Patent Publication Number: US-2007120523-A1

Title: Power supply for electrochemical ion exchange cell

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application is a continuation-in-part of U.S. patent application Ser. No. 11/024,521, to Holmes et al., filed Dec. 28, 2004, entitled “Power Supply for Electrochemical Ion Exchange,” and which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND  
      Embodiments of the invention relate to a power supply for an electrochemical ion exchange cell.  
      A fluid treatment apparatus comprises one or more electrochemical ion exchange cells and is used to replace or add ions to a fluid, remove particles and sediment, and deactivate or reduce the levels of microorganisms in the fluid. The electrochemical cells are used to treat water, and other fluids, such as solvent or oil based fluids, chemical slurries, and waste water. The cell removes or replaces ions in a fluid stream, for example, to produce purified water by deionization, treat waste water, or selectively substitute ions in a fluid. A typical cell comprises electrodes about an ion exchange material which removes or replaces ions in an influent solution to form a treated solution. After the cell is used for some time, the ion exchange material is regenerated by reversing the polarity of the voltage applied to the electrodes. The ion exchange material may be a water-splitting ion exchange membrane (also known as a bipolar, double, or laminar membrane) that is positioned between two facing electrodes, as for example, described in commonly assigned U.S. Pat. No. 5,788,826 to Nyberg, issued Aug. 4, 1998, U.S. patent application Ser. No. 10/637,186 to Holmes et al., filed Aug. 8, 2003, and U.S. patent application Ser. No. 10/900,256 to Hawkins et al., filed Jul. 26, 2004, all of which are incorporated herein by reference in their entireties. Electrochemical ion exchange cells are advantageous because they can be used to efficiently treat an influent solution and are easier to regenerate than chemical cells which require chemicals for regeneration.  
      A power supply is used to apply cell deionization and regeneration voltages to the electrodes of the electrochemical cell. The power supply provides a relatively high voltage to the electrodes and also controls the polarity of the voltage. The voltage level is related to the effectiveness of the electrochemical cell at removing or replacing ions, and the polarity is switched to select de-ionization or regeneration of the cell. As there may be a tendency for the current delivered to the cells to increase beyond desirable limits, due to, for example, an electrical short or a transient low resistance pathway it is also desirable for the power supply to monitor and limit the current supplied to the electrodes. Furthermore, the power supply should also be cost and energy efficient, as ion exchange apparatuses are often used for fluid treatment in economically-developing product markets.  
      Power supplies have been developed for use with ion exchange apparatuses. For example, U.S. Pat. No. 5,055,170 to Saito, issued Oct. 8, 1991, which is incorporated herein by reference in its entirety, discloses a circuit for applying a DC voltage between electrodes in an electrolytic cell having an ion-exchange membrane. The circuit has a transformer to step down an AC voltage, which is then rectified and supplied to the collector of an NPN transistor whose emitter is connected to the positive electrode of the electrolytic cell. The base of the NPN transistor is driven by a control circuit which receives an input based on a measured voltage drop in the cell. However, there are disadvantages of this circuit, for example the output DC voltage is limited in value to the voltage level of the rectified stepped down voltage. Thus, the output DC voltage will never be greater in value than the amplitude of the available AC voltage. Furthermore, the use of a transformer in the circuit driving the electrodes may be undesirable due to the potentially high cost and weight of such a component. Additionally, Saito provides no means to monitor and limit the current delivered to the electrode.  
      In another example, U.S. Pat. No. 4,012,310 to Clark et al., which is incorporated herein by reference in its entirety, discloses a high voltage supply for an electrode of an electrostatic water treatment system. The high voltage supply of Clark et al. comprises a DC multiplier having a center-tapped transformer fed by a transistor oscillator and a DC power supply. The action of the transistor oscillator serves to turn the multiplier on and off to conserve energy, resulting in the charging and discharging of a capacitance between the electrode and a shell around the electrode. However, the use of a transformer, as in the circuit of Saito, is undesirable. The high voltage supply of Clark et al. also has an over current protection which turns off the high voltage supply in the event of an excessive current delivered to the electrode. However, it is undesirable to completely shut down the power delivery to the electrostatic water treatment system, as a complete shutdown will incur an undesirable transient startup time to begin water treatment after the shutdown. Furthermore, the high voltage supply of Clark et al. does not generate a DC voltage which has a selectable voltage level.  
      Another problem is that electrode power supplies typically require the use of components that are rated to withstand the full value of the voltage generated by the power supply. However, as the power supply becomes capable of producing relatively higher voltage levels, the components are required to be rated for these higher voltages which increase their cost of fabrication. Thus, the benefit of an electrode power supply to deliver a relatively higher output voltage is usually offset by the cost of the components of such a power supply.  
      During cell deionization and regeneration, a power supply is used to apply the requisite voltage to the electrodes of the cell. The power supply should allow effective control of polarity for de-ionization or regeneration and voltage levels. It is also desirable for the power supply to monitor and limit the current supplied to the electrodes as the current delivered to the cells can increase beyond desirable limits due to a transient low resistance pathway. Furthermore, the power supply should also be cost and energy efficient, as fluid treatment cells are often used for drinking water applications in economically-developing markets. Thus, it is desirable to have a power supply for an ion exchange apparatus capable of delivering a DC voltage having a relatively selectable polarity and voltage levels, which can limit the current supplied to the electrodes, and that is energy efficient and relatively inexpensive.  
