Patent Application
20120150247
The present invention relates to automated external defibrillators, and, more specifically, to a battery pack for powering the device.
External defibrillators are emergency medical devices designed to supply a controlled electric shock (i.e., therapy) to a person's (e.g., victim's) heart during cardiac arrest. This electric shock is delivered via pads that are electrically connected with the external defibrillator and in contact with the person's body.
To provide a timelier rescue attempt for a person experiencing cardiac arrest, some external defibrillators have been made portable, by utilizing battery power (or other self-contained power supplies). In addition, many portable external defibrillators have programming to make medical decisions making possible operation by non-medical personnel.
These portable external defibrillators, commonly known as automated external defibrillators (AEDs), including automatic and semi-automatic types, have gained acceptance by those outside the medical profession and have been deployed in myriad locations outside of traditional medical settings. Due to the life saving benefits of AEDs, more and more non-medical users are purchasing and deploying AEDs in their respective environments. This allows for a rescue attempt without the delay associated with bringing the person to a medical facility, or bringing a medical facility to the person (e.g., a life support ambulance).
Individuals as well as businesses are purchasing and deploying AEDs. As time is of the essence during any rescue attempt, multiple AEDs may be purchased by any particular individual or user to allow placement at multiple locations. In the case of an individual, this could be on several floors of a home, and in the case of a business, this could be for placement throughout a facility (e.g., factory, office building, or large retail center). Thus, regardless of where the victim is within the home/facility, access to an AED would only be seconds, or minutes, away.
AEDs rely on batteries to provide power. More precisely, AEDs rely on battery packs that have battery stacks, which contain multiple batteries (i.e., cells). To assure that the battery pack is capable of meeting the power demands of the AED, the capacity of the battery pack is continually assessed.
Generally, assessment of the present capacity of the battery pack occurs during routine AED self testing (e.g., schedule, autonomous testing conducted by the unit). If an assessment determines that the battery pack lacks sufficient capacity to perform to a predetermined level, the user is alerted to the need to replace the battery pack.
When to alert a user as to the need to replace the battery pack can be extremely problematic. If a user is alerted too early, battery pack capacity is wasted, as the user replaces a battery pack that could perform. If a user is alerted to late, the AED could be out of service before the timely replacement of the battery pack can occur.
Determining when to alert a user to replace a battery pack is complex. Typically, battery pack capacity is assessed by determining the voltage output delivered under specific load conditions, which places a known load on the battery such that the battery's internal resistance causes a decrease in voltage output. If the voltage output falls below a given pre-determined threshold voltage, the battery pack is considered to lack the necessary capacity. In other words, voltage output is a surrogate for remaining battery pack capacity, thus remaining battery pack life.
Historically, batteries, and the battery packs that use them, had a discharge curve that exhibited a gradual voltage output decline under load. Thus, a threshold voltage output under a known load of a battery pack could be identified that equated to battery pack end of life.
As battery technology has advanced, the discharge curve has flattened out, thus the gradual output voltage decline has been eliminated. More precisely, newer technology batteries, such as Lithium Battery CR-2/3A, exhibit relatively stable voltage output under a known load until near end of life when there is a precipitous drop.
Presently, to provide a timely warning to an AED user of the need to replace a battery pack using newer technology batteries, the threshold voltage under a known load is being continually increased. However, as the threshold voltage under a known load is increased, due to the ever flatter discharge curves, it is becoming ever closer to the normal operating output voltage. As those skilled in the art of assessing remaining battery capacity will appreciate, as the threshold voltage output under load approaches the normal operating output voltage under load, it becomes increasing difficult, due to the ever smaller delta between the two and minor fluctuations in the output voltage due to manufacturing and operational tolerances, to discern when the threshold voltage output has been reached. As a result, to meet the need of assuring proper operation and a timely notification of users as to the need to replace the battery, users are being instructed to replace battery packs earlier than might otherwise be required. As a result, capacity in battery packs employing newer technology batteries is being wasted.
What is needed in the art is a better method of assessing battery pack end of life so additional battery capacity can be utilized to lower user costs. More specifically, autonomous self-tests being conducted on the AED should be able to determine the remaining capacity of the battery pack. Then, the battery pack should remain fully functional for some reasonable period of time thereafter to permit the timely notification of a user as to the need to replace the battery pack and allow a reasonable time to allow replacement before the battery pack is depleted.
Furthermore, other desirable features and characteristics of the present invention will become apparent for the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
The invention is a battery pack topology wherein the battery pack has multiple battery sub-stacks electrically connected in parallel such that the capacity of each battery sub-stack may be utilized but one is reduced unequally as to the others. As a result, one battery sub-stack will reach a point of failure before the other, which causes a drastic, observable change in the output voltage of the battery pack, but provides sufficient reserve capacity to permit a user of a device, such as an AED, having the battery pack to be notified in a timely fashion of the need to replace the battery pack.
