Rogatti motor Germany Rogatti model Rogatti price

Rogatti motor is a single-phase AC commutator motor, suitable for applications with single-phase power supply that require speed regulation and reversal of rotation direction. The stator winding is powered by a single-phase source, and the rotor is an armature winding with a commutator short-circuited via brushes. The brushes can be moved to any position relative to the stator winding as needed. By shifting this position, the rotor's direction of rotation, mechanical characteristics, and operating speed can be changed. When the brushes deviate counterclockwise from the geometric neutral axis, the rotor rotates clockwise; when the brushes deviate clockwise from the geometric neutral axis, the rotor rotates counterclockwise.

Rogatti motor advantages

The motor operates in a self-controlled manner, so it does not require additional starting windings on the rotor like synchronous motors under heavy-load start-up with variable frequency drive, nor does it produce oscillations or lose synchronism during sudden load changes. For small and medium-capacity brushless DC motors, the permanent magnets often use rare-earth neodymium-iron-boron (Nd-Fe-B) materials with high magnetic energy product. Therefore, the volume of rare-earth permanent magnet brushless motors is reduced by one frame size compared to three-phase asynchronous motors of the same capacity. Over the past thirty years, research on variable frequency speed control for asynchronous motors has ultimately focused on finding methods to control asynchronous motor torque. Rare-earth permanent magnet brushless DC motors will surely demonstrate advantages in the field of speed control due to their wide speed range, compact size, high efficiency, and small steady-state speed error. Brushless DC motors possess the characteristics of brushed DC motors and are also frequency-varying devices, hence they are also known as DC variable frequency, with the internationally common term being BLDC. The operating efficiency, low-speed torque, and speed accuracy of brushless DC motors are superior to inverters using any other control technology, making them worthy of industry attention. Products have been produced exceeding 55kW, and can be designed up to 400kW, meeting the industrial needs for energy saving and high-performance driving.

Rogatti motor mechanical characteristics

The reason motors are widely used in electric vehicles is that they offer two main advantages compared to traditional brushed DC motors. (1) Long service life, maintenance-free, and high reliability. In brushed DC motors, due to the high motor speed, brushes and commutators wear out quickly, generally requiring brush replacement after about 1000 hours of operation. Additionally, the technical difficulty of reduction gearboxes is significant, particularly the lubrication of transmission gears, which is a major challenge in brushed solutions. Thus, brushed motors suffer from issues such as high noise, low efficiency, and prone to failures. Therefore, the advantages of brushless DC motors are evident. (2) High efficiency and energy saving. Generally, because brushless DC motors lack friction losses from mechanical commutation and gearbox consumption, as well as losses from speed control circuits, efficiency can typically exceed 85%. However, considering the best cost-performance ratio in actual design and to reduce material consumption, they are generally designed for 76%. In contrast, the efficiency of brushed DC motors, due to consumption by the gearbox and overrunning clutch, is typically around 70%.

Rogatti motor starting

The motor armature circuit resistance and inductance are both small, while the rotating body has a certain mechanical inertia. Therefore, when the motor is connected to the power supply, the armature speed and corresponding back EMF are very small at the beginning of start-up, resulting in a large starting current. The maximum can reach 15 to 20 times the rated current. This current can cause disturbances to the power grid, mechanical shock to the unit, and sparking at the commutator. Therefore, direct-on-line starting is only suitable for motors with power not greater than 4 kilowatts (starting current is 6 to 8 times the rated current). To limit the starting current, a specially designed variable resistor is often connected in series in the armature circuit, with its principle wiring shown in Figure 1. During the starting process, as the speed continuously increases, each segment of the resistor is short-circuited step by step in time, keeping the starting current within a permissible value. This starting method is called series resistance starting, which is very simple, with lightweight equipment, and is widely used in various small and medium-sized DC motors. However, due to high energy consumption during the starting process, it is not suitable for motors that start frequently or for medium and large DC motors. But for certain special requirements, such as urban trams which start frequently, series resistance starting is usually adopted to simplify equipment, reduce weight, and facilitate operation and maintenance. For DC motors with larger capacity, reduced voltage starting is usually employed. This involves supplying power to the motor armature from a separate adjustable DC power source; controlling the power supply voltage allows for smooth motor starting and speed regulation. This method requires more complex power supply equipment.

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