Apparatus for use in recycling of electric motors and method of recycling an electric motor

Abstract

An apparatus 10 for at least partially demagnetising the magnets of a multi-phase permanent magnet motor 1 comprises at least two terminals for connection of the apparatus to at least one phase of the

Claims

1. An apparatus for at least partially demagnetising the magnets of a multi-phase permanent magnet motor comprising:at least two terminals for connection of the apparatus to at least one phase of the permanent magnet motor, andan impedance located in a path between the two terminals, the impedance combining with the inductance of the motor phases connected to the terminals to form a resonant circuit whereby the resonant frequency of the combined apparatus and motor corresponds to a frequency of a back emf generated in the phase windings as the motor is rotated, andoptionally including a switch located in a path between the two terminals, a first side of the switch being connected through a first conductive path to one of the terminals and a second side of the swich connected to the other of the two terminals, the switch when closed providing an electrical path between the two terminals that includes the impedance and when open breaking that path.

2. Apparatus according to claim 1 wherein the apparatus is connected to two phases of a motor, with each phase connected to a respective terminal of the apparatus.

3. Apparatus according to claim 1 or claim 2 in which the impedance comprises a capacitance such that the combination of the apparatus and the motor phase windings forms an LC resonant circuit.

4. Apparatus according to claim 2 in which the capacitance comprises a single capacitor or a set of capacitors connected in series or in parallel or in a mix of series and parallel connection between the switch and a terminal of the apparatus.

5. Apparatus according to claim 1, 2 or 3 in which the impedance may include one or more resistors that are located between the capacitor and the terminal or between the capacitor and the switch.

6. Apparatus according to any preceding claim in which the impedance comprises a capacitor connected in series with one or more inductors that are located between the capacitor and the terminal or between the capacitor and the switch.

7. Apparatus according to any preceding claim which the impedance further comprises a further capacitance on the opposite, second, side of the optional switch to the first capacitance in a continuous path from the other of the at least two terminals and that side of the switch.

8. Apparatus according to any preceding claim in which the magnitude of the reactance matches the magnitude of the motor reactance at resonance, but they are 180 degrees out of phase.

9. Apparatus according to any preceding claim comprising only passive components in the paths between the two terminals.

10. Apparatus according to any preceding claim in which the optional switch comprises a contactor switch capable of being safely closed as the motor is rotating.

11. Apparatus according to any preceding claim further comprising an drive for rotating the motor when connected to the terminals of the apparatus up to a speed that causes a back emf to be generated having a frequency equal to or greater than the resonant frequency.

12. Apparatus according to claim 10 that further includes a means for selectively connecting the drive to the motor rotor and disconnecting the drive whilst the rotor and the drive are spinning.

13. Apparatus according to any preceding claim comprising a control circuit that is configured to cause the apparatus to carry out the steps of the process in response to a single instruction to start the process.

14. Apparatus according to any preceding claim which comprises a configurable impedance enabling the apparatus to be tailored to a range of different motors which have coil windings of differing inductances.

15. An apparatus of any preceding claim in combination with an electric motor in which the capacitance of the apparatus is selected to have a reactance that is substantially equal but opposite to the reactance of the motor phase windings connected to the apparatus such that at the resonant frequency the reactance of the or each closed loop formed by the motor windings and the apparatus approaches zero giving a peak current flow for a given back emf.

16. A method of at least partially demagnetising the magnets of a permanent magnet motor of the kind comprising a rotor having a plurality of permanent magnets and a stator comprising a plurality of phase windings the method comprising the steps of: a) connecting an apparatus comprising an impedance between two or more phases of the motor,b) rotating the motor rotor via an external device,c) whereby upon the motor reaching a predefined rotational speed that generates aback emf having a frequency that is equal to or close to the resonant frequency of the resonant circuit formed by the serially connected impedance of the apparatus and inductance of the phase a current flows through the windings that in turn generates a magnetic field that is sufficient to at least partially demagnetise the rotor magnets when they interact with the generated magnetic fields.

17. The method of claim 15 comprising first rotating the motor in one direction in step (b) and after step (c) repeating steps (b) and (c) with the motor rotating in the opposite direction.

18. The method of claim 15 or claim 16 in which the apparatus connected to themotor phases comprises an impedance in series with a switch and comprising performing step (a) with the switch open initially and closing the switch in step (c).

19. The method of claim 17 comprising at step (b) rotating the motor at a predefined rotational speed where the frequency of the back emf in the motor is above the resonant frequency of the resonant circuit formed by the motor windings and capacitances of the apparatus and after the switch is closed the motor is slowed down to pass through the resonant frequency.

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