BACKGROUND 
     Uninterruptible power supply (UPS) systems typically have backup power supplied by batteries. For example, referring to  FIG. 1 , a UPS system  10  includes power circuitry  12 , a power relay mechanism  14 , and a battery pack  16 . The battery pack  16  includes multiple batteries connected in series to supply DC voltage to the power circuitry  12 . The mechanism  14  connects the circuitry  12  to the battery pack  16  to supply power from the battery pack  16  to the circuitry  12 , to supply from the circuitry  12  to the battery pack  16 , and can disconnect the circuitry  12  from the battery pack  16  to inhibit energy transfer between the circuitry  12  and the battery pack  16 . 
     The mechanism  14  acts as a breaker or switch to act as a disconnecting means, e.g., as required by safety codes because a source of power (here, the battery pack  16 ) must be disconnected from the power circuitry  12  during an emergency, or for non-code purposes such as maintenance of the UPS system  10 . The mechanism  14  can comprise a circuit breaker (with or without a fuse) or a switch  20  (as shown) with a fuse (not shown) to provide desired protection. The term “switch” is used below, but this term refers to a switch or a breaker, as appropriate. The mechanism  14  can disconnect the battery pack  16  from the circuitry  12 , e.g., at the end of a discharge cycle when AC power is not available to the power circuitry  12 , to help prevent deep discharge of the batteries in the battery pack  16  to thereby help prevent damage to the batteries. 
     To disconnect the power circuitry  12  from the battery pack  16 , the mechanism  14  includes an under-voltage relay (UVR) coil and/or a shunt trip (ST) coil  18 . The ST/UVR  18  is controlled by a control voltage V C . The control voltage causes the UVR/ST  18  to actuate the breaker/switch  20  to disconnect the circuitry  12  from the battery pack  16 . An ST is typically used to disconnect the circuitry  12  from the battery pack  16  in times of emergency (providing emergency power off (EPO) functionality). The UVR can also open the breaker/switch  20  in response to the voltage provided by the battery pack  16  dropping below a threshold voltage. 
     The mechanism  14  is configured such that when the switch  20  is opened, the switch  20  must be closed manually to reconnect the battery pack  16  to the power circuitry  12 . Manually closing multiple battery switches after a loss of power is prone to human error. An operator must first locate which mechanisms  14  need to be reset, and then properly reset the mechanisms  14 . This process is tedious and prone to error. A switch that is not properly reset can substantially reduce the run time of the UPS system  10  and result in damage, e.g., due to deep discharge of battery packs  16 . 
     BRIEF SUMMARY OF THE INVENTION 
     In general, in an aspect, the invention provides an uninterruptible power supply (UPS) system including an input configured to receive AC input power, power converter circuitry coupled to the input and configured to convert the AC input power to a first DC power, and to convert a second DC power to the first DC power, an output coupled to the power converter circuitry and configured to be coupled to a load, a battery pack including at least one battery, the battery pack being configured to provide the second DC power, a power relay mechanism coupled to the power converter circuitry and to the battery pack that selectively moves between an open position and a closed position, the power relay mechanism coupling the battery pack to the power converter circuitry when in the closed position and isolating the battery pack from the power converter circuitry when in the open position, and control circuitry configured to provide a control signal, where the power relay mechanism includes a motor actuator coupled to the control circuitry, the motor actuator being responsive to the control signal to change the power relay mechanism from the open position to the closed position. 
     Implementations of the invention may include one or more of the following features. The control circuitry is configured to provide the control signal automatically to the power relay mechanism in response to determining that the AC input power at the input changes from being unacceptable for use in providing the first DC power to being acceptable for use in providing the first DC power. The control circuitry is configured to provide the control signal automatically to the power relay mechanism in response to determining both that the AC input power at the input changes from being unacceptable for use in providing the first DC power to being acceptable for use in providing the first DC power and that at least one further criterion is satisfied. The at least one further criterion being satisfied is an indication that the power relay mechanism is in the open position. The at least one further criterion being satisfied is an expiration of a timer. The power relay mechanism further includes at least one of an under voltage relay and a shunt trip configured to change the power relay mechanism from the closed position to the open position. The motor actuator is further configured to change the power relay mechanism from the closed position to the open position. The power relay mechanism further includes at least one of an under voltage relay and a shunt trip configured to change the power relay mechanism from the closed position to the open position independently of the motor actuator. 
