Hello! I have some questions about potato and lemon batteries, etc. Are they rechargeable? If yes, how much voltage is needed? I used a nail and copper wire in a lemon. I produced 0.5V. The nail probably was not galvanized, because some people produced 1V. What is their current capability? How many mAh (capacity)? If a device consumes a steady 50mA from a 2500mAh battery, how long until the battery runs out? How to calculate? When I put the nail and copper wire in vinegar, they began to rust, and the voltage was falling. I wiped away the rust, and the voltage returned to the previous state. Thanks!
Are they rechargeable
No they are primary cells not secondary cells.
What is their current capability?
Chuff all, a few micro amps for a day or so. The capacity over the drain will give you a first approximation although it willbe an over estimation.
Yes the voltage drops because the chemical reaction causing the voltage is inhibited by the reaction products. Wiping it causes fresh surface to be exposed. The energy required in wiping the contacts is much greater than the energy from the reaction.
Grumpy_Mike: Chuff all, a few micro amps for a day or so.
Then, how come some people can light LEDs with lemon or potato batteries?
Of course you can light LEDs with potato/lemon batteries! Last year in school, one group connected 4 potato batteries in series, and lit up an LED somewhat.
Also... http://www.youtube.com/watch?v=AY9qcDCFeVI LED lights up at 5:03.
This video explains how the lemon battery works
dkl65: What is their current capability? How many mAh (capacity)?
How big is your potato? How much surface area on the electrodes?
How long is a piece of string?
In these batteries, the actual stored energy comes from the (refined) metals used for the electrodes, with the fruit merely providing a conductive liquid (electrolyte) that allows the metals to react. You can get approximately the same energy by sticking the same electrodes into salt water, acids (vinegar), or bases (baking soda.)
A "better" science fair project would involve measuring output while varying the electrolyte composition, concentration, etc.