According to Sprint Electric, these compact regerative four-quadrant DC drives use little space and are very energy efficient. This system lowers demand from the incoming AC supply by using its ability to return the braking energy to the mains. If these drives are operated on equal driving/braking cycles, the cost of running the drive is only the electrical losses in the motor and drive. Fully controllable in both motoring and braking modes,this DC drive package also features less significant lower-speed motoring losses when compared to AC motors; better power conversion efficiency across a wider speed range; and an improved power/torque conversion at lower motor speeds, typically from 10:1 to in excess of 100:1 speed ranges, thereby eliminating the need to oversize the motor to achieve useable low-end torque. The DC drive develops more energy-efficient, full-rated torque at or near-zero speeds, the company says, in exactly the same way as throughout the entire speed range. This is because torque is generated by the linear interaction of the two magnetic fields of the armature winding and the field winding. The commutator ensures that the axes of these magnetic fields are constantly kept perpendicular to each other—in the optimum torque-producing position. The resultant torque is practically a linear function of the two DC armature and field currents. The heat dissipation in the windings at a given torque is constant at any speed (including zero), and therefore the cooling arrangements can be dealt with in standard fashion. The four-quadrant DC drive can also independently set the required current levels in each winding to meet a certain load requirement without the need for complicated algorithms. Taking up little panel space and mounting on standard DIN rail, these drives are designed for use with motors up to 1.8 kW and 2 HP. With four-quadrant operation, torque can be reversed very gently or almost instantly, as required. The DC motor is usually composed of an open-frame through-vent construction.