Mike Swanson
aaf4172b3c
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>
3.4 KiB
Wrightstown Solar - Salvaged EV Battery Analysis
Created: 2026-02-09 Decision: New EVE C40 cells selected over salvaged EV packs
Summary
Salvaged EV battery packs were evaluated as an alternative to new EVE C40 LiFePO4 cells for the 20kWh home storage system. The analysis concluded that new cells are the better choice due to lower total cost, longer lifespan, better safety profile, and simpler integration.
Cost Comparison
| Option | Cost for 20kWh | $/kWh | Expected Life | Chemistry |
|---|---|---|---|---|
| New EVE C40 | $3,800-5,640 | $190-282 | 3,000-6,000 cycles | LFP |
| Salvaged Tesla LFP | $8,500-15,600 | $415-780 | 500-2,000 cycles | LFP |
| Salvaged Chevy Bolt | $9,800-14,000 | $490-700 | 500-1,500 cycles | NMC |
| Salvaged Nissan Leaf | $7,300-10,000 | $365-500 | 500-1,500 cycles | NMC |
Why Salvaged Packs Cost More Than Expected
Voltage Mismatch
EV packs run at 350-400V. The system needs 48V. Options:
- DC-DC converter (400V to 48V): $1,500-3,000
- Complete pack disassembly and reconfiguration: 40-60 hours labor
Proprietary BMS
OEM battery management systems are useless outside the vehicle. Aftermarket replacement (e.g., Orion BMS) costs $800-1,500 plus significant wiring work.
Cooling Systems
Most EV packs are liquid cooled. At home storage discharge rates, passive cooling may suffice, but you're discarding a system the cells were designed around. Adding proper cooling: $500-1,500.
Unknown State of Health
- No reliable way to verify remaining capacity without specialized testing
- Packs from totaled vehicles have unknown fast-charge history and cycle count
- Cells may be at 70% SOH when "retired" -- a 60kWh pack may only deliver 40kWh
- Average EV battery loses 2.3% capacity per year
Chemistry Concerns
Most salvaged packs are NMC (nickel manganese cobalt), NOT LiFePO4:
- NMC thermal runaway: ~210C (410F)
- LFP thermal runaway: ~270C (518F)
- For home storage inside/next to a house, LFP is the responsible choice
Time Investment
- Salvaged EV build: 40-100+ hours (disassembly, testing, rewiring, custom fabrication)
- New C40 build: 10-20 hours per 5kWh pack with off-the-shelf parts
When Salvaged DOES Make Sense
- Tesla Model 3 Standard Range LFP modules at under $100/kWh with verified 85%+ SOH
- Free/very cheap packs from personal connections
- Educational/hobby project where learning is the goal
- Electrical engineering background and high-voltage experience
- However: LFP Model 3 was discontinued in US market due to tariffs, limiting availability
Salvage Sources (For Reference)
- Currents Marketplace (currents.market) -- dedicated EV battery platform
- Greentec Auto (greentecauto.com) -- premium second-life batteries
- Second Life EV Batteries (secondlife-evbatteries.com)
- AZLithium (azlithium.com) -- Chevy Volt, Leaf, BMW i3 modules
- eBay -- wide selection, variable quality
Decision Rationale
New EVE C40 cells win on every metric that matters for this project:
- 50-65% cheaper total system cost
- 3-10x longer lifespan (known cycle life vs unknown remaining)
- Safer chemistry (LFP vs NMC)
- Native 48V configuration (no voltage conversion)
- Standard BMS compatibility (off-the-shelf 16S)
- Known capacity (no degradation mysteries)
- 5x less build time (10-20 hours vs 40-100+)
- Warranty coverage from cell manufacturer