The Dynamotor Simplified

[Robert Murray-Smith] doesn’t like the price of inverters to convert DC to AC. That led him to build a dynamotor, or what is sometimes called a motor-generator set. These devices are just DC motors driving a generator. Of course, motors can also be used as generators and [Robert] had a stack of brushless motors in the form of PC fans. A two-fan dynamotor was born.

The brushless motors are attractive because, traditionally, the brushes are what usually fail on a dynamotor. The fan that will act as a generator needs some surgery, but it is simple. He scraped off all the control electronics and connected wires to the coils to form a three-phase generator. There’s no need for the fan blades in that configuration, either. If you were using ordinary motors and a generator, getting shafts concentric would be an important task. With the fans, it is simple to just line up the mounting holes and you get perfect alignment for free.

How does it work? [Robert] has a second video showing the output on a scope. You can see both videos below. The dynamotor makes a good-looking sine wave, probably much better than most reasonable-priced solid state inverters. He didn’t mention how much current he could successfully draw, but it probably isn’t much. You’d also need a transformer to replace a commercial inverter that would put out line voltage, so that would be some more loos in the system. On the other hand, if you wanted AC at a lower voltage, you might just replace all the transformers, if you were building a piece of gear yourself.

We’ve looked at how these things work in some detail. There were common in old tube radios, particularly military ones.

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The Vibrating Reed Inverter: Possibly The Simplest Inverter You Can Make

Those of us who work on the road have a constant dread of being stuck somewhere without power, facing a race between a publication deadline and a fast-failing laptop battery. We’re extremely fortunate then to live in an age in which a cheap, lightweight, and efficient solid-state switch-mode inverter can give us mains power from a car cigarette lighter socket and save the day. Before these inverters came much heavier devices whose transistors switched at the 50Hz line speed, and before them came electromechanical devices such as the rotary converter or the vibrating reed inverter. It’s this last type that [Robert Murray-Smith] has taken a look at, making what he positions as the simplest inverter that it’s possible.

If you’ve ever played with relays, you’ll probably be aware that a relay can be wired as a buzzer, and it’s this property that a vibrating reed inverter harnesses. He takes an octal relay and wires it up with a small mains transformer for an immediate and very cheap inverter. It’s not perfect, as he points out the frequency isn’t right. The relay will eventually wear out unless the arcing problem is improved with the addition of a capacitor. But it does make a rough and ready inverter if you find yourself in a MacGyver-style tight spot with only your junk box for salvation.

If inverters pique your interest, it might benefit you to know how they work.

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Experimenting With Vibratory Wind Generators

We’ve all got a pretty good mental image of the traditional wind-powered generator: essentially a big propeller on a stick. Some might also be familiar with vertical wind turbines, which can operate no matter which way the wind is blowing. In either case, they use some form of rotating structure to harness the wind’s energy.

But as demonstrated by [Robert Murray-Smith], it’s possible to generate electrical power from wind without any moving parts. With simple components, he shows how you can build a device capable of harnessing the wind with nothing more than vibrations. Alright, so we suppose that means the parts are technically moving, but you get the idea.

In the video after the break, [Robert] shows two different devices that operate under the same basic principle. For the first, he cuts the cone out of a standard speaker and glues a flat stick to the voice coil. As the stick moves back and forth in the wind, the coil inside of the magnet’s field and produces a measurable voltage. This proves the idea has merit and can be thrown together easily, but isn’t terribly elegant.

For the revised version, he glues a coil to a small piece of neoprene rubber, which in turn is glued to a slat taken from a Venetian blind. On the opposite side of the coil, he glues a magnet. When the blind slat starts vibrating in the wind, the oscillation of the magnet relative to the coil is enough to produce a current. It’s tiny, of course. But if you had hundreds or even thousands of these electric “blades of grass”, you could potentially build up quite a bit of energy.

If this all sounds a bit too theoretical for your tastes, you can always 3D print yourself a more traditional wind turbine. We’ve even seen them in vertical form, if you want to get fancy.

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The 19th Century, When Gravity Battery Meant Something Different

The internet is full of dubious content promoting “free energy” devices and other ideas that stretch credibility, so [Robert Murray-Smith] prefaces his demonstration of a gravity battery with a warning to look elsewhere if you are in search of such things. Instead he’s showing us a pair of cells from The Model Engineer and Amateur Electrician, a printed periodical that sounds to us something like an equivalent of Hackaday from the 1890s. (Video embedded below.)

The cells are termed gravity batteries because their constituents settle out into layers not unlike a tequila sunrise under the influence of gravity, something that made them especially suitable for the home constructor in the late 19th century when there were no handy wall outlets from which to snag a bit of power.

The chemistry of each is not unexpected if you spent any time in your high school’s lab, a zinc-copper primary cell with a zinc sulphate/copper sulphate electrolyte and a secondary zinc-carbon cell with a zinc bromide electrolyte and a layer of bromine forming on charging. The construction in large glass vessels is archaic though, and it’s this that’s prompted his video. He poses the question whether this type of cell might be revived using 21st century techniques to produce something of use today. The video is below the break, and even if you are not about to try your hand at electrochemistry it’s an interesting watch.

Thanks [Blaubär] for the tip! Continue reading “The 19th Century, When Gravity Battery Meant Something Different”

Synthesizing Graphene In Your Basement Laboratory

We’re surprised that we haven’t come across any of [Robert Murray-Smith’s] projects before. Looking through his collection of YouTube uploads proves that he’s a very active amateur chemist (we assume this is a hobby because he performs the experiment in a mayonnaise jar). The video we’re featuring today is about ten minutes of his technique for synthesizing graphene. The video can be watched after the break. Be warned that the audio doesn’t sync with the video because he overdubbed the presentation to fix up the poor audio quality from the original.

Graphene is something of a compound-du-jour when it comes to electronic research. You may remember reading about using DVD burners to make graphene film that will go into thinks like super-capacitors to replace batteries. [Robert] starts off his process with a jar of 98% sulfuric acid and 75% phosphoric acid. He pours in powdered graphite (chemical proportions are important here) and gives it a swirl. Next some potassium permanganate is added over about five or ten minutes. From there it goes on the stir plate for three days of constant stirring. During this time the solution will go from green to brown, indicating the presence of graphene oxide.

He goes on from there, but it’s clear he hasn’t found an iron-clad route to his end goal of isolating the graphene for use in constructing things like those super-capcitors we mentioned earlier. If you’ve got a home lab and some interest perhaps you can contribute to his efforts.

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