Patent Application
20110128154
The present invention relates to lead-acid batteries, and more particularly to devices for monitoring and indicating the level of electrolyte within lead-acid batteries.
The proper functioning of a lead-acid battery requires a proper level of electrolyte in each battery cell. If a battery is used with under-filled cells, permanent loss of capacity may result from sulfation of the exposed plates and from excess operating temperature. Additionally, the heat induced from the associated short-circuiting introduces the possibility of explosion due to ignition of cell gasses.
Accordingly, and especially in the field of industrial batteries, it is standard practice to locate a powered probe within a battery cell to measure the level of the electrolyte in the cell. The two main methods for measuring electrolyte levels are 1) a conductive probe unit and 2) an AC powered, locally grounded, capacitance-sensing probe.
The conductive probe unit is based on the principle that when the conductive probe contacts the electrolyte, electricity can flow through the probe and the electrolyte in a closed circuit. A control circuit within the unit monitors for an open circuit condition and alerts the battery user appropriately. Examples of this technology are disclosed in U.S. Pat. No. 5,936,382 issued Aug. 10, 1999 to Jones et al and U.S. Pat. No. 6,040,079 issued Mar. 21, 2000 to Mcmurren.
Unfortunately, conductive probe units have several shortcomings. First, the conductive probe of the unit, which extends into the battery cell, erodes with age. Conductive materials, when placed in an acid environment such as a battery cell, are susceptible to corrosion especially when subjected to electrical current. As the probe material corrodes, particles dislodge from the base probe material; and the probe erodes. An eroded or shortened probe renders the electrolyte level indicator ineffective for accurately determining the electrolyte level. Second, the conductive probe can come into contact with internal cell structure, such as moss shields or lead straps. And such contact can cause a false reading, indicating adequate electrolyte level when in fact the level is low.
The capacitance-sensing probe is a more recent development. An example of such a probe is illustrated in U.S. Pat. No. 6,943,566 issued Sep. 13, 2005 to Florin et al. This type uses alternating current (AC) to measure the capacitance of the electrolyte and the probe that extends into the electrolyte. Current flows between the electrolyte and the probe through the AC circuit. The capacitance of the system changes as the electrolyte level changes, and consequently the capacitance provides an indication of electrolyte level. This change is monitored, and the unit alerts the battery user appropriately.
Unfortunately, capacitance-sensing probes also have shortcomings. First, the probe that extends into the battery electrolyte is an exposed metal, which erodes as discussed above. Second, the probe can contact internal cell structure as discussed above. Third, because the electrical current must flow between the unit and the electrolyte, the probe must be grounded to the cell that it is monitoring. This required grounding is unique to these types of systems and therefore can create confusion during the installation process.
An electrolyte level indicator constructed in accordance with the present invention includes a probe (a) that does not erode, (b) that does not create problems if it contacts solid structure inside a battery cell, and (c) that includes a control circuitry that is independent of the cell being monitored. The level indicator uses capacitance sensing to determine the level of the electrolyte. The level indicator includes a probe having a housing and a capacitive element within the housing. The probe housing is electrically nonconductive and acid resistant, which protects the capacitive element within the housing.
The capacitive element within the probe is regularly charged and discharged using direct current. The control circuit monitors the charge and discharge properties to identify charge and discharge profiles or characteristics. When the encapsulated probe is near or in contact with the electrolyte, the discharge properties of the probe change. The control circuit monitors these changes to determine electrolyte level, and alerts the battery user appropriately. Lights, such as LEDs, can provide the alert to the user.
The probe of the present invention addresses the noted shortcomings of prior art units. First, the probe does not corrode or erode. Second, the probe does not provide a false signal if it comes into contact with solid structure or contaminants inside the battery cell. Therefore, the probe is insensitive to moss shields, lead straps, and contaminants such as oils. Third, the probe enhances safety. Explosions have occurred with some regularity in cells containing metal-probed level indicators. A common theory is that electrical current flowing through a metal probe can produce a spark, which can ignite the flammable gasses produced by a battery. The nonconductive probe housing of the present invention electrically insulates the probe from the electrolyte so that a spark cannot jump between the two, possibly leading to an explosion. Fourth, the level indicator uses direct current to monitor the electrolyte level. The circuit is powered externally and is not grounded to the cell in which it is mounted. Consequently, no current flows into the electrolyte or battery cell.
The length of the probe is selected based on the desired electrolyte level for a given application. Additionally, the indicator light can be included integrally with the probe unit and/or provided in a separate unit that can be mounted on the edge of the battery.
These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiments and the drawings.
A battery electrolyte level monitor constructed in accordance with a first embodiment of the invention is illustrated in
Lead-acid batteries, such as the battery 16, are well-known in the art and will not be described in detail. Suffice it to say that the battery 16 includes a case 26 containing the other components. The battery includes one or more cells each containing an electrolyte 18. The battery also includes a top 28 defining ports 30 and 32, which provide access for inspecting the battery, adding electrolyte, and/or receiving watering systems. The electrolyte is consumed, albeit gradually, during operation of the battery and must be replenished periodically. Such replenishment is typically referred to as “watering”.
