Features of single-phase universal motors:

1. It can be used for both AC and DC;

2. The speed is high, generally 4000~35000 rpm;

3. Convenient speed regulation (voltage and speed regulation), and the speed has nothing to do with the power frequency;

4. Large starting torque, 4~7 times the rated torque;

5. The mechanical characteristics are soft and the overload capacity is strong;

6. The efficiency is generally 30%~70%;

7. Small size and lightweight;

8. Shortcomings: carbon brushes and commutator are worn, reversing sparks, electromagnetic interference, etc.

Single-phase universal motors have four characteristics when the power supply voltage is constant

1. The characteristic of the relationship between current and torque: I=f(T), which is similar to a parabolic characteristic. Without considering the influence of magnetic circuit saturation, T∝I2;

2. The relationship between current and speed: I=f(n), which is similar to a hyperbolic characteristic. When the power supply voltage is constant and the effect of magnetic circuit saturation is not considered, n∝(1/I).

3. The characteristic of the relationship between speed and torque: n=f(T). This characteristic curve is a soft characteristic.

4. The relationship between power factor and torque: COS(ф)=f(T), it is a straight line close to the level. The power factor of this type of motor is high, above 0.9, and the high-speed motor can be above 0.95.

Besides, the no-load speed of a single-phase universal motor is theoretically infinite, so the no-load speed is very high. Therefore, usually considering the mechanical strength of the motor, no-load operation is not allowed for fear of "speeding". But, since the bearing friction, pressure and friction brushes, and armature wind friction need ventilation, fan with the armature, the motor is equivalent to adding a small load, the actual load speed is not Maybe infinite. However, the no-load speed is still relatively high, generally 1.5 to 3 times the rated speed, or even higher.