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Home Made Batteries

Discussion in 'Power Electronics' started by Dustin Smith, Jun 27, 2012.

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  1. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    QUESTION:
    Why do people put salt in homemade batteries when I seem to be getting the same results from regular tap water?

    I've been experimenting with things like salt water batteries and earth batteries. I discovered about three days ago that adding just normal tap water in place of salt water has yielded the same if not higher voltage than the salt water ones I'd made. They have been running in a series for about 3 days keeping a small (i think 3mm) red LED lit quite successfully.
     
  2. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    Often, tap water contains sufficient impurities such as carbonates, sulfides and metal salts to be an effective electrolyte. Try running the experiment again with deionized or distilled water after cleaning all materials with the same water (wear rubber gloves to avoid contamination). It's also possible that electrolytic chemicals are leaching from your spacer media if any (filter paper, paper toweling, etc.)

    You might also ask your municipal water company for an assay of the typical impurities that remain in the water they supply though they may just tell you that the water meets all government standards and is safe to drink.
     
    Last edited: Jun 27, 2012
  3. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    Thanks KJ6EAD,
    So is it safe to say that salt water as an electrolyte will out last tap water? I have no spacer media. And where I live, the government recommends filtering the water or at least boiling it before consumption.
     
  4. CocaCola

    CocaCola

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    Apr 7, 2012
    That really depends on the contaminants in your water... Using 'clean' water and adding your own electrolytic mix, gives you control and consistency...

    After just getting my annual water report ironically 2 days ago, even though my water is well within the legal safe for human consumption standards, I still feel additional filtering is a good option...

    BTW, this brings back some memories as a little kid for me... I remember taking a 35mm film canister some aluminum foil, copper wire, cardboard and epsom salts and making a very primitive battery just to see if it worked... I was probably only 10 years old at the time... I know it's far from the perfect battery but when I hooked my volt meter up and saw it move I was satisfied with my accomplishment...
     
    Last edited: Jun 27, 2012
  5. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    In truth, it's my purpose to discover the best way to use things people normally have around the house to create enough power to operate a nightlight. So using tap water is rather ideal for my plans. Does anyone posses knowledge of different metals and electrolytes and what their combinations can yield as far as voltage and amperage?

    Glad to bring back a fun childhood memory Coca Cola. :)
     
  6. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    Thanks KJ. That's a very comprehensive list. Too bad they wrote it in code, makes it difficult for guys like me to read. But that's ok, I found a link to a periodic chart of elements. :D
     
  7. Solidus

    Solidus

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    Jun 19, 2011
    Voltage potential varies by two factors, dissociative capability and concentration.

    Amperage varies by amount of ions present (amount of electrolyte multiplied by concentration).

    Dissociative capability - ability for a acid or base to put ions into solution, also applies to salts (a salt by definition is an acid anion coupled to a metal cation, so table salt is the sodium salt of hydrochloric acid).

    Basically, there are strong and weak acids, based on dissociation. Strong acids will always form stronger electrolytic solutions. Pour vinegar into a battery and then sulfuric acid at the same concentration and you tell me which one is stronger.

    Concentration - this one's kinda obvious. More ions in solution creates a larger potential. How do you render an acid safe(r) in the lab? Dilute it. Same principle with batteries. Higher concentration, more ions, increased potential. That's the reason 12V high-load car batteries are potent enough to etch metal.

    Car batteries are the reaction of sulfuric acid stripping electrons off of lead plates.

    Amperage is a trickier concept, although not by much. It varies by total amount, although this can be misleading. A water tower-full of brine (salt water) turned into a gigantic battery will sustain a higher amperage than a car battery mainly because it has a higher ionization (amount of creating ions), even though it would have a MINUSCULE voltage. More electron flow is higher current.

    Therefore to increase amperage you can play around with two notions, total volume and concentration. If you have sensitive areas that won't tolerate high concentration but you have sufficient space, you can build a large battery.

    Hopefully this is of some aid to you, I am a chemical engineering major at my university. Let me know if you need any more help.

    solidus

    Edit: as for specific examples, I can end up digging up tables and calculating values for you if you're able to get a water assay or description of your electrolyte source.
     
