2 Point Starter : Circuit, Working, Differences & Its Applications

A starter is a protection device used to protect the electric motor from overload & short circuits. There are different kinds of starters available for motor like; 2-point, 3-point & 4 point starters. These types of starters mainly include a face plate rotator switch with a set of current-limiting transistors. The main difference between these three starters is No Voltage Coil (NVC). This article provides brief information on one of the types of starter namely; 2-point starter, construction, working & its applications.

What is 2 Point Starter?

Definition of 2-point starter: a starter that is used to restrict the starting current of a DC series motor by starting and controlling its speed is known as a two-point starter. The main function of this starter is to defend the DC series motor from overvoltage and high starting current by restricting the high starting armature current to a secure value, by simply connecting a resistance within the series by the armature only at the starting time. This resistance can be decreased gradually whenever the motor gets speed.

2 Point Starter Working

A 2-point starter includes two main parts; a rheostat & a set of contacts. In this starter, the rheostat is mainly used for controlling the flow of current throughout the motor whereas the set of contacts is used for firstly start & after that control the speed of the motor. Whenever the contacts are closed, the motor is directly connected to the power supply to start. Once this motor gets speed, the set of contacts will be opened gradually by increasing the resistance within the circuit & decreasing the flow of current to the motor to control its speed. So, this kind of starter is used commonly in applications wherever exact speed control is required like in industrial equipment & machinery.

2-Point Starter Circuit Diagram

The circuit diagram of the 2-point starter is shown below. This circuit is similar to a three-point and four-point starter because it includes a starting resistance ‘R’ which is subdivided in between the contact studs from 1 to 5. In this circuit, the ‘H’ is a starting handle and is turned on a single side where the other side is easily moved from a strong ‘S’ spring. So that it makes contact with every stud during the starting operation. The starter in the circuit is provided simply with a protective device with no load release.

Working

A two-point starter works by starting the dc motor which has the over-speeding trouble because of load loss from its shaft. To start the DC motor, the control arm will be turned in a clockwise direction from its OFF to ON position against the spring tension. The L & F are two starter points that are simply connected through the motor terminals & supply.

The control arm will be held within the turn-ON position through an electromagnet. Here, the hold-on electromagnet is simply connected with the armature circuit in series. If the DC motor loses its load, then the flow of current reduces, thus the electromagnet strength also reduces. The control arm comes back to its OFF position because of its spring pressure and prevents the DC motor from overspending. Whenever the voltage supply reduces considerably, the starter arm can also return to its OFF position.

Difference between 2-Point Starter and 3-Point Starter

The difference between 2-point starters and 3-point starters includes the following.

Advantages & Disadvantages

The advantages of a 2-point starter include the following.

• This starter helps protect the motor from drawing maximum starting current.
• These starters protect from short circuits and overload faults.
• When the power supply is not there then it automatically turns OFF.

The disadvantages of a 2-point starter include the following.

• It offers no adjustable starting characteristics and a soft stop is not possible at all
• These are mechanically tough
• This starter may decrease the lifespan of the motor.
• This is not used for all types of motors.
• This starter can cause a major dip in voltage.

Applications

The applications of the 2-point starter include the following.

• 2 point starters are used with DC series motors.
• These types of starters are used in cranes.
• These are used in railways for starting and stopping the rail.
• These starters help in starting the dc motor which has an over-speeding problem because of load loss from its shaft.
• These are used normally in applications wherever the motor is anticipated to work above standard speed

Thus, this is an overview of the two-point starter, circuit, working, advantages, disadvantages, and applications. These starters are face-plate type manually operated starters that are used for starting DC series motors because these motors have two terminals only for their insertion within the motor circuit. Here is a question for you, what are four-point starters?