ESP32 Relay Guide - Choosing the Right Module for Home Automation Complete guide to ESP32 relay modules. Compare 1-channel, 4-channel, and solid state relays. Learn safe wiring for AC loads, common mistakes, and which relay to buy. January 24, 2026 Reviews & Comparisons TL;DR - Quick Picks Single device: 1-Channel Relay Multiple devices: 4-Channel Module Heaters/motors: Solid State Relay No wiring: Shelly / Sonoff Why You Need a Relay # ESP32 GPIO pins output 3.3V at a maximum of around 12mA. That's enough to blink an LED, not enough to switch a lamp, fan, or anything connected to mains power. A relay bridges the gap. Your ESP32 sends a small signal to the relay, and the relay switches a much larger load - up to 10A, 20A, or more depending on the relay. ESP32 GPIO 3.3V, ~12mA max. Can control LEDs, transistors, relay coils (with driver). Relay Output Switches 120V/240V AC or high-current DC. 10A typical, some rated 30A+. Safety First # AC Voltage Warning Mains voltage (120V/240V) can kill. If you're not comfortable working with AC wiring, use pre-built solutions like Shelly or Sonoff. Seriously - no project is worth it. Always disconnect power before wiring Use proper enclosures rated for mains voltage Check local electrical codes When in doubt, hire an electrician Relay Types Compared # Type How It Works Best For Downsides Mechanical Relay Electromagnet moves physical contacts General switching, most projects Clicks, wears out (100K cycles), slower Solid State Relay (SSR) Semiconductor switching, no moving parts Heaters, motors, frequent switching Costs more, needs heatsink at high loads Optocoupler Module Relay + optical isolation on one board ESP32 projects (isolation included) Most modules are this type already Quick Decision Guide # Controlling This? Get This Why Single lamp or fan 1-channel relay Simple, cheap LED strip (12V/24V DC) MOSFET module No relay needed, PWM dimming Multiple outlets 4-channel relay One board, less wiring Heater or motor SSR (25A+) Handles inductive loads, no arcing Whole room / many devices 8-channel board Centralized control Don't want to wire AC Shelly or Sonoff Pre-built, safe, works with ESP Relay Module Options # 1-Channel Relay Module # MOST COMMON 10A @ 250VAC $2-4 The simplest option. One relay, one device. Most modules include an optocoupler for isolation, so the relay coil doesn't share ground with your ESP32. ✓ Pros Cheap. Under $3 shipped. Simple wiring. VCC, GND, IN - done. Optocoupler included. Most modules have isolation. ✗ Cons 5V trigger common. Some won't trigger reliably at 3.3V. Audible click. Mechanical = noise. One device only. Need more? Buy more modules. 3.3V vs 5V Trigger Many relay modules expect 5V trigger signal. ESP32 outputs 3.3V. Look for modules specifically marked "3.3V compatible" or use a level shifter. Some modules work anyway - but test before installing. 1-Channel 5V Relay Module (Optocoupler) Standard single relay module with optocoupler isolation. Works with most ESP32 projects. Check trigger voltage compatibility. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress 4-Channel Relay Module # BEST VALUE 4x 10A @ 250VAC $5-8 Four relays on one board. Control lights, fans, pumps - whatever you need. The go-to for home automation projects. Pro tip: These modules often have a jumper to separate relay VCC from signal VCC. Use separate 5V supply for the relay coils if your ESP32's regulator can't handle the current draw. 4-Channel 5V Relay Module Four relays with optocoupler isolation. Ideal for controlling multiple devices from one ESP32. Popular choice for home automation. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress 8-Channel Relay Module # 8x 10A @ 250VAC $10-15 For serious automation. Eight relays, one board. Watch your power supply - all coils on draws significant current. 8-Channel 5V Relay Module Eight relays for large automation projects. Definitely use separate power supply for the relay coils. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress Solid State Relay (SSR) # BEST FOR HEATERS 25A-40A typical $8-15 No moving parts. Semiconductor does the switching. Silent, fast, no contact wear. ✓ Pros Silent operation. No clicking. No contact wear. Millions of cycles. Fast switching. Good for PWM-style control. Handles inductive loads. Motors, solenoids. ✗ Cons Needs heatsink. At high currents, gets hot. Voltage drop. ~1.5V across SSR = heat. More expensive. $8-15 vs $2-3 for mechanical. Small leakage current. May not fully "off" LEDs. When to use SSR: Heaters, heating elements, motors, any load that switches frequently, or anywhere you need silent operation. Fotek SSR-25DA Solid State Relay 25A SSR, 3-32V DC input, 24-380V AC output. Popular choice for heater control. Use with heatsink at higher loads. