Which AC Dimmer Module to Choose: Complete Buyer's Guide

TL;DR: Three questions determine your choice: (1) load type — resistive (heater, incandescent) or inductive (motor); (2) load power in watts → calculate amps → pick a rating with a ×1.3 safety margin; (3) platform — ESP32 dual-core uses rbdimmerESP32, Arduino uses RBDdimmer, single-core ESP32 or Raspberry Pi use DimmerLink. The quick-selection table is at the bottom of this article.

How to Use This Guide

Work through the steps in order. Each step narrows your choice:

1. Step 1: Is your load compatible?
2. Step 2: Calculate current and choose a rating
3. Step 3: Platform and library
4. Step 4: How many channels?
5. Step 5: Standard or high-power module?
6. Step 6: Should you use DimmerLink?

Or jump to the Quick Selection Table.

Step 1: Is Your Load Compatible?

AC TRIAC dimmers work by cutting part of the sine wave (phase-cut control). Not all loads respond well to this.

✅ Fully compatible — resistive loads

These are ideal. Current follows voltage in phase, so TRIAC switching is clean:

• Incandescent bulbs (any wattage)
• Halogen bulbs (direct mains or with transformer — see notes below)
• Heating elements and space heaters
• Electric boilers, kettles, irons, toasters
• Oil-filled radiators and underfloor heating mats
• Any pure resistive heating device

⚠️ Compatible with conditions

⚠️ Inductive loads need a snubber. Motors and transformers cause dv/dt spikes when the TRIAC turns off — these shorten TRIAC lifespan and can cause false triggering. Add an RC snubber (R = 68–100 Ω, C = 47–100 nF class X2 400V) in parallel with the TRIAC. rbdimmer modules already have a built-in RC snubber.

❌ Not compatible

ℹ️ LED strips (12V/24V) use a switching power supply (SMPS) — they are not the same as dimmable LED bulbs. SMPS loads are not compatible with phase-cut dimming. For LED strip dimming use a PWM DC controller, not an AC TRIAC dimmer.

Step 2: Calculate Current and Choose a Rating

Dimmer ratings are in amperes (A). Most loads specify power in watts (W), so convert first.

Formula

I = P / U
For 220/230V mains:  I = P / 220
For 110/120V mains:  I = P / 110

Safety margin

Always uprate the dimmer by a safety factor:

Selection rule: I_dimmer ≥ I_load × safety_factor

Worked example

Example: 800W space heater at 220V

1. I = 800 / 220 = 3.6A
2. Safety margin (resistive): 3.6 × 1.3 = 4.7A
3. Choose an 8A dimmer (next size up from 4.7A) ✅

Load-to-dimmer reference table

Values calculated with ×1.3 safety factor for resistive loads at 220V.

Maximum power by voltage (quick reference)

¹ For 127V mains multiply the 110V values by 1.15 (e.g. 4A → 400W, 8A → 800W).

Step 3: Platform and Library

The microcontroller and software stack determine which library you need and how to wire the ZC pin.

⚠️ Don't use RBDdimmer on ESP32. That library has no IRAM_ATTR on ISR handlers — it crashes when WiFi is active. Use rbdimmerESP32 on dual-core ESP32. See: Wrong Library: RBDdimmer vs rbdimmerESP32

VCC logic level

Do not connect VCC to 12V even if your project uses 12V rails — this will damage the dimmer and your MCU.

Step 4: How Many Channels?

All multi-channel modules share one zero-cross signal — one interrupt pin handles all channels. Each DIM pin is separate.

Step 5: Standard or High-Power Module?

For standard modules handling loads above 200W: add a heatsink to the TRIAC TO-220 tab (with insulating pad — the tab is at mains potential). See: TRIAC Overheating Guide

Step 6: Should You Use DimmerLink?

DimmerLink is a separate controller that handles zero-cross detection and TRIAC timing internally. Your MCU sends only a brightness level (0–100%) via I2C or UART.

See the Platform and Library table in Step 3 for a full list of platforms where DimmerLink is the recommended choice.

Wiring (same for any platform):

DimmerLink  →  MCU
VCC         →  3.3V (ESP32) / 5V (Arduino)
GND         →  GND
SDA         →  SDA (GPIO 21 on ESP32, A4 on Uno)
SCL         →  SCL (GPIO 22 on ESP32, A5 on Uno)

Code:

// DimmerLink — brightness 0–100% via I2C
// Works on any platform, no ISR, no IRAM_ATTR
// Docs: https://www.rbdimmer.com/docs/dimmerlink-I2CCommunication
#include <Wire.h>
#define DIMMER_ADDR 0x50
#define REG_LEVEL   0x10
void setLevel(uint8_t level) {
    Wire.beginTransmission(DIMMER_ADDR);
    Wire.write(REG_LEVEL);
    Wire.write(level);
    Wire.endTransmission();
}
void setup() {
    Wire.begin();
    setLevel(50);  // 50% brightness
}

Quick Selection Table

² "8A+heatsink": for loads above 200W on standard modules, attach a TO-220 heatsink with an insulating pad — the TRIAC tab is at mains potential.

Wiring Checklist

Before powering up, verify:

Safety first:

Power wiring:

Aluminum S (mm²) = I / 5

Wire gauge reference:

Logic wiring:

Next Steps

Now that you've chosen your module:

1. Wiring diagram → Hardware Connection Guide
2. Library setup → Universal Library for ESP32
3. DimmerLink setup → DimmerLink Quick Start

Related Articles

• AC dimmer is not PWM → How Phase-Cut Dimming Works
• Zero-cross not detected → Zero-Cross Not Detected: AC Dimmer Doesn't Respond
• ESP32 crashes with WiFi → ESP32 + AC Dimmer: IRAM_ATTR Causes and Fix
• TRIAC overheating → TRIAC Overheating: AC Dimmer Runs Hot or Burns Out
• LED compatibility → LED Lamps with AC Dimmer: Compatibility Guide

Still have questions?

Ask on forum.rbdimmer.com or open a GitHub Issue.