    
    
     DRAWINGS  
      These features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, which illustrate examples of the invention. However, it is to be understood that each of the features can be used in the invention in general, not merely in the context of the particular drawings, and the invention includes any combination of these features, where:  
       FIG. 1  is a schematic view of an embodiment of a ion exchange apparatus comprising an electrochemical cell having electrodes positioned about membranes;  
       FIG. 2A  is a schematic sectional top view of the electrochemical cell of  FIG. 1  showing a cartridge having membranes with integral spacers that are spirally wound around a core tube;  
       FIG. 2B  is a schematic partial sectional perspective exploded view of an embodiment of an electrochemical cell having membranes wrapped around tubular electrodes which can apply an electric potential in the cell;  
       FIG. 3  is a schematic diagram of an embodiment of a ion exchange apparatus which has dual electrochemical cells and dual power supplies, a solenoid valve system and various filters;  
       FIG. 4  is a schematic diagram of a controller comprising a control unit, power supply and supplemental power supply;  
       FIG. 5  is a schematic diagram of an electrode power supply;  
       FIG. 6  is a schematic diagram of a voltage selector of the electrode power supply of  FIG. 5 ;  
       FIG. 7A -C are schematic diagrams of different versions of zero crossing detectors suitable for use in the electrode power supply of  FIG. 5 ;  
       FIG. 7D  is an integrated zero crossing detector and polarity selector; and  
       FIG. 8  is a schematic view of a current detector appropriate for use in the power supply of  FIG. 5 .  
    
    
     DESCRIPTION  
      Embodiments of the present invention may be utilized as a component of systems and apparatus capable of treating a fluid to extract, replace or add ions to the fluid, remove particles and sediment, and deactivate or reduce the levels of microorganisms in the fluid. While exemplary embodiments of the ion exchange apparatus are provided to illustrate the invention, they should not be used to limit the scope of the invention. For example, the ion exchange apparatus can include an apparatus other than the electrochemical cells or cell arrangements described herein, as would be apparent to those of ordinary skill in the art. Also, in addition to the treatment of water, which is described as an exemplary embodiment herein, the ion exchange apparatus can be used to treat other fluids, such as solvent or oil based fluids, chemical slurries, and waste water. Thus, the illustrative embodiments described herein should not be used to limit the scope of the present invention.  
      An exemplary embodiment of an apparatus  100  capable of treating a fluid by ion exchange is shown in  FIG. 1 . The apparatus  100  comprises an electrochemical cell  102 , which includes a housing  104  enclosing at least two electrodes  106 ,  108  and one or more ion exchange membranes  110 , such as water-splitting ion exchange membranes. A controller  132  comprising a cell power supply  114  and other control elements controls the power supplied to the cell  102  and controls the valve system  118 . The cell power supply  114  is provided to power the electrodes  106 , 108  by supplying a current or voltage to the electrodes  106 , 108 . The valve system  118  controls the fluid supply from a fluid source  120  to provide an influent fluid stream  124  into the cell. The treated fluid is passed out of the cell  102  as a treated or effluent fluid stream  125  which may be stored in a treated fluid tank  126  and/or released from a dispensing device  128 . Electrochemical ion exchange apparatuses are described in commonly assigned U.S. Pat. No. 5,788,812 issued to Nyberg et al., U.S. patent application Ser. No. 10/130,256 also to Nyberg et al.; and U.S. patent application Ser. No. 11/021,931 to Holmes et al., all of which are incorporated herein by reference in their entireties.  
      The electrodes  106 , 108  of the cell  102  are fabricated from electrically conductive materials, such as a metal, metal alloy, or carbon which are resistant to corrosion in the low or high pH chemical environments formed during the positive and negative polarization of the electrodes  106 , 108 , in operation of the cell  102 . Suitable electrodes  106 , 108  can be fabricated from corrosion-resistant materials such as titanium or niobium, and can have an outer coating of a noble metal, such as platinum. The shape of the electrodes  106 ,  108  depends upon the design of the electrochemical cell  102  and the conductivity of the fluid stream  124  flowing through the cell  102 . Suitable shapes for the electrodes  106 , 108  include for example, wires, wire mesh wraps and sheets with punched holes. The electrodes  106 , 108  are arranged to provide an electric potential drop through the membranes  110  upon application of a current to the electrodes  106 , 108 .  
      In one version, shown in  FIGS. 2A and 2B , the cell  102  comprises a cartridge  130  containing a pair of electrodes  106 , 108 , which are wires wrapped on a central riser tube  109  in the center of the cartridge  130  and the wire wrap outside the cartridge adjacent to the inner wall of the housing  104 . The electrodes are located about a stack of spiral wrapped water splitting membranes  110  which are rolled and bound together by an outer netting tube (not shown). In the cell  102 , the fluid stream  124  flows between the membrane layers from the outside to the inside of the housing  104 , and into the top of riser tube  109 , and exits at the bottom of the cell  102 , or fluid flow may be in the opposite direction. The electric potential difference is applied between the two electrodes  106 , 108 , across the stack of spirally wound membranes  110 . Advantageously, the cartridge  130  provides a high density or packing efficiency of stacked membranes  110  between the two electrodes  106 , 108  in a smaller footprint, and also allows easy replacement or cleaning of membranes  110  by changing the cartridge  130 .  
