For direct control of SSRs (control based on mains cycles, zero-crossing switching), we can use the C-IS-0404S module. For SSRs with a maximum current consumption of 13 mA and a switching voltage of 4 V—such as the RGS1A23D25 used here—we can directly use the module’s 5 VDC power output.
The C-IS-0404S module can set the PWM frequency in 1 Hz increments; for example, using a frequency of 2 Hz means the PWM cycle will be 25 steps of 20 ms each = 500 ms, and one PWM step will therefore correspond to 4% of the regulated power. This article describes the calculation method and function of this control.
Fig. 1. Example of direct control of an SSR using the C-IS-0404S module
Notes:
- The UOUT jumper must be set to the 22 V position (the voltage of the switched circuit must be 22 V max.; here, it is 5 V from the internal power supply)
- The module can also measure temperatures in the water heater tank
- The maximum current draw of a single SSR from the DOx is 13 mA; the 5V outputs (terminals B3 + C3) can be loaded with a total current of 40 mA
- If a higher current or higher supply voltage is required, an external power supply of up to 22 V must be used to power the SSR relay control circuits instead of the internal 5 V power supply. The negative terminal of the power supply is connected to the module’s GND, and the positive terminal supplies power to terminals A1+ on the SSR. A similar circuit configuration with an external power supply is used in this example.