Lord Kelvin’s Contraption Turns Drips Into Sparks

It’s easy to think that devices which generate thousands of volts of electricity must involve relatively modern technology, but the fact is, machines capable of firing sparks through open air predate Edison’s light bulb. Which means that recreating them with modern tools, construction techniques, and part availability, is probably a lot easier than most people realize. The fascinating machine [Jay Bowles] put together for his latest Plasma Channel video is a perfect example, as it’s capable of developing 6,000 volts without any electronic components.

Now as clever as [Jay] might be, he can’t take credit for the idea on this one. That honor goes to Lord Kelvin, who came up with this particular style of electrostatic generator back in 1867. Alternately called “Kelvin water dropper” or “Lord Kelvin’s Thunderstorm”, the machine is able to produce a high voltage charge from falling water without using any moving parts.

Diverging streams means a charge is building up.

Our very own [Steven Dufresne] wrote an in-depth look at how these devices operate, but the short version is that a negative and positive charge is built up in two sets of metallic inductor rings and buckets, with the stream of water itself acting as a sort of wire to carry the charge up to the overhead water reservoir. As [Jay] demonstrates the video, you’ll know things are working when the streams of water become attracted to the inductors they are passing through.

Rather than connecting a separate spark gap up to the water “receivers” on the bottom of his water dropper, [Jay] found the handles on the metal mugs he’s using worked just as well. By moving the mugs closer and farther away he can adjust the gap, and a second adjustment lets him move the vertical position of the inductors. It sounds like it takes some fiddling to get everything in position, but once it’s working, the whole thing is very impressive.

Of course if you’re looking to get serious with high voltage experiments, you’ll want to upgrade to some less whimsical equipment pretty quickly. Luckily, [Jay] has shown that putting together a reliable HV supply doesn’t need to be expensive or complicated.

21 thoughts on “Lord Kelvin’s Contraption Turns Drips Into Sparks

  1. Time to figure out how energy efficient this device is, and how much power we can reasonably get out of it.
    My bet is that it won’t produce a lot of power, nor with any noteworthy efficiency. Accumulating a few kV of static charge is after all fairly trivial.

    1. The original setup works drop by drop. Once the charge builds up to very high voltages, the falling drop is almost stopped and it breaks up into tiny splashes. The device is capable of fairly high efficiencies, but that depends on the drop height and how much charge you can accumulate before it strikes through somewhere.

    2. You could set it up outdoors and harvest the energy from rain. Put some large capacitors between the catch buckets and you can harvest quite a bit of energy.

      10KV to 20KV is doable with one of these.

      1. kV states nothing about energy, only electrical potential.

        For an example, 10 kV with 1 µC (Coulomb) behind it isn’t a noteworthy amount of energy. It is 10 mJ, with this one can run a calculator for a few seconds.

        1C at 1V would be far more impressive at a whole Joule. But even this isn’t much energy to speak of.

        The reason I stated, “Time to figure out how energy efficient this device is, and how much power we can reasonably get out of it.” is because I haven’t really found any sources at all stating anything surrounding power.

        The closest I have found to people talking about energy or power is that it can generate a spark, but building static charge is fairly trivial.

        It would be interesting to see someone doing a more clinical test on it.
        Lifting a known quantity of water a known distance is not hard. So the input energy is fairly easy to establish.
        And measuring the voltage over a shunt resistor is likewise easy to measure and log over time, giving us the output energy that the system has generated.

        Even if both these measurements are a bit inaccurate, it would still give a rough picture of overall efficiency and power produced per volume of water for a given distance.

  2. I made one! From junk. I used a plastic bottle for the reservoir, slices from a soda can for the rings, held in place with drinking straws. The collectors were aluminium baking pans. The spark gap was between two paperclips. It worked!

  3. Any idea where the energy comes from?

    The water starts out at a higher potential energy, it flows down into the buckets where it has a lower potential energy. Lots of energy we can draw on of course.

    But then if we just omit the cross-cabling the water would travel basically the same, or? So what is the difference in the end state of the system (when all of the water has flown down) between the one that heated up some air via sparks, but the water ends up in the same position with the same potential energy in both systems. So where did the energy for the sparks came from? Did the water cool down in the sparky version?

    1. The water fell slightly slower because the electric field caused a force between the charged droplets and the rings. This means the water was heated up slightly less than it would have been if it had fallen without the rings and cross-connection.

      It’s very inefficient. The water still splashes down with most of the kinetic energy it would have otherwise had. But efficiency is not its point.

  4. I would quibble with calling the rings “inductors”. Though it’s technically true that any conductor will exhibit a bit of inductance, that’s not their function in this apparatus. Inductors work by storing and releasing energy in the magnetic field from a current flowing through a conductor. Most practical inductors are coil shaped, to superimpose the multiple magnetic fields of multiple windings.

    These rings are not coil shaped, but are continuous round rings, and there’s nothing to cause a current to circulate in a particular direction through them. The device works primarily due to electric fields, not magnetic fields.

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