Patent ID: 8581535

Claim:
A drive unit comprising: a control power supply (+18V) for supplying the drive unit with control power, a power source ( 1 ) producing direct current to one or more inverters, at least one inverter ( 2 ), an energy storage (C) arranged at the output of the power source for smoothing the direct current and storing energy recovered during braking, and a discharge circuit ( 8 , 10 ) including a power resistor ( 8 ) for discharging energy stored in said energy storage, wherein the drive unit further comprises a first and a second switch ( 5 , 6 ) arranged between the power source and the energy storage, the switches are arranged such that they are in default positions when there is no control power in the drive unit, the drive unit is configured such that the power source is disconnected and the energy storage is discharged via said power resistor when the switches are in their default positions, and the first switch ( 5 ) is controlled by the control power of the drive unit and is arranged to switch to the default position when there is no control power in the drive unit, and an engaged position when there is control power in the drive unit.