The probe assembly 12 includes a probe housing 34, a printed circuit board (PCB) 36 (see
The probe housing 34 is perhaps best illustrated in
The probe 34 includes a grommet 35 mounted on the probe portion 40. The grommet is of conventional design to support and seal the indicator 12 within the battery 16.
The cap 38 is perhaps best illustrated in
The material of which the probe 34 is currently fabricated is both electrically nonconductive and acid resistant. The material of the current embodiment is ABS, although a wide variety of other materials could be used. The material prevents electrical conductivity between the capacitive element 60 and the battery electrolyte 18. Further, the probe 34 encapsulates the capacitive element 60 to prevent the element from being contacted by the electrolyte 18; and therefore the capacitive element 60 is not subject to corrosion or erosion.
The material of which the cap 38 is currently fabricated is a clear polycarbonate to permit the transmission of light from the LEDs 68. Other suitable materials could be used.
The control circuit 62 includes the PCB 36 (
An electrical schematic illustrating the control circuit 62 is illustrated in
The pins of the circuit are defined as follows:
The pins are used for programming the microcomputers 63 and 65 during production. The control circuit 62 alternatively can include pre-programmed microcomputers, which eliminates the need for the programming pins. Further alternatively, the control circuit 62 can include a single microcomputer in place the microcomputers 63 and 65.
The capacitive element 60 is electrically connected to the PCB 36 at point 66. The control circuit 62 includes red, green, and blue light-emitting diodes 68 which are controlled to provide a visual indication to the battery user of the electrolyte level. In the current embodiment, the green LED is illuminated when the electrolyte level is above the minimum electrolyte level 20; and the red LED is illuminated when the electrolyte level is below the minimum electrolyte level 20.
The leads 14 are conventional and are connected to the probe assembly 12 in conventional fashion to provide power to the control circuit 62.
The first embodiment of the level indicator 10 is sometimes referred to as the “local” embodiment because all of the components (except the leads 14) are contained within the probe assembly 12.
Assembly of the indicator 12 is straightforward. The probe housing 34 and the cap 38 are injection molded. The capacitive element 60 is inserted into the probe 34 so that the capacitive element 60 is located adjacent or closely proximate to the lower end 44 of the probe housing 34. The PCB 36 is mounted on the top 42 of the probe 34, is supported on the supports 46 and 48, and located by the standoffs 50 and 52 (see
The probe assembly 12 is mounted on the battery 16 by inserting the probe housing 34 through the port 32. The grommet 35 engages the battery to both support and seal the probe assembly 12 within the battery 16. The leads 14 are connected to a source of DC voltage such as the power terminals of the battery 16.
In operation, the capacitive element 60 is repetitively or periodically charged and discharged using direct current. Each charging and discharging of the capacitive element 60 results in a profile or characteristic that is dependent upon the level of the electrolyte 18. If the electrolyte is above the minimum level 20 as illustrated at 22, the charging and discharging have first profiles. And, if the electrolyte 18 is below the minimum level 20 as illustrated at 24, the charging and discharging have second profiles. When the control circuit 62 determines, based on at least one of the charging profile and the discharging profile, that the electrolyte level is above the minimum level 20, the green LED is illuminated. When the control circuit 62 determines that the electrolyte level is below the minimum level 20, then the red LED is illuminated. If desired, the LEDs can flash in a regular or irregular pattern to further attract attention. Alternatively, other indicator techniques can be used such as audible alerts and/or wireless signals. Another possibility is for the control circuit 62 to control an automatic watering system, so that water would be added to the battery 16 automatically upon determination that the electrolyte level is below the minimum level.
An indicator system constructed in accordance with a second embodiment of the invention is illustrated in
The probe assembly 112a is generally identical to the probe assembly 12 of the first embodiment with one exception. The probe assembly 112a does not include an indicator light, such as the LEDs 68. In the second embodiment 110, the indicator LEDs 68 are included within a second or light housing 112b connected to the indicator 112a by a cable 170.
The light housing 112b is injection molded similar to the housing 12 previously described. The housing 112b includes a printed circuit board (not shown) having one or more board-mounted LEDs thereon. As illustrated in
The operation of the second embodiment 110 is generally identical to the operation of the first embodiment 10. The difference is that the indicator LEDs are provided at the edge or the side of the battery 16. In many applications, most notably industrial applications, such positioning of the indicator lights can facilitate observation through the serially aligned LEDs.
An indicator system constructed in accordance with a third embodiment of the invention is not illustrated in the drawings. The third embodiment is sometimes referred to as the “local/remote” embodiment because both the probe assembly and the remote assembly include one or more indicator lights such as LEDs.
The above descriptions are those of the current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents.
