AC welding machine no-load power-saving circuit

AC welding machines work intermittently, and the no-load power consumption during the intermittent period reaches several hundred watts. Continuous manual turning on and off in order to save power will obviously affect work efficiency. Therefore, reducing the no-load loss of the welding machine is of great practical significance. The circuit introduced in this article can make the welding machine automatically cut off the power supply when it is no-load, and automatically turn on the power supply when it is working, which has a significant power saving effect. 　　See the circuit diagram. T1 in the picture is the AC welding machine transformer. After the power switch HK is turned on, the power transformer T2 is powered first, and a DC voltage of about 12V is obtained on the filter capacitor C1. IC1 and IC2 are two 555 time base integrated circuits. Since the voltage on C2 is 0 in the initial state, pins ② and ⑥ of IC1 are low level, so pin ③ is high level, relay K does not pull in, AC contactor KM does not work, and the welding machine is not powered on. At the same time, the multivibrator composed of IC2 and others starts to work, and pin ③ outputs a pulse signal with a frequency of about 10kHz. The signal passes through R5 and is then added to one end of the T1 secondary. The other end of the T1 secondary is connected to the "ground" of the control circuit. Since the T1 secondary winding presents a large inductive reactance to the 10kHz signal, the loop current is very small. , the output voltage of transformer L is also extremely small. Another route is coupled with C4, VDR, VD9 are rectified, and C5 is filtered to obtain the DC voltage to turn on VT1 and cut off VT2. Therefore, there is no charging current in C2, and IC1 pin ③ remains high. The circuit is in no-load energy-saving state. During welding, the welding rod and the workpiece are in contact, the pulse signal output by IC2 is short-circuited, and VT1 loses the bias current cutoff. VT2 is turned on, and the 12V voltage charges C2 through VT2. The potential of pins ② and ⑥ of IC1 quickly rises to above 2/3Vcc. Pin ③ flips to low level, K pulls in, causing KM to pull in, and the welding machine transformer T1 is powered to work. Since the normally closed contact K-2 of K is opened before the normally open contact K-1 is closed, the secondary 30-35V AC voltage will not enter the control circuit when T1 is working. After K-2 is disconnected, the pulse output by IC2 pin ③ turns on VT1 again, VT2 is cut off, and the charging of C2 by 12V through VT2 stops. However, the large working current of the welding machine at this time induces a voltage in the current transformer L. This voltage is rectified by VD5 and charges C2, keeping the potential of IC1's ② and ⑥ pins above 1/3Vcc, and keeping the ③ pin low. flat, K and KM remain closed, and T1 works normally. The function of DW in the circuit is to ensure that the maximum voltage of IC1② and ⑥ pins does not exceed Vcc (12V). When welding is stopped, the secondary current of T1 disappears and the induced voltage in L also disappears. C2 is discharged by R2. After reaching the set time, the potential of IC1 ② and ⑥ pins is as low as 1/3Vcc, ③ pin flips to high level, K and KM are released one after another, and the welding machine returns to the energy-saving state of no-load power-off. L is a self-made through-core transformer, and the number of winding turns is determined according to the test. For debugging, you only need to adjust R2 so that T1 can automatically power off after about 1 minute when welding is stopped. Originally published in the bound edition of "Electronic News" in 2003 by Hu Bing, Jiangsu