     In general, in another aspect, the invention provides an uninterruptible power supply (UPS) system including a UPS input configured to receive AC input power, a UPS output configured to be coupled to a load, a cabinet, a battery pack disposed in the cabinet and including a plurality of batteries coupled together, the battery pack providing battery pack DC power, a power relay mechanism having a relay mechanism input coupled to the battery pack and that selectively moves between an open position and a closed position, the power relay mechanism coupling the relay mechanism input to a relay mechanism output when in the closed position and isolating the relay mechanism input from the relay mechanism output when in the open position, and power converter circuitry coupled to the UPS input, the UPS output, and the relay mechanism output, the power converter circuitry configured to convert the AC input power to an output AC power, to convert the battery pack DC power to the output AC power, and to provide the output AC power to the UPS output, where the power relay mechanism includes a motor actuator coupled to the control circuitry, the motor actuator being configured to automatically change the power relay mechanism from the open position to the closed position in response to at least one criterion including that the AC input power at the UPS input changing from being unacceptable for use in providing the output AC power to being acceptable for use in providing the output AC power. 
     Implementations of the invention may include one or more of the following features. The at least one criterion further includes the power relay mechanism being in the open position. The at least one criterion further includes a DC power at the power relay mechanism having a voltage at least as high as a threshold value. 
     In general, in another aspect, the invention provides a battery pack system including a standard-sized information technology equipment rack, a power output, batteries coupled together to provide a battery-pack DC power, the batteries being disposed in the equipment rack, and a power relay mechanism coupled to the power output and to the battery pack, the power relay mechanism selectively coupling the battery pack to the power output and selectively isolating the battery pack from the power output, the power relay mechanism including a motor actuator to automatically change the power relay mechanism from coupling the plurality of batteries to the power output to isolating the plurality of batteries from the power output in response to a control signal indicative of criteria including that a main power associated with the battery pack system unavailable and a voltage from the plurality of batteries is below a desired level. 
     Implementations of the invention may include one or more of the following features. The criteria further include the expiration of a timer. 
     In general, in another aspect, the invention provides a method for providing automated reconnection of a battery pack to power circuitry, the method including monitoring at least one criterion for selectively coupling a power output circuit and a battery pack, the at least one criterion including an acceptability of a main power source, sending, based on the at least one criterion, a control signal to a motor actuator in a power relay mechanism to couple the power output circuit and the battery pack, and in response to the control signal, connecting the battery pack to the power circuitry. 
     Implementations of the invention may include one or more of the following features. The monitoring includes monitoring safety conditions associated with the power output circuit. The monitoring includes monitoring a timer. 
     In general, in another aspect, the invention provides a computer program product residing on a computer-readable medium and including computer-readable instructions to cause a computer to: monitor at least one criterion for selectively coupling a power output circuit and a battery pack, the at least one criterion including the acceptability of a main power source, and send, based on the at least one monitored criterion, a control signal to a motor actuator in a power relay mechanism to couple the power output circuit and the battery pack. 
     Implementations of the invention may include one or more of the following features. The instructions to cause the computer to monitor cause the computer to monitor safety conditions associated with the power output circuit. The instructions to cause the computer to monitor cause the computer to monitor a timer. 
     In general, in another aspect, the invention provides a power relay mechanism to selectively couple a power output circuit and a battery pack, the power relay mechanism including a switching circuit configured to selectively couple a battery pack to a power output circuit and to selectively isolate the battery pack from the power output, and a motor actuator coupled to the switching circuit and configured to automatically actuate the switching circuit to couple the battery pack to the power output circuit in response to at least one criterion including that a main power associated with the power output circuit changes from being unavailable to being available. 
     Implementations of the invention may include one or more of the following features. The power relay mechanism further includes a control circuit coupled to the motor actuator and configured to provide a control signal to the motor actuator indicative of the at least one criterion. The control circuit is further configured to monitor the main power. The control circuit is further configured to monitor a safety condition associated with the power output circuit and to provide the control signal based in part on a status of the monitored safety condition. The control circuit is further configured to monitor a timer and to provide the control signal based in part on a status of the monitored timer. 
     Embodiments of the invention may provide one or more of the following capabilities. Battery damage in UPS systems due to deep discharge can be reduced. Run time of UPS systems following a power outage can be improved. A battery pack of a UPS system can be disconnected from a UPS system&#39;s power circuitry before full discharge of the battery pack during power outage. Disconnected battery packs of UPS systems can be automatically reconnected to power circuitry of the UPS systems after a power outage in response to power being restored to the UPS systems. Errors in reconnecting battery packs after a power failure can be reduced. Battery packs can be reconnected at correct times after a UPS DC bus has been charged to a suitable level subsequent to power restoration. Damage to UPS systems (e.g., Delta Conversion of UPS) can be inhibited or prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a prior art UPS system. 