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress SSR-40DA 40A Solid State Relay Higher current SSR for demanding loads. Definitely needs heatsink. Good for 3D printer heated beds, large heaters. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress Pre-Built Smart Relays # Don't want to wire mains voltage? These devices have relays built-in, proper enclosures, and certifications. Flash with Tasmota or ESPHome for ESP32-style control. Shelly 1 # RECOMMENDED 16A $15-20 Tiny WiFi relay that fits behind a light switch. Has an ESP chip inside. Works standalone or flash with Tasmota/ESPHome. Shelly 1 WiFi Relay Compact WiFi relay, fits behind switches. 16A rating. Can be flashed with open-source firmware. My top pick for safe, simple smart switches. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress Sonoff Basic # BUDGET PICK 10A $8-12 Inline smart switch. Plug it between your device and the outlet. Easy to flash with Tasmota. Sonoff Basic R3 WiFi Smart Switch Budget-friendly inline relay. 10A. Easy to flash with Tasmota or ESPHome. Good for lamps, fans, simple loads. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress Shelly 2.5 # Two relays in one device. Control two lights, or use for roller shutters/blinds (up/down). Shelly 2.5 Dual WiFi Relay Two 10A relays in one compact unit. Perfect for two-gang switches or motorized blinds. Power monitoring included. Where to Buy: Prices may vary. Click to check current pricing: Amazon.com Amazon.de AliExpress Wiring Basics # Understanding relay wiring is simpler than it looks. There are two completely separate circuits: Control Side (Safe) 3.3V / 5V DC Load Side (Danger) 120V / 240V AC ESP32 5V (or VIN) GND GPIO 5 Relay Module (Input) VCC GND IN Relay Module (Output) COM ← Live in NO → To load NC not used Your Load Lamp, fan, heater... Understanding COM, NO, NC COM = Common. Your power source connects here. NO = Normally Open. Connects to COM when relay is ON. NC = Normally Closed. Connected until relay turns ON. Most projects use COM + NO: power flows to your device only when the ESP32 activates the relay. Active-Low vs Active-High Many relay modules are "active-low" – the relay turns ON when you write LOW to the pin. This seems backwards, but it's how most modules work. Just test yours. Quick Reference # Connection From To Power ESP32 5V (or VIN) Relay VCC Ground ESP32 GND Relay GND Signal ESP32 GPIO 5 Relay IN AC Live Wall outlet Relay COM To Load Relay NO Your device Basic Code Example # #define RELAY_PIN 5void setup() { pinMode(RELAY_PIN, OUTPUT); digitalWrite(RELAY_PIN, HIGH); // Start with relay OFF (active-low module)}void loop() { digitalWrite(RELAY_PIN, LOW); // Relay ON delay(5000); digitalWrite(RELAY_PIN, HIGH); // Relay OFF delay(5000);} For web control, timers, or Home Assistant integration, check out ESPHome - it handles all of that with simple YAML config. Common Mistakes # Using 5V relay module with 3.3V ESP32 without checking. Some work, some don't trigger reliably. Test first or buy 3.3V-compatible modules. Powering relay coils from ESP32's 3.3V regulator. The regulator can't supply enough current. Use VIN (5V USB) or separate supply for relay VCC. No flyback diode. When a relay coil switches off, it creates a voltage spike. Most modules have this built-in, but bare relays need one. Undersizing the relay for the load. A "10A" relay shouldn't run at 10A continuously. Derate by 50% for reliability. Use 20A relay for 10A load. Forgetting about inrush current. Motors and some lights draw 5-10x more current at startup. A lamp that draws 1A steady might draw 10A for a split second. Mixing low-voltage and mains wiring. Keep them separate. Use proper enclosures. Don't run 3.3V signal wires next to 240V mains. Relay Module Comparison # Type Channels Current Trigger Price Best For Mechanical 1 10A 5V (some 3.3V) $2-4 Single device Mechanical 4 4x 10A 5V $5-8 Multiple devices Mechanical 8 8x 10A 5V $10-15 Full automation SSR 1 25-40A 3-32V DC $8-15 Heaters, motors Shelly 1 1 16A WiFi $15-20 Safe, no wiring Sonoff Basic 1 10A WiFi $8-12 Budget smart switch Related Guides # ESP32-CAM Board Overview & Pinout ESP32 Camera Modules Compared How to Flash ESP32 with ESP32-CAM-MB Previous Choosing the Right ESP32 Camera Module - OV2640, OV5640, OV3660 Compared