Need help with auto switching Reverse polarity circuit

Discussion in 'The Projects Forum' started by gunlocators, Dec 4, 2014.

  1. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    Here is what I am wanting to do and cannot figure out how to accomplish it. I want to use 3 9v Batteries in Series and run +/- 27v in to a circuit and I want +/- 27 also out of the circuit. Heres where I am unsure. Although I know I could use a switch to manually change polarity. I am wanting a timed circuit to swap polarity. The timing is not too critical but needs to be between every 2-3 minutes to swap the polarity. Also would be nice to have a way to protect the out going 27v leads as they are going to be electrodes to have some sort of protection in case they were to touch and short out. Thats not absolutely critical but would be a nice feature. I have been stuck for 2 weeks trying to figure out how to get a circuit built that will allow for auto switching of polarity. Any help and assistance or ideas would be GREATLY appreciated.

    A little more info I am building a Colloidal Silver Generator the Silver Electrodes go in distilled water. The reason for reversing polarity a time intervals and back and forth is to ensure one electrode is not eroded over time faster than the other. The process takes 2-3 hours so a manual switch would be a daunting task to baby sit the generator. If some one is willing to help me complete a circuit that will work, I would be very appreciative.

    Thank you
    Rodney W3LDR
    Amateur Radio Operator
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    A H-bridge (made out of transistors, Fets, a relay, or a DPDT switch) is for switching polarity...

    I think you are wasting your time with 9V batteries. Have you looked at their discharge curves?

    I think you are also wasting your time with Colloidal Silver, but you raised the topic...

    One old time Ham to another...
     
  3. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    The colloidal silver is for a friend he swears by it I told him I would help build a generator I dont use it. A HBridge would work but issue is how to make it auro switch every 2 - 3 minutes
     
  4. MikeML

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    I would look at building a classic two transistor multivibrator (link) designed to operate on about 30V; you get an H-bridge and a clock oscillator in one circuit.

    How much current flows through the solution?

    What is the actual voltage between the electrodes with the cell switched either polarity?

    How critical is it that the +- period be exactly equal to the -+ period?
     
    Last edited: Dec 4, 2014
  5. Alec_t

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    Sep 17, 2013
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    If, as the OP states, "the Silver Electrodes go in distilled water", I would think negligible current flows. Distilled water is a very poor conductor.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What are you trying to do?
    Do you want to do electrolysis of the water?
    As stated by Alec_t , distilled water will have hardly any current flowing.
    I know as we used distilled water to cool high voltage generators.

    Bertus
     
  7. crutschow

    Expert

    Mar 14, 2008
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    You could use this circuit to limit the short circuit current and protect the bridge transistors.
    The approximate limit current is 0.7V / R_sense.
    Note that R2 is not needed and can be replaced with a short.
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    As I understand the process you want to limit the current, not reverse it. What do you think is going on? Where are you getting your plans for this device which you can buy on Amazon for a fraction of what it will cost you to build one?
     
  9. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    I want to indeed reverse the polarity. Not sure current between electrodes in water but he has a generator now it does not reverse ot polarization. What happens over time one electrode sluffs off silver and the other does not. Where if it reversed polarity both electrodes would sluff off silver equally over time. Thats what were trying to accomplish. The timing does not have to be perfect however it should be close
     
  10. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    My other thought was to use a relay that normally would be in one state when charged then the other when not charged. But would need to play with maybe a 555 timer to make that work.
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    I don't think it works that way, but since the details of your electro-chemical cell are incomplete its hard to know what you are doing or not doing. For example are the two electrodes made of the same or different material? The reason I ask is that reaction rates are not likely to be the same in both directions. Especially since the electrolyte is so weak and you can't add a catalyst.

    What happens in a normal cell is that with electrodes of different material, the ions migrate from one electrode to the other and the process is generally not reversible. This is obviously not a typical electro-chemical cell, but what makes you think the process is reversible?
     
  12. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    Both electrodes are .9999 fine silver rods 12ga
     
  13. Alec_t

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    From the limited Googling I've done on the subject, typically both electrodes are 'pure' silver wire and need to be physically removed from the water and scrubbed every 5 mins or so to remove deposits. That being the case, the electrodes could simply be swapped over each time. I don't see the need for a polarity reversing circuit at all :confused:.
     
  14. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    There are manufactures using reverse polarity in the units they sell. They claim the electrode wear at a even rate as they sluff off and some say the electrodes do not build up gunk and if so its super slow so your not wiping the electrodes every few minutes. Thats the entire purpose. The setup he has now simply when I open the enclosure he purchased is just 3 9v batteries wired in series going to the electrodes. Oh there is a switch for on off and a led and resistor to indicate there is power on. He states this setup the one side of the electrode does erode at a much faster rate and also says he constantly is cleaning the electrodes. He wanted a reverse polorized unit however they were $250 he said so were trying to save him some money. He a great friend and war vet so I try to help when I can even if I dont agree with his usefulness of a product....
     
  15. Alec_t

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    If he's serious about saving money he should consider replacing the 9V batteries with a mains-powered low-voltage adapter. From what I read, a 12VDC 400mA adapter is a possible supply for these gadgets.
     
  16. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    We are adding a wall wart he said he wanted it on a switch incase he was ever without power Thats a prepper for ya. So it will be switchable power.
     
  17. Alec_t

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    Have you seen this article? The small-print footnote is also worth reading in relation to the promoted products.
    https://www.purestcolloids.com/notcs.php
    The article suggests that your friend's generator is most likely producing silver ions; not colloidal silver.
    It also indicates that AC can be used for the process instead of DC. That being the case, why bother with a switching circuit? Just find a suitable low voltage transformer and attach the electrodes to the secondary.
    However, that article points out that silver ions are rapidly converted to silver compounds and excreted, so are of dubious benefit.
    The link below is concerned with the harmful effects of colloidal silver.
    http://whatstheharm.net/colloidalsilver.html
     
    Last edited: Dec 6, 2014
  18. gunlocators

    Thread Starter New Member

    Dec 4, 2014
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    Yeah I showed him articles he is aware of everything oh well. So on a AC Transformer Low Voltage would you simply attach the leads to the electrodes and run straight into the water? Any electrocution hazard? Would you need a inline safety fuse of some sort?
     
  19. Alec_t

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    A fuse (e.g. 1A rating) would be sensible, in addition to a suitably-sized current-limiting resistor to protect against inadvertent shorting of the electrodes. Providing a good quality AC wall-wart/transformer is used, the primary connections are properly shrouded/enclosed, it is kept well away from the water, and the secondary voltage is only 12VRMS or so, there should be no electrocution hazard.
    Personally, having read the linked articles, I'm sceptical that the setup will produce colloidal silver or have any beneficial effect, and its use is entirely at your friend's risk. If in doubt as to its safety don't build/use it.
     
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