Spec. out a rectifier circuit

Discussion in 'The Projects Forum' started by sigma-man, Aug 10, 2008.

  1. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    Hello all:

    I am a gray haired Industrial Engineer, with limited electrical know-how.

    My problem is how to specify the hardware to subject electric current from a current supply ( solar panel, 12 volt, low amperage power preferred ) to polyphase rectification to obtain a current having a ripple frequency in excess of that of the current from the solar panel source, and supplying the high frequency direct current to a cathode and anode.

    As you can see, I do not know if this is possible using a solar panel, so I am asking for expert help by explaining the end result I am seeking. If polyphase rectification is not possible, I still will need to supply current to the cathode and anode, using a rectifier circuit.

    All help most appreciated. Please respond to my email: len.walde@Gmail.com as well as this Forum.

    Many thanks,
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Where does the polyphase rectification come in? The output of a solar panel is DC - no rectifier needed.

    If your application requires some frequency to be applied to the anode and cathode, you might get there with an oscillator fed by the solar panel output.
     
  3. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    Thank you. I now know I do not need a rectifier with a solar panel supply. It looks like I do need your suggested Oscillator to supply a current with the most active ripple frequency I can find, (at a reasonable cost). After a quick search I found a list of manufacturers. The link is: http://www.digikey.com/scripts/dksearch/dksus.dll?Cat=852334;keywords=oscillator

    Selecting one, "puts me way over my head" as the selection criteria lists: Current Supply, Frequency, Frequency Stability, and Operating Temperature, (-10 to 60 Deg. C ?) guessing? Any help in selecting the Oscillator I need will be most appreciated.

    If it helps, the cathode and anode are immersed in water.

    sigma-Man ( Len)
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    I would be helpful to know the application. What kind of power do you need? Does it matter if the oscillator is sine of square wave?

    "Most active" ripple frequency doesn't translate very well. Do you just want some arbitrarily high frequency? If it's very low power, anything up to 80 MHz is easily come by.
     
  5. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    It is a low power application, hence the goal to use solar, 12 volts and about 6 amps,in the final installation, but using an auto battery charger during development. It is to power a cathode and a anode in a water tank. All i know is what i said before "to obtain a current having a ripple frequency in excess of that of the current from the solar panel source, and supplying the high frequency direct current to a cathode and anode". The more "ripple frequency" the better, to have an effect on the solids in the water --- so they either float or settle-out, or both. sorry I can not be more specific, I just know that a nice smooth "ripple" does not work too well. So, I am looking for an oscellator providing "high peaks and low valleys" or however one might describe the wave action. does this make sense? I know that most applications call for a nice smooth frequency, I am looking for just the opposite!

    Does this help?

    Len
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Sounds like what you're looking for is a square wave generator capable of a broad range of frequencies driving a pair of H-bridges.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is an immediate problem. With only a single supply, the polarity of the anode and cathode remains fixed. This will cause ionic migration onto the anode and affect system efficiency.

    One electrode really needs to be driven positive and then negative with respect to the other to prevent electrode coating.

    Can you tell us the purpose of the device?
     
  8. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    I searched and found a square wave generator circuit and another that added a triangle wave, as below: ( the link is: http://www.play-hookey.com/analog/triangle_waveform_generator.html )

    Generating Triangle Waves
    In the basic square wave generator circuit, a gradually-charging capacitor was used to help set the timing or frequency of the circuit. However, since it was only charging through a resistor, it necessarily charged on a logarithmic curve, rather than as a linear ramp. Can we use an op amp integrator here to obtain a linear triangle wave along with the square wave?
    [​IMG]
    In the circuit to the right, we use a separate integrator to generate a ramp voltage from the generated square wave. As a result, we can get both waveforms from a single circuit. The phase relationship shown between the two output waveforms is correct — remember that the integrator inverts as well as integrating, so it will produce a negative-going ramp for a positive input voltage, and vice-versa.
    Because we are now using an op amp integrator to get the triangle wave, we no longer have a logarithmic response anywhere in the circuit. Therefore, the equation for the operating frequency is simplified to:
    fout = 1 ( R2 )4RtCR1
    The squarewave amplitude is still the limit of voltage transistion, which we are assuming here to be ±10 volts. The triangle wave's amplitude is set by the ratio of R1/R2.

    My question now becomes: "Can I accomplish what I want by using this third option?"
    I do not say I understand all of this, but it "looks like" and "reads like" it may work for me. What do you think? Please.

    Len

    BTW: I am learning! :) I thank you all!
     
  9. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    Super Moderator, you asked the purpose of the device. You may have missed this: "The more "ripple frequency" the better, to have an effect on the solids in the water --- so they either float or settle-out, or both. Sorry I can not be more specific"

    Does this help?
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    Ok, but my comment about needing to drive one electrode with an alternating voltage still applies.

    For significant current, some frequency in the thousands of Hertz range will be easier than millions of Hertz. One dodge might be to bias the non-driven electrode at 6 volts, and apply 0 - 12 volts to the other. Current will depend on electrode spacing, area, and conductivity of the water.
     