      The electrodes  106 , 108  can also have other shapes, such as concentric spheres, parallel plates, tubular wire meshes, discs, or even conical shapes, depending on the application. For example, a parallel plate cell comprising a pair of electrodes that are parallel plates on either side of a water-splitting membrane  110 . Instead of one membrane  110 , a plurality of stacked membranes  110  can also be used in this cell. In the parallel plate cell, the fluid stream  124  flows perpendicular to and through, or between the surfaces of, the membranes  110 . As another example, a disc cell, comprises a pair of electrodes comprising discs on either side of a stack of water-splitting membranes  110 . In the disc cell, the fluid stream  124  flows through the membranes  110  and is assisted by gravity. The electric potential drop is applied between the two disc electrodes. The membranes  110  are also shaped as circular discs and can also have separators (not shown) between them.  
      The electrochemical ion exchange apparatus  100  comprises a controller  132  which controls the operation of the apparatus  100  and supplies control signals and power to components of the apparatus  100 . The controller  132  illustrated schematically in  FIG. 4  comprises an electrode power supply  114 , a supplemental power supply  98 , and a control module  140 . The power supplies  114 , 98  are capable of generating voltages having selectable level and polarity to deliver power to components of the electrochemical ion exchange apparatus  100 . The voltage levels generated are controlled by the controller and depend on the component requirements, the operating conditions of the apparatus  100 , or other factors. For example, the electrode power supply  114  is used to generate a relatively high voltage to deliver power to the electrodes  106 , 108  of the electrochemical ion exchange cell  102  while the supplemental power supply  98  is used to generate relatively low voltages to deliver power to components such as the solenoids or motors of the valve system  118 , components of the controller  132 , and other components in the electrochemical ion exchange apparatus  100  requiring power.  
      The control module  140  is capable of generating and receiving signals and instructions to individually and collectively operate components of the electrochemical ion exchange apparatus  100 . The control module  140  comprises electronic circuitry and program code to receive, evaluate, and send signals. In one version, the control module  140  comprises a microcontroller  152  which is typically a single integrated circuit device that comprises several of the components of the control module  140 . For example, the microcontroller  152  may comprise a CPU, memory, program code, input and output circuitry, and other circuitry that may be specialized or adapted to particular tasks. The microcontroller  152  is advantageous because it encapsulates a relatively high degree of functionality into a single programmable component. One example of suitable commercially available microcontrollers  152  are the PICmicro® series of microcontrollers, such as for example the 28/40-Pin 8-Bit CMOS Flash PIC16F87X Microcontroller, available from Microchip located in Chandler, Ariz. Another example of a suitable commercially available microcontroller  152  is the 68000 available from Motorola Corp., Phoenix, Ariz. There are many other microcontrollers and microprocessors that can be used as the microcontroller  152 , as would be apparent to one versed in the art.  
      In one version, the power supply  136  and a portion of the control module  140 , such as the microcontroller  152 , can together form a controlled power supply  156 . The controlled power supply  156  combines the generation of voltages and current to deliver power to the components of the ion exchange apparatus with the programmability and control functionality of the microcontroller  152 . The controlled power supply  156  may also be part of a controller  132  having a control module  140  and other components besides the microcontroller  152 .  
      The electrode power supply  114  depicted in  FIG. 5  comprises a voltage selector  320  to receive the AC voltage and selectively couple the AC voltage to a rectified voltage supply  324 . The voltage selector  320  selectively couples the AC voltage by segmenting the voltage signal into pre-selected portions, for example, the entire positive component of a sinusoidal signal trace, or a portion of the positive component, such as a ¼ wavelength of the entire sinusoidal signal that has a positive value higher than zero, or a ½ wavelength, or other such portions. The voltage selector  320  switches the electrode power supply  114  between an on state and an off state based on a control input received from a control input source  328 . In one version, the control input source  328  is a human operator of the ion exchange apparatus  100 . In another embodiment, the control input source  328  is a controller such as the microcontroller  152 , and the control input is optionally an automated control input. The control input can comprise a control input signal.  
      The electrode power supply  114  comprises one or more output terminals  160 . In the on state, the electrode power supply  114  supplies the output voltage, produced by the rectified voltage supply  324  from the AC voltage to at least one of the output terminals  160  of the electrode power supply  114 . In the off state, the electrode power supply  114  does not supply the output voltage to the output terminals  160 . In one version (not shown), the output terminal  160  comprises a single output terminal. In this version, the voltage at the output terminal is referenced to ground and the circuit is completed through ground. In one version, the output terminals  160  comprise a pair of terminals  160   a,b . One of the terminals  160  comprises an electrically hot terminal and the other of the terminals  160  comprises a grounded terminal, wherein the grounded terminal is electrically connected to the common ground. In this version, the voltage output by the power supply comprises both the voltage between the terminals  160   a,b  and has a magnitude equal to the magnitude of the voltage between the electrically hot terminal and ground. In another version, the output terminals  160  comprise a positive electrically hot terminal and a negative electrically hot terminal. In this version, the voltage output by the power supply comprises the voltage between the terminals  160   c,d . When the power supply is in the on state, the positive electrically hot terminal has a voltage that is positive relative to ground and the negative electrically hot terminal has a voltage that is negative relative to ground.  
