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In more
detail: Oxygen is subtracted from the air and the hydrogen
is fed from the high pressure tank to the fuel cell. Therefore,
the hydrogen pressure is reduced in 2 steps, by means of
regulators and valves supplied by Swagelok. The first step
is from 200 bars to 30 bars and the second step is from
30 bars to 5.5 bars. All hydrogen systems have been tested
by Leak Control and can withstand a pressure of 1100 bars.
The
8 kW fuel cell consists of several devices, from which the
most important one is the stack. In the stack, the hydrogen
(H2) and oxygen (O2) are separated by a membrane. At the
anode side, a catalyst splits the hydrogen molecules into
protons and electrons (2H2 -> 4H+ + 4e-). The protons can
go through the membrane to the oxygen at the cathode side,
but the electrons cannot and have to go through an external
circuit, forming a complete circuit. The reaction on the
cathode side is then as follows: 4H+ + 4e- + O2 -> 2H2O.
As you can see, pure water is the only exhaust coming from
the fuel cell!
For
the energy storage system, 32 Maxwell Boostcaps are used.
A boostcap is an ultra capacitor, a sort of battery which
can store and release energy really fast. The capacity of
one boostcap is 3000 Farad, which is incredibly high compared
to capacitors used in electronics (in the order of microFarads).
Not only energy generated by the fuel cell, but also energy
recovered by regenerative braking, will be stored in these
boostcaps. When the boostcaps are fully charged, the Forze
II has a maximum power of 28 kW (38 HP).
The
voltage produced by the fuel cell is not high enough to
charge the boostcaps, so a DC/DC converter is implemented
in the kart. It converts the voltage coming from the fuel
cell to the desired voltage for the ultra capacitors. Another
important property of the DC/DC converter is that it works
as a diode. The DC/DC converter makes it impossible to have
a current flowing back into the fuel cell. The DC/DC converter
is developed in cooperation with ECN.
The
two motors used are Perm 132 DC electro motors. These motors
are not connected directly to the boostcaps, because a throttle
is needed. Each motor is controlled by a separate motor
controller. This way an electronic differential is possible.
Currently, we are developing a motor controller which can
control both motors, but is half the weight and just a third
of the size of the two off-the-shelf controllers. This controller
will also have a lot more features, like for instance a
reverse mode.
All
the electronic parts are controlled by two printed circuit
boards (PCB’s), which Greenchoice Forze developed in cooperation
with Betronic. The PCB’s were produced by Cyner. Most of
the micro controllers placed on these PCB’s are supplied
by NXP.
Of course,
all this technology has to be protected by bodywork. The
bodywork is made of a special composite, which is by far
not as polluting as other composites. A natural fiber, flax,
is used for bodywork of the Forze II in combination with
a bio-based resin. This bio-based resin is developed by
DSM. The whole bodywork is 70% renewable. The Forze II is
the first application of this composite and in that way,
it served as a testing platform for DSM. After it was finished,
the whole bodywork was painted by Van den Berg Autoschade
with Glasurit products.
The
Forze II is, from a mechanically point of view, constructed
as a race kart. The most significant feature of such a vehicle
is the lack of a suspension. All damping has to be done
by the chassis (5) itself, which demands special care during
design and construction. The chassis of the Greenchoice
Forze kart, the Forze II, has been developed in cooperation
with Kombikart Racing Parts B.V.
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