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Basic AC power wattmeter module for SCT-013 clamp

$ 1,00 $ 1,00

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Basic AC Power Wattmeter for SCT-013 clamps — single, dual, or triple-load configuration on a clean I²C bus. Drop-in PZEM / JSY / HLW replacement that integrates natively with Home Assistant via ESPHome. Bring your own SCT-013 clamp (any voltage-output variant) and you have a complete wattmeter with tariff-grade Wh accounting in minutes.

Pick this if you're hitting any of these walls:
  • You already own SCT-013 clamps from earlier projects
  • You can't power down the wiring for install (clip-on is non-invasive)
  • Your tariff went hourly and your UART meter loses energy in the read-reset gap
  • You need 2 or 3 loads measured on one module with shared voltage reference
  • Your PZEM / JSY works, but you need a second one and your ESP32 UARTs are taken

Choose your channel count

Variant Voltage input Current channels (SCT-013) What it measures Energy (Wh)
UI1 1 (line-to-neutral) 1 jack U, I, P, PF, frequency, energy — one load ✅
UI2 1 (shared) 2 jacks Shared U + per-channel I, P, PF on two loads ✅
UI3 1 (shared) 3 jacks Shared U + per-channel I, P, PF on three loads ✅

Five lines of YAML — module in Home Assistant

rbamp:
  - id: rbamp_main
    address: 0x50
    data_ready_pin: GPIO4

sensor:
  - platform: rbamp
    rbamp_id: rbamp_main

What you get

I²C bus architecture

Multiple modules share two ESP32 signal lines (SDA + SCL). Default address 0x50; reprovision each module to a unique 7-bit address in 0x08..0x77 before sharing the bus. Up to ~16 modules on a single I²C bus, Basic and Standard tiers mix without distinction.

Atomic period latch

Master sends CMD_LATCH_PERIOD; the module returns period_avg_P_W (float32 average active power for the period). Master multiplies by wall-clock dt to get Wh. No read-reset gap. Drift-free tariff metering at hourly cadence and beyond.

5 kHz hardware sampling

True-RMS calculation over 1000 samples per 200 ms window on-module via DMA. Your ESP32 reads pre-computed values, not raw ADC samples. Frees the host MCU for application logic.

Native ESPHome integration

Auto-discovery via the rbamp-esphome external_component. Roughly 5 lines of YAML for a single module. All sensors surface as native Home Assistant entities — U_rms, I_rms, P_active, PF, frequency, energy accumulator.

What's in the box

  • rbAmp Basic SCT-013 Wattmeter module (PCB)
  • 1 / 2 / 3 × 3.5 mm stereo jacks on the board for SCT-013 clamps (depends on variant: UI1 / UI2 / UI3)
  • Screw terminals for the voltage input (one set, line + neutral)
  • Quick reference card with link to documentation

SCT-013 clamps are NOT included. Buy separately — we recommend YHDC SCT-013-030 (30 A, 1 V output) as the default for residential single-load monitoring, or SCT-013-100 (100 A, 1 V output) for main-feed monitoring.

Compatible clamps: any voltage-output SCT-013 (5 / 10 / 30 / 50 / 100 A — all with 1 V full-scale output). NOT compatible: SCT-013-000 (current output 50 mA — use the rbAmp Basic CT TA Wired variant for current-output sensors).

Real-time data (refreshed every 200 ms)

Register Description
U_rms RMS line voltage (V)
I_rms[ch] RMS current per channel (A) — 1, 2, or 3 channels depending on variant
P_active Active power per channel (W, signed — direction-flow diagnostic)
Q_reactive Reactive power (var, signed: + inductive, − capacitive)
PF Power factor (signed: leading / lagging)
Frequency Line frequency (Hz)
period_avg_P_W Atomic period latch — average active power for the current period (see Atomic period latch section below for master-side Wh computation)

Atomic period latch (UI configurations)

Item Description
CMD_LATCH_PERIOD Master-issued command. Atomic snapshot: closes the current period + opens the next, in one I²C transaction.
period_avg_P_W Float32 register. Average active power for the closed period — master reads this after each LATCH.
Atomicity guarantee Every 200 ms power sample lands in either the previous or the next period — never in a read-reset gap. Drift-free Wh accounting against utility meter.
Mode 1 — continuous One LATCH per period boundary. Optimal for tariff billing: 1-min logs, 15-min peak demand, hourly tariff zones, daily totals. Minimum I²C transactions.
Mode 2 — event-based Two LATCHes for arbitrary start / end. Clean period for event-driven accounting: contactor close / open, EV charging session start / stop.
Master computation Wh = period_avg_P_W × dt / 3600 where dt = master's wall-clock interval between LATCHes (in seconds).
Multi-channel (UI2 / UI3) Single CMD_LATCH_PERIOD atomically snapshots all channels simultaneously. Per-channel period_avg_P_W[ch] registers — read each after one LATCH, compute per-channel Wh against the same wall-clock dt.

Compatibility

Specifications

Spec Value
Supply voltage (VCC) 5 V DC (on-board 3.3 V regulator)
I²C / DataReady logic level 3.3 V (ESP32 / Raspberry Pi GPIO direct, no level shifter)
Current draw <20 mA typical
I²C address 0x50 default, reprovisionable to 0x08..0x77
DataReady pin Open-drain, idle HIGH, ~10 µs LOW pulse every 200 ms — falling-edge interrupt
AC voltage range 90–280 VAC, 50/60 Hz
AC current range 0.25–100 A (depends on SCT-013 model)
U_rms accuracy ±2–3%
Accuracy (current) module ~0.5% + sensor (SCT-013) 1–3% — total = module + sensor
Current noise floor ~150–200 mA (SCT-013 clamp-limited)
Sampling rate 5 kHz per channel (5,000 samples per second)
Real-time integration window 200 ms
ADC resolution 12-bit
AC mains isolation Full galvanic (isolated voltage front-end + SCT-013 clamp toroid + I²C bus)
Connector for SCT-013 3.5 mm stereo jack (TRS) per channel
Connector for voltage input Screw terminals (line + neutral)

Installation safety

⚠️ SCT-013 clip-on install is non-invasive — clamp around a live conductor without powering down the wiring. Careful jaw alignment matters: poor seating adds 1–2% error. All work must follow local electrical codes. For panel-level work, a qualified electrician is strongly recommended.

⚠️ The module ships as a bare PCB. The Basic line does not include enclosures — for DIN-rail housings or panel boxes, use third-party project enclosures.

This module is not certified for revenue metering (utility-grade billing). For commercial accounting, use a certified meter alongside rbAmp for diagnostic / per-circuit detail.

Warranty and support

Upgrade pointer

Looking for higher accuracy? rbAmp Standard tier delivers sub-0.5% real-world accuracy, sub-10 mA noise floor, signed power for solar bidirectional, diagnostic alarms, and traceable factory calibration. Drop-in upgrade on the same I²C bus (different address range).