How to Test a Smooth Start Angle Grinder

Due to the design features, the start of the angle grinder is associated with high dynamic loads. Due to the mass of the working disk, inertia forces act on the gearbox axis at the beginning of rotation. This entails some negative points:

Axle loads during an abrupt start create an inertial jerk, which, with a large diameter and mass of the disk, can pull the power tool out of your hands;

As a result, the brushes wear out and both windings of the electric motor overheat. With the power tool turned on and off constantly, overheating can melt the insulation of the windings and lead to a short circuit, followed by expensive repairs.

Large torque with a sharp set of revolutions prematurely wears the gears of the angle grinder;

In some cases, breaking off the teeth and jamming of the gearbox is possible.

Overloads that the working disk perceives can destroy it when the engine starts.

Therefore, the presence of a protective casing is mandatory.

To better understand the mechanics of work, consider the device angle grinder in the drawing. All elements experiencing overload during a sharp start are clearly visible.

Schematic drawing of the location of the working bodies and control systems in an angle grinder

To reduce the detrimental effects of abrupt start, manufacturers produce an angle grinder with speed control and soft start.

The speed control is located on the tool handle

But only middle- and high-priced models are equipped with such a device. Many home masters acquire angle grinders without a regulator and slowdown of starting revolutions. This is especially true for powerful specimens with a cutting disc diameter of more than 200 mm. Such an angle grinder is not only difficult to hold in your hands during startup, the wear of the mechanics and electrical parts is much faster.
There is only one way out. to set the soft start angle grinder yourself. There are ready-made factory devices with a speed regulator and a slowdown in engine start-up at startup.

Ready-made device for adjusting the soft start

Such blocks are installed inside the case, in the presence of free space. However, the majority of angle grinder users prefer to make an angle grinder on their own for a smooth start-up, and connect it to the gap in the power cable.

Видео: How to Test a Smooth Start Angle Grinder

How to make a do-it-yourself soft start circuit for an angle grinder

A popular circuit is implemented on the basis of a phase-control control chip KR118PM1, and the power unit is made on triacs. Such a device is quite easy to mount, does not require additional settings after assembly, and therefore, a master can make it without a specialized education, it is enough to be able to hold a soldering iron in your hands.

Soft start adjustment circuit diagram for angle grinder

The proposed unit can be connected to any power tool, designed for an alternating voltage of 220 volts. Separate removal of the power button is not required, the modified power tool is turned on with a standard button. The circuit can be installed both inside the case, an angle grinder, and in the gap of the power cable in a separate case.

The most practical is to connect the soft starter to the outlet from which the power tool is powered. The input (connector XP1) is supplied with 220 volt power. An outlet is plugged into the output (XS1 connector), into which the angle grinder plug is plugged.

When the start key closes, the angle grinder, voltage is supplied to the DA1 chip through the common power circuit. On the control capacitor there is a smooth increase in voltage. As the charge, it reaches the working value. Due to this, the thyristors in the microcircuit do not open immediately, but with a delay, the time of which is determined by the charge of the capacitor. The thyristor VS1 triac opens with the same pause.

Watch a video with a detailed explanation of how to make and which scheme to apply

In each half-period of alternating voltage, the delay decreases in arithmetic progression, as a result of which the voltage at the input to the power tool gradually increases. This effect determines the smoothness of the engine starting angle grinder. Therefore, the speed of the disk increases gradually, and the gearbox shaft does not experience inertial shock.

The set-up time to the operating value is determined by the capacitance of the capacitor C2. A value of 47 microfarads ensures a smooth start in 2 seconds. With such a delay, there is no particular discomfort to start working with the tool, and at the same time, the power tool itself is not subjected to excessive loads from a sudden start.

After turning off the angle grinder, the capacitor C2 is discharged by the resistance of the resistor R1. At a nominal value of 68 kΩ, the discharge time is 3 seconds. After that, the soft starter is ready for the new start-up cycle of the angle grinder.
With a little refinement, the circuit can be upgraded to an engine speed controller. To do this, the resistor R1 is replaced by a variable. By adjusting the resistance, we control the engine power, changing its speed.

Thus, in one housing it is possible to carry out an engine speed controller and a soft start device for a power tool.

The remaining parts of the circuit work as follows:

• Resistor R2 controls the magnitude of the current flowing through the control input of the triac VS1;
• Capacitors C1 and C2 are control components of the KR118PM1 chip used in a typical switching circuit.

For simplicity and compactness of installation, resistors and capacitors are soldered directly to the legs of the chip.

Triac VS1 can be anything, with the following characteristics: maximum voltage up to 400 volts, minimum throughput current 25 amperes. The magnitude of the current depends on the power of the angle grinder.

Due to the soft start, the angle grinder, the current will not exceed the rated operating value for the selected power tool. For emergency cases, for example, jamming of the angle grinder disk, a current margin is required. Therefore, the value of the nominal value in amperes should be doubled.

The ratings of the radio components used in the proposed electrical circuit are tested on angle grinders with a power of 2 kW. The power reserve is available up to 5 kW, this is due to the peculiarity of the operation of the KR118PM1 chip.
The working scheme, repeatedly executed by home masters.