Abstract:
An instant water heater utilizing positive temperature coefficient plastic electrically conductive material structures for electrodes. The heating of the water is not generated by the electrodes, but instead by the resistance of the water to the electrical current flowing between them. The material of the electrodes undergoes a phase change at certain temperatures when whereby it converts from electrically conductive to electrically non-conductive at a predetermined temperature. The output temperature of the water is determined by a combination of the area of the electrodes that confront one another, the water&#39;s conductivity, the flow rate of the water and the current limiting capability of the conductive electrode materials positive temperature coefficient, which reduces or stops the heating of the water when the intended water temperature is achieved.

Description:
CROSS REFERENCE TO OTHER APPLICATIONS  
       [0001]     This is a continuation-in-part of applicant&#39;s co-pending U.S. application Ser. No. 11/111,670, filed Apr. 21, 2005, which is not being abandoned. 
     
    
     FIELD OF THE INVENTION  
       [0002]     An instant water heater which heats water flowing between two immersed electrodes, using improved electrodes with positive temperature cutoff (PTC) properties, increased efficiency and longevity.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates to water heaters of the type which heats water that flows between two electrodes, rather than by providing a hot element which is contacted by the water. In this invention, the water is heated by electrical current flowing through the water when the water is between the two electrodes.  
         [0004]     So-called “instant” water heaters differ from conventional water heaters by their lack of a storage tank for hot water. Instead of heating and storing water for future usage, instant water heaters accept cold or cool water, heat it, and deliver it directly to the user point on demand. Such heaters find their most common usage in sink faucets, showers and tubs, although they can be provided for any other usage that requires hot water.  
         [0005]     Among their advantages is that they can be placed very near to the use point. Pipes of substantial length need not be emptied of cold water before hot water arrives from a central source, for example. Also, it is much easier to run an electrical circuit to a distant heater than to provide a distant tank, and a long pipe to convey hot water from a central source to a distant use point.  
         [0006]     Legionnaire&#39;s Disease is well known as a consequence of water stored for long periods at moderate temperature. Having no storage of the water at all profoundly reduces risk of such disease.  
         [0007]     Presently-known instant water heaters do have major disadvantages, including short product life, dry-fire burn-out, short service life, liability to water damage, moderate rates of flow, high energy consumption, and release of metal ions into the water.  
         [0008]     Another disadvantage of existing instant water heaters is their inability to accommodate varying input voltages and amperage along with water flow that matches their intended use. A complaint often heard is that the wrong instant water heater was purchased from many different available models. The necessary wide range of variables, such as voltage, circuit breaker amperage, and service flow in gallons is simply too confusing for many customers.  
         [0009]     It is yet another disadvantage of existing instant water heaters that they often burn out or break coils due to water hammering, air in the water lines, or current overloads. These pose an electrical danger from direct contact of live broken coil ends to the water. The electrical current then passes directly into the water. Manifolds that are connected to ground with a grounding wire corrode, and it is only a matter of time before a corroded manifold or a burned out coil releases a full current into the water and out a faucet or other plumbing fixture when in use, to the risk of the user.  
         [0010]     It is a disadvantage of conventional electrode water heaters to have to contend with the wide variation of water conductivity of drinking water, both in the United States and in other parts of the world. Water conductivity is measured in microsiemens, which is the same as micro mhos. Mhos are the inverse of ohms, and therefore represent the conductive characteristics of water, which absorbs more power as it becomes more conductive. Water conductivity in the United States can range from 50 microseimens to over 1,500 microsiemens. Foreign countries can have as high as 1,800 microsiemens.  
         [0011]     The disadvantage occurs when their electrodes must be sized such that they are capable of attaining satisfactory performance with 50 microsiemen water, but must then regulate a potentially hazardous 30 times the current draw when the water is at 1,500 microsiemens. For example, an electrode water heater on a 50-amp breaker must attain an acceptable performance of 40 degrees of temperature rise from its cold water inlet to its hot water outlet. If the water is conductive to 50 microsiemens and the heater passes 1 gallon per minute, the power required is 26.8 amps at 220 VAC. In this case, there is no disadvantage to using an electrode since this is below the current rating of its 50-amp breaker. If, for example the water conductivity is 1,500 microsiemens, the potential load would then become 804 amps. This power must be regulated to below the 50-amp circuit breaker and more specifically, to the 26.8 amps to meet the 40-degree temperature rise at 1 gallon per minute. The condition is exacerbated when 3 gallons per minute are required. The potential current draw for the flow rate is a staggering 2,400 amps.  
