Homemade phase loss protection controller

1. Production

1. Phase loss protection controller without external voltage control, as shown in the figure above. The working voltage is provided by capacitor step-down. When the phase is lost, the relay is closed to play a protective role. R1, R2, R3, R7 use 3W gold film resistors, and other parts are selected according to conventional models. The whole machine is required to have good ventilation.
2. Phase loss protection controller with external control voltage type, as shown in the figure below. The control power supply is provided by the transformer on the machine tool. When the phase is lost, the thyristor is triggered and turned on, driving the relay to pull in, which plays a protective role.

2. Debugging

Connect a switch in series to any phase of the three-phase circuit, connect the phase loss protection board and power on. When the switch is closed, the relay should not be attracted and the LED should not light up; when the switch is open, the relay will be attracted after a delay of about 1S.

The LED is on. Connect the normally closed contact of the relay in series with the control circuit.

When a phase is lost, the control circuit power supply will be automatically cut off to achieve the effect of phase loss protection.

After actual measurement, the voltage at point a in the upper figure is about 130V, and the voltage at point a in the lower figure is about 100V. The shell can be made of plastic plate to improve the insulation performance.