get stalled by mistakes and childrens' fingers.

For each kind of application, I'd like to hide the batteries in a box, together with a device that cuts out or limits the current as appropriate, perhaps with an audible or visible warning and a time limit as a function of the current. The limiter needs to have a low voltage drop.

Since I'm not familiar with practical applications of positive temperature coefficient resistors or recent semiconductor solutions, I'd be grateful for design proposals, preferably ones that could be assembled by beginners in electronics, and that use standard readily-available components.
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