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Build a better battery!


	13/11/03 @ 15:54 GMT	anthony

Everyone has seen a lemon battery, two simple zinc and copper electrodes which musty give somewhere bettween one and two volts. I recently remember seeing Volatiare's (right name?) first battery. By putting lots of cells in series he got about 20 or 30 volts. I wonder if we could work on the same principle.

Instead of working with one whimpy lemon lets work with lots in paralell or series, CHaOS style. Else build a battery cell with lots of plates stuck into lemon juice. We then need to power something pretty impressive off it, could we generate sparks?

A simple fish tank with a copper electrode at one end and zinc at the other. If the kids slot in bimetalic plates of copper/zinc the voltage starts to go up. I like the idea od generating sparks, or maybe powering a plasma globe, it should also keep the current down.


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Build a better battery! | 8 comments | Create New Account

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Build a better battery!

Authored by: Dave on 13/11/03 @ 17:05 GMT

Me and Rosy had a think about batteries after the tour. It would be difficult to power anything very impressive with them as their internal resistance is so high...

You may be able to make sparks if you wired up loads of lemons to a capacitor and then to a spark gap, so you can store up the energy.

Plasma globes work like a tesla coil, by forming very high voltages at several kilohertz... I would have thought that considering the amount of light that they give off they must use quite a lot of energy so it would require a stupid number of lemons...

The other problem is explaining the fecking things, as electrochemisty is somewhat complex, and there are allways many reactions that can be happening at the same time. If we wanted to explain it you would want to start with the two half cell things eg:

Zn -> Zn²⁺ at one side

and on the other side copper in copper sulphate

Cu²⁺ -> Cu

and explain that the copper likes being an ion less than the Zinc does and to react it has to chuck electrons around the circuit....

Could you seperate the two half cells using a partially permiable membrane? let OH^- through but not Zn²⁺ or Cu²⁺...

[ Reply to This ]

	Build a better battery!
	Authored by: rosy on 13/11/03 @ 17:26 GMT
	I think the first battery guy was called Volta. [ Reply to This ]

Build a better battery!

Authored by: anthony on 13/11/03 @ 17:45 GMT

Cheers. After thinking about this the two half cell reactions in the lemon must be...

Red-
2H⁺ + 2e- ----> H₂

-Ox
Zn ----> Zn²⁺ + 2e-

There is after all no Cu²⁺ to be had. Certainly if you did this in a fish tank with lots of plates it would have more in common with a car battery than a lemon.

I wonder if we could get a car battery, dilute the acid, and run that instead to show how a battery works.

I don't think it's a matter of teaching electrochemistry but it is a way to iluustrate how a battery works and that questions notions of electricity and where anergy comes from. To power something pretty chuncky from lemons would be pretty impressive for children and adults.

We wouldn't need much juice to power a CD walkman and speakers! I open the floor to suggestions.

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	Build a better battery!
	Authored by: anthony on 13/11/03 @ 17:53 GMT
	To link in more chemistry you could have a lump of zinc fizzing away in acid beside it. As essentially the battery is just splitting the reaction into it's too parts, at one side you're making the gas and at the other you're eating the zinc. [ Reply to This ]

	Build a better battery!
	Authored by: Dave on 13/11/03 @ 18:38 GMT
	Yeah that is what we decided, it is kind of hard to explain, as you have to get through dissasociation of water first. We did lead acid batteries at school - it just needed lead plates (preferably ones on one side that are a bit corroded) and a sulphuric acid electrolyte. It was quite impressive when it was charging as it produced a great plume of sulphuric acid aerosol... Ok we did build quite a big one ;) It is probably the best bet for getting a resonable current. [ Reply to This ]

	Build a better battery!
	Authored by: anthony on 13/11/03 @ 23:42 GMT
	I don't think you need to go over the dissociation of water either. But anyway, much nicer in every way to do it as a lemon and avoid lead-acid batteries. The downside is recharging as clearly it's hard to supply H2 to the electrode. unless it's possible to do it at the same time as electrolysing the water?...?... This gives another reason to want a low current. I would prefer having lots of lemons in series. It would be a fun demo to have a nest of lemons and wires to power something or other. [ Reply to This ]

Build a better battery!

Authored by: Dave on 14/11/03 @ 10:46 GMT

Sorry I think I meant dissacosiation of water into H⁺ and OH^- to explain what is happening at teh other electrode...

I htink the advantage of lead acid batteries is that because they don't have a membrane at all they can have much lower internal resistances than a Lemon, so we are more likely to get a resonable amount of power our of one...

[ Reply to This ]

	Build a better battery!
	Authored by: Anonymous on 16/11/03 @ 22:36 GMT
	Agreed. To get much power it has to be done without lemons, but a lemon juice battery with Zn and Cu will produce similar amounts of power. My electrochemistry is slowly coming back to me... I think what determines the current is the "current denisty" of the electrodes. On the recharging note it would be possible. In recharging oxygen would be made on the copper electrode. I also wonder what could be done with a high potential difference from a lot of lemons just very little power. [ Reply to This ]