The present invention relates to a drive unit for at least one electric motor. The drive unit comprises: 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 (2), at least one inverter producing current to the motor, an energy storage (C) arranged at the output of the power source for smoothing direct current and storing energy recovered during braking of the motor, and a discharge circuit (8,10) for discharging the energy stored in said energy storage, wherein the discharge circuit includes a power resistor (8) arranged to discharge the energy stored in the energy storage. The drive unit further comprises a first and a second switch (5,6) arranged between the power source and the energy storage, and the switches are arranged such that they are in default positions when there is no control power in the drive unit, and the drive unit is arranged such that the power source is disconnected from the motor and the energy storage is discharged via said power resistor when the switches are in their default positions.