As shown in
One way to choose to disconnect the secondary battery from the heating element, and to choose to commence recharging the secondary battery from the output of the fuel cell, is to make this choice based upon the sensed temperature rising above some second predetermined threshold. Another way to do this is to sense when the fuel cell is delivering some threshold amount of current at some threshold voltage, and to use these events to choose to disconnect the heating element and to recharge the secondary battery.
It will be appreciated that when the fuel container is connected to the battery pack, it is disposed to deliver fuel to the fuel cell.
The secondary battery may be literally in parallel with the fuel cell. In an exemplary embodiment, however, the connection between the fuel cell and the secondary battery is via a charging circuit that protects against overcharging of the secondary battery. In a simple case the secondary battery may have a voltage, when fully charged, that is less than the voltage output of the fuel cell, meaning that the fuel cell can charge the secondary battery directly. Alternatively, the secondary battery may have a voltage, when fully charged, that is higher than the output voltage of the fuel cell, in which case the charging circuit may contain a DC-to-DC voltage converter, for example a switching power supply, to develop such voltage as is needed to charge the secondary battery.
The type of battery employed for the secondary battery is preferably selected from a technology and chemistry that permits satisfactory function (here, development of power for the heating element) even at temperatures that are below the temperature at which the fuel cell requires heating. Stated differently, the battery is selected so that it operates even at temperatures that are below the operating temperature of the fuel cell.
It is perhaps instructive to discuss in some detail the context for the invention.
Many fuel cell systems, including some of the systems described in the above-mentioned patents, are large non-portable fuel cells employed to power a house or building. Such fuel cells are typically used in a setting where alternative power is available from a mains (AC) power grid. Some such systems use power from a power grid for temperature conditioning. The context of the invention, however, is a portable system in which mains (AC) power is not necessarily available. Typical applications might include a small consumer electronic device such as a wireless telephone or a notebook computer, where light weight, small size, and independence from a power grid are important features.
Describing this embodiment in more detail, in this exemplary embodiment, battery pack 12 contains, among other things, a fuel container 15, a direct methanol fuel cell 16, a heating device 14, a temperature sensor 13, a secondary battery 17, a control circuit 18, and a battery installation detection switch 19. The secondary battery 17 and fuel cell 16 are typically within a single housing.
As shown in
Those skilled in the art will have no difficulty devising myriad obvious improvements and variants of the invention without undue experimentation, all of which are intended to be encompassed within the claims which follow.
This application claims priority from U.S. application Ser. No. 60/521,654 filed Jun. 11, 2004, which application is incorporated herein by reference for all purposes.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB05/51933 | 6/10/2005 | WO | 00 | 11/21/2006 |
Number | Date | Country | |
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60521654 | Jun 2004 | US |