      The electrode power supply  114  comprises the rectified voltage supply  324  to produce the output voltage from the selectively coupled AC voltage. The output voltage produced by the rectified voltage supply  324  comprises a non-zero pulsating DC component. That is, the voltage output by the rectified voltage supply  324  comprises a DC voltage that can vary from about +1.2 volts to a peak of about +320V and back down to +1.2 V. The DC output voltage comprises a DC component that pulses at a frequency that is related to the input frequency and can have a maximum of twice the input frequency. For an input AC frequency of about 60 Hz, the DC output voltage comprises a DC component having a maximum frequency of about 120 Hz. For an input AC frequency of about 50 Hz, the DC output voltage comprises a DC component that can have a maximum frequency of about 100 Hz. While the output voltage does vary as a function of time, it is described as DC because the polarity of the output voltage is constant over many periods of oscillation. For example, the voltage output by the rectified voltage supply can comprise a full-wave rectified version of the AC voltage.  
      The rectified voltage supply  324  shown in  FIG. 5  is a diode-bridge full-wave rectifier  328  and comprises a plurality of diodes  332  in a diode-bridge arrangement. The rectified voltage supply  324  produces an output voltage comprising the full-wave rectified version of the portion of the AC voltage allowed to pass through the voltage selector  320  and may comprise a full-wave version of the AC voltage, or may comprise rectified segments of the AC voltage. The rectified voltage supply  324  can comprise other elements, such as other kinds of diodes, or diodes used with capacitors.  
      The rectified voltage supply  324  can comprise other components or arrangements for example the rectified voltage supply can comprise capacitors and diodes. In one exemplary embodiment, the rectified voltage supply  324  comprises two diodes that are connected to the input, one able to pass current from the input and the other able to pass current into the input. The ends of the diodes are attached to two capacitors (capacitor  1  and capacitor  2 ), and the ends of the capacitors are connected to the neutral pin of the AC input. The output voltage is taken to include both capacitors between it&#39;s pins. When the input signal is a positive voltage pulse, current flows through the forward diode, onto capacitors and out of the neutral AC pin, charging capacitors. When the input signal is a negative voltage pulse, current flows through the reverse diode, off of the capacitor  2  and out of the neutral AC pin, thereby charging capacitor  2 . If the circuit is run with a power input that is higher than it&#39;s power output, the capacitors will be charged to give a combined output voltage of twice the voltage magnitude of the chopped AC input signal. If necessary, the voltage can be stepped up further by applying the output of the voltage multiplier to another pair of capacitors, however, the current available is limited by the input power rating of the rectifier.  
      In one embodiment, the voltage selector  320  is enabled to perform the selective coupling based on zero-crossing events in the AC voltage. That is, the selective coupling functionality of the voltage selector  320  in such embodiments is either enabled or disabled in relation to the zero-crossing events. When the selective coupling functionality is enabled, the voltage selector  320  can couple or decouple the AC voltage to the rectified voltage supply  324 . When the selective coupling is disabled, the voltage selector  320  can not change the coupled or decoupled status of the AC voltage relative to the rectified voltage supply  324 . The enabling of the coupling functionality of the voltage selector  320  serves to reduce electromagnetic noise and interference, increase the expected operational lifetime of the electrode power supply  114 , and provides a degree of safety of the operation of the electrode power supply  114 . The voltage selector&#39;s coupling functionality is enabled within a predetermined AC voltage level or time increment relative to zero-crossing events in the AC voltage. For example, the voltage selector  320  optionally is enabled to selectively couple the AC voltage to the rectified voltage supply  324  based on a comparison of a voltage level of the AC voltage with a predetermined voltage level.  
      The electrode power supply  114  also comprises a current detector  232  to detect the current level delivered to electrodes  106 , 108  in association with the DC voltage, and generate a current detection signal in relation to the detected current level. An exemplary embodiment of a current detector  232  is shown in  FIG. 8  and comprises a sense resistor  236 , a light-emitting diode (LED)  240  connected across the sense resistor  236 , and a photo-transistor  244  optically coupled to the LED  240 . The sense resistor  236  is arranged in series with one node of the DC voltage delivered to the output terminals  160 , and may coincide with a series output resistor used by the DC voltage supply  164  for similar or alternative purposes. The sense resistor  236  is able to hold its resistance stable under a wide range of voltage, current or temperature conditions. In one version, the sense resistor  236  has a value of from about 0.1 Ohms to about 10 Ohms, and a suitable value is 1 Ohm. The current level running through the sense resistor  236  is coupled to the photo-transistor  244 , which is in a common-collector or emitter-follower configuration, to generate the current detection signal at the node V CURRENT DETECT . In one version, the current detector  232  generates the current detection signal and the control module  140  is capable of receiving the current detection signal. For example, the controller  132  may comprise a controlled power supply  156  in which the current detector  232  generates the current detection signal and the microcontroller  152  is capable of receiving the current detection signal.  
      The electrode power supply  114  comprises a zero crossing detector  336  to detect zero-crossing events in the AC voltage and produce an indication related to the zero-crossing events. The voltage selector  320  is enabled to selectively couple the AC voltage to the rectified voltage supply  324  based on the indication. In one embodiment, the indication comprises an indication signal produced by the zero-crossing detector  336 . The indication signal can have a variety of formats. For example, the indication signal can comprise a relatively high voltage level when there is no zero-crossing event in the AC voltage and a relatively low voltage level when there is a zero-crossing event in the AC voltage. Or, the indication signal can comprise a pulse train with the pulses located at the zero-crossing events. Or, the indication signal can comprise a square wave with the higher voltage portion of the square wave located at the zero-crossing events. Or, the indication signal can comprise a relatively low voltage level when there is no zero-crossing event in the AC voltage and a relatively high voltage level when there is a zero-crossing event in the AC voltage. Other embodiments of the indication signal are also possible, including embodiments having at least one of: inverted voltage pulses, inverted square waves, or modulated signals.  
