Reverse Polarity Circuit

Discussion in 'General Electronics Chat' started by TCA, May 22, 2011.

  1. TCA

    Thread Starter New Member

    May 20, 2011
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    Dear All, I'm very new to electronics and would really appreciate some help with a reverse polarity circuit for a salt water electrolysis unit. The electrolysis unit is low voltage 6 - 10 volts DC and has a variable current rating up to 30amps. What I would like is every time the unit switches on the polarity of the plates would be reversed, thus helping to keep the electrolysis plates clean. For example the unit would run for 12 hours with plate 'A' positive and plate 'B' negative, it would turn off for 12 hours (no power), then turn on again (via standard 240v timer switch turning mains power on and off) with plate 'A' negative and plate 'B' positive and so on. From a bit of google research I understand that I would need a flip-flop circuit (chip?) which changes it's state every time the power is turned on, and this chip? would activate the coil of a DPDT relay wired as a reversing switch??
    If any one could draw me a diagram with component list that would be great.
    Thank you all in advance for your help.
     
    Last edited: May 22, 2011
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Of course you realize that you will be creating Bleach water by using sodium chloride as an electrolyte. Sulfuric acid, or sodium hydroxide, or potassium hydroxide are the common electrolytes for creating oxygen and hydrogen from water. No Chlorine.
     
  3. Ron H

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    Apr 14, 2005
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    IIRC, chlorine and hydrogen gases are produced, leaving aqueous sodium hydroxide (NaOH), which is alkaline and caustic. When I experimented with this many years ago, I seem to remember that some NaOH (at least, I assumed it was NaOH) precipitated out.
     
  4. Kermit2

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    Yes, it is releasing chlorine gas. But after the chlorine has been evolved in the solution for a few minutes, sodium hypochlorite begins to form from the free chlorine dissolved in solution. It is a secondary reaction and very low yield. Just a few sniffs of the water used in the experiment will reveal its presence. Don't sniff it while its bubbling though, Chlorine gas is very toxic.

    Read this for an example of using salt water and electricity to generate bleach
    http://www.globaltreat.com/hypochlorite-generator.html
     
  5. TCA

    Thread Starter New Member

    May 20, 2011
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    Yes - it is a chlorine generator for a swimming pool. The problem is to make the electrodes self-cleaning so that I don't have to acid wash every couple of weeks, which reduces life of electrode plates.
     
  6. Kermit2

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    The problem you will have is relays have no 'memory'. If you turn off the power, they revert to the 'original' state. No way to make one of them activate on one power cycle and not have it activate the next . For this to work the way you have envisioned it will require a micro controller and memory. Relays cannot provide either/or switchability unless you keep some portion of your circuit alive with voltage at all times.
     
  7. pistnbroke

    Member

    May 9, 2011
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    Easy .....just put in your DPCO relay to change the polarity and then a 24 hr mains timer which goes on/off in hour intervals to switch the relay ....during your 12 hr cycle the plates will change polarity every hour and when the whole thing is off for 12 hours ..no problem..it just starts where it left off ....If you make it a mains voltage relay its even easier


    or just build a 555 timer circuit to work the relay if its on /off is about 1 hr it does not matter if it looses power when the pool is not on as when power is returned it will change one hour later etc ...
     
    Last edited: May 24, 2011
  8. TCA

    Thread Starter New Member

    May 20, 2011
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    All excellent ideas - thank you. I'm a bit worried about having mains voltage any where near the electrode DC supply so the idea of the relay having it's own permanent DC supply would work. The change of polarity every hour would also work if this was the easiest approach - would there need to be any off time, before it switched polarity. I have been thinking down the line of 555 or 556 dual timers??? It would be good if I really knew what they where. With capacitors charging and discharging to cause opening and closing of the reverse polarity DPDT relay? I'm a molecular biologist by profession so all this new stuff is overloading my brain!! Any diagrams would be really appreciated. Thank you.
     
  9. pistnbroke

    Member

    May 9, 2011
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    the off time is when the relay contacts are moving ....the 240v coil is isolated from the contacts so thats not a poblem ..you could use an isolating transformer with earthed screen ... to feed the mains timer to feed the relay .if you know nowt thats the easy way OR ...if you google 555 timers there are lots of circuits out there .
    Another thought ...use the mains timer to power a transformer mains to 12v ..and use that to power a relay ( ac relay or rectify the transformer output) . That would give you isolation and simplicity ..if you are no good with a soldering iron forget the electronics ..all the bits you need are at Tandy/dick smith/radio shack
     
  10. jaclement

    Active Member

    Apr 15, 2009
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    Why rectify the 6 to 10 volt output of the supply transformer I am asuming that there is a supply transformer).Just run the raw AC to the electrodes. Then the polarity will change every 1/2 cycle.
     
  11. pistnbroke

    Member

    May 9, 2011
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    well I did think of that but not being an expert on pool clorinators thought that was not the way to do it .....you have a solution get on with it
     
  12. Ron H

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    Apr 14, 2005
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    I'm no chemist, but I think that, if you use AC, you'll have hydrogen and chlorine coming off each electrode simultaneously. They will combine to form HCl (hydrochloric acid), which will in turn combine with the sodium hydroxide, and you will wind up with salt water, which is what you started with. It may not happen exactly llike that, but I think the result is correct.
     
  13. Kermit2

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  14. jaclement

    Active Member

    Apr 15, 2009
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    The hydrogen and chlorine will be generated in the same place on alternate 1/2 cycles. They will not recombine spontaneously , any more that if you mixed the 2 gasses in a test tube. Something must provide enough energy to start that reaction. The chlorine will disovle in the aquious solution until it is satuarated,and then the excess will bubble out. If you add acid at this point. you will get a tremendous release of chlorine gas
     
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