         [0012]     Since prior to this invention, electrodes could not be resized on the fly, regulating this amount of power has been costly. Typically, the common approach to electrode water heaters design is to use triacs, IGBT&#39;s, mosfets and other sine wave chopping devices to regulate the high current so that the circuit breakers do not trip. For low power requirements such as light dimmers, this is the preferred and inexpensive method. However, to regulate the high current potentials of electrode water heaters, these methods are economically and technically unacceptable.  
         [0013]     It is yet another disadvantage of electrode water heaters that suggest methods of power regulation using said wave-chopping devices, that such devices can introduce harmonics in the line and heat the wiring without tripping the circuit breaker. Wires can become extremely hot, causing serious fire hazard. One solution to this disadvantageous condition is called “current matching”. However, current matching for electrode water heaters and boilers is nearly impossible to accomplish with such a widely varying electrical load without mechanically moving the electrodes as is done in large, expensive industrial electrode boilers. To do this in a home appliance such as an instant water heater would be too costly and would introduce wear parts that would greatly increase the failure modes of the device.  
         [0014]     Yet another disadvantage of electronically regulating high current via AC wave chopping is the electromagnetic emissions that disrupt communications television signals and create radio static interference. These emissions are not allowed in Europe&#39;s “Flicker Standard” and can violate FCC regulations.  
         [0015]     It is another disadvantage of electrode water heaters that in order to match the load to the line without the said expensive sine wave chopping devices, the preferred method is to physically move the electrodes via electric motors. This is done to either increase their relative distance from each other, or to pull them upward leaving less of the electrode submersed, hence reducing their surface area disposed in water.  
         [0016]     It is an object of this invention to provide an electrode water heater whose current draw is passively and automatically regulated without chopping the sinusoidal AC electrical power which heretofore was necessary to regulate 1,500 amps, or more, down to within the required amperages of household circuit breakers.  
         [0017]     It is another object of this invention to provide this regulation with no moving parts.  
         [0018]     It is yet another object of this invention to accomplish this regulation with no electronic components such as triacs, IGBT&#39;s or mosfets sized to accommodate the high currents mentioned.  
         [0019]     It is another object of the invention to regulate water temperature to an acceptable temperature by utilizing the merits of a Positive Temperature Coefficient conductive material that becomes non-conductive at a known temperature, and where necessary, utilizing less expensive state of the art electronic technology for a finer temperature setting.  
         [0020]     It is another objective of this invention to regulate water temperature by way of the water transferring its heat into the Positive Temperature Coefficient material, and rendering it, or some varying portion thereof non-conductive.  
         [0021]     It is yet another objective of the invention to regulate a high inrush of current by way of the material&#39;s electrical resistance heating itself from within so that it, or some varying portion thereof becomes non-conductive so as to appropriately reduce the active area of their opposed conductive faces.  
         [0022]     It is yet another object of the invention to utilize a dynamic phase change location as a means to appropriately adjust the virtual effective size of the electrodes, in essence interpreting that dynamic as an electrode that passively and automatically changes its size to accommodate proper current draw and water temperature based on water conductivity and/or water flow.  
         [0023]     It is another object of the invention to provide a temperature control valve disposed between the inlet and the outlet of the water heater&#39;s housing so as to provide a means to lower the outlet temperature of the water to below the PTC temperature of the material.  
         [0024]     It is yet another object of the invention to restrict the flow of water through the water heater to a rate that will always allow for the PTC effect to render the electrodes non-conductive.  
