why DC motors are always started through starters?
Not only DC motors but also AC motors. Starter is required for only large size motors since large size motors take more time to gain speed than small motors. When motor is started it has low speed which does not produce back emf hence very large current is drawn by the motor which may destroy the coil inside. Since small motors gain speed very quickly they produce back emf very fast at start hence they do not require starter.
Always? not in my experience. I suppose that depends on ones definition of starter if the definition includes anything that starts a motor, then the answer is obvious, if nothing starts the motor, then the motor doesn't start. Perhaps you could add some more information, like the size of the motor and it's application.
DC motor starters The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current, is the armature resistance. Usually the armature resistance of a motor is less than one ohm; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices. * Therefore the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation build up, the resistance is gradually cut out. However, if you one can produce initial movement of the armature then you do not need a resistance starter!
Not always ,It depends on it c/cs and starting current precisely, as an example your CD driver contains a dc motor but it is too small no need to stater.