      In one embodiment, depicted in  FIG. 7B , the zero-crossing detector  336   b  comprises a component device consisting of a diode  122 . The diode allows current to pass between the diode input  145  and the diode output  144  terminals when the voltage applied between its input  145  and output  144  terminals is of the correct polarity and above the diode&#39;s threshold conduction voltage. In one version the diode  122  allows current to pass when the voltage applied between its terminals is above +1.5 volts. When the voltage applied between the terminals of the diode  122  falls below about +1.5 volts, the diode  122  switches from on to off and prevents the flow of current. The diode  122  switches from off to on or from on to off when the voltage of the AC source  158  passes through about +1.5 volts. For an AC source  158  having a frequency of about 60 Hz, the diode  122  switches at about 1/120 second intervals, or every time the AC source  158  passes through about +1.5 volts. The output from the zero-crossing detector  336   a  comprises an alternating voltage with varying portions and low portions, the varying portions corresponding to the portions of the AC source  158  voltage having a value of greater than the threshold value of about +1.5 volts and the low portions having a value of about zero volts. The output of the zero-crossing detector  336   b  resembles a half-wave rectified version of the AC source  158  voltage and zero-crossing events are indicated by the beginning and ending of each half wave positive component of the output signal. Diodes having other threshold voltages can be used, as would be apparent to one versed in the art.  
      In another embodiment, as depicted in  FIG. 7A , the zero-crossing detector  336   a  is an integrated circuit comprising a comparator  121 . The comparator  121  detects when the voltage across its pins  147 , 149  changes polarity. The output of the comparator  121  is comparatively high when the voltage on its first pin  147  is more positive than the voltage on its second pin  149 , and comparatively low when the voltage on the first pin  147  is less positive than that on the second pin  149 . For example, the comparator  121  may output a voltage of about 12 volts when the voltage at the first pin  147  is more positive than the voltage at the second pin  149 , and a voltage of 0.2 volts when the voltage at the first pin  147  is less positive than the voltage at the second pin  149 . Thus, the comparator output comprises a square wave and zero crossing events are indicated by the edges of the square waves, that is, the portions of the signal comprising a step up or step down. The comparator can be supplied with a DC voltage from the supplemental power supply, wherein the comparatively high voltage value output by the comparator  121  is about the value of the voltage supplied to the comparator  121  by the supplemental power supply. Comparators having some other values of voltage output can be used, as would be apparent to one versed in the art.  
      In another embodiment, as depicted in  FIG. 7C , the zero crossing detector  336   c  comprises an LED  142  and a phototransistor  141  which are optically coupled together. In the on state, the phototransistor  141  conducts between the input and output terminals  111 ,  112 , and in the off state the phototransistor  141  substantially does not conduct between the input and output terminals  111 ,  112 . When the LED  142  is on, the light triggers the light sensitive phototransistor  141  which then is conducting. The LED  142  trigger characteristics are substantially similar to those of a standard diode, that is, the LED  142  is in the non-emitting state when the voltage between it&#39;s input and output terminals is less than a threshold value and is in the on or emitting state when the voltage between it&#39;s input and output terminals is higher than the threshold value. In one version, the threshold voltage of the LED  142  is about +1.5 volts however other LEDs having other threshold values can be used, as would be apparent to one versed in the art. The output from the zero-crossing detector  336   c  depends on the connection of the phototransistor terminals  111 , 112 . When a DC voltage is applied between the terminals  111 ,  112  the output of the zero-crossing detector  336   c  comprises a square wave voltage signal. Alternately, the output signal can comprise a current signal, that is, components of the controller  132  or microcontroller  152  can be connected to the zero crossing detector  336   c  output circuit and receive an indication of the zero crossing event by sensing the flow of current through the device.  
      In one embodiment, the voltage selector  320  comprises a relay  340  to receive the voltage of the AC source  158  and selectively couple the AC voltage to the rectified voltage supply  324 . In the embodiment shown in  FIG. 6  the relay  340  comprises a single-pole, single-throw semiconductor switch  340   a . The semiconductor switch  340   a  regulates current flow through a junction, much like a transistor, and can be switched on or off by applying a voltage at the gate pin  123 . The semiconductor switch  340   a  is used to turn the AC power supplied to the voltage rectifier  324  on and off. In one embodiment, the semiconductor switch  340   a  is operated by the zero crossing detector  336  such that it switches on or off in relation to zero crossing events of the input AC voltage. In another embodiment, the semiconductor switch  340   a  is operated by the controller  132  which delivers a signal to the semiconductor switch  340   a  in relation to the zero-crossing detector signal and also inputs from other portions of the apparatus  100  such as the current detector  232 , or an on-off switch operated by a user. In other embodiments, the relay  340  comprises a single-pole single-throw mechanical relay or a double-pole double-throw semiconductor or electro-mechanical relay.  
      In one embodiment, the zero-crossing detector  336  is integrated with the voltage selector  320 . In this embodiment, the voltage selector  320  and zero-crossing detector  336  comprise a single discrete component (not shown). In such an embodiment, the indication signal generated by the zero-crossing detector  336  may be a signal internal to the integrated voltage selector and zero-crossing detector  336 .  