  11. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    I agree, I want to prevent both electroplating and biofilm buildup on the electrodes. To this end, won't periodically reversing the polarity of the electrodes do this? I am planning on spacing Aluminum electrode panels at about 10 MM to minimize fouling and maximizing the effect of the linear triangle wave along with the square wave. how about this arrangement?

    My thanks to all for the help and patience.
     
  12. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    Super Moderator:

    Earlier today I posted a Quick Reply suggesting that we periodically reverse the polarity of the electrodes to prevent electroplating and biofilm buid-up on the electrodes that I described as aluminum plates separated by a 10 mm gap (designed to avoid fouling) The addition of Square wave/Triangle wave frequencies should provide the "ripples' we are looking for. What do you think?

    Many thanks for all of your help!

    P.S. My earlier Quick reply seems to have been lost. I hope this summary helps.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
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    In order to get the triangle wave you seek from the op-amps in your schematic, you'll need both a positive supply and a negative supply.

    What are the solids in the solution? What is the solution? If you answer these, we might be better able to understand the extremely vague concept of "more ripple."

    Are you perhaps getting your requirements from a website? If so, can you share the link?
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    I think that you will run into problems using aluminum for plates in water that contains contaminants; they will corrode and erode due to electrolytic action. Stainless steel would last considerably longer, although the electrical properties are not nearly as good as aluminum. The trade-off is that a stainless steel plate array will require far less maintenance than one made from aluminum.

    If you are indeed using just 12v, you could use a 555 timer IC to generate square waves over a broad range of frequencies, from < 1Hz to as high as 500kHz. You could use the output of the timer to drive an H-bridge; one side of the bridge connected to one set of plates, and the other side of the bridge connected to the other set of plates.
    Here is a tutorial on the 555 timer:
    http://www.uoguelph.ca/~antoon/gadgets/555/555.html
    Another tutorial, with animations:
    http://williamson-labs.com/555-tutorial.htm
    Yet another tutorial:
    http://www.electronics-tutorials.com/devices/555.htm
    Forrest M. Mims III wrote a series of mini-notebooks that are very easy to read, and make great reference books.
    http://www.forrestmims.com/engineers_mini_notebook.html
    Volume I and Volume IV are particularly handy to have.

    Pure water is normally an insulator. However, certain contaminants such as sodium, baking soda, etc. can cause the water to conduct electricity, which will result in the release of hydrogen and oxygen gasses. While the amount of gasses released will be rather small, they are explosive, so you must not use a device like this in a confined space which would allow the gasses to accumulate over a period of time.
     
    Last edited: Aug 13, 2008
  15. sigma-man

    Thread Starter New Member

    Aug 10, 2008
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    The technology I am adapting to my invention is electrocoagulation. The following is a brief explanation as adapted from a 10 year old patent. I offer this as information sufficient to explain the application I am seeking help with and still protect the intellectual property I am developing. I feel I can accomplish my approach with a simple sine wave but it will work much better with a Square Wave/Triangle Wave Generator – recognizing however that the cost my make this improvement impossible. I hope all of this helps each of you help me and is very much appreciated!

    Len


    The electrocoagulation water treatment tank includes two or more electrode plates mounted in an open top of the tank The electrode plates are separated using insulating support spacers for providing proper spacing and insulation between the plates. The electrode plates are connected to electric leads attached to an independent DC power supply . The DC power supply is mounted in the batch tank and next to the water treatment tank The electrode plates are used for providing current to the waste water and for removing various contaminates in the water by electrocoagulation. The contaminates removed from the water in the form of floating material or foam float out and over the open top of the tank for dewatering. ( Note: The electrode plates are aluminum and intended to be sacrificial and replaceable – Len)

    The top of the electrode plates include tabs used for connection to the ends of the electric leads. The plates are placed in the tank with alternating spacers to provide electrical insulation as well as proper distance between the electrode plates . The spacers can be constructed with various thicknesses and insulating materials to optimize the process and electrode plate spacing. On large sized electrode plates, center spacers can also be used to prevent electromagnetic attraction from pulling the center portions of two adjacent plates closer together. The use of both variable thickness spacers as well as variable thickness electrode plates allows for the optimization of contaminate removal in the waste water when using the subject batch tank system .

    The polarity of the DC current to the electrode plates can be reversed periodically to help reduce the build up of scale on the plates. Scale is a natural result of the electrocoagulation process, which if not displaced by the reversing of the polarity, will eventually plug the plates. The amount of voltage and amperage to the plates will be determined by the quantity and type of contaminates in the water. Also, the electrode plates with spacers can be configured to allow for different voltages and/or amperages to be applied simultaneously. This type of power flexibility to the plates aids in the optimum removal of the contaminates with minimum power applied or the removal of specific contaminates at different electrode plate locations.



    I will now study Sgt. Wookie's suggested tutorials to add to my education. Many thanks for this.

    Len
     
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