In an exemplary embodiment, the battery pack includes two battery stacks configured in parallel. As a result, each battery stack is a battery sub-stack within the battery pack. The inequality in capacity utilization between the battery sub-stacks results from a difference in voltage drop relative to each branch of the parallel circuitry. In an illustrative example, this voltage drop difference is created by employing a different number of diodes on each branch. As those skilled in the art will appreciate, other electronic devices could be used to create different voltage drops, but diodes work well as the voltage drop, which is generally constant, as it is generally independent of current being drawn, except at very low current draws, from the associated battery sub-stack.
Other features, attainments, and advantages will become apparent to those skilled in the art upon a reading of the description when taken in conjunction with the accompanying drawings.
Turning now to the drawings,
Referring to
The AED unit 100 includes a battery pack 126 that provides the main power. As illustrated, the battery pack 126 slides into a battery slot 128, but it could an internal battery pack. Where the battery 126 is removably secured in the battery slot 128, a faulty battery can generally be replaced by a user.
The AED unit 100 typically have many operating modes, with some being sub-modes of primary modes. There are two primary modes—OFF and ON. The OFF mode has several sub-modes including SELF-TEST and AUXILIARY. The OFF-SELF-TEST sub-mode is the default mode. More specifically, the AED unit 100 must always be in an operational mode. Thus, when the AED unit 100 is referred to as being in the OFF mode, it is in one of the sub-modes. When the AED unit 100 is in the OFF SELF-TEST sub-mode, a user considers the AED unit 100 to be OFF.
In the OFF SELF-TEST sub-mode, the circuitry 200 of the AED unit 100 utilizes minimal power to maintain basic functions of the AED such as running a clock 210 (which is shown as having a backup battery) and autonomously (i.e., without human intervention) initiating self-tests, so that scheduled self-diagnostic maintenance checks in response to the passage of time are performed. The results of the self-test in this illustrative AED 100 are displayed by an active status indicator 114, over which the AED programming has autonomous control.
For a rescue attempt, the AED unit 100 is put into the ON mode from the OFF SELF-TEST sub-mode by operation of the ON/OFF switch 108. After the rescue attempt, the AED unit 100 may be put back into the OFF SELF-TEST sub-mode by operation of the ON/OFF switch 108, or the programming may automatically put the AED into the OFF SELF-TEST sub-mode.
Continuing with
For a typical AED application, a suitable battery cell 406 is a 3 v battery, such as a Duracell Lithium CR-2/3A, and a battery sub-stack 402, 404 is four batteries electrically connected in series giving the battery sub-stack an initial output voltage of 12 v. These batteries have an initial capacity of about 1.5 Ah. In this exemplary embodiment, each battery sub-stack 402, 404 is generally identical (to the degree permitted by manufacturing tolerances) as they employ the same type and number of battery cells 406, but this is not required.
The two battery sub-stacks 402, 404 are connected via a load allocator 407 that places the battery sub-stacks in parallel. Therefore, one battery sub-stack is on branch A, and the other on branch B.
The illustrated load allocator 407 includes three identical diodes 408, 410, 412 wherein two 408, 412 are in series and in parallel with one 410. The diode configuration of the load allocator 407 (two on branch A and one on branch B) creates an unequal voltage drop across the branches A, B of the battery pack 126. Since the branch voltage drops are unequal, the current drawn over time, or the capacity used, from each individual battery sub-stack 402, 404 will be different. As a result of the load imbalance, battery sub-stack 404 (the battery sub-stack on the one diode branch) will be depleted prior to battery sub-stack 402.
In addition, a diode on each branch of the parallel circuit prevents one battery sub-stack 402, 404 from charging the other battery sub-stack in the event they should have different voltage potentials. As those skilled in the art will appreciate, the identified suitable batteries are not rechargeable; therefore, these batteries should not be subjected to a charging current.
As shown in
More precisely,
As shown in
As used herein, a voltage discontinuity means a precipitous voltage output drop of the battery pack from one operational voltage to another under a known load. An operational voltage means a voltage in combination with a remaining capacity that is capable of operating the device for at least one cycle.
The voltage output discontinuity results from the failure of the ability of one battery sub-stack to provide any current. In other words, prior to the failure of one battery sub-stack, both battery sub-stacks contributed current and the resulting output voltage was 9.75 volts under load. After the voltage discontinuity, which resulted from an end of life event wherein one battery sub-stack (e.g., a failure of at least one battery cell 406 in the battery sub-stack 404), the current draw on the remaining battery sub-stack resulted in a voltage output under load of 8.6 volts. The testing was continued until a simulated interval 420, where at that point the battery pack 126 was unable to provide an operational voltage.
This accelerated life test indicates the battery pack 126 had sufficient operational voltage to operate for a simulated 420 intervals and give a noticeable event at approximately simulated interval 380. This noticeable event, of output voltage discontinuity, can be used to alert a user of a need to replace the battery, which is discussed below.
