How to Make an AC Softstarter




Introduction: How to Make an AC Softstarter

About: Awesome Electronics Tutorials, Projects and How To´s

In this project I will show you why my new autotransformer keeps tripping my circuit breaker and how I built an AC softstarter in order to "softly" start the transformer so that it does not trip my circuit breaker. Along the way we will find out how exactly this problem gets created and how you can fix it easily. BTW, such softstarters are also useful for motors ;-) Let's get started!

Step 1: Watch the Video!

Make sure to watch the video since it will give you pretty much all required information to build an AC softstarter. During the next steps though I will present you some additional information.

Step 2: Order Your Components!

Step 3: Build the Circuit!

Here you can find the schematic of the project along with reference pictures of my finished board.

Step 4: Upload the Code!

Here you can find the code for the Arduino Nano. UPLOAD IT! And maybe understand it along the way ;-)

Step 5: 3D Print the Enclosure and Put Everything Inside There!

Here you can find the .stl files for the enclosure as well as reference pictures of my finished project.

Step 6: Success!

You did it! You just created your own AC Softstarter!

Feel free to check out my YouTube channel for more awesome projects:

You can also follow me on Facebook and Twitter for news about upcoming projects and behind the scenes information:

Be the First to Share


    • Made with Math Contest

      Made with Math Contest
    • Unusual Uses Contest

      Unusual Uses Contest
    • Micro:bit Contest

      Micro:bit Contest



    2 months ago

    I too have a big old variac, with similar issues.
    I use a suitably rated tungsten filament lightbulb in series with the variac.
    At switch on the bulb glows quite brightly but then, in less than a second or so, fades as the primary winding of the variac charges.


    Question 6 months ago

    Normally when people put out a schematic they also put out an explanation of what that circuit does and how it works, especially since this circuit is playing with 240 volt A/C and is lethal . You do not .

    Would you care to explain please.


    Answer 6 months ago

    did you watch the video?


    6 months ago on Step 6

    Hi Scott, could you please upload the updated code that you talked about in your comments on youtube video to start the circuit at peak. I got the point that i need to change the ocr1b to 313, but what about the values that the checked in the if block.