         [0025]     It is another object of this invention to regulate potentially thousands of amps with no electronic components. While the invention at first appears to defy the laws of physics by regulating its potential amperage draw without increasing its heat proportionally, as in the case of variable transformers, it must be understood that it is the load that is modulating itself. The result is a kinetic servo loop. The inverse occurs when the water&#39;s conductivity decreases, and an additional dynamic occurs when the flow of water acts upon the electrode&#39;s temperature the complex dynamics of which will become apparent in the detailed description of the invention.  
         [0026]     Any plastic electrode that can be used in a domestic water supply and that exhibits PTC characteristics at an appropriate temperature to deliver usefully hot water can be used. However, other properties become dominant when using them in affordable water heaters with a suitably long life and a minimum usage of electrical current. Interestingly, it is not possible to boil water when plastic electrodes are used because when boiling temperatures are reached, cavitation occurs on the surface and prevents the flow of electrical current. This saves the large cost of temperature and pressure valves for standard water heaters.  
         [0027]     For example, many plastic electrodes too quickly become coated with insoluble mineral deposits, such as the carbonates of calcium and magnesium, and other deposits which coat the electrode and limit its useful life. Purity of its ingredients is a prime requirement.  
         [0028]     Other complications are the conductive transmissibility of electrical current from the surface the electrode into the water on its surface. There is a puzzling relationship between the conductivity of the electrode body itself and the connectivity of the surface in the water.  
         [0029]     Still another complication is the need to reduce electrical consumption in the electrodes itself. It should be remembered that the heating of the water itself, and not by thermal circuitry of the cool water with the surface of the electrode. Embedded with these is the means to manufacture the product. A conductive package to improve the gross functions can, if too much is needed, prevent the economical usage of injection molding. This invention solves this issue.  
         [0030]     This invention proposes to solve in large part the above problems, thereby to provide an improved instant water heater.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0031]     An instant water heater according to this invention comprises a heating chamber having an inlet and an outlet. Water to be heated enters the chamber through the inlet, and after being heated, exits through the outlet to a point of use.  
         [0032]     A pair of spaced-apart Positive Temperature Coefficient electrodes is mounted in the chamber, so disposed and arranged that an appropriate volume of the water passes between them so as to be heated by current that flows through the water from one electrode to the other.  
         [0033]     According to a preferred application of the invention, the precise temperature to which the water is heated is maintained by the addition of an electronic temperature control circuit. A first order temperature is attained by the positive temperature coefficient conductive polymer&#39;s phase change temperature and a more precise electronic temperature setting by the user. For this specific application of the invention, the Positive Temperature Coefficient electrodes have a phase change temperature tolerance of several degrees F., and therefore are not normally used for laboratory use for fine adjustment of temperature. Their purpose is to regulate the water temperature, to an acceptable first order temperature, and regulate current draw in amps. A potentiometer dial setting can be adjusted to the desired fine temperature to within less than one degree F., or finer.  
         [0034]     In most applications the order of magnitude to which the PTC electrodes can control temperature will be acceptable, thereby negating the need for any electronic controls.  
         [0035]     According to this invention the Positive Temperature Coefficient electrodes are principally formed of, and their exposed surfaces are specifically made of, either an electrically conductive ceramic or polymeric resin.  
         [0036]     According to a preferred but optional feature of the invention, the polymer electrode is loaded with a “conductive package” comprising two or more of the following: graphite as natural graphite, synthetic graphite, purified graphite, expandable graphite, expanded graphite, graphite flake and graphite fiber, and carbon as carbon black, purified carbon, carbon fiber, carbon fibrils, and carbon nano tubes to reduce the bulk electrical resistance of the material, provide suitable conductivity for the electrode, and to provide for enhanced connectivity with the water. This conductive package is preferably provided in the form of a good packing ratio of assorted sizes and correct proportions to give the best result as will later be described.  
         [0037]     The Positive Temperature Coefficient (PTC) of the polymer relates to the temperature at which the material makes a phase change from electrically conductive to non-electrically conductive. The material maintains its crystalline structure up to its PTC temperature, in most cases around 60 degrees C., wherein it changes to an amorphous condition. This temperature is just short of the polymer&#39;s melt/flow point, but low enough where the material maintains enough of its structural integrity for the purposes of this invention.  
