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claudetools/projects/wrightstown-solar/documentation/bms-comparison.md
Mike Swanson aaf4172b3c sync: Add Wrightstown Solar and Smart Home projects 
New projects from 2026-02-09 research session:

Wrightstown Solar:
- DIY 48V LiFePO4 battery storage (EVE C40 cells)
- Victron MultiPlus II whole-house UPS design
- BMS comparison (Victron CAN bus compatible)
- EV salvage analysis (new cells won)
- Full parts list and budget

Wrightstown Smart Home:
- Home Assistant Yellow setup (local voice, no cloud)
- Local LLM server build guide (Ollama + RTX 4090)
- Hybrid LLM bridge (LiteLLM + Claude API + Grok API)
- Network security (VLAN architecture, PII sanitization)

Machine: ACG-M-L5090
Timestamp: 2026-02-09

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-10 18:44:35 -07:00

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# Wrightstown Solar - BMS Comparison (Victron CAN Bus Compatible)
**Created:** 2026-02-09
**System:** 16S5P, EVE C40 20Ah, 48V, Victron MultiPlus II + Cerbo GX
---
## Quick Comparison
| BMS | Price | Current | Balancing | Victron Method | Complexity |
|---|---|---|---|---|---|
| **JK BMS B2A8S20P** | $80-150 | 100-200A | 2A Active | dbus-serialbattery (USB) | Moderate |
| **SEPLOS V3/V4** | $150-250 | 100-200A | Passive | Native CAN | Easy |
| **Overkill Solar (JBD)** | $280-320 | 100A | Passive | dbus-serialbattery (USB) | Moderate |
| **123SmartBMS Gen3** | $300-400 | Configurable | 1A Active | Native USB to Cerbo | Easy |
| **REC BMS Q16** | $559 | Varies | 0.9A Passive | Native CAN (plug & play) | Easiest |
| **Batrium WatchMon** | $650-850 | High (shunt) | 28Ah/day | Native CAN | Complex |
| **Daly Smart BMS** | $80-150 | 100A/50A charge | 30mA Passive | dbus-serialbattery | Moderate |
| **Orion BMS** | $500+ | Configurable | Active options | Native CAN | Easy |
---
## Recommended: JK BMS B2A8S20P (150A Version)
### Why This BMS for EVE C40 Cylindrical Cells
- **2A active balancing** -- Critical for cylindrical cells which have more cell-to-cell variation than prismatic. With 5P strings, mismatches multiply. Passive balancing at 30-200mA takes days; JK's 2A active balancing corrects in hours.
- **150A rating** -- 16S5P is 100Ah, so 150A provides headroom for inrush and peak loads
- **$80-150** -- Best value in the market
- **Huge DIY community** -- Every problem already solved on forums
### Specs
- Current ratings: 100A, 150A, 200A options
- Balancing: 2A active (best in class at this price)
- Communication: Bluetooth, RS485, CAN, UART
- Monitoring: Real-time via smartphone app
- Temperature: Multiple sensor inputs
### Victron Integration
```
JK BMS --[USB-UART cable ($15)]--> Cerbo GX
|
dbus-serialbattery
(free open-source driver)
|
DVCC enabled
|
Victron MultiPlus II
```
**Required:**
1. USB-UART cable (~$15)
2. dbus-serialbattery driver (free, install via SSH on Cerbo)
3. DVCC enabled in Cerbo settings
### [WARNING] Known Gotcha: Reversed CAN Pinout
JK BMS has CAN-H and CAN-L SWAPPED compared to Victron's RJ45 pinout. Solutions:
- Buy pre-made JK-to-Victron cable (AliExpress)
- Make your own cable and swap pins 7 & 8
- Use USB-UART connection instead (avoids CAN entirely -- recommended path)
### Known Issues
- Firmware updates frequently with no changelog -- check forums before updating
- SOC can jump from 85% to 100% prematurely during fast charge
- Battery capacity/consumed Ah data may not transmit to Cerbo via some driver versions
- Inconsistent quality control between batches -- test thoroughly on arrival
### Where to Buy
- AliExpress: $80-120 (multiple sellers)
- Amazon: $120-180 (JKBMS official store)
- EEL Battery, SeLian Energy (resellers)
---
## Alternative: SEPLOS V3/V4 (Easiest Native CAN)
### Why Consider
- Native Victron CAN protocol -- no drivers needed
- One CAN cable to Cerbo, auto-detects
- Multiple units can chain on one CAN link (good for expansion to 4 packs)
- $150-250 is reasonable mid-tier pricing
### Drawbacks
- Passive balancing only (slower than JK's active)
- Less community documentation
- Setup can be tricky initially
### Where to Buy
- Seplos.com (official)
- AliExpress, Alibaba
