Multiple PZEM-004T v3 on ESP32 zero/failed reads

[DurraniHakim27]

Multiple PZEM-004T v3 on ESP32 (mandulaj/PZEM004Tv30) — individual OK, combined → zero/failed reads

Hello! thanks for the library. I’m seeing a reproducible issue when connecting multiple original PZEM-004T v3 meters to a single ESP32 UART using your PZEM004Tv30 library. Each meter works correctly when connected alone, but once I attach more than one meter to the same RX/TX pair, all meters return zero values or fail to read. I already assigned unique addresses for each PZEM. Details below.

Hardware & wiring

• MCU: ESP32 DevKit
• PZEM Serial: Serial2 (example: RX = GPIO16, TX = GPIO17) — PZEM modules operate at 9600 baud (open Serial Monitor at 115200 for logs)
• PZEM modules: 5 × PZEM-004T v3 (original)
• Addresses assigned: 0x01, 0x02, 0x03, 0x04, 0x05 (I verified each responds when connected alone)
• Power: common 5V supply for PZEMs; common ground tied to ESP32
• Wiring: PZEM TX lines tied to ESP RX; PZEM RX lines tied to ESP TX (all modules on same TTL pair)

Observed behavior

Single meter connected: works perfectly.

Addr 0x01 RESPONDED: V=232.40 V, I=0.171 A, P=21.70 W, E=0.050 kWh, F=50.0 Hz, PF=0.53

Two or more meters connected to the same UART: all return zeros or fail.

Addr 0x01 READ_FAILED (dt=55 ms)
Addr 0x02 READ_FAILED (dt=50 ms)
...or sometimes:
Addr 0x02 RESPONDED: V=0.00 V, I=0.000 A, P=0.00 W, F=0.0 Hz, PF=0.00

I also tried scanning addresses 0x01–0xF7 while multiple meters were connected. When tested singly, each replied correctly, but with others connected, no valid responses were received.

What I tried

• Confirmed all devices have unique addresses and share common ground.
• Verified each device individually works on the same UART.
• Added inter-read delays (100–500 ms) and sequential polling logic.
• Tried powering via both ESP32 5 V and external regulated 5 V (same result).

Questions

1. Does the ESP32 have limits on how many PZEM modules it can handle on the same UART port?
2. Should I consider switching to ESP8266 instead for better compatibility?
3. Or do I need to add any extra components (e.g. diode, resistors, transistors) to make multi-device communication stable?

[joaoairton]

I'm also facing the exact same problem, the only difference is that I'm using 3 PZEM-004T modules.

[renga95]

I'm having the same problem. My project uses three PZEM-004T-100A (v3.0) microcontrollers, but I can't seem to read two of them simultaneously in TTL. I modified the 1K resistor on the PZEM-004T to operate at 3.3V DC, but it still doesn't work. In fact, it causes the ESP32 to restart when I try to read the data.

[randybb]

#141