Build Instructions

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• 1

  DIY Soft Start & Speed Control for Angle Grinder

  An angle grinder can jerk suddenly when it is switched on directly from the AC mains. This sudden start can be uncomfortable and may create a safety risk for the user.  The PCB of this project from JLCPCB

  In this project, I designed a compact Soft Start and Speed Control circuit for an angle grinder.

  The circuit has two main functions:

  • Soft Start: Limits the high starting current and allows the motor to start more smoothly.
  • Speed Control: Allows the motor speed to be adjusted using a potentiometer.

  The circuit uses two 120-ohm, 5-watt resistors for the Soft Start function and a 12-volt DPDT relay to bypass the resistors after approximately 2 seconds.

  For speed control, a BTA41 TRIAC is used to control the AC power supplied to the motor.

  The PCB is compact and can be adapted for other motor-driven power tools such as drills and cutting machines.

  Let's build it!
• 2

  The Schematic

  The circuit consists of two main sections: the Soft Start and Speed Control circuits.

  The Soft Start section uses two 120-ohm, 5-watt resistors to limit the starting current.

  When the grinder is switched on, the motor initially receives power through these resistors. After approximately 2 seconds, the relay activates and connects the motor directly to the AC mains.

  The Speed Control section uses a BTA41 TRIAC to adjust the motor speed.

• 3

  PCB Design

  After completing the schematic, I designed a compact PCB to fit all the components into a small space.

  The PCB contains the Soft Start circuit, relay, power supply section, TRIAC Speed Control, and adjustment potentiometers.

  The goal was to keep the board as compact as possible while maintaining enough space between the high-voltage sections.

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