         FIG. 2  is a block diagram of an embodiment of a UPS system according to the invention. 
         FIG. 3  is a schematic of a portion of a power relay mechanism shown in  FIG. 2 . 
         FIG. 4  is a block flow diagram of a process of reconnecting a battery pack to power circuitry shown in  FIG. 2 . 
         FIG. 5  is a perspective view of batteries in an equipment rack, shown schematically in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention provide techniques for reconnecting batteries to power circuitry in UPS systems. A motor actuator is provided in a power relay mechanism of a UPS system that can close a circuit breaker or switch (hereafter “switch”) without human involvement. The motor actuator can respond to power being available to a UPS system to close a switch that has been opened in response to a loss of supply power, a reduction in supply power, a voltage from a battery pack below a threshold, or other reason. Intelligence within the UPS system controls the motor actuator to close the switches as appropriate. Other embodiments are within the scope of the invention. 
     Referring to  FIG. 2 , a UPS system  50  for use with an external AC power supply  46  and a load  48  includes UPS power circuitry  52 , a power relay mechanism  54 , a battery pack  56 , a battery monitor unit  58 , and a motor unit  60 . The motor unit  60  includes a motor actuator control, a power supply, and a drive circuit. Batteries  57  in the battery pack  56  may or may not be modular batteries. The power circuitry  52  is configured to selectively convert and supply power from the external AC power source  46  or the batter pack  56  to the load  48  with desired voltage characteristics (e.g., voltage) as directed by a control circuit  62  of the power circuitry  52 . The battery monitor unit  58  is configured to monitor voltage and temperature of the batteries  57  in the battery pack  56  and provide this information to the control circuit  62  via a controller area network (CAN) bus. The monitor unit  58  can also help adjust the float charge voltage depending on the temperature. The circuitry  52 , as shown in this example, is disposed in a housing  53  and the mechanism  54 , the battery pack  56 , the battery monitor unit  58 , and as also shown in  FIG. 5  the motor unit  60  are disposed in a standard-sized information technology rack/cabinet  61  (e.g., 600 mm or 750 mm in width, 1080 mm in depth, and 2000 mm in height), although other configurations and physical layouts may be used. 
     The control circuit  62  is configured to provide one or more signals for use in controlling the power relay mechanism  54 . The control circuit  62  can determine when the power source  46  is operational and providing adequate power to the UPS  52  to power the load without using power from the battery pack  56 , can determine whether the power source  46  is down or otherwise unacceptable for powering the load and the power circuitry  52  is being powered from the battery pack  56 , and can determine when power returns to being supplied from the AC power source  46  instead of from the battery pack  56 . The control circuit  62  provides a signal to the motor unit  60  indicating that power from the AC power source  46  has changed from being unacceptable to power the load  48  to being acceptable to power the load  48 . The control circuit  62  can also provide a signal to the motor unit  60  to cause the relay mechanism  54  to disconnect the battery pack  56  and the power circuitry  52 , e.g., in response to determining that the power from the source  46  is unacceptable for charging the batteries  57 , in response to determining that an emergency exists such that battery power should not be provided, etc. The control circuit  62  can also send signals to the relay mechanism  54  on a line  74  indicating an emergency, an undervoltage condition (e.g., the voltage supplied by the batteries  57  is below a desired level), etc. in order to cause a disconnection of the battery pack  56  and the power circuitry  52 . The control circuit  62  can send the disconnect signal for various reasons, e.g., to help avoid deep discharge of the batteries  57 . 
     The motor unit  60  is configured to monitor relevant conditions of the UPS system  50  and signals from the control circuit  62 , and to supply open-switch and close-switch signals to control the power relay mechanism  54 . The motor unit  60  monitors the state of the power relay mechanism  54  via a signal received from an auxiliary contact  70  of the power relay mechanism  54 . The motor unit  60  further monitors the state of the external AC power source  56  via the signal from the control circuit  62 . The motor unit  60  is configured to respond to the power returning to being supplied from the power source  46  instead of from the battery pack  56 , the output power having a voltage higher than a threshold value for safe operation of the power relay mechanism  54 , and the auxiliary contact  70  indicating that the switch  66  is open, to automatically (without human involvement) send the close-switch signal to actuate the relay mechanism to connect the power circuitry  52  and the battery pack  56 . Thus, the motor unit  60  may automatically cause the relay mechanism to connect the power circuitry  52  and the battery pack  56  in response to a single indication from the control circuit  62  that the AC power source  46  is again properly running. The motor unit  60  can also respond to the indication from the control circuit  62  to disconnect the battery pack  56  from the power circuitry  52  to send the open-switch signal to the relay mechanism  54 . 