  8. duke37

    duke37

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    Jan 9, 2011
    I thought voltage was dependant on the chemical reaction and the concentration would affect the cell resistance.
    For details of the potentials available in batteries you could look up a book written by my brother-in-law.
    'Specific energies of galvanic reactions, and related thermodynamic data' Chapman Hall 1973
     
  9. Solidus

    Solidus

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    Jun 19, 2011
    You are completely correct about the reaction specificity.

    I was just giving him some general information about acids and bases and how they work in a battery role. You can make an acid-only battery, although they're fairly weak because of the hydrogen ion being used.

    Okay, I'll look that up. I also have electro and thermo tables that you can use if anyone wants me to put scans up.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You mean like a lead-acid battery? Two plates of lead and sulphuric acid (in its discharged state).
     
  11. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    Thanks very much Solidus. You've been very helpful, and your detailed explanation broken down to terms I can understand. I appreciate it, because I've been going to the HKU and have yet to earn a degree!

    HKU (Hard Knock University)

    If you think the electro and thermo tables are not too difficult to decipher, I'd like to take a look at them if you had a moment to scan them.

    Duke, I'll take a look for that book as well, thanks.
     
  12. Solidus

    Solidus

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    Jun 19, 2011
    Yes. Where the acid and electrodes are the only thing interacting in one single "pot" if you will.

    Dustin, you can also have what are known as "half-cells", where one metal electrode is in one cell and another (different) metal electrode is in another. You connect the two cells chemically by a "salt bridge". This is a tube that has a less-reactive electrolyte in it (so it doesn't interfere with the acid or base in the two cells) and serves to make an electron bridge.

    It doesn't make much difference for you over the single-pot battery as mentioned above, but in chemistry labs, it allows us to analyze and watch the dynamics of a battery change over time, because each cell stays independent of one another apart for electrons.

    I found some of my equation tables, I'll work on getting them scanned and uploaded in a while.

    Rest assured, I'll walk you through the process. Don't worry, I won't give you a bunch of random, nonsensical-looking equations and expect you to follow them yourself :p

    solidus
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I wouldn't call a lead acid battery "weak", although maybe you mean weak like chemists do when they describe HF as a "weak acid" and then look for something to store it in...
     
  14. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    I've heard of the salt-bridge battery idea and seen it drawn on paper. I fail to understand what to make the salt bridge out of. It would be more useful as I understand it because it's not constantly active (meaning the electrodes are not being used up all the time). It's only active when you are using power from it. I emailed a gal from youtube named Jeri about the salt bridge where I first saw it, but have received no reply. Could you direct me to a good source to make the bridge? I first thought of stuffing salt into a straw, but I don't think that would work so well! Ha ha
     
  15. Solidus

    Solidus

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    Jun 19, 2011
    My original intention by saying "weak" is I was thinking of a beaker of sulfuric acid. A very slight voltage can be measured across sulfuric acid if inert electrodes are used.

    This is because dissociation is a dynamic process, and because the sulfuric acid is in solution (H2SO4) it constantly dissociates into SO4 (2-) and 2H+, and vice versa.

    Of course, because you're not changing the beaker in anyway, the net function will always be zero, and what little voltage you measure is usually reducing the thermal energy of the system. That's what I mean by weak. I should have probably said miniscule.

    However, you raised a valid point on that misunderstanding, and a car battery is by no means weak.

    You need a metal for strength. Lead is used because it has 4 electrons to donate (increased potential) and because both the II and IV sulfate forms are solid, and won't contaminate or reduce the efficiency of the battery in the process.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Start with and aqueous solution of sodium chloride in dihydrogen monoxide.

    Any battery where the electrodes are being "used up" all the time is not a good battery.
     
  17. Solidus

    Solidus

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    Jun 19, 2011
    Haha.

    1. Take a piece of tubing.
    2. Roll up a piece of paper (paper towels work best, most absorbent) and push it into the tubing.
    3. Soak the paper in concentrated salt water

    solidus
     
  18. Solidus

    Solidus

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    Jun 19, 2011
    He is on the right track. If you remove the salt bridge, there is no net transfer of electrons and so the redox at the anode/cathode should stop.

    It does pay to be weary though and not lax about it, it will most likely be in an aqueous solution so oxide corrosion can still occur.
     
  19. Dustin Smith

    Dustin Smith

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    0
    Jun 27, 2012
    Well, I don't think my homemade batteries are good anyway. But I'm having fun with them and learning a lot. However, I must admit that they are getting better. Especially with help from friendly people here on this forum.
     
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