This machine reduces the inrush current through lighting the lamp at the time of its inclusion. With the closure of the contacts of the switch Q1 lamp EL1 begins to glow dimly, since the current flows through it only during the positive half-cycles of the mains voltage on bottom, under the scheme, the supply lead. During the negative half cycle charging the capacitor C1. As the voltage on the capacitor reaches voltage stabilizing Zener diode VD2, open SCR VS1 and the lamp will flash almost full intensity.
Fig. 1
Shown parts are designed to work the machine with a lamp (or lamps) with a capacity of up to 150 watts. For more powerful load (500… 700 W) must be set with a valid VD3 diode rectified current 2…3 A (e.g. KD202L). Trimester while can not install on the radiator.
Establishing automatic when the power diode VD3. Instead of the resistor R3 is preferably temporarily solder variable, resistance 15 ohms or 22 ohms. After a few seconds after powering on the device in the network should light flickering light bulb EL1. If glow it's not, pick a variable resistor current control electrode of SCR. Then measure the voltage across the capacitor. If it exceeds 50, the condenser is replaced by another with a higher nominal voltage or less sets Zener voltage stabilization.
After that, connect the diode VD3 and measure the AC the voltage across the lamp. Change it in one direction or another by selecting a resistor R1, but greatly reduce the resistance of the resistor by comparison with the said scheme is not desirable, otherwise it will decrease the duration preheating filaments of the lamp (it should not be less than 2 C) before turning on the SCR.
Authors: Father and son Chumakov, Dzerzhinsk; Publication: www.cxem.net