My goal is to work with my son to make a home made battery. The basic battery uses a lemon (or lemon juice) with a copper part and zinc part. But that only produces about .8v. (I think this is called a wet cell.)
My question is, what are the 2 best metals to use to maximize voltage? What are the best 2 metals to use to maximize runtime? I want to run an LED for about 8 hours consecutively. (But LEDs draw about 3.0-3.2 volts, even red ones.)
Should I try lead in place of zinc? What lead items can I use? How much lead is in solder?
Thanks for the help.
Sig: Say no to fixed width HTML tables. They look terrible in most browsers.
I'm not sure which metals are best, but have you considered 3 (or more) lemons in series, that should give you just enough to light a red LED. You normally need a current limiting resistor in series with the LED, but I expect the internal resistance of your lemon will limit the current to a safe value. Have you tried measuring the current?
You could try different metals as part of your experiment.
To reply to me directly:
It's not what's best but what is most practical (read available and cheap)eg You wouldn't consider Gold and Platinum foils for example, readily available but very expensive. Cheapest and most readily available is Sheet Copper or Copper-plated PC board and Zinc coated (galvanized iron). Carbon rods used to be readily salvaged from flashlight batteries before they went into more exotic chemistries. Aluminum foils tend to develope an insulating Anodic Coating, a process use to make Capacitors. You need more Voltage ? Use several Cells in series ie make a battery of cells. Electrolytes, HCl, Hydro-Chloric (muriatic acid) is readily available from the hardware stores, Sulfuric acid , H2SO4 is a little harder to get but is used in Automotive Batteries other acids eg Citric acid (lemon juice), Formic acid and Vinegar (acetic Acid)are not as highly Ionizing as HCL, H2SO4, HNO3, Nitric acid or H3(PO4) Phosphoric Acid don't even think about HF (Hydro-Fluoric Acid) same class as HCN, Prussic acid or Hydrogen Cyanide both are extremely toxic ! anyway, so much for the lesson in practical Chemistry and Physics.
Lead is available 95/5 lead/tin, 50/50 lead/tin and 65/35 lead/tin, the most common grade of electronic Solder You could take some Wire solder and hammer it flat.
you could use a copper penny or a piece of copper pipe or copper wire. You could find a SILVER dime or quarter or some Sterling SILVER jewellry You could find some Gold jewellry You could recover some Mercury and use that for an electrode (Not Recommended) You could take some (un-plated, un-coated) nails for Iron electrodes You could recover the Tungsten filement from a light bulb you can find Aluminun foil in any kitchen
You will find a table "Electro-motive series" in a good physics or chemistry textbook or indeed on the internet. You may use that table to deduce the best metals to use. Try magnesium in place of zinc.
On Fri, 13 Jan 2006 11:55:11 +1300 in article , email@example.com spoke thusly...
You are correct. I did find those tables. The positive electrode corresponds to the metal with a positive "electric reduction potential" (ERP) I think it was called. The negative electrode metal corresponds to the negative ERP. Subtract the 2 and you get the total potential, which is the POTENTIAL voltage produced by the cell. The ACTUAL voltage is less than that.
So, for the negative part, lithium is -3.04. I don't think that's practical because I thought elemental lithium was very toxic to the skin and other organs. Next best was Mg (magnesium?) at -2.38. But that's hard to find. Next best was aluminum at -1.66, and I do have aluminum foil. Next best is silver at -.799. I might have some old silver plated US coins before 1964.
For the positive electrode we have gold at +.799 (I do not have any gold coins but I might have gold-plated headphone plugs) and copper at +.34.
So if I use aluminum and copper, we have a potential voltage for one cell of: .34- (-1.66) of 2.0 volts. Looking at studies the actual voltages runs about
60-80% of potential voltage.
Before I start linking multiple cells together I want to maximize the voltage for one cell. Other studies I read yesterday showed the electrolyte with the lowest pH produced the most voltage. I think vinegar was the best overall.
Sig: Say no to fixed width HTML tables. They look terrible in most browsers.
Besides voltage, also consider surface area of the electrodes to extract more total energy. Electrodes using small rods probably won't work very well. Better to use plates of several square inch area. The battery will produce more current with larger area electrodes.
Magnesium is available in rod form with a wire already connected to it. It is used as a sacricial anode in water heaters and evaporative coolers. Check your hardware stores. If it is lower pH you need, acetic acid(vinegar) won't get you much lower than 4. Best bet is pool acid(hydrochloric acid) or battery acid(sulfuric acid). CAREFUL with both of these! Both are toxic and highly corrosive-sulfuric mixed incorrectly with water can boil and splatter on you.
No- carbon ions are notoriously difficult to utilize in solution.