      In one embodiment, when the voltage of the AC source  158  is coupled to the rectified voltage supply  324 , i.e., when the electrode power supply  114  is selected to be in the on state, the output voltage produced from the AC voltage is supplied between the output terminals  160   a,b . The electrode power supply  114  comprises at least one pair of output terminals  160   a,b , and when the electrode power supply  114  is selected to be in the on state, the output voltage is supplied between the pair of output terminals  160 . When the voltage selector  320  does not couple the AC voltage to the rectified voltage supply  324 , i.e., when the electrode power supply  114  is selected to be in the off state, the voltage supplied to the output terminals  160   a,b  by the power supply  114  comprises at least one of: a substantially zero voltage, or a floating voltage.  
      The electrode power supply  114  shown in  FIG. 5  comprises a polarity selector  348  to select the polarity of the output voltage relative to the electrochemical ion exchange cell  102 . The polarity selector  348  provides at least one of the following functions: selecting the polarity of the output voltage to the output terminals  160   a,b , or selectively coupling the output terminals  160   a,b  to the electrodes  106 , 108  of the electrochemical ion exchange cell  102 . The polarity selector  348  is controlled by the controller  132  and selects the polarity of the output voltage at the output terminals  160  of the electrode power supply  114 . For example, the polarity selector  348  can be used to select the polarity of the output voltage delivered to the electrodes  106 , 108  of an electrochemical ion exchange cell  102 . In such an embodiment, the polarity selector  348  can be used to select the polarity of the output voltage supplied to the at least one electrochemical ion exchange cell  102 . In one mode of operation, the polarity selector  348  can select a positive output voltage polarity at the output terminals  160   a,b  to provide a positive voltage between the electrodes  106 , 108  of the at least one electrochemical ion exchange cell  102  to enable the cell  102  to operate in the regeneration mode. In another mode of operation, the polarity selector  348  can select a negative output voltage polarity at the output terminal  160  to provide a negative voltage between the electrodes  106 , 108  thus enabling the cell  102  to operate in de-ionization mode.  
      The polarity selector  348  is controlled by the control module  140  and selectively couples the output terminals  160   a,b  of the electrode power supply  114  to the electrodes  106 , 108  of the electrochemical ion exchange cell  102 . For example, in one version, the ion exchange apparatus  100  comprises at least one electrode power supply  114  and a plurality of electrochemical cells  102  including at least a first electrochemical ion exchange cell  102   a  used for fluid treatment and a second electrochemical ion exchange cell  102   b  operated in regeneration. In such an embodiment, the polarity selector  348  can be used to provide a connection between the terminals  160   a,b  of the electrode power supply  114  and the electrodes  106 , 108  of the first electrochemical cell  102  wherein the voltage polarity of the connection is a positive voltage polarity. The polarity selector  348  can also be used to provide a connection between the output terminals  160   a,b  of the electrode power supply  114  and the electrodes  106 , 108  of the second electrochemical cell  102   b  wherein the voltage polarity of the connection is a negative voltage polarity.  
      The polarity selector  348  optionally comprises a relay. For example, in one embodiment, the polarity selector  348  can comprise a double-pole double-throw relay  97 . The double-pole double-throw relay  97  can be used to select the polarity of the output of the electrode voltage supply  114  at the output terminals  160 . The double-pole double-throw relay breaks the circuit before making the circuit, thereby protecting against shorts. When the output terminals  160   a ,  160   b  are connected to the electrodes  106 ,  108  respectively, the relay  97  controls the polarity of the voltage applied to the electrodes as follows: When the relay  97  of the polarity selector  348  is in position  1 , the positive terminal is connected to the inner electrode  106  and the negative terminal is connected to the outer electrode  108 . When the relay  97  of the polarity selector  348  is in position  2 , the positive terminal is connected to the outer electrode  108  and the negative terminal is connected to the inner electrode  106 . The polarity selector  348  is activated by the polarity control input.  
      In one version, the electrode power supply  114  is configured to be controlled by a controller such as the microcontroller  152 . For example, the control input and the polarity control input are optionally provided at least in part by the microcontroller  152 . In such a version, the voltage selector  320  and the polarity selector  348  are configured to be capable of being connected to the microcontroller  152  to receive the control input signal and the polarity control input signal, respectively, from the microcontroller  152 . The microcontroller  152  generates at least one of the control input signal or the polarity selection signal based on at least one of: an input received from a user, or data stored in a memory accessible by the microcontroller  152 . In one embodiment, the zero-crossing detector  336  is configured to be connected to the microcontroller  152 . For example, the zero-crossing detector  336  is optionally configured to provide the indication signal to the microcontroller  152 , which can then generate the control input signal provided to the voltage selector  320  at least in part based on the indication signal.  
      The ion exchange apparatus  100  may comprise a plurality of fluid treatment cells  102  and a plurality of electrode power supplies  114 . In one version, shown in  FIG. 3 , the ion exchange apparatus  100  has two electrochemical treatment cells  102   a,b , two power supplies  114   a,b  and a valve system  118 . The electrochemical cells  102   a,b , power supplies  114   a,b  and valve system  118  are controlled by a controller  132 . Each of the power supplies  114   a,b  independently comprises necessary components, for example, the components shown in the embodiment illustrated in  FIGS. 5 and 6 . However, in another version, the power supplies  114   a,b  may have certain components in common, for example, they may share a single zero-crossing detector  336 , as the zero-crossing signal generated by the zero-crossing detector  336  is dependent only upon the AC voltage, and thus may be commonly used by a plurality of power supplies.  
