Wireless battery monitoring system and method

[0001] The present invention relates generally to battery monitoring systems such as battery modules used with uninterruptible power supply (UPS) systems.

[0002] To provide continuous power to a load in applications that require continuity of power, such as in hospitals and critical processes in both industrial and commercial settings, a UPS system is typically used to switch between a primary and one or more alternate power sources in the event of failure or instability of the primary source. FIG. 1 illustrates portions of a typical UPS system 10. One or more input power lines are connected to a UPS module 12, and a battery module 14 is connected to the UPS module. If the input power fails, the battery module 14 provides power to the UPS module 12. The battery back up power may be required when power from the AC power sources are performing outside of acceptable limits or fail completely.

[0003] Battery monitoring systems are often employed to monitor the battery modules and insure that viable back-up power exists. With some known battery monitoring systems, a wire is run from each battery measuring point to a single central voltage data collection point. For series strings of batteries, such a wiring arrangement can be problematic for a variety of reasons. For instance, high voltages are involved and there are potential safety agency issues. Small wires are difficult to protect and install in a heavy current environment, and the wiring may be vulnerable, and particularly prone to damage during field battery maintenance. Isolation is required at the collection point, making accurate differential measurements difficult.

[0004] Further, the wiring can be expensive, and factory installation typically exhibits high labor costs. Because of the wiring, after-market field installation costs can cost as much or more than the monitoring equipment itself. Prior to installation, wired battery monitor systems require a site survey. Multiple custom battery rack configurations make determining wiring needs difficult. Wired battery monitor systems require up-front knowledge of the battery room configuration to determine wire lengths, conduit runs, etc. Inaccurate site surveys can cause significant back charges for revisions.

[0005] Additionally, long strings of batteries will become charge-imbalanced over time, thus affecting reliability and autonomous battery operation time. Imbalanced battery strings also will exhibit a lessened life expectancy for some of the individual batteries.

[0006] The present application addresses shortcomings associated with the prior art.

[0007] In accordance with aspects of certain teachings of the present disclosure, a wireless battery monitoring system and method are presented. The system includes a receiver and a plurality of wireless transmitters. The transmitters are connectable to a corresponding battery and are encoded to identify the corresponding battery. The transmitters are programmed to transmit data regarding the corresponding battery, such as voltage, temperature, balancer activity, etc., to the receiver.

[0008] In certain embodiments, the transmitters transmit the data at random time intervals. A plurality of load devices may further be connected across each of the corresponding batteries to provide balancing. The transmitted data may include a checksum to provide a means to verify the data received by the receiver.

[0014] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0015] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0016] FIG. 2 is a block diagram of an exemplary battery monitoring system 100 in accordance with certain teachings of the present disclosure. The system 100 monitors a plurality of batteries 110. In other embodiments, each cell within a battery could be monitored, or a plurality of cells within a single battery, or a plurality of batteries within a cluster. Wireless transmitters 112 are connected to each of the batteries, and a receiver 114 receives bursts of data from the transmitters 112. The transmitters 112 send the data over a wireless medium such as RF to avoid the problems with wires discussed in the Background section hereof. FIG. 3 is a block diagram illustrating an exemplary wireless transmitter 112. The illustrated wireless transmitter 112 includes a battery connection 120, an analog sensing power supply section 122, a micro controller 124 and an RF section 126 connected to an antenna 128.

[0017] The transmitters 112 are connected directly across the corresponding battery 110, allowing the system to monitor operational power and battery voltage information, while providing the means to connect a small load 116 across the battery 110 to achieve balancing. The load 116 may be achieved by switching a resistor across the battery 110, or by conductively modulating a semiconductor connected across the battery 110. The load 110 is configured to draw a current within an order of magnitude of the normal battery leakage current. The system battery charger can readily supply the required balancing currents. This arrangement produces a minimal impact on overall system efficiency.

[0018] The transmitters 112 are encoded so that the battery string information is provided as well as the individual battery identifier in the string. Data relating to the battery voltage, temperature, and balancer activity, for example, is monitored. A checksum is further added to the data.

[0019] The transmitters 112 provide short, quick bursts over time. In exemplary embodiments, the bursts are sent at random time intervals. For instance, if a 10 second average reporting latency is used, the transmitters 112 can be programmed to send out a burst randomly within 5 to 15 seconds after the last burst. The randomness assures that the bursts from multiple transmitters will have little impact on the system when a collision occurs between two transmitter bursts. In the event of an occasional collision, the receiver will recognize it received bad data via a checksum error and simply discard the data.

[0020] The likelihood of a collision can be readily calculated. For instance, a suitable transmitter 112 is a mini-microcontroller with an on-chip RF transmitter, such as an Atmel AT86RF401. With such a transmitter device, the data rate is 10 k baud. Fewer than 100 bytes would be sufficient to encode a burst, so no more than 10 ms would be used out of 10 seconds, or 0.1% of the bandwidth is used per transmitter 112. For 40 batteries, 4% of the bandwidth would be needed, resulting in a collision occurring about every 2 minutes. The odds of two subsequent collisions for the same transmitter are quite small, and the odds of three subsequent collisions is so small as to be inconsequential, resulting in reliable data over a 30 second period. Optimum burst transmission rates can be determined for various applications. Speeding up the data burst rate results in more collisions, but reduces the overall latency in the process.

[0021] FIG. 4 is a flow chart illustrating an exemplary series of data-handling events. Of course, these process steps could be varied as necessary based on the particular system arrangement. As a data packet is received in block 200, the receiver 114 checks the validity of the packet in decision block 202. If the packet is valid, the receiver 114 timestamps the data in block 204 and adds the data to the appropriate category in the database in block 206. In block 208, the receiver provides the database when requested by the system monitor. If the packet is invalid or otherwise corrupted due to a collision, the checksum will fail and it is discarded in block 210.

[0022] Generally, in applications such as described herein, two-way communications is not required. While two-way communications would prevent collisions and maximize transfer rates, it is wasteful if there is no need for real-time data. The balancing function of the transmitter 112 is performed in real time, but the transmitted data is not involved in real-time control.

[0023] To avoid additional wiring in the battery cabinet or battery area, the small transmitting antenna 128 is included within the housing enclosing the transmitter. The transmitter's microcontroller printed circuit board includes an etched pattern constituting a tuned loop antenna. Alternately a manufactured antenna could be used for increased gain, such as a surface mount chip antenna. Suitable antennas are available from gigaAnt (www.gigaant.com), for example.

[0024] The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.