ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

How to Learn DOL Electric Motor Control – A Basic Motor Controller Guide for Direct On Line Electrical Motor Controls

Updated on January 27, 2013
By Zureks (Own work) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0) or GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
By Zureks (Own work) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0) or GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

The electric motor is by far one of the best known invention ever developed by the ingenuity of man. It is the most innovative piece of electrical device that converts electrical energy to mechanical energy, and conversely, it is also capable of generating electrical energy from mechanical energy or more commonly known as generators, which produces electricity while the motor is coupled to and driven by a gas or a diesel engine.

Electric motors are widely used in various applications as prime movers of machines utilized in diverse applications and industry such as electric cars, the electric locomotive, elevators, escalators, water pumps, air compressors, electric fans, hand drills, sewing machine, washing machine, microwave ovens, alternators that recharges a car battery, CD and DVD drives, or even the smallest device such as battery operated wrist watches, and with a whole lot more of other uses and specific applications which we may not even be aware of, but which are just common things within our reach in our everyday life.

By en:User:C_J_Cowie [GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
By en:User:C_J_Cowie [GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Depending on the types of application governed by the manner of operation and the motor capacity involved for a specific load to be driven, an electric motor is most certainly operated by means of an electrical activation and control system known as a motor controller. Motor controllers are basically the most indispensable component of electric motors which plays a significant part in essentially providing a suitable operation required with the many methods involved in running and stopping an electric motor.

Although there are a variety of complex methods which can be implemented, this article aims to cover some of the most fundamental electric motor control applications with alternating current (AC) induction motors commonly used in every industry, and the most basic type of motor controller is the Direct On Line (DOL) motor controller.

Direct On Line Motor Controller (DOL)

The simplest method of motor control is the Direct On Line (DOL) motor controller, which directly supplies the line voltage to the motor via a switch or by a single unit magnetic contactor. This type of motor controller is applied mostly to small size motors because small motors does not cause too much load burden that can adversely affect the supply source voltage coming from the electric power grid.

The CAD drawing on the right shows an electrical diagram of a typical method of 3 phase DOL motor power circuit controller.

Direct On Line (DOL) Motor Controller | Source: CAD drawing by ianjonas
Direct On Line (DOL) Motor Controller | Source: CAD drawing by ianjonas

The main circuit breaker acts as the main switch supplying power to the system. It is also equipped with over current and short circuit protection that automatically trips-off to disconnect the supply of electricity to disable the load upon detection of fault in the load circuit.

The main magnetic contactor acts as the motor operation switch which connects and disconnects the supply voltage coming from the main circuit breaker to the motor. When the main contactor is closed, the supply voltage proceeds to the motor terminal which runs the motor.

The thermal overload relay serves to detect motor overload current which when detected will instantaneously disconnect the control circuit of the motor controller to stop the operation to prevent burning of the motor.

Direct On Line (DOL) Control Circuit Diagram | Source: CAD drawing by ianjonas
Direct On Line (DOL) Control Circuit Diagram | Source: CAD drawing by ianjonas

The DOL control circuit diagram shown on the right illustrates a typical switching system for a DOL motor controller. When the human operator pushes the RUN push button switch, the control circuit becomes complete which permits power to travel down to the main contactor coil which energizes the main contactor. Once the main contactor is powered up, its internal three pole mechanical contacts (refer to the motor control diagram) closes which connects the source voltage to proceed to the motor terminal, hence running the motor.

Going back to the control circuit diagram, since the auxiliary normally open contact of the main contactor which is connected in parallel across the RUN push button switch was already at closed state following the activation of the main contactor coil, electricity continues to flow down to the main contactor coil even after the operator releases his finger from the RUN push button switch, this serves as the holding contact switch which maintains a complete circuit to run the motor continuously without further human intervention, providing ease of use for operator convenience to switch ON and switch OFF the motor only once via the RUN and STOP push button swithces.