      While a single power supply  114  can also be used, the dual power supply  114   a,b  allows one power supply  114   a  to operate the first cell  102   a  for both deionization and regeneration, and the other power supply  114   b  to operate the other cell  102   b  also for both functions. This way both cells  102   a,b  can be operated independently or simultaneously. The power supplies  114   a,b  each have two output terminals  157   a,b  and  153   a,b . In this version, each power supply  114   a,b  is connected to a single cell  102   a,b , respectively, for example, the power supply  114   a  is connected to cell  102   a  and power supply  114   b  is connected to cell  102   b . The level of the voltage output between the terminals  157   a,b  and  153   a,b  is controlled by the controller  132 . Each power supply  114   a,b  is capable of providing a bias voltage to each of the cells  102   a,b  respectively, to operate the connected cell for fluid treatment or regeneration. In the version shown, each power supply  114   a,b  is capable of outputting a voltage from between about −300 volts and +300 volts. For example, the power supplies  114   a,b  can output a positive voltage of up to about 300 volts and a negative voltage less than about −300 volts, between the output terminals  157   a,b  and  153   a,b.    
      In yet another version, the dual power supply  114   a,b  is set up so that the polarity of each of the power supplies  114   a,b  is a fixed polarity so that one power supply always provides a voltage with a positive polarity, and the other a negative polarity. Thus, the first power supply  114   a  comprises a first output terminal  157   a  having an always positive polarity, and the second power supply  114   b  comprises a first output terminal  153   a  having an always negative polarity. This version allows a first power supply  114   a  to be used solely for deionization of fluid in both of the cells  102   a,b , and a second power supply  114   b  only for regeneration of both cells  102   a,b.    
      In a further version, each power supply  114   a,b  is independently connected to both cell  102   a  and cell  102   b , and can be used to drive either cell  102   a,b  in the deionization or regeneration mode. This version provides duplicate capabilities and is especially useful if one of the power supplies  114   a,b  fails, as the other power supply can be used to operate both cells  102   a,b . In this version, power source  213  comprises additional switches, such as additional polarity selector components, and the controller  132  comprises program code to detect operation (or failure) of each of the power supplies  114   a,b  and can operate the switches to substitute one power supply for the other as needed.  
      In operation, the controller  132  controls the power supplies  102   a,b  for switching them on and off, and controls the supply voltage provided between the output terminals  157   a,b  and  153   a,b . In addition, the controller  132  controls a valve system  118  to regulate the flow of fluid through the cells  102   a,b , while controlling the connection to, and voltage supplied at, the terminals  152   a,b  and  153   a,b  of each of the power supplies  11   4   a,b . In this way, the controller  132  is able to operate the cells  102   a,b  for fluid treatment, and also to operate one cell  102  in the fluid treatment direction while the other cell  102  is being regenerated.  
      The apparatus  100  further comprises a fluid piping system which has a first fork  163  that splits into two pipes to allow the incoming fluid stream  124  to flow along one side of the fork toward a first cell  102   a , and another side of the fork towards cell  102   b . In one version, the valve system  118  comprises four solenoid valves  119   a - d  which are provided in the piping system to control the flow of fluid through the various pipes. The first pair of solenoid valves  119   a,b  is positioned in the pipe between the first fork  163  and each of the treatment cells  102   a,b  to control incoming fluid flow to each of the treatment cells  102   a,b . Between the first valve  119   a,b  and the cell  102   a,b , respectively, is second fork  165   a,b . At the second fork  165   a , fluid flowing through the apparatus  100  can flow to the treatment cell  102   a  or to the drain  190 . Between the second fork  165   a,b  and the drain  190  is a second solenoid  119   c,d , which controls fluid flow to the drain  190 . The valve system is controlled by a controller  140  which operates the valves in conjunction with the power supplies  114   a,b  to treat fluid and regenerate the cells  102   a,b.    
      During operation of cell  102   a  for fluid treatment, valve  119   b  is shut and valve  119   a  is open. Fluid flows from the outlet of the sediment filter  181 , through valve  119   a  and into cell  102   a  through the first orifice  146   a . A forward voltage is applied to the electrodes  106   a ,  108   a  of cell  102   a  and fluid passing through the cell  102   a  is treated. Fluid exits cell  102   a  through the second orifice  148   a . The dispensing device  128  is opened and treated fluid passes out of the system output  162 .  
      The cells  102   a,b , solenoids valves  119   a - d  and outputs  148   a,b  arranged in the configuration shown allows for the cells  102   a,b  to be used to regenerate each other, for example as follows: During operation of cell  102   a  in the treatment mode and operation of cell  102   b  in the regeneration mode, valve  119   b  is shut and valve  119   a  is open. Valve  119   c  is shut and valve  119   d  is open. Fluid flows from the outlet of the sediment filter  181 , through valve  119   a  and through the first orifice  146  of cell  102   a  . Voltage is applied between the electrodes  106 , 108  of cell  102   a  and fluid passing through the cell  102   a  is treated. Fluid exits cell  102   a  through the second orifice  148   a . Dispensing device  128  is shut, thereby blocking the flow of treated fluid to the output  162 . Instead, the fluid flows into cell  102   b  through the second orifice  148   b . A reverse voltage is applied to the electrodes  106 ,  108  of cell  102   b . Fluid flows from the second orifice  148   b  of cell  102   b  to the first orifice  146   b  of cell  102   b  and picks up ions. Re-ionized fluid exits the first orifice  146   b  of cell  102   b , flows through valve  119   c  and to the drain  190 , where it exits the ion exchange apparatus  100 . Fluid passed through cell  102   b  in this manner rinses the cell  102   b  of impurities and can be said to recharge the cell  102   b  for future fluid treatment use. Another version of the valve system  118  can also have five solenoids valves  119 , as shown, which are used to control the flow of fluid through the cells  102   a,b , to a drain  190 , and to a fluid output which outputs treated fluid for a user.  