         [0038]     When the polymer is below its phase change temperature, conductive paths are inherently created to form conductive pathways through the carbonaceous material. As the phase change temperature is approached, these paths disconnect. Since this is the point at which no additional electrical current can pass through the material, it ceases to increase in temperature and holds a “tripped” temperature while a maintaining trickle current passes through it. Upon cooling, it returns to its previous crystalline structure whereby the components of the carbon package reconnect at least in part, but never in the exact same formation as before. Not reconnecting in the exact way makes the material become more resistive the second time it is brought to its phase change temperature. It continues to become more resistive for about 3 or 4 more cycles where it then stabilizes to a resistance that will endure thousands, perhaps hundreds of thousands of cycles.  
         [0039]     Since the PTC temperature of the polymeric or ceramic material is typically higher than a normally desired water temperature, say for a shower or washing hands, a water temperature control channel can be molded into the main housing of the water heater, disposed between and connecting the cold water inlet to the hot water outlet. This allows for cold water to bypass the heating chamber and mix directly with the exiting hot water. Perpendicular to this molded channel is a threaded needle valve used for controlling the amount of cool water to be mixed into the hot stream.  
         [0040]     The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]      FIG. 1  is a schematic drawing showing the basic components of an electrode water heater.  
         [0042]      FIG. 2  is a schematic drawing showing an electrode water heater with its electrodes reduced in size to accommodate highly conductive water.  
         [0043]      FIG. 3  is a schematic drawing showing a method of reducing the area of opposed faces of electrodes without reducing their size.  
         [0044]      FIG. 4  is a schematic drawing showing greater spaced apart electrodes as an alternate method of accommodating high conductivity water without reducing their size.  
         [0045]      FIG. 5  illustrates a microscopic view of carbon fibers contacting each other within the microstructure of a polymeric Positive Temperature Coefficient conductive polymer when it is below its phase change temperature, fibers being an illustrative example.  
         [0046]      FIG. 6  illustrates a microscopic view of carbon particles with gaps between them within the microstructure of positive temperature coefficient conductive polymer when it is above its phase change temperature.  
         [0047]      FIG. 7  is a schematic drawing showing a conductive portion, a phase change point and a non-conductive portion of a positive temperature coefficient conductive polymer when in use as an electrode within an instant water heater.  
         [0048]      FIG. 8  is a schematic drawing showing that the phase change point of the electrodes has shifted toward the outlet of the water heater during an increased flow of water, a decrease of water conductivity, a lowering of the current draw via its electronic controls, or any combination thereof.  
         [0049]      FIG. 9  is a schematic drawing showing the phase change point of the electrodes very close to the inlet of the water heater indicating extremely high conductivity water, or very low water flow or combination thereof.  
         [0050]      FIG. 10  is a schematic drawing showing the positive temperature coefficient state, meaning its entire temperature is below its phase change temperature.  
         [0051]      FIG. 11  is a schematic drawing showing the positive temperature coefficient polymer electrode in a totally nonconductive state meaning its entire temperature is above its phase change temperature.  
         [0052]      FIG. 12  is a schematic drawing of an instant water heater showing its electrodes, an inlet and outlet thermistor and a control box showing a temperature setting dial and an amperage setting dial.  
         [0053]      FIG. 13  is a perspective view illustrating the water heater with its cover shown in phantom lines.  
         [0054]      FIG. 14  is a section view showing the waters flow path through the heater, from the inlet, through the inlet ground screen, through and between the blades of the electrodes, through the outlet grounding screen and out its outlet.  
         [0055]      FIG. 15  is a perspective section view which shows the upper and lower electrodes and spacer pieces that direct the water in a predetermined circuitous path between their blade.  
         [0056]      FIG. 16  is a section view of the water heater&#39;s inlet and outlet locations in phantom while illustrating the needle valve that bleeds cool inlet water over to the outlet port to achieve a desired lower outlet water temperature.  
