The Practical Potato Cell

Potato batteries, lemon batteries, they’re all good fun for the classroom — but is there a way of making them better? [Marcel Varallo] decided to give it a shot — and we gotta admit, it’s a pretty cool idea!

Normally for these fruit and vegetable batteries you poke some leads into the battery, connect it to a clock, and bob’s your uncle. But what if we made them resemble batteries? [Marcel] took some copper pipe, cut it down to size, and poked it through a potato. Now he had a potato-cored, copper tube. Stick a zinc nail in the middle, and you’ve got yourself a battery cell! Or as [Marcel] likes to put it.. a Mar-Cell. Or the more scientific term.. the Solanum tuberosum based electron differencer V1.0.

Each potato cell produces approximately 0.8V, so if you throw eight in series, you’ll have the equivalent of a 6V battery, just maybe not the same mAh rating.

For another cool way to demonstrate electricity to youngsters, we love this lemon battery hack — it’s actually quite elegant.

32 thoughts on “The Practical Potato Cell

          1. There was a guy who worked on the manhattan project or something who told a story about how they weren’t allowed to take anything from the site that may resemble components. So you would have an orange taken off you and destroyed, just because it was round and segmented. Can’t recall who it was though.

  1. I’m curious, what exactly is the mAh rating of these batteries? I wonder if you could make a usable potato flashlight, perhaps with a quick load mechanism that clamps down into a potato so you could swap them out on the fly. I wonder how much potato mass would be needed for decent flashlight.

    1. Yeah you’re talking about a very compact version. It could be done, but too early at the moment. I can only imagine it wouldn’t be the brightest, but just a novel build anyway. I’ll attach an LED to it for you and measure some current then throw it on my blog for you.

  2. I would worry more about the internal resistance before the mAH. To make things worse, now you’ll have 8X the resistance when you put 8 of them in series. High internal resistance means that it can’t deliver a high enough current for powering your toys.

  3. When you say zinc nails, surely you mean a galvanized steel nail. I suspect that a solid zinc nail would not be strong enough to drive. About ESR, sure this will be low current. It’s for kids! My kid demo will be complete if the potato battery can run a self color cycling LED (already have a bag full;)

    Thanks for the fun post!

    1. Yeah sorry, was a bit tired at the time I wrote that. Galvanised. The zinc was the important bit, but yeah it was steel core.

      What do you mean by self color cycling? I just had an LED hooked up to it and I’m having to make a better one anyway because I need it for something that uses a little more than what a few LEDs use.

  4. I wonder if a potato could be bred or genetically engineered to produce more energy?

    It would be amazing if a person could grow their batteries in the back yard and throw them on the compost pile when they go bad.

    1. The amount of *energy* is pretty much fixed based on the amount of zinc that get oxidized. The potato doesn’t add *energy* to it. You could get more *current* and *power* out of it by adding salt. You could even make the battery with just salt solution.

      1. Yes I’m aware of the fact that the potato is just used for the suspension solution. If it’s possible to breed a potato with a higher salt content it would result in a better battery. A salt solution is liquid and thus impractical for a battery.

        1. Even a tightly packed sponge or paper towel or rag can be used for soaking up a salt solution. You can easily make a gel out of dissolving corn starch in cold water and then bringing that to a boil. Add salt to the mix and that will improve on the internal resistance. I would guess you’ll need around 4-5 table spoon of start per cup of water to make something with the consistency of glue.

          I stress the word “energy” because it is grossly misused for the HaD target readers here. The potato part doesn’t affect the energy. It might dry up etc, but you’ll get the same energy by using a salt solution. At the end of the day, the energy of this battery comes from zinc that is mined/refined etc. and that’s a pretty inefficient way of using it. You are better off fermenting the potato into alcohol if you want to talk about extracting energy from a potato.

    2. When first calculated out how many I would need for my application, it was some ridiculous number like 6,000 or 60,000. I can’t remember which. But I daydreamed a little about growing them near the surface and dropping probes in. After a while you move your probes to the next field while you regrow the old dead one. Like crop rotation. Probe rotation. I was also wondering if you were gentle enough about it and only drew a little current etc. could you keep the potatoes at a healthy enough level that they wouldn’t die from the whole experience. God forbid plants actually feel pain.

      Anyway, after all that daydreaming I got a little more realistic about it. I mean I need 5 volts at 500ma. But that’s peak. So my first calculations were maximum needed. The other thing was that I only need it between about 9am and 5pm. So that’s less power used again. With a low power sleep circuit attached I could save power outside business hours. Of course with the potatoes naturally decaying, if you don’t use it you’re going to loose a certain amount of it anyway. So I thought about working out where the optimal usage and decay points were and offloading the excess power somewhere fresh for later. Again I got a little silly and came up with a few potato capacitor models that I could use like capacitor/battery banks.

      In the end I had a spare night babysitting my 3d printer and decided “carpe solanum tuberosum.”

      1. The potatoes don’t make they power they are just the suspension solution for the metal electrodes as mentioned above in the comments… so once your probes oxidize you are out of power… probably before the potato decays lol.

  5. this is nothing new. It’s the same experiments we did in science at pre school. Pre school mentality. Any elecryte will do the trick as long as snide and cathode have a potential. Why re invent the wheel

    1. Correct. I’m just compensating for the lack of resources to purchase and house a whole potato per cell (due to the power I need for my next project that uses it I would require a lot of potatoes) and so have had to get a little creative about how I use that potato and other components.

      I was also considering a wafer type like a voltaic pile but found it to be labour intensive. So when I figured the copper tube and just punching it through the spud and whacking a nail in, I would like to think it was enough of an achievement that I should get 2 gold stars while the preschoolers can have one for effort. :P

      Seriously though, I’m quite chuffed that the easier solution came out looking like an actual battery :)

      1. I can’t see a voltaic pile would be that labour intensive. I can slice a single potato into 2mm slices with a knife in just few minutes to make microwave potato chips. A vegetable mandoline/slicer can easily cut that down to below a minute.

  6. Nice, thanks for sharing. Keep at it!
    You might just invent the first commercially viable organic battery! If not someone may be able to add to your findings like Thomas Edison did for the light bulb.
    The following is a snippet of the light bulb’s invention history.
    Henry Woodward invented the first light bulb and patented it. Then he sold the patent the Thomas Edison who had perfected the light bulb.

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