---
## Premium Option: REC BMS Q16 (Zero Hassle)
### Why Consider
- TRUE plug and play -- one CAN cable, auto-detected, DVCC works immediately
- Most reliable Victron integration available
- Professional-grade, excellent documentation
- SOC/SOH calculation, cell resistance measurement
### Drawbacks
- $559 -- nearly 4x the JK price
- Passive balancing only (0.9A) -- slower for cylindrical cells
- No active balancing option
### Where to Buy
- Off Grid and Marine Energy (OGM Energy): $559
- REC-BMS.com (official)
---
## Budget Option: Daly Smart BMS [NOT RECOMMENDED]
### Why to Avoid for This Build
- 100A discharge but only **50A charge** -- will bottleneck solar charging
- 30mA passive balancing -- useless for large cells (would take 200+ hours)
- CAN speed mismatch: Daly defaults to 250kbit/s, Victron uses 500kbit/s
- Developers of dbus-serialbattery specifically do NOT recommend Daly for new builds
- Bad CAN communication implementation
---
## Victron Side Configuration
### Hardware Required
**Cerbo GX ($320-350) -- Recommended**
- Native BMS-CAN port (500kbit/s)
- 2x USB ports for dbus-serialbattery driver
- Built-in display, Ethernet, WiFi
- VRM remote monitoring portal
**Budget Alternative: Venus OS on Raspberry Pi 4 (~$100)**
- No native CAN bus -- needs USB CAN adapter ($20-40)
- More complex setup
- Works for USB-UART BMS connection (JK, Overkill)
### CAN Cable Pinout (Cerbo GX BMS-CAN RJ45)
| Pin | Function |
|---|---|
| 3 | GND |
| 7 | CAN-H |
| 8 | CAN-L |
Only 3 wires needed. Always verify against your specific BMS datasheet.
### Software Settings
1. **Update firmware** on Cerbo GX, MultiPlus II, and any MPPTs to latest
2. **Battery Monitor:** Set to BMS (not "Automatic")
3. **DVCC:** Enable
4. **DVCC Sub-settings:**
- Limit managed battery charge voltage: OFF (let BMS control via CVL)
- SVS (Shared voltage sense): ON
- SCS (Shared current sense): OFF
- STS (Shared temperature sense): Optional
5. **BMS-CAN speed:** 500kbit/s (default, don't change)
### dbus-serialbattery Driver (for JK/Overkill/Daly via USB)
- Install on Cerbo via SSH
- Edit `/data/etc/dbus-serialbattery/config.ini`
- Set BMS type and serial port
- Free, open source: https://github.com/Louisvdw/dbus-serialbattery
### DVCC Explained
DVCC allows the BMS to send real-time limits to the Victron system:
- **CVL** (Charge Voltage Limit) -- max voltage the battery will accept
- **CCL** (Charge Current Limit) -- max charge current right now
- **DCL** (Discharge Current Limit) -- max discharge current right now
The Cerbo relays these to the MultiPlus and any solar chargers, preventing overcharge, over-discharge, and overcurrent dynamically.
---
## Common Mistakes to Avoid
1. **CAN speed mismatch** -- Victron is 500kbit/s, some BMS default to 250kbit/s
2. **JK pinout reversal** -- CAN-H and CAN-L are swapped on JK BMS
3. **Enabling DVCC without setting battery monitor** -- set monitor FIRST
4. **SVS with disconnect BMS** -- if BMS disconnects on overvoltage, turn SVS OFF
5. **Multiple BMS on CAN** -- only ONE BMS should control Victron via DVCC (use master/slave for multi-pack)
6. **Charging below 0C** -- LFP cannot be charged below freezing; ensure BMS low-temp cutoff is configured
7. **Passive balancing on large cells** -- 30mA on 20Ah cells takes forever; use active balancing
---
## Sources
- [Victron Compatible BMS - DIY Solar Forum](https://diysolarforum.com/threads/victron-compatible-lifepo4-bms.47111/)
- [Victron Community - Compatible BMS List](https://community.victronenergy.com/questions/13574/list-of-compatible-bms-vebus-or-canbus.html)
- [JK BMS and DVCC - Victron Community](https://community.victronenergy.com/t/jk-bms-and-dvcc/29580)
- [REC BMS Victron Integration Guide - OGM Energy](https://ogm-energy.com/community/ogm-user-forum/topic/154310/)
- [dbus-serialbattery GitHub](https://github.com/Louisvdw/dbus-serialbattery)
- [Victron DVCC Documentation](https://www.victronenergy.com/media/pg/CCGX/en/dvcc---distributed-voltage-and-current-control.html)
- [VE.Can to CAN-bus BMS Cables](https://www.victronenergy.com/live/battery_compatibility:can-bus_bms-cable)
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