         [0057]      FIG. 17  is a perspective view of an optional variation of the PTC water heater with electronic printed circuit board, inlet and outlet thermistors, said water heater being the type used in laboratories or any use where temperature requires critical temperature regulation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0058]     Although this invention contemplates a number of physical arrangements for effective heating and for regulation of electrical current so as not to induce undesirable harmonics that can overheat electrical-wiring, the principal advantages of this invention are derived from the use of unique PTC electrodes which they all use.  
         [0059]     A basic schematic of a prior art electrode water heater is shown in  FIG. 1  (Prior Art). Water  2  flows between two electrodes  1  and  3  while power  7  is regulated by way of an electronic circuit  9  to provide a pre-selected water temperature based on a combination of the water&#39;s electrical conductivity and the area of the opposed faces  5  of said electrodes  1  and  3 .  
         [0060]     Should the water conductivity become extremely high, a solution shown in  FIG. 2  (Prior Art) for stopping a overcurrent condition would be to shorten the electrodes thereby reducing the area of their said opposed faces  5  such that it would better match the available power to the water&#39;s conductivity. However, should the water&#39;s conductivity drop, it is impossible to put the material back. This illustration, although simplistic, will be more appreciated as the PTC effect on this invention is further understood.  
         [0061]     Since it is not possible nor practical to dynamically change an electrode&#39;s length, another scheme is suggested in  FIG. 3  (Prior Art) involving moving one electrode  3  in relation to the other, thereby reducing the area of said opposed face  5  to a much smaller area. Another option shown in  FIG. 4  suggests separating electrodes  1  and  3  thereby reducing the amount of current deployed into the water.  
         [0062]     As will later be described in further detail, Positive Temperature Coefficient Polymers are loaded with distinctive carbon and graphite particulates ranging from carbon black, one of the most common, to carbon fibrils one of the most recently invented forms of carbon. In essence, the basic theory behind the PTC effect is that any crystalline polymer will experience a PTC effect when it reaches its softening temperature.  FIG. 5  shows conductive paths (sometimes called “strings”)  15  formed by carbon particles that touch or connect to other strings  17  that together form conductive pathways throughout the material.  
         [0063]     As the material passes through its phase change temperature, said strings  15  shown in  FIG. 6  disconnect as shown at  19 , and the gaps disallow electrical conductivity, therefore to increase the material&#39;s electrical resistance. Certain mixes become completely non-conductive at a temperature that, to a certain degree, can be selectably established by its formation.  
         [0064]     An improved and simplified scheme of the invention is shown in  FIG. 7 . In cases where close or critical temperatures are required, the current will be controlled with electronic circuitry  27 . Typical proportional, integral and derivative (PID) math is employed for tight servo-loop control using thermistors or other temperature sensing devices.  
         [0065]     For domestic or commercial use of hot water, such electronic circuitry  27  is not necessary when taking advantage of the PTC effect of the electrodes of this invention to joule heat water. In these applications, water flows  2  between said electrodes  1  and  3  while power  7  is applied to them. It is understood that in  FIG. 7 , this is a medium flow rate of a common faucet. Although this can vary greatly from faucet to faucet, for illustrating the value of the PTC effect on the invention, we shall call this flow rate 1 gallon per minute. As water  2  makes its way through the heater between said electrodes  1  and  3 , its temperature increases because it is contained between and within a conductive path length  21  of said electrodes  1  and  3 . Upon reaching the PTC temperature of said electrodes  1  and  3 , said water no longer continues to heat. Said conductive path length  21  terminates at the location  25  of the phase change temperature of said electrodes  1  and  3 . The remaining non-conductive path length of said electrodes  1  and  3  is heated by the already hot water of said conductive path length  21  and also by some residual current passing through said electrodes  1  and  3 . These-two sources of heat energy maintain the remaining said non-conductive path length  23  of said electrodes  1  and  3  at or above its PTC temperature. Therefore, the remaining said non-conductive path length  23  of said electrodes  1  and  3  discontinues its joule heating of the water because it is no longer conductive.  
