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The problem
Solar home systems and small institutions run on lead-acid banks that die young — not from age, but from chronic undercharging, deep discharge and nobody watching the state of charge. A voltmeter alone cannot tell you the bank's health because voltage sags under load and recovers at rest. This project builds a proper monitor: a 24 V bank (four 12 V batteries) with a precision voltage divider, a Hall-effect current sensor for charge/discharge current, and solar input measurement at the charge controller. An ESP32 computes state of charge by coulomb counting corrected with rested-voltage, tracks bulk/absorption/float stages, and publishes everything over Wi-Fi via MQTT to a dashboard with SOC gauges, 24-hour charge-cycle graphs and backup-time estimates. The project states the method's limits plainly: coulomb counting drifts and needs periodic full-charge resets, which the firmware performs automatically.
Divides the 24 V bank voltage into the ESP32 ADC range so the bank voltage is measured accurately.
Follow the working sequence
How it works
- The voltage divider, Hall-effect current sensor and solar input tap are wired to the ESP32 on the 24 V bank + solar demonstration rig.
- Firmware samples voltage and current, integrates current over time for coulomb counting, and corrects SOC with rested-voltage lookup.
- Every 10 seconds (design target) the ESP32 publishes voltage, current, SOC, solar watts and charge stage as JSON over Wi-Fi via MQTT.
- The dashboard renders the SOC gauge, charge-cycle graphs and the backup-time estimate from the live stream.
- Charge-stage logic classifies bulk/absorption/float from the voltage and current signatures each cycle.
- When SOC falls below the low threshold, an alert fires; at the critical threshold the load-shed relay opens.
- A detected full charge (float at low current) resets the coulomb counter, bounding long-term drift — the key to usable SOC.
Tech stack:
- ESP32 development board
- 24 V battery bank (4x 12 V, demo)
- Precision voltage divider network
- Hall-effect current sensor (ACS758 class)
- Solar panel + charge controller (demo)
- Relay module (load-shed output)
- MQTT broker + web dashboard
- Arduino IDE (C/C++ firmware)
| Parameter | Value |
|---|---|
| Controller | ESP32, Wi-Fi MQTT telemetry (JSON payloads) |
| Bank | 24 V nominal (4x 12 V lead-acid, demonstration scale) |
| Voltage sensing | Divider network; approximately +/-1% typical (expected) |
| Current sensing | Hall-effect, bidirectional charge/discharge |
| SOC method | Coulomb counting + rested-voltage correction + auto full-charge reset |
| Reporting | 10-second design-target interval; MQTT reconnect with backoff |
| Dashboard | SOC gauge, charge-cycle graphs, stage indicator, backup estimate, alerts |
| Load shed | Relay output at critical SOC (configurable) |
Project features
- [State-of-charge tracking] Coulomb counting with rested-voltage correction and automatic full-charge resets gives a usable SOC figure — far beyond a raw voltmeter.
- [Charge-stage detection] Firmware identifies bulk, absorption and float stages from voltage/current signatures and displays the active stage.
- [Live bank dashboard] SOC gauge, bank voltage, charge/discharge current, solar watts and backup-time estimate, all from live telemetry.
- [Charge-cycle graphs] 24-hour plots of solar input, SOC and current show the full daily cycle for the report's analysis section.
- [Backup-time estimate] Remaining backup hours are estimated from SOC and the recent average load — the number users actually care about.
- [MQTT telemetry] The ESP32 publishes bank readings as JSON over Wi-Fi via MQTT with a design-target 10-second interval.
- [Protection alerts] Low SOC, over-voltage and over-current thresholds raise dashboard alerts; a relay can shed non-critical load at critical SOC.
What is included
- Working solar + battery demonstration rig (bank, panel, controller, sensors, ESP32)
- Complete firmware source (SOC engine, stage detection, MQTT, load-shed)
- Live web dashboard (gauges, charge graphs, backup estimate) demonstrated with the rig
- Circuit and wiring documentation
- Voltage/current calibration procedure against reference meters
- Component list with ratings
- Project report PDF (lead-acid background, SOC methods, charge stages, methodology)
- PPT presentation for final review
- Viva Q&A preparation document (coulomb counting, charge stages, Hall sensing, MQTT)
- Setup and demonstration guide
Limitations & prerequisites
- SOC by coulomb counting drifts between full charges; the auto-reset bounds it, but the figure is an estimate (approximately +/-5-8%, expected), not a laboratory measurement.
- Demonstrated at 24 V demo-bank scale; the method scales but larger banks need re-rated sensing and protection.
- Rested-voltage correction needs genuine rest periods — a continuously cycled bank leans on coulomb counting alone.
- Lead-acid behaviour is assumed; lithium banks need different voltage curves and are listed as future scope.
- Battery terminals and the charge controller carry real energy — assembly follows the supervised build guide.
Frequently Asked Questions
How is state of charge calculated?
By coulomb counting — integrating charge/discharge current over time — corrected with rested-voltage lookup and automatic resets at detected full charge. The report explains why a voltmeter alone is misleading and how the reset bounds long-term drift.
What are the charge stages it detects?
Bulk (constant current, voltage rising), absorption (constant voltage, current tapering) and float (maintenance voltage) — classified from the voltage/current signatures each cycle and shown live on the dashboard.
How accurate is the SOC?
Approximately +/-5-8% (expected) between full-charge resets — honest and usable for backup planning. The manual documents the drift sources and the reset logic that contains them.
What happens at low battery?
A low-SOC alert fires first; at the configurable critical threshold the load-shed relay disconnects non-critical loads to protect the bank from deep discharge.
Can it work with lithium batteries?
The sensing hardware transfers directly, but lithium needs different voltage curves and protection logic — documented as future scope in the report.
Is this project suitable for a final-year project?
Yes — for Electrical Engineering programs. It covers battery sensing, SOC algorithms, charge-stage analysis, MQTT telemetry and protection logic, all strong viva material. Suitable for B.E./B.Tech final-year projects in Electrical Engineering.
Components & software requirements
- ESP32 development board
- 24 V battery bank (4x 12 V, demo)
- Precision voltage divider network
- Hall-effect current sensor (ACS758 class)
- Solar panel + charge controller (demo)
- Relay module (load-shed output)
- MQTT broker + web dashboard
- Arduino IDE (C/C++ firmware)
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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