20 April 2021

Difference Between DOL Starter and Soft Starter

DOL starter and soft starter are both two different types of motor starter. They are used for the safe starting and stopping of an induction motor. These two motor starters are vastly different from one another. So here this article gives the difference between soft starter and soft starter to better understand this topic.

What is a DOL starter? 

DOL stands for, direct online stater, it is a method of starting a three-phase induction motor. In DOL, an induction motor is wired directly into its three-phase supply, and the DQL starter supplies the motor terminals with the full line voltage.

What is a Soft starter?

The soft starter is a semiconductor-based motor starter that regulates the voltage supply to the motor with a thyristor. To minimise the inrush current that can harm the motor windings, the voltage is decreased at startup. When the motor reaches its rated speed, the voltage is progressively increased.

Difference between Direct online starter and soft starter:

  • DOL is a type of motor that supplies full voltage to the motor at startup, while the soft starter is a type of motor starter that reduces the voltage to the motor at startup.
  •  DOL does not reduce the starting inrush current, while the soft starter reduces the starting inrush current.
  • DOL is used for low-rated motors below 5 Hp, while the soft starter is used for heavy motors above 5 Hp.
  • DOL cannot prevent the mechanical jerks at startup, while soft starters are no mechanical jerks at starting and stopping of the motor.
  • Direct online starters offer high starting torque, while soft starters offer low to medium starting torque.
  • DOL has a very simple design, while the soft starter has a very complex design with logic circuitry.
  • The huge current draw causes voltages to dip in the circuit, while the soft starter does not cause any voltage dip in the line.
  • DOl is very cheaper, but the Soft starter is very expensive.
  • DOL is smaller in size, while the Soft starter is larger in size due to the complex circuit and large heat sinks required for thyristors.
  • DOL is no acceleration or deceleration control, while the SOft starter acceleration and deceleration can be programmed for starting and stopping a motor.
  • Dol starter has efficiency is less than a soft starter, while the soft starter has high efficiency.
  • DOl motor needs frequent maintenance, while the Soft starter needs less maintenance than the DOL starter.
  • DOL startup cycles are limited to a few times in a minute otherwise the winding would overheat, while the soft starter increases the startup cycles of the motor significantly.
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