The table is based on reduction potentials, which means you have the metal
*ions* in solution (like auric chloride, Au(3+) + 3Cl(-) since it ionizes in solution) and, somehow or another, you apply a certain amount of voltage (or produce a certain amount) to cause zero current, depending on whether it wants to be in or out of solution.
A classic example is the gravity cell, where you put a wire at the bottom among copper sulfate crystals. Fill with water and put a zinc bar anode on top. The heavy, Cu-saturated solution remains at the bottom, keeping it (to some extent) from depositing directly on the zinc, which would be useless. Instead, the zinc's potenential is brought down to the copper wire by an external circuit (the load), where the copper plates out. The plating action frees sulfate ions, which grab protons and form sulfuric acid, which attacks the zinc, freeing some electrons in the process (Zn(0) = Zn(2+) +
If you use salt water instead, sodium cannot come out of solution (too damn reactive!), and zinc can't reduce it anyway (2.7 vs. 0.76V!). The only reaction that can occur is hydrogen being displaced (having null potential by definition, H > H+ + e- = 0V). Zinc is above hydrogen (by 0.76V), so that'll work. The reaction would be 2H2O + Zn > Zn(OH)2 + H2. The cathode can be something unreactive like platinum or, cheaper yet, graphite can be used.
This reaction is used in "dry cells", except the electrolyte is NH4Cl, and they add manganese dioxide for the dual purpose of absorbing the hydrogen (also preventing polarization) and generating more voltage (2MnO2 + H2 >
Mn2O3 + H2O). In total, the reactions produce about 1.5V, and there you go!
If you use inert electrodes, they do not contribute any voltage. If you use a solution of a noble ion (like Cu(2+) or Au(3+)), making sure to seperate it (permeable membrane, etc.) from the reactive anode, you can drive up the voltage.
Aluminum works fine in acid (hydrochloric) or basic solution, where the oxide is unstable. I've had about 0.8V from the reduction of hydrogen in NaOH solution (Al + 2H2O > AlO2- + 3H, that's the aluminate ion).
-- Deep Fryer: a very philosophical monk. Website:
On Fri, 13 Jan 2006 21:56:42 GMT in article , firstname.lastname@example.org spoke thusly...
Yes, but carbon has a relatively low reactivity.
Gold is an excellent conductor of electricity, but it is expensive. That's why you see gold-plated connectors on audio plugs, as well as on PC cards (and the slots they go into). And I think many of the runways in PC boards are actually made of a micro thin layer of gold.
Though gold is a better conductor of electricity, I don't know if that means electrical noise from external sources is reduced. Regular headphones sound the same to me.
So, as copper is the next best thing, it is more widely used.
Sig: Say no to fixed width HTML tables. They look terrible in most browsers.
Charles Jean wrote: : Magnesium is available in rod form with a wire already connected to : it. It is used as a sacricial anode in water heaters and evaporative : coolers. Check your hardware stores. : If it is lower pH you need, acetic acid(vinegar) won't get you much : lower than 4. Best bet is pool acid(hydrochloric acid) or battery : acid(sulfuric acid). CAREFUL with both of these! Both are toxic and : highly corrosive-sulfuric mixed incorrectly with water can boil and : splatter on you.
Isn't magnesium also available in those fire-starting kits? The kits where you scrape magnesium shavings off, and then use a flint to start the fire?
A Man wrote: : On Fri, 13 Jan 2006 19:35:46 GMT in article : , email@example.com spoke : thusly... :> Magnesium is available in rod form with a wire already connected to :> it. It is used as a sacricial anode in water heaters and evaporative :> coolers. Check your hardware stores.
: And at $30-50 each (I had to replace one once), not a great choice for budget : armchair scientists, but thanks anyway. But then, science is not about cost, : is it? :)
Here is what I was talking about in a previous post:
Search by item number Enter item number 23131 There you go -- the price is only $6.99. I'm sure you can find this at your local camping store, as well.
Usually in simple homebrew batteries the positive electrode cannot have much improvement over hydrogen (going downward) in the electromotive series.
Also lithium has severe spontaneous rections with water. So do all other metals in the first column of the periodic table - there is some fame for at least sodium and potassium to react with water so violently as to achieve spontaneous combustion. All metals in the first colum of the periodic table also react with air so rapidly that a shiny bare metal surface lasts only seconds. Metals in the first column of the periodic table are normally kept in a petroleum product to protect them from water and air - but lithium has the extra problem of floating in anything that is liquid at or near room temperature and any Earth surface atmospheric pressure.
