Overview

The PZEM-004T (specifically Version 3.0) is a single-phase AC electrical energy monitoring module manufactured by Peacefair. Designed for safe, non-invasive AC power measurement, it pairs an onboard SD2004/V9881 metering IC with a Current Transformer (CT) coil—either a closed-core or open/split-core transformer—to calculate six electrical parameters: voltage, current, active power, total energy consumption, grid frequency, and power factor.

The module features internal optocouplers that provide galvanic isolation between high-voltage mains AC ($80\text{V}$ to $260\text{V}$) and the low-voltage 5 V TTL UART communication lines. It uses a standard Modbus-RTU serial protocol over UART (9,600 bps), making it widely deployed in ESPHome, Home Assistant, and Arduino whole-house energy monitor builds.

Quick reference

Terminals & Connection Blocks

High-Voltage Mains Terminals (Screw Terminal Block)

Low-Voltage Control Header (4-pin 0.1" Header)

Specifications

Modbus-RTU Protocol Overview

The PZEM-004T v3.0 uses Modbus-RTU over 9,600 baud serial. Default Modbus slave address is 0x01 (programmable from 0x01 to 0xF8).

• Read Input Registers: Send 0x01 0x04 0x00 0x00 0x00 0x0A [CRC16].
• Response Payload (10 Registers / 20 Bytes):
  • Voltage (2 bytes, $/10 \to \text{Volts}$)
  • Current (4 bytes, $/1000 \to \text{Amperes}$)
  • Power (4 bytes, $/10 \to \text{Watts}$)
  • Energy (4 bytes, $/1 \to \text{Watt-hours}$)
  • Frequency (2 bytes, $/10 \to \text{Hz}$)
  • Power Factor (2 bytes, $/100 \to \text{PF}$)

Wiring

Example

#include <PZEM004Tv30.h>

// SoftwareSerial or HardwareSerial (e.g. Serial2 on ESP32)
PZEM004Tv30 pzem(Serial2, 16, 17); // RX=16, TX=17

void setup() {
  Serial.begin(115200);
}

void loop() {
  float voltage = pzem.voltage();
  float current = pzem.current();
  float power   = pzem.power();
  float energy  = pzem.energy();
  float pf      = pzem.pf();

  if (!isnan(voltage)) {
    Serial.print("Voltage: "); Serial.print(voltage); Serial.println(" V");
    Serial.print("Current: "); Serial.print(current); Serial.println(" A");
    Serial.print("Power: ");   Serial.print(power);   Serial.println(" W");
    Serial.print("Energy: ");  Serial.print(energy);  Serial.println(" kWh");
    Serial.print("PF: ");      Serial.println(pf);
  } else {
    Serial.println("Error reading PZEM-004T!");
  }

  delay(2000);
}

Common mistakes

• Looping both Live and Neutral through the CT coil: Net magnetic flux equals zero; current reads 0.00 A.
• Conflating v1.0 and v3.0 modules: Legacy PZEM-004T v1.0 used a custom ASCII protocol at 9,600 baud. Version 3.0 uses Modbus-RTU commands. Modern software libraries (ESPHome pzemac) require v3.0.
• Forgetting VCC supply to 4-pin header: The UART optocouplers are powered from the 4-pin header VCC/GND. Leaving VCC un-powered prevents serial data transmission.

Notes

• Split-Core vs Solid-Core CT: Split-core CT models feature a snap-open hinge, allowing installation around existing house wiring without disconnecting mains power circuits.