Convenient and fast power line break detection circuit

Most small household appliances use 2-core or 3-core power cords. After being bent and squeezed countless times during long-term use, one of the wires in the power cord may break. Since the breakpoint is sealed by the PVC outer layer and cannot be seen, it is difficult to accurately locate the breakpoint.

The circuit shown in the figure below can detect the breakpoint position conveniently and quickly, and is suitable for single-core, 2-core and 3-core power cables. The circuit mainly uses a CD4069 six-inverter CMOS chip, in which N3 and N4 are used as pulse generators with a frequency of about 1000Hz, and N1 and N2 are used to detect whether there is a 220V AC electric field in the live wire, and also have the function of buffering the weak AC voltage sent from the detection head. The potential of the output pin 10 of N2 can turn on or block the oscillation circuit. When the detection head is far away from the AC electric field, the output of pin 10 is low, D3 is turned on, and the oscillation circuit is blocked. At this time, the 6th pin of N3 is low. T1 is cut off and LED1 does not emit light. When the probe moves closer to the AC electric field, the 10th pin of N2 is high during each positive half cycle of 50Hz, and D3 is cut off at this time, and the oscillation circuit works immediately. LED1 flashes under the control of T1. Since the flashing frequency is 50Hz, LED1 appears to be in a continuous light state to the naked eye.

Since the circuit is very power-saving, the power supply can be a 3V button battery or two No. 5 batteries. The quartz crystal circuit can be installed in a PVC tube to make a portable device, and a 5cm long, 2mm diameter wire is used as a probe. To facilitate the detection of a thicker three-core power cable, the probe can be bent into a "J" shape to increase the detection sensitivity.

Before detection, remove the load at the other end of the power cord, use a multimeter to measure the faulty core wire, then connect the live wire to the faulty wire, and connect the remaining wires to the neutral wire. Use the probe to move slowly along the broken wire. The point where LED1 suddenly goes out or lights up is the breakpoint.