ESP32 Forum

Posted: **Tue Apr 16, 2024 10:16 pm**

I was hoping to save some room in my project enclosure by using a 2-channel SSR instead of using two 1-channel SSR's. However, no matter what I try, the 2-channel SSR's will just not work. I have tried two of these 2-channel SSR's and get identical behavior from both.

The relay ignores my sketch code and will continue blinking my LED 'load' with the USB cable disconnected. This may be difficult to believe but that is what happens.

I am using an ESP-WROOM-32 (30-pin) MCU.

For the sake of clarity here is a grab of the 2-channel SSR in question:

: 61Y00GILzNL._SL1500_.jpg (89.62 KiB) Viewed 991 times

My sketch is a bare-bones BLINK sketch that works well for testing relays.

Code: Select all

 // initialize pin numbers:
  const int grnLed =  5; 
  const int redLed = 19;
  
  void setup() {
  	pinMode(grnLed, OUTPUT); 
    pinMode(redLed, OUTPUT); 
  }

  void loop() {
     digitalWrite(grnLed, HIGH);
     digitalWrite(redLed, LOW); 
     delay(5000);

     digitalWrite(grnLed, LOW); 
     digitalWrite(redLed, HIGH);
     delay(5000);
  }

If I switch out the 2-channel SSR and replace it with two 1-channel SSR's of the same make, the SSR's fire off the attached LED 'load' as expected. Here is the 1-channel SSR used:

: 51jcLxjLlbL._AC_SL1010_.jpg (38.64 KiB) Viewed 991 times

If I switch out both SSR'S and replace them with a non-SSR 2-channel relay as shown next:

: IMG_0247 copy.jpeg (127.3 KiB) Viewed 991 times

then the LED's are switched ON/OFF without any issue whatsoever.

While I can live with the non-SSR relay I would prefer to use the SSR version because of its longevity and and non-clicking behavior.

If anyone can point out my overlooked mistake with these 2-channel SSR's I would be very grateful.

Thank you.

Posted: **Tue Apr 16, 2024 10:27 pm**

What's the relais' specified (signal) input voltage? A 5V SSR may have difficulties working off the ESP's 3.3V IOs.

Posted: **Tue Apr 16, 2024 10:31 pm**

I was concerned about that as well but the other relay's work with the 3.3V logic input from the ESP board without issue.

I could try boosting the pin logic to 5V but that means more hardware in my enclosure. However, if this works it will have solved this puzzle.

Thanks for your post.

Posted: **Wed Apr 17, 2024 5:56 pm**

OK I used an UNO to retest these same 2-channel SSR's and got the same exact behavior with this 5V logic HIGH board. I am not an UNO fan but they are good for testing purposes when 5V logic is required.

The UNO GPIO pin voltages are: 5.219V (HIGH) and 5.8 mV (LOW). According to the spec sheet these voltage values are within spec. The 1-channel SSR's work as expected, the 2-channel SSR does not.

Again, for the sake of clarity, the 2-channel will continue blinking the LED 'loads' with the USB cable disconnected and 120VAC connected. The 1-channel SSR's will go out with the USB cable disconnected and 120VAC connected.

I may opt to return these because I cannot get them to work as they should. If I am overlooking something I have no idea what it is.

All comments and suggestions are welcome.

Thank you.

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