2-Channel 5V Solid State Relay Module (HFS4-2A-05DM) High-Level Trigger - 240VAC 2A SSR

Specifications:

• Relay Model: HFS4-2A-05DM (Solid State)
• Channels: 2 Independent Channels
• Input Control Voltage (Logic): 5V DC
• Trigger Type: High-Level Trigger (Active HIGH)
• 2.5V - 5V: Relay ON
• 0V - 1.5V: Relay OFF
• Load Voltage: 75V AC to 264V AC (50/60Hz)
• Load Current: 2A max per channel (Resistive Load)
• Switching Type: Zero-Cross Switching
• Isolation: Phototriac Isolation

Applications:

• Silent Home Automation: Control bedroom lights or fans without the disturbing clicking sound.
  
• PID Temperature Control: Ideal for heating elements where rapid, frequent switching is required.
  
• Active-High Systems: Perfect replacement for circuits designed with NPN drive logic where a HIGH signal is meant to activate the load.

Project Evolution

• Prerequisite: If you have used standard Low-Level trigger relays, you might have dealt with inverting your code logic (digitalWrite(LOW) to turn ON).
  
• The Upgrade: This High-Level Trigger SSR allows for Direct Logic Control. Your code becomes more intuitive: digitalWrite(HIGH) actually turns the device ON. This prevents "boot-state glitching" where relays turn on briefly when a microcontroller reboots (as pins float high or start low).
  
• Effort Level: Intermediate.
  
• Minimum Hardware: Arduino Uno/Nano + AC Load.

Virtual Technician: Wiring & Safety Guide
⚠️ DANGER: HIGH VOLTAGE This module switches 110V/220V AC. Do not touch the board while powered.

Pinout:

• DC+: Connect to 5V (Arduino 5V).
• DC-: Connect to GND (Arduino GND).
• CH1: Connect to Digital Pin. Send HIGH (5V) to turn ON.
• CH2: Connect to Digital Pin. Send HIGH (5V) to turn ON.

Package Includes :

1 X 2-Channel 5V Solid State Relay Module (HFS4-2A-05DM) High-Level Trigger - 240VAC 2A SSR

Frequently Asked Questions (FAQ)

1. Can this relay switch DC loads like a motor?
   No, this is an AC-only SSR. Using it with DC voltage will cause the relay to latch ON and never turn OFF.
2. What is "High-Level Trigger"?
   It means the relay turns ON when you apply a voltage (3.3V-5V) to the signal pin. It stays OFF when the signal is 0V (GND).
3. Does this work with 3.3V logic (ESP32)?
   Yes, usually 3.3V is sufficient to trigger the High state, but ensure your ground (DC-) is common.
4. Can I dim lights with this module using PWM?
   No, this is a Zero-Cross SSR. It is NOT suitable for phase-angle dimming.
5. Why use High-Level instead of Low-Level?
   High-Level is often safer because if a wire breaks or the controller loses power (0V), the relay defaults to OFF.
6. Is it safe to use for a ceiling fan?
   Yes, provided the fan current is under 2A.
7. Why does the relay stay ON even when I remove the signal?
   If testing with a DC load (multimeter), it latches. It requires an AC load to switch off at the zero-crossing.
8. What is the "Resistive Fuse" for?
   It acts as a safety barrier, blowing if the current exceeds safe limits to protect the chip.
9. Can I use this for a water heater?
   No. Water heaters draw 10A-15A. This module is rated for 2A max.
10. Does it make a clicking sound?
    No, it is completely silent.
11. Do I need an external power supply?
    The control side draws very little current, so it can be powered directly from the Arduino's 5V pin.
12. Can I use this to switch 110V AC (US Standard)?
    Yes, it works from 75V AC up to 264V AC.
13. Is this isolated?
    Yes, it uses an optocoupler/phototriac for isolation.
14. Why is there no 'NC' (Normally Closed) terminal?
    SSRs are Normally Open (NO) switches only.
15. Can I mount this on a DIN rail?
    Not directly, but it fits standard DIN rail clips (sold separately).
16. What happens if I exceed 2 Amps?
    The SSR chip will overheat and fail.
17. Can I use 4 of these at once?
    Yes, an Arduino can drive multiple modules easily.
18. Is this compatible with Raspberry Pi?
    Yes, the high-level trigger is compatible, but ensure the Pi supplies enough current if driving many at once.
19. What is the difference vs. mechanical relay?
    SSRs are faster, silent, and spark-free but handle less current.
20. Can I use it to switch a contactor?
    Yes, it is excellent for switching the coil of a large AC contactor.