24 V Battery Box + 2 kW Inverter/Charger + Solar Suitcase
EMP-aware liners, SB50 quick-swap, and transfer-switch-safe outputs. This is a field-ready backup core for gamers, creators, and neighbors.
Safety (No Backfeeding. No Smoke.)
- AC to house: Only via listed transfer switch/interlock with a proper inlet. Never backfeed a dryer outlet. Label everything.
- Fusing: Place the main DC fuse as close as practicable to battery + (Class-T recommended for high interrupt DC). Sheath longer unfused runs.
- CO hazard: If you add a fuel generator later, operate outdoors far from openings; use CO alarms.
Design Targets
| Battery | 24 V (8s) LiFePO₄, 100–200 Ah |
|---|---|
| Inverter/Charger | ~2 kVA (120 V AC), low idle draw, built-in charger |
| Solar | MPPT 30–60 A, PV suitcase 400–800 W |
| Quick-Swap | Anderson SB50 DC in/out |
Charge Profile (24 V LiFePO₄)
| Bulk/Absorb | 28.0–29.2 V (per battery datasheet) |
|---|---|
| Float | ~27.0 V (or disable for mobile) |
| Low temp | Charge ≥0 °C unless battery has heater |
Set per your battery manufacturer; typical parameters shown.
Outputs
- AC: 120 V GFCI duplex + L5-30 inlet to transfer switch
- DC: 24 V posts, SB50 port, USB-C PD hub (via buck)
Bill of Materials
Core Power
| Battery | 24 V LiFePO₄ (8s) 100–200 Ah with BMS |
|---|---|
| Main DC fuse | Class-T 200–300 A + covered block |
| Shunt | 500 A/50 mV smart shunt (Bluetooth app) |
| Bus bars | Positive/negative, 250–300 A rated |
| Inverter/charger | ~2 kW 120 V unit (with charger) |
| MPPT | 30–60 A, 100–150 V PV input |
Distribution & IO
| DC distro | Blade-fuse block + breakers as needed |
|---|---|
| Quick-swap | Anderson SB50 panel + pigtails |
| AC | L5-30 inlet to transfer switch / interlock |
| Solar | PV suitcase (2×200–400 W), MC4s, combiner if ≥3 strings |
Wiring & Enclosure
| Enclosure | Rugged tote/Pelican or battery box w/ vents |
|---|---|
| Wire | Welding cable 2/0–2 AWG (DC main), 6–10 AWG (MPPT), 12–14 AWG (loads) |
| Lugs | Tinned copper lugs + heat-shrink |
| Protection | TVS diode (SMCJ33A) across 24 V, DC breakers |
| EMP-aware | Bonded steel inner liner or conductive fabric bag for radios/routers |
| Labels | Heat-shrink labels: BAT+, CLASS-T, BUS+, INV, MPPT, SB50 |
Size wire via ampacity & voltage-drop tables. Fuse to protect the smallest downstream conductor.
Wiring Maps
DC Backbone
BAT+ → [Class-T 200–300 A] → BUS+ → (A) Inverter/Charger + (B) MPPT BAT+ + (C) DC Distro
BAT− → [Shunt: BAT side] → [Shunt: SYS side] → BUS− → Inverter/Charger − / MPPT BAT− / Distro −
SB50 Port (in/out) → BUS via 125–200 A breaker (as appropriate)
Shunt sense → battery monitor app. Keep sense leads short & protected.
TVS (SMCJ33A) across BUS+ to BUS− with short leads (spike clamp).
AC Leg (Transfer-Switch-Safe)
Inverter AC-OUT → GFCI duplex (local)
Inverter AC-OUT (L5-30) → Exterior inlet → Transfer switch / interlock → Selected house circuits
(Neutral bonding per inverter manual & local code; GFCI/AFCI as required.)
Solar Suitcase (MPPT)
PV Panels → MC4 leads → (Combiner with string fuses if ≥3 strings) → PV Disconnect → MPPT PV+
MPPT BAT+ → Fused link (60–80 A max per controller) → BUS+
MPPT BAT− → BUS−
Connection order: Battery to MPPT first; PV last. Disconnect PV first; then battery.
