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Best metals to make homemade battery?

Discussion in 'Electronic Basics' started by A Man, Jan 12, 2006.

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  1. A Man

    A Man Guest

    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.
     
  2. Gareth

    Gareth Guest

    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.

    --
     
  3. 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.

    Rbrowsers.
     
  4. Yukio YANO

    Yukio YANO Guest

    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

    Yukio YANO
     
  5. A Man

    A Man Guest

    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.
     
  6. Charles Jean

    Charles Jean Guest

    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.
     
  7. Bill Bowden

    Bill Bowden Guest

    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.

    -Bill
     
  8. Rich Grise

    Rich Grise Guest

    That will make a very good capacitor. :)
    There have never been silver plated US coins. They were some silver
    alloy, until they decided to omit silver entirely, and came up with
    that copper/nickel sandwich.

    There _is_ silver plated silverware, however. :) Poke a fork in your
    lemon, and you'll have a lot of electrode area too! :)
    Does that table have carbon?

    And what is the table actually of? I thought gold was practically inert,
    i.e, neutral, more or less. Can you expand on this?
    Until the oxide layer forms on the aluminum.
    Good Luck!
    Rich
     
  9. Rich Grise

    Rich Grise Guest

    Add the H2SO4 to the water - do not _EVER_ add water to concentrated
    H2SO4!

    Good Luck!
    Rich
     
  10. Tim Williams

    Tim Williams Guest

    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+) +
    2e-).

    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).

    Tim
     
  11. A Man

    A Man Guest

    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.
     
  12. A Man

    A Man Guest

    On Fri, 13 Jan 2006 19:35:46 GMT in article
    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? :)
     
  13. Guest

    Guest Guest

    : 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?

    Seems like a good source of Mg to me....

    Joe
     
  14. Guest

    Guest Guest

    : On Fri, 13 Jan 2006 19:35:46 GMT in article
    : <>, 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:

    Go to www.campmor.com
    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.

    Have Fun,

    Joe
     
  15. Bill Bowden

    Bill Bowden Guest

    Gold is an excellent conductor of electricity, but it is expensive.

    Gold is not as good as copper, gold has 1.4 times more resistiance than
    copper.
    Copper is used because it has has much less resistance than gold.
    Gold is used only because it doesn't corrode.

    -Bill
     
  16. 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:

    1. 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.

    2. 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):

    1. pH of 0

    2. Temperature where product of molarities of H+ and OH_ ions is 1E-14
    (a bit above 20 degrees C)

    3. 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.

    - Don Klipstein ()
     
  17. 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.

    - Don Klipstein ()
     
  18. I have heard the saying:

    "Do as you oughta - add acid to water"!

    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.

    - Don Klipstein ()
     
  19. Jasen Betts

    Jasen Betts Guest

    gold is a so-so conductor of electricity, but is very resistant to
    tarnishing that's why it's used to coat contacts.

    silver is a marginally better conductor than copper.

    Bye.
    Jasen
     
  20. ehsjr

    ehsjr Guest

    Actually, as I recall gold is the third best conductor.

    Only copper and silver are better - silver is best.
    Ed
     
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