Next in line are the metals of the second column of the periodic table. But calcium, strontium, barium and radium go plop-plop-fizz-fizz in water (to form hydrogen and hydroxide of the metal in question) - that leaves beryllium and magnesium as usable in that column of the periodic table. Of these, beryllium has bigtime toxicity and cost problems, leaving magnesium as the most electropositive common metal.
Aluminum's main problem is its tendency to form an insulating oxide layer.
1964 and older US dimes and quarters and 1965 and older Canadian dimes, quarters and nickels are solid silver alloy that is mostly silver...BUT:
Silver is not more electropositive than hydrogen (useful for negative terminal) on the electromotive scale but below copper (good for positive electrode and and not much more useful in homebrew batteries that typically have plenty of hydrogen ions that limit the potential of the negative electrode). I would use copper. In addition, achievement of positive electrode much improving over hydrogen in a cell having water typically requires at least one of:
The cell having a solution of a salt of a metal that is below hydrogen on the electromotive scale. But a simpler homebrew cell with that tends to have problems with the dissolved salt reacting spontaneously with any metal positive electrode material higher in the electromotive series.
Oxidizing agents such as some metal oxides - like lead dioxide or manganese dioxide - which I do not cosider quite to be in the realm of homebrew "science fair" batteries.
The positive electrode in a homebrew science fair style cell has little chance of benefiting much from choice among metals below hydrogen in the electromotive series.
The positive electrode will in most homebrew batteries be no better or not much better than hydrogen. So I would expect only about 1.66 volts.
Slightly more voltage, much more current, but with the disadvantage of making the negative electrode react spontaneously. Metals well above hydrogen in the electromotive scale outright go plop-plop-fizz-fizz in strongly acid solutions. Life of a zinc electrode could be merely a day in vinegar, a couple days in lemon juice, a week in orange juice, a month in a tomato, and a few months in a potato - and I might be somewhat optimistic for at least some of these!
Standard conditions for electromotive scale are solvent being water. In addition, when hydrogen is involved (most cases of homebrew batteries with positive electrode being below hydrogen on the electromotive scale):
pH of 0
Temperature where product of molarities of H+ and OH_ ions is 1E-14 (a bit above 20 degrees C)
The atmosphere above the solvent having hydrogen of pressure (or partial pressure in a gas mixture) 760 mmHg.
Additional requirement whether or not hydrogen is involved:
Concentration of ions of active ingredients is 1-molar (or is it
1-normal?) 1 molar is per liter grams in solution being same as molecular weight. For 1-normal grams in solution is molecular weight divided by valence.
But with typical homebrew batteries concentration of compunds of the negative electrode material likely to be less than 1-molar and even
1-normal, I would expect potential to improve a little from the electromotive value of the negative electrode metal. Maybe aluminum's
1.66 will improve to 1.75 or 1.8 or so (with pH 0) oe be 1.5-1.6 (if pH is between 2 qnd 3) - maybe only if you draw no more than a fraction of a microamp. But don't expect positive elecrodes to gain much over hydrogen, which normally forms bubbles on the positive electrode when current is taken from such an electrochemical cell.
In most cells with water solvent and where the positive electrode reaction is reduction of dissolved ions (most homebrew batteries but not usual commercial ones with carbon positive electrodes), the positive electrode potential is limited to that for dissolved ions of active ingredient. In any case carbon is not an active ingredient.
In acid solution, positive electrode potential is largely limited to how low in the electromotive series hydrogen is.
Also - keep in mind that positive ions of an active ingredient low on the electromotive scale may get spontaneously reduced by the negative electrode.
A homebrew battery with aluminum and copper electrodes in a 1-molar (or
1-normal?) aqueous solution of a copper compound should deliver 2 volts - except the aluminum will like to replace the copper ions - getting simultaneously corroded and plated with copper, spontaneously.
Relevance of gold is for either 1-molar or 1-normal solution of a gold salt. The positive electrode will plate with gold when current is drawn. Voltage attributable for that electrode is fully available if the electrode is or is covered with gold - easily enough achievable once current flows assuming solution of a gold salt.
Carbon is not on the scale since there are no carbon compounds that form carbon ions when dissolved in water. Use of a truly inert positive electrode has its potential determined by what positive ions in the electrolyte contact the positive electrode.
And I remember a comic strip having a character saying, "Or is it, to keep the lab placid, add water to acid?" BAD MOVE!!! (Comic strip character adds water to acid and then appears to make the school nurse's day interesting!) I say "water to acid means that you're plastered"!
Same for sodium and potassium hydroxides - mixing these with water can cause boiling.
One reason for adding to water rather than adding water - that way if boiling occurs and causes splashing, what splashes out will be mostly water. Another reason - water makes a better heatsink than acids and alkali metal hydroxides.
And in any case, add slowly and cautiously while mixing.