Science Buddies: "Ask an Expert"

Hi,

I am trying to make a big potato battery to keep a small light bulb lit as long as possible. I am using copper and zinc nails and copper wire. Could you suggest any other materials to make the chemical reaction last longer and thus allow the light bulb to be lit longer. Or any ideas that you can give me to make the battery last as long as possible would be greatly appreciated.

Thanks!

Copper and zinc are good for batteries and can produce a fair amount of current with only a nail-sized electrode. You may be running up against the problem of the electrolyte (the potato) not having enough free acid available. If you are stuck with a potatoe you are just limited in current. If you can experiment with other items such as lemons or vinegar you will see a dramatic difference (but only if allowed).

Hi novisibles,

I've removed your duplicate posts and moved the one that had already received a response into its own thread. It's best if all experts who respond to you can see the entire conversation with you, which won't happen if you post in multiple threads. It's also preferable to create your own instead of adding to an old thread because experts might not realize that you're a new poster doing a slightly different project.

Here are links to the similar projects you found, for everyone's reference:
https://www.sciencebuddies.org/science- ... e27#p29737
https://www.sciencebuddies.org/science- ... =26&t=4960
https://www.sciencebuddies.org/science- ... =31&t=5515

Best wishes,
Amanda

When you start out on a quest, there is no guarantee you will achieve your goals. We often learn more from our failures than from our successes.

Some of the factors you are fighting with a potato are: moisture loss, fairly high resistance, oxidation of the electrodes

If you pre-soak the potato in water, keep it in a sealed container during the experiment, you can reduce the effects of moisture loss.
You can try different placements of the electrodes. My best guess is that you want the electrode surfaces to be parallel to each other. Closer to gether will reduce resistance; however, it will deplete the electrolyte faster, so you have a variable that you can experiment with.
You should clean the electrodes before each trial to at least start with as little oxidation as possible.

@ Amanda:
Thanks! I'm sorry for the trouble. It's my first time here and I was a little desperate. I'm glad to see how good this all works

@ Craig:
Thanks a lot for your answer. I will try different distances than, and something else I understood might also affect the reaction: the surface of the zinc and copper. I was using nails, i will try it out now with some plates and very very fresh potatoes. I'll let you know next week how it went.

Chao!

Hi,
here i am again with a question:

I have now tested different distances and positions with the zinc and copper pieces and have come to the conclusion that I need to have fresh potatoes and they last for around two weeks to keep a little led light lit up (i am working with 40 potatoes in circuit). If I want the led to be bright i have to change the position of the pieces every day.

This gives me enough power for a small led light to be well lit, and although i am getting 30 volts i can't get a small bycicle bulb to light up. It needs 6 volts and it has 0.6 watts.
I guess it's because i need more amperage. One solution i thought of is using a condensator and than storing energy there. Can you give me any tips?
would having more potatoes actually help?

Thank you for any hints you can give me!

It looks like you are up against the power limitations of potatoes. Putting multiple potatoes in series to produce 30 volts is an interesting exercise in circuits, but only if you can benefit from the increased voltage. Most electrical devices are current sensitive and an LED in particular. At its rated current flow an LED produces a specific amount of light, and typically that is at 1.6 volts. At half that current you would see about half the light and that would probably be at about 1.59 volts. When you connect the potatoes, my guess is that the potatoes are current limiting and producing enough current to illuminate the LED. As an interesting observation, measure the voltage across the LED when it is powered by the potatoe, you will not see anything close to 30 volts.

Second exercise: Assuming your meter is a multimeter and can also be set to read current, measure the current through the LED and make a note of it. Then, split your 40 potatoe battery into two 20 potatoes in each string and put the two strings in parallel. This should give a single battery with considerably higher current capability, possibly almost double. Measure the LED's current and voltage again.

Now, I hope this next part is not necessary and it is not intended to be condescending, but lets just make sure. For connecting potatoes in series, the copper electrode of one connects to the zinc electrode of the next, so the voltages are added together. (Like the button side and flat side of flashlight batteries.) Then the two groups are connected in parallel by taking the copper end and connecting it to the other copper end and then to the LED, and then the zinc end to the zinc end and then to the other LED lead.

I am not sure about which end is positive. It has been a long time (40 years) since I was involved in electrochemistry, but my guess is that the copper end is positive. Let me know if this is correct. LEDs are polarity sensitive and will only light one way.

Increasing the surface area of the electrodes in each cell should lower the internal resistance and increase the current capabilities; however, more surface area and a higher current load means the electrolyte will be used faster.