# Q & A: How many potatoes in a potato battery?

Q:
how many potatos would u use for a potato battery
- clair delk (age 11)
albany, In, USA
A:
I would just use one potato, at least for starters. If you want to get much current out of one of these batteries, you need to use lots of copper wire or sheet inserted in the potato, as well as lots of zinc-coated nails. There's not much point in using more potatos until you've used so much copper and zinc that the potato is starting to get crowded.

One of the main problems with potato batteries is their resistance to electrical flow. You can make many potato batteries and hook them up in series to make a combination battery with more voltage (the voltages add), but also more resistance (the resistances add too). You can hook the batteries up in parallel to get more current out of the combination battery at the same voltage as one battery, overcoming the resistance problem slowly, at the expense of more copper, zinc, (and space on your potato). It depends on what you want out of your battery!

If you want to hook up your batteries in parallel, then you can use the same potato and put all the copper nails on one side and all zinc ones on the other, and electrically connect all the copper together into one terminal of the battery, and connect all the zinc together to make the other terminal. If you want to hook them up in series, then I'd recommend using separate potatoes for each stage, because the electrical current might take a "shortcut" through the potato if you had just one.

Mike W. (and Tom)

(published on 10/22/2007)

## Follow-Up #1: getting power from potato batteries

Q:
I tried EVERY (almost) combination...3, 4, 5 potatoes; serial, parallel connections; combination of fruit and potatoes- nothing...i get notjing. The bulb is fine and wires are fine- i tested them with a battery. Does this really work? I am starting to doubt it.
- reena (age 37)
Virginia
A:

It is quite hard to get much power from these. Do you have access to a volt/ohm/amp meter? They're cheap and easily available. You can use them to find out how much voltage and current you get from one battery. You can also check what the bulb needs, and then figure out how many batteries you need in series to get enough voltage times how many in parallel to get the current.

Are you sure the nails are zinc-coated? If they don't have the right coating, you may not be getting much of any power from the battery.

With your meter you can test the voltage. You can also test how much current flows when the bulb is connected, and how much the voltage then drops.

What sort of bulb are you using? If you'd like to see some light without using too big a set of potato batteries, you should get a single LED bulb, which works on low current and voltage. It will only work with one direction of current, but that's not much problem, since there are only two directions to test.

Mike W.

(published on 10/17/2013)