DOL (Direct Online) Motor Starter

Published by ASHA CHAUHAN on

DOL Starter :- It is very easy circuit, Full form of DOL – Direct online Starter/circuit.

Very easily design circuit, controlling and operating. Provide a power for motor start-up time full starting torque at starting. DOL Starter a power connection supply to motor terminal in delta connection.

DOL ( Direct online ) Starter is used for small motor, fan and like that small conveyer means No more load take this starter, because it was more used full only for minimum load machine.

What is DOL Starter ??

The most fundamental, economical, as well as an easy method for running a three-phase induction motor is named as the DOL starter. The attractiveness of this kind of starter is, it can be connected straightly to the motor, and it doesn’t affect the induction motor.  The Direct Online Starter consists of a protective device as well as main contacts. Let us discuss an overview of DOL.

The Direct Online starter includes circuit breaker or MCCB, overload relay and contactor for the protection of motor.

The unlocking of an electromagnetic contactor can be done through the thermal overload relay beneath fault conditions. Usually, the controlling of contactor can be done by using separate buttons like start and stop.

An auxiliary contact is used on the contactor across the start button because the contactor is electrically latched while the working of an induction motor.

DOL Wiring diagram

The wiring or connections of DOL starter includes mainly four parts such as main contact, normally open contacts, normally closed contacts, and connections of relay coil as well as thermal overload relay.

The connection of the main contact can be done by using the following steps.

  • The Contactor can be connected between relay coil, thermal overload relay, and voltage supply
  • The L1 contactor is connected to R-phase circuit breaker or MCCB
  • The L1 contactor is connected to Y-phase using circuit breaker or MCCB
  • The L3 contactor is connected to B-phase using circuit breaker or MCCB

The connection of NO/NC contact

DOL Starter

The connection of NO/NC contact can be done by using the following steps.

  • The normally open contact is from contactor points.
  • The Contactor Point connected to Start Button & Point of Contactor is connected to general Start wire or stop switch.

The normally closed contact id from contactor points.

The connection of thermal overload relay (OLR)

The connection of thermal overload relay can be done by using the following steps.

  • The T1, T2, and T3 are connected to the relay
  • This relay is connected among motor as well as main contactor
  • The normally closed connection of this relay is connected to stop switch as well as the mutual connection of start or stop switch.

How to work DOL starter ??

DOL Starter

The 3 phase DOL starter wiring diagram is shown below. The DOL starter joints the 3 phase main wiring with the induction motor namely L1, l2 and L3 when the start switch is pressed.  Generally, the Direct Online starter working can be done in two different stages namely DOL starter control circuit and DOL starter power circuit.

The control circuit is attached to any two of the phases and activated from the two phases only. Whenever we push the start switch, then the current will flows through the control circuit as well as contactor wind also. The contactor coil can be boosted by the current to make the contacts close, and thus three phase supply becomes obtainable for motor.

When we push the stop button, then the flow of current through the contact will be stopped, therefore electrical power supply to the induction motor will not be accessible, as well as the same thing will occur while overload relay works.

As the motor supply breaks, then the machine will move toward to relax. The contactor coil gets power supply even though we open start switch because it will obtain supply from the main contacts as demonstrated in the above Direct Online starter circuit diagram.

Advantages & Disadvantages

The advantages of this starter include the following.

  • The Direct Online starter is an inexpensive starter.
  • It gives almost complete starting torque at the beginning.
  • The designing, operating and controlling this starter is very easy.
  • Understanding and troubleshooting are very easy.

The disadvantages of this starter include the following.

  • Starting current is very high
  • This starter causes an important dip in voltage, therefore appropriate only for small motors.
  • The lifespan of the machine can be reduced.
  • It is hard mechanically.
  • Needless high opening torque
Applications of DOL Starter

The applications of this starter include the following.

These starters are very useful in motors when the 3-phase induction motor is at low rating as well as the input is very low (5V) then that will function at low speeds & lower rating.

These starters are used where maximum currents do not cause any damage such as to run small compressors, conveyor belts, water pumps, fans, etc.

Thus, this is all about DOL Starter, and the main features of this DOL include three phase connection, High starting torques, voltage dips, mechanical load, current peaks, and very easy switching devices. These are mainly applicable to where maximum currents do not cause any damage such as to run small compressors, conveyor belts, water pumps, fans, etc.

What is single phase DOL starter wiring diagram?


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