DC motors in various designs

In addition to AC motors, geared motors, and frequency converters, we also offer DC motors. For larger orders, we offer an exceptionally favourable price-performance ratio. The following DC motors are available from us: permanent magnet DC motors, shunt-wound motors, and series-wound motors.

Permanent magnet DC motor!

In smaller motors (actuators, blowers, and radiator fans in motor vehicles), the stator magnetic field is often generated by permanent magnets. With the development of high-quality DC motors, these magnets have become increasingly powerful, now allowing the construction of motors whose performance is comparable to that of electrically excited motors. However, the cost of permanent magnets is often higher than that of an excitation winding in larger motors. Like separately excited machines, permanent magnet DC motors have very high inrush currents. Their operating characteristics are explained by the underlying mathematics. Permanent magnet machines have the advantage that no energy is required to generate the magnetic field. This improves efficiency, especially at low overall power outputs. The disadvantage is that field weakening is impossible, thus limiting the possible speed range.

DC motor with smooth surface

Shunt-wound motor

In a shunt-wound motor, the field winding and armature winding are connected in parallel. AC operation is difficult because the field and armature currents have different phase relationships due to the high reactive component of the current through the field winding (high inductance). The speed of large shunt-wound motors is almost independent of the load. Shunt-wound motors can run away if the field circuit is interrupted, as the speed and current draw increase drastically when the field collapses, even with the same supply voltage. Shunt-wound motors can operate as generators (e.g., for braking) if an auxiliary voltage source or residual magnetism ensures that excitation is present when braking begins. With increasing excitation or speed, the generated voltage also increases – this is the voltage that opposes the supply current during motor operation and ensures a constant speed. It is therefore also called back EMF. The armature terminals are designated A1 and A2, and the field winding terminals E1 and E2.

Series-wound motor

The series-wound motor, also called a main-wound motor, has its field winding and armature winding connected in series. Unlike a shunt-wound motor, the field winding must therefore have a low resistance. When powered by alternating current, both the field and the armature current reverse direction after each half-cycle, allowing the motor to be used with AC voltage. However, to prevent eddy currents, the stator's iron core must be made of laminated steel. Starter motors for internal combustion engines are also series-wound motors. The speed of series-wound motors is highly load-dependent (series-wound behaviour). If the torque output decreases, the armature speed increases due to the lower current and the resulting weakening of the field. This can lead to the motor "running away," meaning it destroys itself due to the centrifugal forces. Therefore, series-wound motors must be operated with a minimum load (motor fan, gearbox, etc.). Series-wound motors, especially when operating on AC voltage ("universal motor," e.g., in vacuum cleaners), have a significantly lower inrush current than shunt-wound or permanent magnet motors. However, they deliver a high starting torque for a short period. Therefore, they are used in starters, trams, and electric locomotives, where they can withstand short-term overloads.