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AC and DC Voltages for Electrolysis

Discussion in 'General Electronics Discussion' started by LarryParis, May 22, 2015.

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  1. LarryParis

    LarryParis

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    May 22, 2015
    Hi. I want to use electrolysis to remove rust. Usually, an auto battery charger is used, but today the new digital ones will not work in this case. It happens that I have an AC transformer which drops 120v to 6 or 12v. My unease about trying it is the polarity issue. The setup it the negative goes to the rusted item and the positive to the anodes in a solution of water and washing soda. Thanks in advance for any help.LarryParis
     
  2. poor mystic

    poor mystic

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    Apr 8, 2011
    A full-wave rectifier, usually consisting of 4 diodes, will remove rust faster, I presume, since it provides current over the full cycle of the AC potential instead of only a half-cycle.
     
    hevans1944 likes this.
  3. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Remove rust from what?
    I believe the galvanic reaction will etch away just as much good steel as the rust areas, unless you mask off the materials (steel) you don't want to be removed.
     
  4. hevans1944

    hevans1944 Hop - AC8NS

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    I've never tried this, but it sounds fascinating. You probably need an electrolyte, but I have no idea what would work. Also, it would be a good idea to connect the primary of the transformer to a Variac (variable AC autotransformer) so you can control the current. Definitely do as @poor mystic suggests and use a full-wave bridge rectifier. Probably don't need any filter capacitors for rust removal... ions in solution move waaaay slower than the line frequency.
     
  5. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I don't know what washing soda is, but I know the better the conductivity is, the better it will work.
    The best electrolyte is a strong salt water. I don't remember the exact concentration we used to use (cation deburring), but I remember it was 8 times saltier than the ocean.
    Another good electrolyte to use is calcium chloride. Just an electrolyte bath will render some rather crude results, but when an electrolyte is pressurized and directed to a particular area to be worked on, the results are quite impressive.
     
  6. poor mystic

    poor mystic

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    Apr 8, 2011
    I heard of the technique some time ago. Sodium Carbonate (washing soda) was the electrolyte mentioned.
     
  7. LarryParis

    LarryParis

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    May 22, 2015
    Best thanks to everyone replying to my post. If anyone is interested in electrolysis Youtube has quite a lot on the technique. It works on a wide variety of metals, from coins to machinery,and of course handtools, and while it doesn't remove pitting, it doesn't add to it either.Poor Mystic is right that sodium carbonate is the go-to chemical in the water, not so with table saltwater, although ocean saltwater does work on preserving wrecks. I got the transformer (really nice) from a Thrift and assumed it rectified the ac, which has me wondering what ac applications it is designed for--something medical?
     
  8. LarryParis

    LarryParis

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    May 22, 2015
    I forgot to add this is a great forum, and thanks again for your quick replies. Larryparis
     
  9. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I'm sure your right about the sodium carbonate for rust removal, but as someone who was is the business for 15 years, I can say firsthand that regular old table salt (sodium cloride/NaCL) works quite well.
     
  10. poor mystic

    poor mystic

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    Apr 8, 2011
  11. LarryParis

    LarryParis

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    May 22, 2015
    Electrolysis is said to work best with very low voltages, say a battery charger's trickle rather than 10 volts. I would not fly in the face of Tha fios agaibh experience, but I think the issue is how efficient the solution is, not whether it works or not. When the world was young an electrician told me that even so-understood nonconducters, wood, plastic, rubber etc. would carry current if the voltage was great enough. Anyway, to add what poor mystic wrote, to keep the current low it was also suggest putting a light in the circuit to bolster the resistance. The 12v bulb is new to me, and it does sound like a good safety precaution.
     
  12. poor mystic

    poor mystic

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    Apr 8, 2011
    Yes, Larry, I believe you're right. It might be best to try the lowest voltage that will drive current through the work. A long, slow job might give better results than a quicker, high current job.
     
  13. LarryParis

    LarryParis

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    May 22, 2015
    If I may hijack my own thread, what are the advantages of using low volt ac? And would it make sense to rectify what I have to dc? I read something very recently, saying the polarity of both ac and dc are the same in low voltages. The article was frankly over my head, but what I just said is the sense I got out of it. I probably got it wrong. (I'm a tool nut, practically out of control, so I'll try to salvage any hand tool no matter how rusted it is. The electrolysis method is very labor UNintensive. You set it up, walk away, return to it in a day or two, but do it outdoors. The hydrogen gas it gives off is dangerous in low-ceiling basements.
     
  14. poor mystic

    poor mystic

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    Apr 8, 2011
    " ...the polarity of both ac and dc are the same in low voltages?"
    No, there's an error - in AC polarity changes continuously, which is why its' "alternating".
    As for the question of why, exactly, low currents are better, I think it better to ask a chemist. Or possibly, Tha fios agaib might have something to say. ?
     
  15. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Low currents MAY be better if they prevent a layer of gas bubbles from forming on the anode and cathode. Those bubbles don't conduct electricity as well as the electrolyte does. This is just my guess because it has been years since I played with electricity and conductive water solutions. And "play" is the operative term here: I was probably six or seven years old "experimenting" with Lionel train transformers (AC of course!) using carbon electrodes salvaged from dry cells. All I found out was I had to add some table salt to the water to get any appreciable current. Plenty of bubbles came up though.:eek:
     
  16. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    You want to stick with DC. Remember if you use AC, your Anode becomes a Cathode and the Cathode becomes an Anode every half of a cycle. So, it will become destructive to your Anode and If your electrolyte has a metallic reservoir, that will get desolved away too.

    Its better to use DC, or a pulsing DC rather than AC.
     
  17. poor mystic

    poor mystic

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    Apr 8, 2011
    I agree that you need DC, because you are engaged in electrolysis, which is a polarity-dependent phenomenon.
     
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