It is good advice to change batteries in your fire alarms at least once a year. Even our low-power LCD calculators need new batteries from time to time. But at the University of Oxford, they have an electric bell that has been ringing essentially non-stop on one set of batteries for about 178 years! Is the energy crisis solved then? Perhaps not. The bells require a high voltage but very little current and the pair of batteries — piles in the parlance of 1840 — have kept the charge flowing for about 10 billion rings. As you can see in the video below, though, the ringing isn’t very vigorous.
How does it work? When you think of converting electrical power to mechanical motion you probably think of a motor, even though there are plenty of other transducers like speakers, muscle wires, and solenoids. Arguably the first device was electrostatic bells that were invented by a Scot named [Andrew Gordon] around 1742. [Ben Franklin] made them famous, though, so they are often called Franklin bells.
Continue reading “The Bells! The Bells! One Battery Since 1840”
There’s a proverb that says ‘Speak softly and carry a big stick’. Now that stick can come in a high-voltage form factor. The device above, which reminds us of a side-handled baton with a coke can stuck on the end, is a portable Van de Graaff generator.
Although debated in the comments, the creator of this hack claims you can shock someone with 84 kV of electricity using the device. Of course as a weapon it’s lacking since we’re talking about static electricity; the voltage can be through the roof but the current is extremely low. Despite that, there are some fun things you can do with them. The video after the break show it throwing off sparks with the lights dimmed. [Yardleydobon] also includes a few other tricks at the end of his tutorial. He makes a set of Franklin Bells using two more soda cans with the aluminum tab from one suspended in between them. As he charges it up, the tab dances back and forth, ringing the ‘bells’ it runs into. Once they are charged, the ringing can be restarted by discharging just one of the cans.
Continue reading “High Voltage: Build Your Own 84 KV Lightning Stick”
It looks like we now have another way to annoy ourselves with extremely high voltage.
The bells operate under the same principles as the electrostatic see-saw we covered last month. A voltage is applied to one can while the other can is grounded. An insulated pendulum is placed between each can, and with a little coaxing can be made to oscillate back and forth between the cans. As the pendulum touches the charged can, it is repelled as it gains the charge and moves to the grounded can. There, the charge is released and the cycle continues again. A homemade Cockcroft Walton multiplier is used to generate the +35kV needed to get the pendulum moving.
[Ben Franklin] invented the Franklin Bells while he was investigating electricity in the 1750s. Originally an extension of the kite & key experiment, the bells were historically used to warn of approaching thunderstorms – when the bells rang, the atmosphere was charged and lightning could strike. Even though the voltage between the bells is huge, very little current is drawn – the Oxford Electric Bells have been ringing since 1840 using the same electrostatic battery.