Circuit for Soft Start Module

Wichit Sirichote,

Simple CMOS control voltage for firing Crydom Soft-Start Module.

I noticed my wife mixer when start up, the induction motor draws higher current than normal running. I think better to insert the circuit that gradually applies power the motor. I found the nice module made by Crydom that uses solid-state relay in conjuntion with soft start circuit. The module has CMOS logic for controlling. We can apply the low power logic to control such AC machine easily.

Figure 1: The soft-start circuit gradually applies power when start up.

Hardware Schematic

The control circuit is very simple. I wired the circuit with 6-pin power terminal. The CMOS power supply was built with small transformer, halfwave rectifier, and one electrolytic capacitor. S1 is push button, when pressed, the control voltage then applies to the SST240, the power then gradually applied to the induction motor. Datasheet shows the ramp time is approx. 180ms.

Figure 2: Hardware schematic.

The circuit was built and put in plastic box. We see that we can use terminal for wiring power circuit easily.


Figure 3: Soft-Start Control Box (click to enlarge).

Figure 4: The circuit was tested with my wife mixer.



Schematic circuit.pdf
SST240 Soft-Start Module sst240.pdf

19 Aug 2006

recovered 17 December 2015