Direct Online (DOL) Starter
DOL Direct Online Starter is the simplest form of motor starter that connects the motor
directly to the power supply. It consists of a magnetic contactor that connects the motor
with a supply line & an overload relay for protection against overcurrent. There is no
voltage reduction for safe starting a motor. Therefore the motor used with such starters
has below 5 hp rating. It has two simple push buttons that start & stop the motor.
Pressing the start button energizes the coil that pulls the contactors together to close
the circuit. And pressing the stop button de-energizes the contactor’s coil & pushes its
contacts apart thus breaking the circuit. The switch used for turning ON/OFF the power
supply can be of any type such as rotary, level, float, etc.
Although, this starter does not provide safe starting voltage the overload relay provides
protection against overheating & overcurrent. The overload relay has normally closed
contacts that energize the contactor’s coil. When the relay trips, the contactor’s coil
de-energize and break the circuit.
, Advantages of DOL Motor Starter
● it has a very simple & cost-effective design.
● It is very easy to understand & operate.
● it provides high starting torque due to the high starting current.
Disadvantages of DOL Motor Starter
● The high inrush current can damage the windings
● The high inrush current causes voltage dip in the power line.
● It is not suitable for heavy motors
● It can decrease the lifespan of a motor
DOL Direct Online Starter is the simplest form of motor starter that connects the motor
directly to the power supply. It consists of a magnetic contactor that connects the motor
with a supply line & an overload relay for protection against overcurrent. There is no
voltage reduction for safe starting a motor. Therefore the motor used with such starters
has below 5 hp rating. It has two simple push buttons that start & stop the motor.
Pressing the start button energizes the coil that pulls the contactors together to close
the circuit. And pressing the stop button de-energizes the contactor’s coil & pushes its
contacts apart thus breaking the circuit. The switch used for turning ON/OFF the power
supply can be of any type such as rotary, level, float, etc.
Although, this starter does not provide safe starting voltage the overload relay provides
protection against overheating & overcurrent. The overload relay has normally closed
contacts that energize the contactor’s coil. When the relay trips, the contactor’s coil
de-energize and break the circuit.
, Advantages of DOL Motor Starter
● it has a very simple & cost-effective design.
● It is very easy to understand & operate.
● it provides high starting torque due to the high starting current.
Disadvantages of DOL Motor Starter
● The high inrush current can damage the windings
● The high inrush current causes voltage dip in the power line.
● It is not suitable for heavy motors
● It can decrease the lifespan of a motor