         [0066]     As said water flow  2  doubles, using the illustrative value of 2 gallons per minute,  FIG. 8  shows that the said conductive path length of water  21  increases in length in comparison to  FIG. 7 , moving away from the water heater&#39;s inlet and toward its outlet. The said PTC phase change  25  location remains at the same temperature as in  FIG. 7 , but has moved because the flow has increased and has cooled the said conductive path length of water  21  in a proportional manner. Since the said water flow  2  has increased by 100%, it takes 100% more energy to elevate the water temperature to the PTC temperature. Therefore, said conductive path length  21  of said conductive electrodes  1  and  3  has doubled. However, the water output temperature remains the same, essentially the electrode&#39;s PTC temperature.  
         [0067]     As water flow is halved, using the illustrative value of ½ gallon per minute,  FIG. 9  shows that the said conductive path length  21  decreases in length in comparison to  FIG. 7 , moving toward the water heater&#39;s inlet and away from its outlet. The said PTC phase change  25  location remains again at the same temperature as in  FIG. 7 , but has moved because the flow has now decreased and the said conductive path length of water  21  has heated in a proportional manner. Again, but conversely, since the flow has decreased by 50% it takes 50% less energy to elevate the water temperature to the PTC temperature. Therefore, the said conductive path length  21  of said conductive electrodes  1  and  3  has been halved and again, the output temperature remains the same, essentially the electrode&#39;s PTC temperature.  
         [0068]     It will be observed that an identical but inverse result as described for water flow occurs with variation in water conductivity.  
         [0069]     As water conductivity lowers by 50% using the illustrative value of 1 gallon per minute,  FIG. 8  shows that the said conductive path length of water  21  increases in length in comparison to  FIG. 7 , moving away from the water heater&#39;s inlet and toward its outlet. The said PTC phase change  25  location remains at the same temperature as in  FIG. 7 , but has moved because the waters conductivity has decreased and the flowing water has cooled the said conductive path length of water  21  in a proportional manner. Since the said water conductivity has decreased by 50% it takes 100% more path length to elevate the water temperature to the PTC temperature. Therefore, said conductive path length  21  of said conductive electrodes  1 , 3  has doubled. However the water output temperature remains the same, essentially the electrode&#39;s PTC temperature.  
         [0070]     As water conductivity doubles, using the illustrative value of an unchanged 1 gallon per minute,  FIG. 9  shows that the said conductive path length  21  decreases in length in comparison to  FIG. 7 , moving toward the water heater&#39;s inlet and away from its outlet. The said PTC phase change location  25  remains again at the same temperature as in  FIG. 7 , but has moved because the water&#39;s conductivity has now increased and the said conductive path length of water  21  has heated in a proportional manner. Again, but conversely, since the water conductivity has increased by 100% it takes 50% less path length to elevate the water temperature to the PTC temperature. Therefore, the said conductive path length  21  of said conductive electrodes  1 , 3  has been halved and again, the output temperature remains the same, essentially the electrode&#39;s PTC temperature.  
         [0071]     Attending to the complex dynamics of water conductivity and flow for electrode water heaters has been expensive and difficult for regulating output temperature. This invention passively compensates for both of these critical aspects of electrode water heating.  
         [0072]     Of course, there are limits to the dynamics of the invention. However, when said electrodes  1  and  3  are sized properly in relation the variations in water conductivity that is available from United States and other water infrastructures, acceptable flow rates and available power, the benefits of the invention are far more favorable than the prior art.  FIGS. 10 and 11 , although similar in appearance, illustrate these limits and the safety inherent in the invention.  
         [0073]     When water enters at a flow rate above what the available power can heat, the entire said flow path  21  of said electrodes  1 , 3  becomes conductive. This is because said water  2  cools the entire said electrodes  1 , 3  to below their PTC temperature. Conversely, in  FIG. 11 , the said non-conductive path length  23  entirely encompasses said electrodes  1 , 3  rendering them into a non-conductive condition when the water is shut off, or the flow is so low that their temperature is elevated to their PTC temperature. In the case where the water is shut completely off, the amount of water remaining inside the water heater is so small in comparison to a standard 40 gallon storage water heater that the stand-by heat loss through the walls of the water heater becomes insignificant.  
