A new concept for marine electric motors

Most electric motors on the market today use permanent magnets or an electric current passing through coils of copper to create the magnetic poles and fields that make the motor turn. The new motors that have been developed by Volabo use a cage made up from aluminium strips to create the magnetic field.

By pairing these strips in alternative ways during operation, a variety of different magnetic pole formats can be created, each combination giving the motor different characteristics. A large number of pole pairs is selected for high acceleration with high torque demand, whereas in rolling operation at constant speed, a smaller pole pair number is used.

With conventional electric motors the designers try to find a balance within the set parameters that creates a good compromise between the RPM, the torque and the efficiency. With the new motor the ability to vary the pairings of the coils means that these parameters can be varied to match the demands on the motor and this gives a lot more flexibility for marine operation. For instance the motor can be programmed to provide a high torque when the boat is coming onto the plane and then the torque can be reduced and the RPM increased once on the plane. As a result, the manufacturer claims that the electric motors can achieve significantly higher efficiencies than conventional electric motors, especially in the partial load range.

With the Volabo motor the control of the various pairings of the coils is done under electronic control so that the operator does not have to make any adjustments. This means that the load and the motor speed will be varied according to the demands on the motor giving a lot more flexibility.

The designers claim that one of the advantages of the new concept is that more powerful electric motors can be used whilst still operating at the relatively safe voltage of 48. Volabo has used a 100 kW version in a road vehicle but for their first marine use the motor is rated at 50kW. The motor is compact with a diameter of 30cms and a length of 45cms and the total weight of 60kgs includes the control system. The manufacturer expects 48 volt motors up to 300kW to be feasible, with the lower production cost and compact design expected to attract interest.