Building a Battery from Molten Salt

During World War II a scientist named Georg Otto Erb developed the molten salt battery for use in military applications. The war ended before Erb’s batteries found any real use, but British Intelligence wrote a report about the technology and the United States adopted the technology for artillery fuses.

Molten salt batteries have two main advantages. First, you can store them for a long time (50 years or more) with no problems. Once the salt melts (usually from a pyrotechnic charge), the battery can produce a lot of energy for a relatively short period of time thanks to the high ionic conductivity of the electrolyte (about three times that of sulfuric acid).

[OrbitalDesigns] couldn’t find a DIY version of a molten salt battery so he decided to make one himself. Although he didn’t get the amount of power you’d find in a commercial design, it did provide 1.6V and enough power to light an LED.

The electrolyte was a mixture of potassium chloride and lithium chloride and melts at about 350 to 400 degrees Celsius. He used nickel and magnesium for electrodes. Potassium chloride is used as a salt substitute, so it isn’t dangerous to handle (at least, no more dangerous than anything else heated to 400 degrees Celsius). The lithium compound, however, is slightly toxic (even though it was briefly sold as a salt substitute, also). If you try to replicate the battery, be sure you read the MSDS for all the materials.

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Homemade High Voltage Caps

Do you happen to have any 15,000 volt capacitors sitting around? [Ludic Science] didn’t so he did the next best thing. He built some.

If you understand the physics behind a capacitor (two parallel conductors separated by a dielectric) you won’t find the build process very surprising. [Ludic] uses transparency film as an insulator and aluminum foil for the conductive plates. Then he wraps them into a tube. He did throw in a few interesting tips about keeping the sheets smooth and how to attach the wires to the foil. The brown paper wrapper reminded us of old caps you might find in an antique radio.

The best part by far, though, was the demonstration of drawing an arc from a high voltage power supply with and without the capacitor in the circuit. As you might expect, playing with a few thousand volts charged into a capacitor requires a certain amount of caution, so be careful!

[Ludic] measured the capacitance value with a standard meter, but it wasn’t clear where the 15,000 volt rating came from. Maybe it was the power supply he used in the video and the capacitor could actually go higher.

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Second grade science project: a steam engine


If you’re looking for a way to let the kids get hand-ons with science this is a perfect example of how to do it. [Erich] wanted to help out with his 7-year-old’s science project. They decided to build a working model of a steam engine but couldn’t find online instructions appropriate for the age group. So the two of them not only pulled off the build, but then they wrote a guide for others to follow. The thing about it is, you really have to understand a concept to teach it to someone else. So we think the write-up is equally important to having actually done the experiment.

Steam can scald you if you’re not careful. But you don’t really need steam to explore the concepts of a steam engine. The main reason to use steam is that it’s a fairly rudimentary way to build pressure which can be converted to motion. For this demonstration the blue balloon provides that pressure. It’s feeding a reservoir that connects to the valve built out of straws. A plastic piston inside pushes against the crank shaft, spinning the cardboard wheel on the left. When the piston travels past the valve opening it releases the air pressure until the machine makes a revolution and is in place for the next push. This is well demonstrated in the clip after the break.

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