---
type: project
name: wrightstown-solar
display_name: Wrightstown Solar Battery System
last_compiled: 2026-05-24
compiled_by: DESKTOP-0O8A1RL/claude-main
sources:
  - projects/wrightstown-solar/session-logs/2026-02-09-session.md
---

# Wrightstown Solar Battery System

## Overview

A DIY home solar battery storage project at the Wrightstown residence. The system adds battery storage and whole-house UPS capability to an existing grid-tie solar installation (Fronius IG Plus inverter). The design uses LiFePO4 cylindrical cells assembled into modular 5kWh packs, a Victron MultiPlus II inverter/charger, and a Victron Cerbo GX for system management.

- **Status:** Planning / initial research phase as of 2026-02-09. No hardware purchased yet.
- **Existing solar:** Fronius IG Plus (grid-tie only, no battery port)
- **Goal:** Add battery backup, whole-house UPS with <20ms transfer, generator failover capability
- **Expansion target:** Up to 20kWh (4 packs of 5kWh each)
- **Related project:** [[wrightstown-smarthome]] — planned future integration via Victron Modbus TCP

## Tech Stack

- **Cell chemistry:** LiFePO4 (Lithium Iron Phosphate) — EVE C40 (IFR40135) cylindrical cells
- **Pack configuration:** 16S5P per pack (80 cells per 5kWh pack)
- **BMS:** JK BMS B2A8S20P 150A (recommended)
- **Inverter/charger:** Victron MultiPlus II 48/5000
- **GX device (system manager):** Victron Cerbo GX
- **BMS integration method:** dbus-serialbattery driver via USB-UART cable (not CAN direct)
- **Existing inverter:** Fronius IG Plus (grid-tie, retained — MultiPlus creates micro-grid for Fronius to sync during outages)

## Architecture

### Battery Pack Design
- Cell: EVE C40 (IFR40135) — 3.2V nominal, 20Ah, 64Wh per cell, 366g, 50–60A continuous discharge
- Configuration: 16S5P = 16 cells in series × 5 in parallel
  - Voltage: 51.2V nominal (48V system)
  - Capacity: 5kWh per pack (100Ah)
- Modular: build in 5kWh increments; target up to 4 packs (20kWh)
- 5kWh chosen over 10kWh for: cost spreading, manageable builds, fault isolation, single-person liftable weight

### Power Architecture
- Victron MultiPlus II as central inverter/charger: AC-coupled to Fronius IG Plus
- MultiPlus creates a micro-grid so Fronius can continue producing during grid outages
- <20ms transfer time (UPS-grade seamless switchover)
- Physical relay disconnect ensures zero backfeed to grid
- Generator input supported as third source
- Cerbo GX manages BMS-inverter communication and system telemetry

### BMS Integration
- JK BMS B2A8S20P 150A: 2A active balancing (critical for cylindrical cells)
- Integration path: USB-UART cable → dbus-serialbattery driver → Cerbo GX
- [WARNING] JK BMS CAN bus pinout is reversed — do NOT use CAN direct; use USB-UART path

### Alternative BMS Options (Researched)
| BMS | Notes |
|---|---|
| SEPLOS V4 ($150–250) | Native CAN, no pinout issue |
| REC Q16 ($559) | Plug-and-play Victron integration |
| Daly | Not recommended (no active balancing) |

## Deployment / Hosting

- Entirely on-premises at Wrightstown residence
- No cloud services involved in core system operation
- Future: Victron Modbus TCP integration with [[wrightstown-smarthome]] Home Assistant for monitoring

## Configuration / Credentials

*(not documented)* — No credentials or cloud accounts required for this project. Victron Cerbo GX may use VRM portal (Victron Remote Monitoring); if configured, store VRM account credentials in SOPS vault under `projects/wrightstown-solar/`.

## Active Work / Open Items

All items pending as of the 2026-02-09 initial research session:

- [ ] Finalize BMS selection (JK BMS B2A8S20P confirmed as recommendation; alternatives noted)
- [ ] Source EVE C40 cells — Grade A, matched, with test data (required for 16S5P pack)
- [ ] Order Victron MultiPlus II 48/5000 + Cerbo GX
- [ ] Design physical cell holder and bus bar layout for 16S5P cylindrical pack
- [ ] Plan sub-panel / transfer switch wiring
- [ ] Build Pack 1, run for 1 month before expanding to additional packs
- [ ] Plan Victron Modbus TCP crossover with [[wrightstown-smarthome]] Home Assistant

## Key Events / History

### 2026-02-09 — Initial Research and Planning Session
- Session run on machine: ACG-M-L5090
- Researched and selected EVE C40 (IFR40135) LiFePO4 cells over salvaged EV battery packs
- Determined 16S5P / 5kWh modular pack design
- Selected Victron MultiPlus II 48/5000 as inverter/charger for UPS-grade seamless transfer
- Evaluated 8 BMS models; recommended JK BMS B2A8S20P 150A ($80–150)
- Selected Cerbo GX ($320–350) as GX device over Raspberry Pi
- Analyzed salvaged EV battery options (Tesla LFP, Chevy Bolt, Nissan Leaf) — rejected due to cost and complexity
- Budget estimates established:
  - Phase 1 (5kWh + full Victron system): $2,175–2,945
  - Full 20kWh system: $3,635–5,750
  - Battery-only cost: $86–153/kWh
- Created project documentation structure:
  - `projects/wrightstown-solar/PROJECT_INDEX.md`
  - `projects/wrightstown-solar/documentation/system-design.md`
  - `projects/wrightstown-solar/documentation/bms-comparison.md`
  - `projects/wrightstown-solar/documentation/ev-salvage-analysis.md`
  - `projects/wrightstown-solar/documentation/parts-list.md`
- No hardware purchased or deployed this session. All work was research and planning.

## Anti-Patterns / Warnings

- [WARNING] **JK BMS CAN bus pinout is reversed.** Use USB-UART path with dbus-serialbattery driver. Do NOT attempt CAN direct connection.
- [WARNING] **Salvaged EV packs were explicitly rejected.** Most salvage is NMC chemistry (less safe than LFP for home use), unknown state of health, requires voltage conversion and custom BMS. New EVE C40 cells are cheaper and simpler.
- **The Fronius IG Plus cannot directly interface with batteries** — it is grid-tie only. The MultiPlus II creates the micro-grid; do not try to connect batteries to the Fronius directly.
- **Buy Grade A matched cells with test data.** Mismatched cells in a 16S5P pack will cause balancing problems even with active balancing.
- **Build Pack 1 first and run for 1 month before ordering materials for additional packs.** This is an explicit project decision to validate the design before scaling.

## Backlinks

- [[wrightstown-smarthome]] — Related project at same residence; planned Victron Modbus TCP crossover for Home Assistant monitoring