There are two circuit disconnection in the control system. Aside from the OFF push button switch, the thermal overload relay also serves as a disconnecting switch that renders an open or incomplete control circuit which deactivates the main contactor to stop the motor upon detection of motor overload current.

Forward and Reverse Selection of Motor Rotation

Electric motors can run in both forward and reverse direction depending on the requirement of the application where it is to be installed, for example, like in a conveyor system which would require moving on both direction of items contained in the conveyor table. When such arrangement is necessary for a certain type of application, then a forward reverse motor controller is applied to the control circuit of the electric motor to achieve this purpose. Again the device required for the possibility of this operation is the magnetic contactor.

Reversing motor rotation of 3 phase AC induction motors can be achieved by means of interchanging the configuration of any two of the three motor terminals U1, V1, W1 with respect to the reference supply voltage L1, L2, L3. The CAD drawing below provides a visual explanation for this method of operation.

Forward Reverse Motor Rotation Selection Control | Source: CAD drawing by ianjonas
Forward Reverse Motor Rotation Selection Control | Source: CAD drawing by ianjonas
A Typical Magnetic Contactor for Motor Control By david shummer (de mes archives) [Public domain], via Wikimedia Commons
A Typical Magnetic Contactor for Motor Control By david shummer (de mes archives) [Public domain], via Wikimedia Commons

You will notice from the motor control diagram above that there are two units of magnetic contactors (forward contactor and reverse contactor) connected in parallel across each other. Notice that the line side terminals of these two contactors follows a common connection configuration for the supply voltage L1, L2, L3, while the load side terminals of these two contactors have different configuration for the motor terminals U1, V1, W1. The forward contactor is connected to make L1 connect to U1, L2 to V1, L3 to W1 which makes the motor run in the forward direction. While the reverse contactor is configured with two terminals in the reverse order, with L1 connected to W1 instead of U1, then L3 connected to U1 instead of W1, while maintaining only L2 connected to V1.

Forward Reverse Motor Rotation Control Circuit | Source: CAD drawing by ianjonas
Forward Reverse Motor Rotation Control Circuit | Source: CAD drawing by ianjonas

The forward reverse control circuit diagram illustrated above shows two DOL control circuit with two magnetic contactors to accommodate both the forward and reverse motor rotation, but with the inclusion of an additional interlocking normally close contacts each inserted for each contactor coils. These interlocking contacts are intended as a safety precautionary feature to prevent simultaneous activation of both contactor coils at the same time, which if not prevented can destroy the electric motor.

When the forward contactor coil is activated, its auxiliary normally close contact connected before the reverse contactor coil will be opened, thereby preventing any power to flow to the reverse contactor coil in case of accidental pressing of the reverse push button switch while the motor is running in the forward direction with the forward contactor coil energized.

Similarly, when the motor is running in the reverse direction with the reverse contactor coil energized, it is not also possible to power up the forward contactor coil because of the presence of an open reverse contact switch provided by the energized reverse contactor coil, thus, preventing the motor to run in forward direction while it is actively running in the reverse direction.

Another indispensable electrical control method for AC induction motors is the star delta motor controller.

Motor Controllers are also an indispensable part of Industrial Process Automation Technology.

I, the copyright holder of this work, hereby publish it under the following licenses:

How to Learn Electric Motor Control – A Basic Motor Controller Guide for Electrical Motor Controls by ianjonas is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      Raghu 

      18 months ago

      What is the star and Delta ?

    • profile image

      rakesh kumar 

      3 years ago

      M hindi m 3 phase currcuit k bare m

    • profile image

      kapilwankhede30 

      3 years ago

      It's like a nice application

    • profile image

      zubaiirullah 

      6 years ago

      defrent motor electrical controling manual

    • Jyothidas profile image

      Jyothidas 

      6 years ago from Bangalore

      It is a good tutorial .. awesome

    • profile image

      orraca-tetteh 

      6 years ago

      please try to send me more of such diagrams orracatettehb@yahoo.com

    • profile image

      waseem akram 

      6 years ago

      main jana chata hu ke contarol currcuit ke ba rey main.

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)