The softstart function allows not to have sudden motor starts and consequent high current peaks. When switched on, the number of motor revolutions is brought progressively from zero to the adjustment value set by the potentiometer.


The minimum adjustment level is the minimum engine rpm value at which the governor brings the engine into control condition. This value depends on the circuitry that reads the information from the rpm sensor: the presence of offset and voltage drops in this circuit leads to a minimum rpm value of 400-450 rpm

The maximum adjustment level is the maximum engine rpm value at which the governor brings the engine into control condition. This does not correspond to the typical maximum rotation value of the motor (from 12000 rpm to 16000 rpm depending on the model). For the values of the components that define it, the maximum adjustment level brings the engine to a number of revolutions of approximately 10000 rpm. It is possible to reduce this value (5000 rpm, 2500 rpm).


The circuit of the MST_K07_CL regulator is equipped with the following protections:

   1. overload protection
   2. thermal protection of the TRIAC
   3. protection against disconnection of the rpm sensor.

The overload protection is implemented by the microcontroller that "senses" the overload condition. In the presence of an overload condition for a minimum time of 2s, the micro switches off the TRIAC and puts the circuit in protection mode (circuit on but TRIAC not activated). In this case, to reactivate the regulator, after having removed the overload condition, it is necessary to remove the power supply for a couple of seconds and then reactivate it.

The thermal protection of the TRIAC prevents overheating of the TRIAC by switching off the regulator (protection mode). Except that the TRIAC must be equipped with a heatsink (see BOX version) when the regulator works with motors with heavy loads at very low speeds, the TRIAC tends to heat up. If the heatsink used is not of sufficient size and / or it is not ventilated (wound is not present) the TRIAC goes into thermal dispersion, behaving like a closed switch, i.e. it passes all the input voltage to the output. In this case the governor no longer controls the motor which rotates at maximum speed. To sense the temperature of the TRIAC, a sensor (composed of a diode and a resistor) is welded to the metal body of the TRIAC which acts on the TRIAC driver circuit, inhibiting it when the TRIAC temperature exceeds a threshold of 80 C. When the motor stops due to thermal protection, to restart the regulator it is necessary to act as in the case of the overload protection, i.e. turn off and turn on the power supply after allowing it to cool.

The protection against disconnection of the rpm sensor prevents the governor from rotating without control at the maximum rpm due to the electrical break or disconnection of the rpm sensor. As is well known, the regulator implements a closed loop control. If for some reason the feedback coming from the sensor is lost (due to disconnection or breakage of the sensor) the ring opens and the information on which the regulator calculates the ignition of the TRIAC is missing. When this condition occurs, the regulator is put in the protection mode from which it is possible to exit only by switching it off and on again (after checking the electrical connection of the sensor or its integrity).


The electrical connections of the MST_K07_CL speed regulator must be made taking into account the function of the individual connectors as shown in the following photo. versione classica MST_K07_CL

Fig. 5 - electrical connections of the MST_K07_CL regulator in the standard version

The power connector (the one in blue with 4 places) must be connected to the mains voltage (220V) and to the motor. The speed sensor is connected to the two-way blue connector. For this connection there is no polarity to be respected when connecting the sensor wires as the signal coming from the sensor is of the alternating type.

The AUX connector

IThe AUX connector allows to interface the MST_K07_CL regulator to an external board which can be an Arduino or similar. This connector is present only in the digital version and can be used for the different operating modes of the regulator.

Connettore AUX MST_k07_CL


The use of the AUX connector allows you to use the regulator in different ways as you can:

    1. read the motor rotation speed from the ROT pin;
    2. read / force the speed setting or the voltage of the PWM pin;
    3. force the regulator internal voltage to 5V from the outside through pins 5V and GND;

More information on how to connect the MST_K07_CL regulator to the washing machine motor (model 3064) is shown at the following link:

Particular attention must be paid when handling the regulator as the metal parts present may be under the line with consequent danger of electric shock.