Build — Step by Step
- Layout & plate: Dry-fit battery, inverter/charger, MPPT, bus bars, fuse block. Ensure service clearances and airflow.
- Main fuse: Mount Class-T fuse block within a few inches of battery + (short, protected run). Size at 1.25× your max continuous DC current to the inverter (2 kW @ 24 V ≈ 83 A; allow surge).
- Shunt: Place shunt on battery negative (battery-side only to battery). All other negatives land on shunt system side → bus −.
- Bus bars & lugs: Fit positive/negative bus bars. Crimp lugs with a hex die; no tinned solder blobs. Heat-shrink all terminations.
- Inverter/charger: Run 2/0–2 AWG from BUS to inverter DC lugs via appropriate DC breaker. Mount GFCI outlet. Add L5-30 inlet to connect to your home transfer switch/interlock.
- MPPT: Land BAT+/- to BUS via fused link. Add PV disconnect. Pre-wire MC4 pigtails for the suitcase.
- Quick-swap: Panel-mount Anderson SB50 and wire to BUS through a breaker (so a remote pack can charge the box or the box can power external DC).
- EMP-aware touches: Bond any metal liner to BUS− (chassis). Store spare comms (router, LTE modem) in a conductive pouch when not deployed.
- Programming: Set inverter/charger for 24 V LiFePO₄: Absorb 28.4–28.8 V, Float ~27.0 V (or off). Set low-voltage cutoffs per battery manual.
- Bring-up sequence: Verify polarity with meter. Close main DC. Power inverter (no loads). Program MPPT. Connect battery first, then PV. Plug a small AC load. Watch shunt amps & temps.
Solar MPPT Suitcase (400–800 W)
Panel Configs
- 2S of “24 V-class” panels: Vmp ≈ 70–74 V (good for 100 V MPPT)
- 2S2P (four panels): ~800 W → fuse each string if 3+ parallel (per 690.9 rules)
- Use MC4 inline fuses/breakers in the suitcase if needed
Cold Voc must stay under the controller’s PV max.
Deploy & Stow
- Open suitcase, set tilt ~latitude (see helper)
- Connect battery to MPPT (verify app shows 24 V)
- Connect PV last; watch charge current rise
- Stow: PV off first; then open battery fuse to MPPT
Battery Runtime & Load Planner
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Total Use / Day | 0 Wh | ||
Runtime at 100% = (Capacity × Eff) / Total_Watts. Solar harvest extends runtime.
Solar Size Helper
| Harvest (kWh/day) | — |
|---|---|
| Charge amps @ 28 V | — |
Rule-of-thumb: Wh/day ≈ PV_W × SunHours × 0.75.
Pre-Flight Checklist (Print)
- Battery SOC ≥ 50%, lugs tight, no warm spots
- Class-T fuse intact; DC breakers labeled
- Shunt online in app; inverter idle ~spec
- AC side: GFCI tests OK; transfer switch verified
- Solar suitcase: MC4 leads clean, tilt set
- Spare fuses, SB50 pigtail, MC4 tool in pouch
Quick Start (Lid Card)
- Close main DC breaker; power inverter → test outlet
- To power house: plug L5-30 into inlet → operate transfer switch/interlock
- Charge from wall: plug AC-in to inverter/charger; confirm charge amps
- Charge from solar: connect battery to MPPT → connect PV last
- Shutdown: PV off → open DC → AC off
Sources & Standards
- NEC Article 702 — optional standby systems (transfer equipment, no backfeed). ECM summaries (2020–2025).
- OSHA & CPSC generator hazard sheets (CO, shock) for general backup-power safety context.
- ABYC E-11 excerpts and marine OCP practice; Blue Sea Class-T specs & DC ampacity/voltage-drop methods.
- Victron SmartShunt & SmartSolar manuals — battery-first PV connection order; firmware/config basics.
- RELiON/Battle Born LiFePO₄ voltage parameters (24 V absorb/float).
- Anderson SB50 datasheets (ampacity, keyed housings).