The different capacity being drawn from each battery sub-stack, or load sharing between the battery sub-stacks, under different load conditions is shown in
These graphs were created using an iterative test procedure using a battery pack 126 having the same construction as that used in the simulated life testing discussed above. Starting with new batteries, a 50 ohm resistor was placed across the terminals of the battery pack 126 for 40 minutes. The 50 ohm resistor was removed and the voltage output determined. Using the known voltage output, a resistor giving a load consistent with a current draw of 1 mA was connected across the battery pack 126 terminals, and the current from each battery sub-stack obtained. Then, a resistor giving a load consistent with 100 mA was connected across the battery terminals, and the current from each battery sub-stack obtained. Finally, the procedure was conducted with a resistor giving a load consistent with a 1.5 A draw. This iterative procedure was repeated some number of times. The average voltage output from the battery pack 126 over the test was 11V.
As shown in
As those skilled in AED design will appreciate, many AEDs are intended to meet a once in a life time need, but have many operational modes whether in storage or in use that use battery pack capacity at varying rates. For example, during storage, an AED continually performs scheduled self tests. These self tests vary in scope and duration. For example, a daily self test uses very little battery capacity, while weekly, monthly and quarterly self tests use ever increasing amounts. Generally, the increased amount of battery capacity used in various self tests results from degree the testing involves the shock circuit. In tests that are more frequent, the shock system may be not charged or only partially charged where in the less frequent tests it could fully, or almost be fully, charged.
For example, when stored and OFF with no self-testing occurring (e.g., the AED is merely reporting operational status using an active indicator), the load and associated current draw is in single digit milliamps, but relatively continuously. When OFF and conducting a daily self-test, the load is marginally higher having a current draw in the hundreds of milliamps (e.g., 100-200) for some short duration. However, when OFF and performing weekly, monthly, or quarterly self-tests, the load can be significant with the current draw (either battery limited or device limited) approaching several amps (e.g., 2 amps) for some number of seconds, becoming longer for the less frequent tests (e.g., 2 seconds weekly, 10 seconds quarterly). In the event of the AED is used in a rescue, the load and associated current draw is generally equivalent in amount and duration to that in longest self-test.
Referring to
The above usage pattern of the battery pack 126 makes diodes preferred for the load allocator 407, as diodes have generally constant voltage drops over a wide current range. This diode characteristic maximizes battery pack 126 life by keeping the voltage drop associated with the load allocator 407 as small as possible under all potential AED uses, even during high current events. Schottky diodes, which are illustrated, are available with forward-voltage drops between approximately 0.15-0.45 volts. Other more conventional diodes, such as silicone diodes, could be used, but the available forward-voltage drops are between approximately 0.7-1.7 volts. Precise diode selection is a matter of design choice considering such factors as maximum current flow and maximum reverse voltage.
As discussed above, the significant drop, or discontinuity, in output voltage indicates a failure in battery sub-stack 404. As those skilled in the art will appreciate, the diodes used in the battery stack affect when the significant drop in output voltage of the battery pack 126 will occur. More specifically, the objective is to create a different voltage drop between the branches of the circuit containing the battery sub-stacks. The closer the created voltage drops are, the longer the time until the significant drop will occur, assuming two equal battery sub-stacks. As a result, less residual capacity will remain in the battery pack 126, or in the still functioning battery sub-stack. On the other hand, the greater the disparity in the voltage drops, the shorter the time until the significant drop and the greater the residual capacity in the battery pack 126 or the still functioning battery sub-stack.
It, therefore, should be appreciated that there is a tradeoff between the amount of residual capacity and the timing of the occurrence of the significant voltage drop. As the significant voltage drop is used to signal the need to replace the battery pack, this will establish the duration of the notice period before AED failure, and the time in which the battery must be replaced to avoid an out-of-service condition.
As addressed above, the voltage discontinuity can be used as a triggering event for the AED to notify a user of the need to replace the battery pack 126. For example, during a self-test, the self-test could determine the output voltage of the battery pack under a known load condition, such as a “battery test event.” Then based on a pre-determine threshold voltage, determine whether to alert the user to the need to replace the battery pack. The threshold voltage would be set between the output voltage before the discontinuity and the output voltage after the discontinuity.
In the alternative, self-tests that run frequently on the AED, such as periodically, would determine a change in output voltage of the battery pack 126 by comparing the ultimate output voltage with a previous output voltage. For example, a self-test is run in which an output voltage of the battery pack 126 is determine and then this ultimate output voltage is compared to the penultimate output voltage. The delta between the two, would be compared to a predetermine voltage delta and if equal to or greater than the predetermined voltage delta, the programming would trigger some type of user alert, such as through the ASI. It would also be possible for programming to compare some number of prior output voltages, such as five prior output voltages be they the last five or say five of the last 10. For those skilled in the art of programming AEDS, the programming required is straight forward based on the description of the requirements provided.
In addition, other diode configurations could be used. More specifically, a single Schottky diode could be used on one branch and a single silicone diode on the other. As a result, each branch could only have one diode instead of one branch having two. As applied to the embodiment depicted in
Alternative embodiments of the invention will become apparent to one of ordinary skill in the art to which the present invention pertains without departing from its spirit and scope. Thus, although this invention has been described in exemplary form with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of the construction and the combination and arrangement of parts or steps may be resorted to without departing from the spirit or scope of the invention. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.
