Why DC motor starting torque
Because of the armature circuit resistance and inductance are small, rotating body has certain inertial, so when the motor is powered on, starting at the beginning of armature speed and the corresponding counter electromotive force is small, the starting current is very large. Can be up to 15~20 times the rated current. This current will enable grid disturbances, unit from mechanical impact, commutator sparks. So directly closing up moving only applies Yu power not is greater than 4-kilowatt of motor (up moving current for rated current of 6~8 times). motor can divided for two big class: a said Reed magnetic type, completely of DC motor are is Reed magnetic type of, Reed magnetic type of features is charged brush, rotor coil through electric brush provides Reed magnetic current, Reed magnetic current of size decided magnetic field of size also on decided has torque of size. A induction type, squirrel-cage motor is a typical representative of DC motor using Hall device, frequency conversion DC motor (it essentially belongs to AC motors) are also inductive. DC motor rotor magnetic field or magnetic inductive current generates a magnetic field (cage), provided either by permanent magnets (Hall), were relatively weak, less powerful than the excitation current, so it can produce starting torque also is much smaller.