Saft lithium-ion batteries take to the waves
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Saft Rechargeable Battery Systems product story
Edited by the Engineeringtalk editorial team
Mar 20, 2001
A new design of water scooter is made possible by high-power, lightweight rechargeable lithium-ion batteries from Saft.
A new design of water scooter is made possible by high-power, lightweight rechargeable lithium-ion batteries Saft High Energy rechargeable lithium-ion batteries, originally designed to power electric vehicles, are now taking to the waves in the new generation of Delfjet electric jet-propelled water scooters.
The lithium-ion batteries have proved so superior to the nickel-cadmium batteries used in the prototype, offering nearly twice the capacity at around one third of the weight, that it is believed that the Delfjet design would not be a viable commercial proposition without them.
The Delfjet concept was developed in Germany by Jurgen Grimmeisen, who wanted a watersports machine capable of pulling a swimmer with high speed and dolphin like manoeuvrability both on the water surface, and below it.
The reaction to the initial prototype, which was powered by an underwater petrol-engine, showed that as well as great potential in the sports and leisure market, it would also have more serious applications such as for lifeguard duty on beaches.
Later prototypes progressed through more hydrodynamically styled versions, designed to reduce water resistance, while the method of propulsion changed to a silent, high-tech, Newtor brushless 42V electric motor driving an impellor for the water jet.
Power for the electric motor was drawn originally from conventional nickel-cadmium batteries, but their low endurance (25Ah capacity) and high weight (35kg) was a problem, especially as the design weight of the Delfjet without batteries was just 16kg.
The Delfjet design team called on the Saft Industrial Battery Group to find an alternative battery technology.
It was soon apparent that the ideal answer would be the High Energy (HE) lithium-ion cells, which Saft had originally developed for electric vehicle applications to pack as much power as possible into a lightweight and space efficient package.
These cells have a nominal capacity of 43Ah and a nominal voltage of 3.6V.
This enables a 42V battery to be constructed using just 12 cells in series, with a total weight of 12kg, virtually doubling the battery capacity compared to the original nickel-cadmium batteries at around one third of the weight, and in a much smaller volume.
The batteries are housed in a watertight compartment within a removable nosecone unit which simply plugs into position within the main body of the Delfjet.
The Delfjet pilot lies prone on the machine and steers by weight-shift for both left/right and diving/surfacing.
The 3.6kW (5 horse power) standard sport version, which can be operated without a licence, is capable of reaching surface speeds of 25km/h or 20km/h below the surface, with an endurance of 60 minutes.
The Delfjet can dive up to 2.5m below the surface after which a safety switch will automatically cut the power.
As a further safety measure the motor will stop immediately the throttle is released and, thanks to its low centre of gravity achieved by the use of lightweight batteries, the Delfjet will float gently on the surface of the water, where it can be used as a swimming aid.
A 5kW (7 horse power) professional version of the Delfjet, powered by 14 cells in series, is also available for more serious licenced users such as for lifeguard duties, professional diving or military applications.
Trained divers can also over-ride the diving fail-safe to reach depths of 40m, while for professional diving applications the Delfjet can be adjusted to dive as deep as 120m.
The top-of-the-line Delfjet features 28 cells (two parallel groups of 14 in series) which provide a three hour duration.
The Saft lithium-ion batteries are fitted with an electronic control management system for the monitoring of charge and discharge voltages, as well as temperature, and can be charged in-situ in only two hours.
If it is not possible to wait for recharging then the nosecone, which contains the batteries, is simply unplugged as a complete unit and replaced by another nosecone holding a freshly charged battery.
The HE cells are capable of more than 1000 charge/discharge cycles, and in this application are expected to have a service life of over 18 years.
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