• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Need circuit help? Post them in the comments! I've answered over 50,000!

Blog | Categories | About | Contact | Calculators-online
You are here: Home / Motor Controller / PWM Motor Soft Start Circuit to Prevent High Consumption during Power Switch ON
warning message: electricity is dangerous, proceed with caution
triacpwmdriver

PWM Motor Soft Start Circuit to Prevent High Consumption during Power Switch ON

Last Updated on April 7, 2020 by Swagatam 214 Comments

In this post I have explained an effective PWM motor soft start circuit which can be used for enabling heavy motors with a soft start and thus prevent the equipment from drawing dangerous high currents.

Table of Contents
  • Why a Soft Start
  • Using PWM Concept
  • Example circuit for a variable 48V motor controller with soft start
  • How it Works
  • Video Clip:
  • Integrating a zero Crossing Triac  Controller

Why a Soft Start

High wattage motors such pump motors or other forms of heavy industrial motors tend to draw huge current during their initial power switch ON, which in turn impacts the associated fuses and switches adversely causing these to either blow of or degrade overtime. In order to remedy the situation a soft start circuit becomes highly imperative.

In a few of my previous articles I have explained regarding a related topic, which you may learn comprehensively through the following posts:

Soft start circuit for pump motors

Soft start circuit for refrigerators

Although the above designs are quite useful, these may be considered slightly low tech with their approach.

In this article we'll see how the process may be implemented using a much sophisticated PWM based motor soft start controller circuit.

Using PWM Concept

The idea here is to apply a gradually incrementing PWM to a motor each time it's switched ON, this action allows the motor to attain a linearly increasing speed from zero to maximum within a stipulated period of time, which may be adjustable.

Note: Please use a Darlington BC547 configuration at pin#5 of IC2 instead of a single BC547. This will produce a more effective response compared to a single BC547

Example circuit for a variable 48V motor controller with soft start

Dc motor soft start with speed control
##PLEASE CONNECT A 1K FROM PIN5 OF IC2 TO GROUND, WHICH IS MISTAKENLY NOT SHOWN IN THE ABOVE DESIGN##

How it Works

Referring to the figure above, the production of the linearly incrementing PWM is achieved with the help of two 555 IC, configured in their standard PWM mode.

I have already discussed the concept elaborately in one of my earlier articles explaining how to use IC 555 for generating PWM.

As may be witnessed in the diagram, the configuration employs two 555 ICs, IC1 being wired like as astable, while IC2 as a comparator.

IC1 generates the required clock signals at a given frequency (determined by the values of R1 and C2) which is applied to pin#2 of the IC2.

IC2 utilizes the clock signal to generate triangle waves across its pin#7, so that these may be compared with the potential available at its control voltage pin#5.

Pin#5 acquires the required control voltage via an NPN emitter follower stage made with the help of T2 and the associated components.

When power is switched ON, T2 is fed with a ramping or a gradually increasing voltage at its base via R9, and due to the proportionate charging of C5.

This ramping potential is appropriately duplicated across the emitter of T2 with respect to the supply voltage at its collector, meaning the base data is converted into a gradually increasing potential ranging from zero to almost the supply voltage level.

This ramping voltage at pin#5 of IC 2 is instantly compared with available triangle wave across pin#7 of IC2, which is translated into a linearly incrementing PWM at pin#3 of IC2.

The linearly incrementing process of the PWMs goes on until C5 is fully charged and the base of T2 attains a stable voltage  level.

The above design takes care of the PWM generation each time power is switched ON.

Video Clip:

The following video shows a practical test result of the above PWM circuit implemented on a 24V DC motor. The video shows the PWM pot adjustment response of the circuit on the motor, and also an additional battery indicator LED response while the motor is switched ON and OFF.

Integrating a zero Crossing Triac  Controller

In order to implement the PWM motor soft start circuit effect, the output from pin#3 of IC2 is required to be applied to a triac power driver circuit, as shown below:

The above image shows how the switch ON soft start PWM control may be implemented on heavy motors for the intended purpose.

