An uninterruptible power supply (UPS) is a type of power supply used to power and protect an electrical load that is sensitive to fluctuations in or the absence of electrical power. The UPS can be connected between the load and a source of electrical power, such as a mains power source or other commercially provided electric power. The UPS uses commercially supplied AC power to charge a DC battery and provide the AC power to load. Upon outages of power, the load draws its AC power from the DC battery typically through a DC to AC inverter. This isolates the load from power surges or brownouts and also furnishes a source of power during brief outages.
Commonly, a UPS comprises a rectifier, inverter, battery charger, DC battery, and other components, all housed within a single case or package. FIG. 1 shows a typical prior art UPS 1 used to provide regulated uninterrupted power. The UPS 1 includes an input filter/surge protector 2, a transfer switch 3, a controller 4, a battery 5, a battery charger 6, an inverter 7, and a DC-DC converter 8. The UPS also includes an input 9 for coupling to an AC power source and an outlet 10 for coupling to a load.
The UPS 1 operates as follows. The filter/surge protector 2 receives input AC power from the AC power source through the input 9, filters the input AC power and provides filtered AC power to the transfer switch 3 and the battery charger 6. The transfer switch 3 receives the AC power from the filter/surge protector 2 and also receives AC power from the inverter 7. The controller 4 determines whether the AC power available from the filter/surge protector is within predetermined tolerances, and if so, controls the transfer switch to provide the AC power from the filter/surge protector to the outlet 10. If the AC power from the rectifier is not within the predetermined tolerances, which may occur because of “brown out,” “high line,” or “black out” conditions, or due to power surges, then the controller 4 controls the transfer switch 3 to provide the AC power from the inverter 7. The DC-DC converter 8 is an optional component that converts the output of the battery 5 to a voltage that is compatible with the inverter 7. Depending on the particular inverter 7 and battery 5 used the inverter 7 may be operatively coupled to the battery 5 either directly or through a DC-DC converter 8.
Electrical devices having installed batteries, such as UPS's have the potential to cause safety problems, even when the electrical device is not operating. For example, short circuits can occur in electrical devices during transport. These short circuits can present a fire hazard.
Another problem that can occur is where a component in circuitry connected to a battery during shipping develops a fault that causes it to generate heat. An example is a printed wiring board or electronic capacitor electrically connected to a battery during shipping, which can develop an internal fault through contamination, defect, or dendritic growth. Such conditions may result in the release of battery energy and may not cause protective fusing to actuate but have been know to give rise to high temperature and initiate afire. Moreover, the subsequent feeding of the fire by electrical energy of the battery may cause normally non-combustible materials such as printed wiring assemblies to burn.
Yet another concern is that electrical devices with installed batteries may pose risks other than those associated with the “chemical” hazard of electrolyte or other battery components, or the risk of short circuit. One important concern in this regard is the risk arising from the possible generation of a dangerous quantity of heat owing to the unintentional and uncontrolled release of energy stored within a battery. Heat evolution associated with such an energy release can affect the device itself, packaging materials or other adjacent cargo in such a way as to initiate fire, and/or generate smoke. Even without a short circuit condition existing, an unacceptable situation may arise when a component in circuitry connected to a battery becomes heated to a point where combustion is initiated in the component itself, or in nearby materials, including packaging materials.
In response to these concerns, organizations such as the United States Department of Transportation (USDOT), and the International Air Transport Association (IATA) have established regulations relating to the shipment of electrical batteries and battery-powered devices (see, e.g., IATA Regulations Special Provision A123 and USDOT Research and Special Programs Administration Notice No. 99). These regulations provide that electrical batteries and battery-powered devices must have their batteries protected from short circuits and/or insulated during transport. Because the batteries of many electrical devices are located inside the chassis of the devices, compliance with these regulations can be difficult, time-consuming, and error-prone.