Looking Inside Toshiba’s Fuel Cell
Toshiba Corp. has been a constant front runner in the competition to develop fuel cells for mobile equipment. While the firm has exhibited a host of prototypes at various shows, it has never brought any to market … until now. Construction puts safety first, making extensive use of metal parts such as stainless steel and aluminum alloy. We took one apart to see how it works, in cooperation with development engineers involved in fuel cells, mobile equipment, and other items.
“I’m impressed simply by the fact they actually went commercial,” says one engineer in the mobile gear field.
At the end of October 2009, Toshiba released a limited 3000 units of the “Dynario” fuel cell for mobile equipment. That act—releasing a fuel cell to the market in spite of the current depression—earned praise and astonishment from engineers in mobile equipment, fuel cells, and other fields.
Many of the other companies engaged in fuel cell development immediately bought sample units to verify operation. A variety of opinions have already been released, such as, “It’s a pretty mature design, with air inlet humidity stabilized and no smell of the methanol fuel left” and, “It feels hot to the touch, although only as hot as bathwater.”
We picked up a sample ourselves to analyze its operating characteristics, and asked Toshiba to help us take a closer look at its components.
Actual Cost 30,000 Yen or More?
The Dynario (Fig. 1) is a direct methanol fuel cell (DMFC) with a USB connector that allows it to charge mobile equipment. The maximum output, together with the internal Li-ion rechargeable battery, is 2 W (5 V, 400 mA). It is charged with 14 mL of methanol, which, according to Toshiba, “is enough to charge a piece of mobile equipment about two times.” We used an LED lamp with a power consumption of 1 W to verify that it generated enough output for about 11 (11 Wh).
Fig. 1 Charging Mobile gear via USB Toshiba's fuel cell can charge mobile equipment via a USB connector, and is refilled with a 50 mL bottle of fuel. (Photo: Eiji Yamanishi)
The Dynario is priced at 29,800 yen, which is pretty expensive for an external charger. Toshiba explained “There are a number of custom components that just pushed the price up.” In fact, when we took it apart we were surprised at how many parts were inside (Fig. 2). In addition to the actual fuel cell, there were ultra-miniature pumps and valves, as well as microcontrollers, control ICs, control boards, and other circuit components. The case was so sturdy it almost seemed like overkill, with a metal exterior and reinforcing members. Most of the people who looked inside, including mobile equipment and fuel cell engineers, agreed that it was almost certainly impossible to sell it for only 30,000 yen, considering components, manufacturing and other costs.
Fig. 2 Major Fuel Cell Components There are two generating units, fitted together facing in different directions. There was a large number of components including the generating control system and reinforcing members, in addition to the actual MEAs generating the electricity.
Signs of Struggle in the Fuel Valve
The Dynario has the all-important generating units mounted in the center of the case, one on the front and other on the back. The center of the case also holds a cylindrical Li-ion rechargeable battery manufactured by Sanyo Electric Co., Ltd., and two control boards mounting the power switch and input/output (I/O) pins, among other things.
The fuel tank is located on one side of the case. The case itself has aluminum alloy front and back, with plastic on top and bottom. An engineer in the fuel cell industry commented Toshiba seems to have used a lot of metal parts to maximize durability, strength and other characteristics, given that this is the first volume-production model.
The generating unit positions the generating cell between a stainless steel lattice and a plastic holder that acts as the fuel supply plate. The two are riveted together, making it impossible to remove the generating cell without destroying them.
The stainless steel lattice is the air inlet for the generating cell, while the generating cell control board, fuel pump, fuel valve, and a few other components are mounted on the fuel supply plate side (Fig. 3). The control board holds the ICs controlling the fuel pump, fuel valve, an 8-bit microcontroller, and more.
![[Fig. 3 Multiple Control ICs] The generating unit main board holds control ICs for a number of components, including the fuel pump and fuel valve. Many of them were developed especially for fuel cell application.](http://fuelcellsworks.com/news/wp-content/uploads/2010/01/z3.jpg "z3")
[Fig. 3 Multiple Control ICs
Methanol flows from the tank to the fuel supply plate, and is then pumped through the MEAs (a). The amount of fuel injected from the tank is controlled by the fuel valve (b). A piezoelectric device is used to vary pump internal pressure and inject the fuel (c).
It appears that Toshiba had a tough time designing the fuel valve, as it protrudes 6 mm beyond the other components. While the fuel pump and control board have all been thinned down, only the fuel pump appears to have had insufficient development time. For this reason, it has been positioned off-center and the two generating units adjusted to make room for it, keeping case thickness to a minimum.
The fuel pump itself was manufactured by Murata Manufacturing Co., Ltd. It uses a piezoelectric device, and is quite thin (24 mm × 33 mm × 1.325 mm). The pump discharge rate is probably 0.001 mL/s, with a pressure of 35 kPa.
When methanol fuel is supplied to the generating cell, it first passes through the fuel valve, then through the fuel supply plate inlet. The fuel pump then distributes it throughout the cell from the two holes in the center of the plate.
The generating cell consists of a membrane electrode assembly (MEA) measuring 81 mm × 52 mm, and a collector. The MEA uses four single cells, each measuring 81 mm × 9 mm (Fig. 5). As each cell probably has an electromotive force of about 0.3 V, that means the generating unit would generate a bit over 1 V. The step-up circuit on the generating unit control board probably boosts this to about 5 V.
Fig. 5 Cell Output Density about 25 mW/cm2 The generating unit consists of an MEA with four single cells in series, for a total MEA area of about 40 cm2. There are two generating units, so output density is probably about 25 mW/cm2.
Cell output density can be calculated as about 25 mW/cm2, leading a fuel cell engineer to theorize it was deliberately kept low because of heating issues. Toshiba has said that it developed fluorine- and hydrocarbon-based solid polymer films, but it is unclear which was used in this product. Several fuel cell experts, however, commented that it is most likely the fluorine-based design.
Test Board Used As-Is.
The power switch and I/O pins are both mounted on the control boards. The Dynario is equipped with a Li-ion rechargeable battery, which supplies electricity to the load until output from the generating unit stabilizes at start-up, as well as powering the generating unit control circuit and other components.
The Li-ion rechargeable battery and generating unit both seem to be controlled by the 8-bit microcontroller (with internal flash memory) on the control board that also holds the power switch. Judging from the fact that the microcontroller is a rewritable chip, the number of test lands left on the board and other points, one fuel cell engineer pointed out that they seem to have used the test board design in this product.
The board with the power switch also has a 2 Mbit flash memory, probably used to log an operating history, including charge times and temperature change. The Li-ion rechargeable battery is connected to the board with the I/O pins, supplying power to drive the generating unit circuit through it.
Given that this is the first volume-production fuel cell for mobile gear, Toshiba gave top priority to assuring safety. For example, an auto-stop function has been added to halt operation when it becomes too hot. A temperature sensor at the generating unit air inlet ensures that surface temperature does not exceed a preset maximum. Our tests showed that the auto-stop function triggers when the surface temperature reaches about 45°C.
The fuel cell is said to incorporate other functions as well, such as disabling operation at temperatures of 100°C or higher, and breaking high input currents through the I/O pins.
