Patent Grant
7579806
Due to the chemical reaction process in a fuel cell, the fuel cell generates moisture. In cold environments that moisture needs to be prevented from freezing.
Many patents and patent publications discuss direct methanol fuel cells and approaches for controlling the temperature thereof. These include U.S. Pat. No. 4,650,729 to Nakamura et al., U.S. Pat. No. 6,387,556 to Fuglevand et al., and PCT publication no. WO 2004/017447 to Mardilovich et al.
A temperature sensor and a heating device are provided to prevent moisture from freezing in a direct methanol fuel cell. To achieve this, a secondary battery is connected in parallel to the fuel cell. When the temperature drops to a predetermined level, the secondary battery, using electricity it has stored from the fuel cell, heats a ceramic device. This device is located near the cell, the fuel container or both. When the fuel cell again reaches the desired temperature, it begins normal operations and also charges again the secondary battery. The heating system is prevented from working if a fuel container is not installed in a battery pack or if the battery pack is not connected to an electronic device or if that electronic device is turned off.
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 |
|---|---|---|---|---|
| PCT/IB2005/051933 | 6/10/2005 | WO | 00 | 11/21/2006 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2005/120161 | 12/22/2005 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4650729 | Nakamura et al. | Mar 1987 | A |
| 4670702 | Yamada et al. | Jun 1987 | A |
| 5302471 | Ito et al. | Apr 1994 | A |
| 20030138676 | Leban | Jul 2003 | A1 |
| 20030224224 | Okada et al. | Dec 2003 | A1 |
| 20040219409 | Isogai | Nov 2004 | A1 |
| 20050206342 | Aleyraz et al. | Sep 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 2004-081388 | Mar 2004 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20080030164 A1 | Feb 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60521654 | Jun 2004 | US |
