A Water Activated Flashlight?

Water powered flash light

We’ve all seen lemon batteries or potato clocks, but have you ever seen a water activated battery?

[Nathan Stubblefield] was an American inventor (born 1860) who never got quite as much recognition as some of the other great inventors of the time, [Tesla, Bell, Edison etc] — though he did demonstrate some very interesting wireless telephony technology. In addition to dabbling with invisible radio waves, [Stubblefield] filed a patent for something called an Earth Battery, which makes use of two coils of dissimilar materials (a voltaic couple) submerged in water (or moist earth). As you can imagine, it wasn’t overly effective, nor efficient by any means — but it worked.

[Lasersaber] has been playing around with the “Stubblefield Coil” recently, and designed a working flashlight using the theory. He designed a 3D printed coil holder which allows you to easily wrap copper and magnesium strips around it to create the coil. Three of these cells go together in series to produce your water battery (and handle of the flashlight).

It’s not quite done yet, but he has plans to wrap it in a porous material that can dry out quickly — that way when you need the flashlight you can dunk it in a bucket of water, and hopefully have a run time of half an hour, before needing more water. It won’t last forever mind you.

[Thanks Mike!]

34 thoughts on “A Water Activated Flashlight?

  1. That’s not water powered. No energy is extracted from the water, it’s purely used as an ion transport like every other electrochemical cell out there.

    The video names this properly – it’s not water powered, it’s water *activated*. Water activated batteries are stored dry and sealed, and have an incredibly long shelf life, unlike normal batteries that die within a few years of being manufactured even if they were never used. Once it’s activated it’s got a finite lifetime and capacity, like any battery, and is discarded after use.

    1. Big Clive did a video on these. Somebody in the comments said the same thing, and somebody else pointed out that they aren’t water-activated batteries. They’re conventional batteries, with a water sensor, using a transistor.

      These have the advantage of a very long shelf-life. But I’d imagine that life jackets are periodically inspected, and have a limited storage life, so it’d be more practical, in many ways, to just use an ordinary battery rather than a weird one like this.

  2. Finite lifetime is defined by oxidation of the copper/magnesium electrodes, I guess?
    Also, these coils look a bit large. It would be nice if the electrodes could be somehow shrunk into smaller volume. Maybe by making the electrodes something like foil layers wrapped together with some insulation between. The insulation should be able to soak the water/electrolyte.
    But maybe I am just describing the “water activated” battery, as pelrun said?

  3. Please, please, don’t ever use the words “water powered” ever again. It’s like talking about a “wire-powered circuit”- the water is part of the process but it’s not the source of energy. Anyone who describes anything except a hydroelectric power station or deuterium fusion as “water powered” is a crank, and HaD should be better than that.

    Sadly there are still people who believe you can run a car on water using a magical HHO generator or whatever, and bandying around the phrase “water powered” when it’s not appropriate or correct can only make it worse. We are constantly fighting a battle against shitty local news outlets who run “local shed inventor creates water powered XYZ” stories to fill space because they don’t have any real content to run or anyone on staff who knows it’s physically impossible.

      1. And your point is…?
        This car uses a flow battery (http://en.wikipedia.org/wiki/Flow_battery) which is effectively the same as a normal battery, except the reactants are in solution. In no way does the water itself provide power. Again, it is analogous to saying that a circuit is “wire-powered”. The water is just a transport medium for the actual reactants.

        It’s rather amusing that the url says “salt water powered” and the actual title says “Salt Water Flow Cell”. Maybe they corrected it after publication.

        Just to reiterate: You *cannot* extract energy from water under any normal circumstances (excluding antimatter and the like). To extract energy from water, you would have to find a lower energy state for the H2O to go into, and there isnt one.

  4. “These observations indicate that Stubblefield had managed indeed the direct conversion of earth energy to light and warmth.”

    Yeah, I’m sure he did.

    What about converting light and warmth (coming from the sun) to electricity?
    Seems to be more promising.

      1. Got one. Except it’s likely, being Chinese, to be a fake, as usual. The fake being using a non-rechargable primary cell for the power, because it’s cheaper. It’s a real solar cell, to give the false impression it is what it’s sold as. Loads of these have turned out to be fake, dunno if any of the cheap keyring ones are actually genuine.

  5. Water-activated devices aren’t unheard of – radiosonde transmitters and some emergency devices use them. There are also “Aquacells” that are manufactured using the same technology.


    One of the more interesting discussions I’ve seen was around using the the electrolysis in salt water vessels for low-level electrical power, since the zinc anodes are sacrificial anyway. The consensus was that the voltage was too low (less than 2V if I recall) to be useful for much.

    1. As a full time livaboard and long distance cruiser, I would really be interested to take a look at that discussion… gotta link? All my lighting is led based, with minimal draw. and that might provide an interesting alternative to the current solar/lead acid battery system.
      Not a replacement mind you but in addition, or emergency backup. Interesting concept.

      1. You’re essentially making a less-efficient battery, for very likely a greater price. Just use an ordinary battery. Soz!

        If you were thinking of something like the sacrificial anode they put on large metal boats, then drawing a current would increase the rate of corrosion. Indeed some large boats run a current through theirs, in the opposite direction, to reduce corrosion.

        Sacrificial anodes, boat corrosion, electrolysis, and most chemical batteries, all work on the same principle.

    2. Got a link to the zinc anode discussion?… Interesting concept as backup power for LED nav lights. Now I have to go search that out. Backup power is always an issue on a small offshore vessel.

    3. Electrolysis is pretty much the exact same principle as a battery like this, working in the opposite direction. Pretty sure you can’t do both at the same time.

  6. Ok, now it really has me curious… with a bronze cathode, and a zinc anode, in salt water should generate 0.75V (alum/zinc anode would give 0.8V but erodes at 30-50 times the relative rate of zinc at a given current). 16 bronze-zinc cells in series would give me a nominal 12V. Thinking a strip of plastic with a series of holes drilled. Cathodes = bronze bolts
    Anodes = threaded “pencil zincs” (made to go in engines and heat exchangers) Thread em through the holes in the plastic strip and wire em up ???

    Question… have not gone searching yet, but what is relationship between cathode/anode spacing in the electrolite to whatever? On first glance it would seem closer would be better, using threaded parts would make it trivial to get a repeatable spacing.

    Hmmmm… Total emergency load running 3 LED navigation lights and GPS is at (measured and verified) 530mA (150mA ea for the lights and 80mA for GPS) Wonder how long a 5/8″ x 3″ pencil zinc would last?

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