     The relay mechanism is configured to respond to the signals from the motor unit  60  to disconnect the battery pack  56  from, and reconnect the battery pack  56  to, the power circuitry  52 . Referring also to  FIG. 3 , the power relay mechanism  54  includes a disconnect mechanism  64  (a UVR and/or an ST), a switch  66 , and a motor actuator  68 . The switch  66  is coupled and configured to selectively relay energy between the battery pack  56  and the power circuitry  52  as regulated by the disconnect mechanism  64  and the motor actuator  68 . The disconnect mechanism  64  is configured to open the switch  66  to disconnect the power circuitry  52  from the battery pack  56  in response to a control signal received on a line  74  from the control circuit  62 . The motor actuator  68  can receive control power (PWR), the open-switch signal (OPEN), and the close-switch signal (CLOSE) from the motor unit  60 . The motor actuator  68  is configured to respond to the close-switch signal to move the switch  66  to its closed position and to respond to the open-switch signal to move the switch  66  to its open position as shown in  FIG. 3 . 
     In operation, referring to  FIG. 4 , with further reference to  FIGS. 2-3 , a process  110  for disconnecting and automatically reconnecting the battery pack  56  to the power circuitry  52  includes the stages shown. The process  110 , however, is exemplary only and not limiting. The process  110  may be altered, e.g., by having stages added, removed, or rearranged. 
     At stage  112 , an inquiry is made as to whether the AC power source  46  is operational and providing acceptable power to the power circuitry  52 . The control circuit  62  monitors the power provided by the power source  46 . If the power provided from the source  46  is acceptable, then the process  110  remains at stage  112  with the control circuit  62  monitoring the power from the source  46 . If the power is unacceptable, then the process proceeds to stage  114 . 
     At stage  114 , the control circuit  62  changes the power source for the load  48 . If the power provided by the source  46  drops below a desired level, or is deficient in some other manner, the control circuit  62  determines that the power is unacceptable, and causes power to be provided from the battery pack  56  through the power circuitry  52  to the load  48 . 
     At stage  116 , an inquiry is made as to whether to disconnect the battery pack  56  from the power circuitry  52 . The control circuit  62  determines whether the switch  66  should be opened. The circuit  62  monitors the battery voltage as indicated by the battery monitor unit  58  and monitors the EPO signal on the line  72  for emergencies. The control circuit  62  can also monitor for other reasons for opening the switch  66 . If the control circuit  62  does not determine that the switch  66  should be open, then the process  110  proceeds to stage  118 . If the control circuit  62  determines that the switch  66  should be opened (e.g., due to undervoltage, emergency, etc.), then the process  110  proceeds to stage  122 . 
     At stage  118 , an inquiry is made as to whether the AC power source  46  is operational and providing acceptable power to the power circuitry  52 . If acceptable power is now being provided, then the process  110  proceeds to stage  120  where the control circuitry  52  causes power from the source  46  to be used, converted, and provided to the load  48 . If unacceptable power is available from the source  46 , then the process  110  returns to stage  114 . 
     At stage  122 , the switch  66  is opened. For example, the control circuit  62  responds to an emergency indicated on the line  72  by sending a control voltage signal to the disconnect mechanism  64 . The disconnect mechanism  64  responds to the control signal from the control circuit  62  to open the switch  66 , thereby disconnecting the power circuitry  52  from the battery pack  56 . Alternatively, the control circuit  62  sends one or more signals to the motor unit  60  to actuate the motor actuator  68  to open the switch  66  (e.g., in response to determining an undervoltage condition). 
     At stage  124 , an inquiry is made as to whether the external AC power source  46  returns to operational status, providing acceptable power for powering the load  48 . The control circuit  62  monitors whether the power received from the AC power source  46  returns to acceptability. If the circuit  62  determines that the power from the AC power source  46  has not returned to acceptable status, then the process  110  remains at stage  124 . If the control circuit  62  determines that the power received from the external AC power source  46  is acceptable (e.g., the power source  46  is again operational and producing enough power to power the load  48  as desired), then the process  110  proceeds to stage  126 . 