         [0074]      FIG. 12  is a schematic view of a PTC electrode water heater with added components and electronics used to maintain accurate output temperatures. Water  2  flows past an inlet thermistor  29 , between said electrodes  1  and  3 , is heated and its temperature measured by an outlet thermistor  31 . The electronics illustrated as item  27  of  FIG. 12  can be designed and adapted by any competent electronics engineer. There are two user controls  35  and  33  that are unique to the invention and are noteworthy. These consist of a current limit knob  35  that is used to limit the amount of current that can be drawn by the water heater and an outlet water temperature knob  33  used to set the temperature of the water.  
         [0075]     In  FIG. 13 , an instant PTC water heater  15  is shown in perspective view with its plastic injection molded cover  41  removed and outlined in phantom. A main housing  47 , a bottom cover  57  and an inlet/outlet manifold  55  comprise the major components of the instant PTC water heater. Water enters  49  at the inlet side of said manifold  55  and exits  51  at the outlet side of manifold  55 .  
         [0076]     An electrical cord  53  is secured to its three respective lugs, namely the power lugs  39 , 40 , and a grounding lug  40 . A wire  61  is run from said grounding lug  38  to said manifold  55  and attached with a screw  59 . Two wires run from said power lugs  30 , 40  to the electrode connections  45 . An angle bracket  56  is disposed on the top face of said bottom cover  57  and staked in place via protruding molded-in studs. A throttle screw  44  is threaded into a retaining plate  46  with matching threads. Turning said knob  44  allows an adjustment for cool inlet water to mix with the hot water thereby adjusting the outlet water temperature. The details of which are shown in greater detail in  FIG. 16 .  
         [0077]      FIG. 14  constitutes a section view of the embodiment of  FIG. 13  that shows heating of the water. The water inlet flow  49  entering said inlet manifold  55  and passing through a conductive plastic inlet screen  58  through a molded-in channel  72  in said main housing  47  and between the two electrodes  65 , 67 . The water takes a circuitous route between said electrodes  65 , 67  during which it is joule heated by electrical current passing through it. It exits through a molded-in channel  74  of said main housing  47  and past a restriction orifice  54 . Restriction orifice  54  is sized so that its flow rate limits the amount of water passing through the water heater. Limiting the flow insures that the performance of the water heater meets a specific rated temperature rise. It also insures that higher flow rates do not cool the electrodes while passing potentially high conductivity water that may draw excessive current. The said restriction orifice  54  limits the flow so that the PTC effect of said electrodes  65 , 67  will reach non-conductivity before exceeding the line&#39;s circuit breaker rating.  
         [0078]      FIG. 15  shows a cut-away of the corner of the embodiment of  FIG. 13  illustrating said main housing  47 , and said electrodes  65 ,  67 . The water maintains a circuitous path between the blades of electrodes  65 , 67  and does not spill over or under said blades, plastic spacers  73 , 76  are disposed between said electrodes  65 , 67 . These plastic spacers  73 , 76  forcibly route the water only in the spaces  75  between the blades of said electrodes  65 , 67 . This long linear path length facilitates the creation of a clear and concise place as shown in  FIG. 7  at which said PTC effect  25  is located within the total water path length.  
         [0079]      FIG. 16  is a section view of a more refined embodiment of  FIG. 13 . It shows said throttling screw  44  threaded into said retaining plate  46 . Retaining plate  46  is fastened to main housing  47  with screws  80  and washers  82 . A seal retaining cup  78  is disposed between retaining plate  46  and main housing  47  to compress resilient seal  85  against a smooth portion of throttling screw  44  so as to seal against leakage. Throttling screw  44  adjusts the water temperature to a desired temperature by increasing or decreasing the space  91  between its end and the surface of bottom housing  57 . In operation, water enters molded-in channel  72  through inlet orifice  89 , whereby most of the flow  97  is directed between said electrodes. An adjustable percentage flows past said throttling screw  44  through opening  91  and mixes with exiting hot water  95  leaving the water heater through exit orifice  93  at the desired water temperature.  