      Various other components can be added to the apparatus to improve fluid treatment and cell operations. For example, a fluid flow sensor  204  can be positioned along the fluid stream  125  to measure fluid flow rates. A suitable sensor is a Hall Effect sensor which outputs a voltage which oscillates with a frequency that corresponds to the rotational frequency of a turbine placed in the fluid stream (not shown). A pressure sensor  159  can also be provided to output a fluid pressure signal to the controller  132 . The apparatus  100  can also include a sediment filter  181  that serves to filter out particulates from the fluid stream  124 . The apparatus  100  can further include an activated carbon filter  187  that sits in the common output pipe  151  and treated fluid passes through the activated carbon filter  187  on the way to the output  162 . The apparatus  100  can also include an ultraviolet antimicrobial filter  161  in the fluid stream  125  between the flow pressure sensor  159  and the dispensing device  128 .  
      In one embodiment, the polarity selector  348  is capable of selectively connecting, optionally at the same time, the regeneration electrode power supply to one of a plurality of electrochemical ion exchange cells  102 , and the re-ionization power supply to a different one of the plurality of electrochemical ion exchange cells  102 .  
      In one version the power supply  136  comprises a plurality of electrode power supplies  114 . For example, in a version of the ion exchange apparatus  100  comprising two electrochemical fluid treatment cells  102   a,b , the power supply  136  may comprise two electrode power supplies (not shown) each electrode power supply  114  capable of generating a DC voltage having a selectable voltage level and polarity for a pair of electrodes  106 , 108  in one of the electrochemical ion exchange cells  102 . In one version, each electrode power supply  114  independently comprises necessary components, for example, the components shown in the embodiment illustrated in  FIGS. 4 and 5 . However, in another version, a plurality of electrode power supplies  114  may have certain components in common. For example, a power supply  136  comprising a plurality of electrode power supplies  114  may have only a single zero-crossing detector  268 , as the zero-crossing signal generated by the zero-crossing detector  268  is dependent only upon the AC voltage, and thus may be commonly used by each of the plurality of electrode power supplies  114 .  
      In one version, the power supply  136  also comprises one or more supplemental power supplies  98 . In one version, the supplemental power supply  98  is capable of generating a supplemental DC voltage to deliver power to components of the ion exchange apparatus  100  other than the electrodes  106 , 108 . In one version, the supplemental power supply  98  is capable of generating the supplemental DC voltage having a voltage level of from about 1 Volts to about 30 Volts, for example, the supplemental power supply may comprise a DC rectified voltage supply  99   a  to generate 5 Volts to power the microprocessor of the controller  132 . Another power supply  99   b  generating a different, non-adjustable voltage of, for example, about 12 Volts can be used to power the electric motor  128  or solenoids  119  of the valve system  118 . The microprocessor power supply should have a low voltage ripple of less than about 0.1 Volts. One version of the supplemental power supply  98  comprises a transformer, a bridge rectifier, at least one capacitor, and a voltage regulator.  
      The ion exchange apparatus  100  typically comprises one or more sensors to sense a property of a component of the apparatus  100 . The sensor may detect an event or measure a property. For example, the sensor may be a position sensor that senses the position of the rotor in the valve  116  or detects the arrival of the rotor at a certain position. In another example, the sensor may be a conductivity ion sensor that measures directly or indirectly the concentration of ions in the fluid being treated by the ion exchange apparatus  100 . The sensor may be placed at certain points in the fluid stream such as, for example, at the inlet  32  or outlet  36  of the electrochemical ion exchange cell  102 , or at a combination of these locations or others. The sensor can be also temperature or valve position sensors.  
      The controller  132  receives signals from the sensors and may use these signals to generate control signals for the power supply  114 , such as the voltage selection signal. For example, the microcontroller  152  may generate a voltage selection signal that is in relation to signals from the power supply  136 , such as the current detection signal, and a signal from the sensor, such as an ion concentration signal. In another example, the microcontroller  152  may also generate the polarity selection signal in response to signals from the sensor. In another version, the controller  132  may use a combination of signals, such as those generated by the power supply  114  and the sensor, to generate a series of control signals for the power supply  114 . For example, the controller  132  may generate a voltage selection signal and a polarity selection signal that evolve in time in response to conditions in the apparatus  100  sensed by the sensor and conditions in the power supply  114  or the apparatus  100  communicated by the power supply  114  to the controller  132 , for example communicated by the current detection signal.  
      The present invention has been described with reference to certain preferred versions thereof; however, other versions are possible. For example, the power supply  136  can be used in other types of applications, as would be apparent to one of ordinary skill, such as to power a motorized tap to control the water or fluid output. Also, the various components of the power supply  136  described to illustrate an exemplary power supply can be substituted by other equivalent components as would be apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.