The electric drill and electric hammer used in the home decoration are more familiar and different electric tools, they are usually equipped with the universal motor , with speed, steering transformation and torsion characteristic adjustment and other basic control functions, to adapt to different task objects. The question is, why exactly is the series excitation motor drive mode used?
On the one hand, in order to simplify the control mode and minimize the weight of the tool as much as possible, on the other hand, we must eliminate the danger caused by drilling and vibration blade overload. The external characteristics of the drive motor are relatively soft, that is, when the rated load is exceeded, the motor speed decreases rapidly with the increase of the load.
The motor power is AC power supply, the motor itself is a classic DC motor. The excitation winding and armature winding form a series loop by brush and commutator, which has very unique advantages: both AC or DC power supply; high working speed, small volume, light weight, smooth speed, wide range, simple and reliable control; speed is basically constant when less than rated load, and speed drops rapidly beyond a certain load value. Therefore, most electric tools use string motors, simple control, high cost performance, safety and reliability and other excellent characteristics to establish the firm position of string electric motors in the field of electric tools. The basic structure of the motor for the stator, armature and casing, specific use conditions, such as frequent start, high speed, large vibration, and variable load conditions, etc., can lead to motor blocking, then motor stator winding and armature temperature rise, in practical application we will feel the electric tool serious heat.
For the above reasons, the armature quality and performance requirement of the series motor is very high. The universal motor rotor part of "coil commutator" armature, through the carbon brush and stator part of the excitation winding directly connected, so the armature current and excitation current size is exactly the same, although essentially is a typical dc motor, but different from ordinary dc motor, namely starting torque is larger, soft characteristics, so power tools are widely used in string motor rather than ordinary dc motor.