     At stage  126 , an inquiry is made as to whether the switch  66  should be closed. The control circuit  62  determines whether the switch  66  should be closed based on one or more criteria. For example, the circuit  62  monitors a timer, monitors safety conditions such as whether a door to a cabinet housing the battery pack  56  is open, whether an emergency is indicated on the EPO line  72 , etc. If the control circuit  62  determines that the switch  66  should not be closed, then the control circuit  62  does not send a close-switch signal to the motor unit  60 , and the process  110  returns to stage  124 . If the control circuit  62  determines that the switch  66  should be closed, then the process  110  proceeds to stage  128 . 
     At stage  128 , the switch  66  is closed automatically. The control circuit  62  sends a control signal to the motor unit  60  indicating that the power from the source  46  has returned to being acceptable. The motor unit  60  responds to knowledge that the switch  66  is open as indicated by a signal from the auxiliary contact  70 , and the control signal from the control circuit  62 , to send a close-switch signal to the motor actuator  68 . The motor actuator  68  responds to the close-switch signal to move the switch  66  from its open position to its closed position. The process  110  returns to stage  112 . 
     Other embodiments are within the scope of the invention. For example, while the discussion above describes the decision as to whether the switch  66  should be closed being performed in the control circuit  62 , this decision can be performed elsewhere in the system  50 , such as in the motor unit  60 , in the battery monitor unit  58 , or elsewhere. Further, the process  110  can be modified from the depiction in  FIG. 4  and the description above. For example, stage  126  can be eliminated. Thus, the process can proceed directly from stage  124  to stage  128  where the motor unit  60  would respond to an indication of the AC power source  46  being operational to automatically cause the switch  66  to close without waiting for a command signal from the control circuit  62 . Also, the decision on whether to close the switch  66  can be made at various places in the system  50 , such as in the control circuit  62  or in the battery monitor unit  58 . Further, the control circuit  62  may send a signal indicating to the motor unit  60  to cause the relay mechanism to connect the battery pack  56  to the power circuitry  52 , with this signal not necessarily indicating that the power from the source  46  has returned to being acceptable to power the load  48  from being unacceptable to power the load. 
     Further, the control circuit  62  may analyze information in addition to information that the power from the AC power source  46  has changed from being unacceptable to power the load  48  to being acceptable to power the load  48  in order to determine to whether indicate to the motor unit  60  to close the switch  66 . The control circuit  62  may, e.g., start a timer when the power returns to being acceptable to power the load  48  and then send an indication to the motor unit  60  to close the switch  66  in response to the timer expiring. Further still, a DC voltage on a bus connecting the UPS power circuitry to the power relay mechanism can be monitored, and the switch  20  prevented from being closed unless this voltage is at or above a threshold voltage, e.g., in Delta Conversion systems. Still other criteria may also be examined. The control circuit  62  may send a single signal to the motor unit  60  after analyzing multiple criteria, or may send multiple signals that each may indicate a determination based on one or more criteria and the motor unit  60  can analyze these signals to determine whether and when to send the switch-close signal to the motor actuator  68 . Multiple indications may be combined into a single signal from the control circuit  62 . Similar techniques may be employed to determine whether and when to send the switch-open signal to the motor actuator  68 . In order to accommodate these embodiments of the control circuit  62 , the motor unit  60  may be configured to wait for an indication from the control circuit  62  to actuate the motor actuator  68  after the control circuit  62  has indicated that power has returned to being provided by the AC power source  46 . Thus, the motor unit  60  may cause the switch  66  to close in response to an indication from the control circuit  62  that the AC power source  46  is again properly running and one or more other indications from the control circuit  62  indicative of one or more other criteria.
An uninterruptible power supply system includes power converter circuitry configured to convert AC input power to a first DC power and a second DC power to the first DC power, a battery pack configured to provide the second DC power, a power relay mechanism coupled to the power converter circuitry and to the battery pack that selectively moves between an open position and a closed position, the power relay mechanism coupling the battery pack to the power converter circuitry when in the closed position and isolating the battery pack from the power converter circuitry when in the open position, and control circuitry configured to provide a control signal, where the power relay mechanism includes a motor actuator coupled to the control circuitry, the motor actuator being responsive to the control signal to change the power relay mechanism from the open position to the closed position.