In the image above we see how triac driver isolators with zero crossing detector can be employed for driving the motors with the linearly incrementing PWMs for executing a soft start effect.

The above concept effectively takes care of the start ON overcurrent situating on single phase motors.

However in case a 3 phase motor is used, the following idea can be used for implementing the proposed 3 phase soft start on motors.

You'll also like:

  • 1.  RPM Controller Circuit for Diesel Generators
  • 2.  How to Make a 3 Phase VFD Circuit
  • 3.  High Current Sensorless BLDC Motor Controller using Back EMF
  • 4.  GSM Pump Motor Controller Circuit using Arduino
  • 5.  Electric Wheelchair using BLDC Motor
  • 6.  Single Phase Variable Frequency Drive VFD Circuit

Filed Under: Motor Controller Tagged With: High, Motor, Prevent, PWM, Soft, Start

About Swagatam

I am an electronics engineer and doing practical hands-on work from more than 15 years now. Building real circuits, testing them and also making PCB layouts by myself. I really love doing all these things like inventing something new, designing electronics and also helping other people like hobby guys who want to make their own cool circuits at home.

And that is the main reason why I started this website homemade-circuits.com, to share different types of circuit ideas..

If you are having any kind of doubt or question related to circuits then just write down your question in the comment box below, I am like always checking, so I guarantee I will reply you for sure!

Previous Post: « Up/Down LED Indicator using LM3915
Next Post: How to Make Dog Barking Preventer Circuit using High Frequency Deterrence »
Subscribe
Notify of
guest
guest
214 Comments
Inline Feedbacks
View all comments

Primary Sidebar

circuit simulator image

Subscribe to get New Circuits in your Email

Categories

  • Arduino Projects (90)
  • Audio and Amplifier Projects (132)
  • Automation Projects (17)
  • Automobile Electronics (101)
  • Battery Charger Circuits (84)
  • Datasheets and Components (105)
  • Electronics Theory (140)
  • Free Energy (38)
  • Games and Sports Projects (11)
  • Grid and 3-Phase (19)
  • Health related Projects (25)
  • Home Electrical Circuits (12)
  • Indicator Circuits (15)
  • Inverter Circuits (89)
  • Lamps and Lights (142)
  • Meters and Testers (71)
  • Mini Projects (46)
  • Motor Controller (64)
  • Oscillator Circuits (28)
  • Pets and Pests (15)
  • Power Supply Circuits (89)
  • Remote Control Circuits (50)
  • Security and Alarm (64)
  • Sensors and Detectors (103)
  • SMPS and Converters (31)
  • Solar Controller Circuits (60)
  • Temperature Controllers (42)
  • Timer and Delay Relay (49)
  • Transmitter Circuits (29)
  • Voltage Control and Protection (38)
  • Water Controller (36)

Other Links

  • Privacy Policy
  • Cookie Policy
  • Disclaimer
  • Copyright
  • Videos
  • Sitemap

People also Search

555 Circuits | 741 Circuits | LM324 Circuits | LM338 Circuits | 4017 Circuits | Ultrasonic Projects | SMPS Projects | Christmas Projects | MOSFETs | Radio Circuits | Laser Circuits | PIR Projects |

Social Profiles

  • Twitter
  • YouTube
  • Instagram
  • Pinterest
  • My Facebook-Page
  • Quora
  • Stack Exchange
  • Linkedin
  • Recent Comments

    • Swagatam on Simple Buck Converter Circuits using Transistors
    • David on Simple Buck Converter Circuits using Transistors
    • Swagatam on Clap Switch Circuits with Relay ON/OFF: [Tested]
    • Mark on Clap Switch Circuits with Relay ON/OFF: [Tested]
    • Swagatam on Boost Converter Calculator

    © 2025 · Swagatam Innovations