         [0080]     The object of this invention is not to define the operation of electronics required to regulate a PTC plastic electrode water heater, but to include the optional embodiment of controlling temperature more accurately through the use of electronics.  FIG. 17  is an alternate embodiment of  FIG. 13  showing a printed circuit board  101 . Printed circuit board with its electronics  101  serve to regulate the temperature of the water in use to within smaller temperature tolerances. Such an embodiment requires that it incorporate a pressure sensing device  105  that when in operation senses a pressure drop which activates said electronics. A current sensing device  103  provides input to a microprocessor  107  that triggers the proper firing angle of the AC sine wave by way of triac  113  that is heat-sink mounted to a face  119  of the inlet/outlet manifold  121 . An inlet thermistor  117  provides input to the microprocessor when the flow of water stops by its increase in temperature. An outlet thermistor  115  provides input to the microprocessor by measurement of the output temperature of the water.  
         [0081]     The preferred conductive package of this invention uses-carbon in two or more of its forms. As previously mentioned, these carbonaceous materials are physical forms of graphite and of carbon in various shapes. Physical shapes make a considerable difference in this invention because much depends on linkage between adjacent particles, and conductance through them. Graphite flake offers advantages because of its shape and cross-section, for example.  
         [0082]     The designer of these electrodes will consider their properties and their interlinking and separation in the two states of the plastic above and below the transition temperature.  
         [0083]     It is a considerable advantage to proportion the sizes of the particles used to provide an optimum “fit”. If only large particles were used, there would be considerable voids between them that would more advantageously contain conductive particles. Just as a pile of round marbles leaves voids between them which could be filled with small particles such as pebbles or sand, so with this invention smaller particles, or even carbon black could be incorporated to advantage. This is called a “packing ratio” which relates to placing smaller particles in voids between the larger ones. It is an attainable objective to provide nearly identical electrical results with less loading of packed material, thereby facilitating the manufacturer of the product by affordable injection molding.  
         [0084]     There are limitless combinations of these materials, from which the designer will select the one most appropriate to his intended application. Graphite flake with interposed smaller graphite fibers and perhaps some carbon black constitutes one useful combination.  
         [0085]     The amount of carbonaceous material to be added to the plastic material is ordinarily determined by considerations of bulk resistivity (which is lowered by the carbonaceous material) and the surface connectivity with the water or other liquid to be heated (which increases with increased carbon). This is a “balancing act” which requires only some reasonable trial and error work to establish an intended result. It is well within the skill of a good formulator.  
         [0086]     It is important that the material used in these electrodes be as pure as possible because of the tendency for salts to deposit on the electrode in a very short period of time if certain elements are in the materials where they act as “seeds” for deposition of insoluble salts. It is especially important to eliminate the following: ions of calcium, iron, aluminum and silicon, and silicates and carbonates, especially calcium carbonate. Unfortunately some of these elements get into the plastic material during the manufacture of the plastic itself, and during the manufacture of the electrode, unless great care and preparation are taken. Even medical grades of these plastics generally include enough of them to adversely affect the useful life of the electrode.  
         [0087]     It is possible, with great effort, to produce plastic with sufficiently low levels of impurity, and this is an unusual requirement for an optimum electrode to be made. Similarly as to the carbonaceous materials. Carbonaceous materials are available in a purified condition, and these should be used.  
         [0088]     In any event, the materials and their combination in the electrode should be as devoid of the aforementioned impurities as possible to the extent that the electrodes will have a significant life span. For optimum life span, impurities of the type described should be present in the electrode in less than about 100 parts per million. It is possible and preferred to keep them as close to 10 PPM as possible. The carbonaceous materials are available with almost no impurities. The manufacturer/molder should be cautioned that surface contamination of a previously used machine must be eliminated, lest these impurities enter the product.  
         [0089]     An important advantage of the packing ratio is that it provides better conductivity with the use of less conductive packaging material. This enables better performance with less added material. As a consequence the electrode material can more readily be injection molded. When too much conductive package must be added, injection moldability becomes questionable because of the greatly increased pressures required by the machinery. Use of the injection molding process is highly advantageous because of it obvious economy. The use of this packing ratio consideration reducing the amount of conductive material for the same results.  
         [0090]     This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.