24 V Victron OR 48 V EG4 — pick your poison (both battle-tested)
Two complete, field-ready builds. Same mission: safe backup power, fast solar, clean AC, no gatekeeping.
Safety (read, then build)
- AC to house: Use a listed transfer switch/interlock & proper inlet (NEC Art. 702). No backfeeding dryer outlets. Label circuits.
- DC fusing: Main fuse as close as practicable to battery + (Class-T preferred). Protect the smallest downstream conductor.
- MPPT sequence: Battery → MPPT first; PV last. Reverse to shut down (PV off → battery off).
Variant A — Victron 24 V
Specs
| Battery | 24 V (8s) LiFePO₄, 100–200 Ah |
|---|---|
| Inverter/Charger | Victron MultiPlus 24/2000 (120 V AC) |
| Solar | External MPPT (e.g., 100/50–150/60), 400–1200 W PV |
| Quick-swap | Anderson SB50 DC in/out |
LiFePO₄ charge (24 V)
| Absorb | ≈ 28.4 V (per Victron lithium guidance) |
|---|---|
| Float | ≈ 27.0 V |
| Low-V shut | ≈ 22–24 V (per battery datasheet) |
Set in VEConfigure or DIP; storage mode optional. See the “Settings” section below.
AC I/O
- GFCI duplex for local loads
- L5-30 feed to inlet → transfer switch/interlock
Wiring (DC backbone)
BAT+ → [Class-T 200–300 A] → BUS+ → (A) MultiPlus + (B) MPPT BAT+ (C) DC Distro
BAT− → [Shunt BAT side] → [Shunt SYS side] → BUS− → MultiPlus − / MPPT BAT− / Distro −
SB50 port ↔ BUS via 125–200 A breaker (charge in or power out)
Wiring (AC, transfer-safe)
MultiPlus AC-OUT → GFCI duplex
MultiPlus AC-OUT (L5-30) → exterior inlet → transfer switch or interlock → selected house circuits
(Neutral/ground bonding per MultiPlus manual & local code)
Wiring (Solar)
PV → MC4 → (Combiner w/ string fuses if ≥3 parallel) → PV disconnect → MPPT PV+
MPPT BAT+ → fused link (per controller) → BUS+ | MPPT BAT− → BUS−
Sequence: connect battery to MPPT first; PV last. Stow PV first; then open battery fuse.
Settings — Victron MultiPlus 24/2000 (quick start)
- Charger: Absorb 28.4 V; Float 27.0 V; Absorb time ~1–2 h (or per BMS/battery). Storage ≈ 26.4–26.8 V if enabled.
- Inverter: LV shutdown ≈ 22.0–22.8 V; LV restart ≈ 24.0 V; Search mode optional to cut idle draw.
- AC input limit: set to your branch (e.g., 15 A) so charger won’t trip breakers.
- PowerAssist: enable if you want the battery to assist a weak AC source.
Program via VEConfigure/MK3-USB or VictronConnect (GX path). DIP switch table is in the product manual.
Step-by-Step (build)
- Dry-fit: battery, MultiPlus, MPPT, Class-T fuse block (near battery), shunt, bus bars, DC breakers, SB50, GFCI, inlet.
- Crimp: use 2/0–2 AWG welding cable for inverter DC; 6–10 AWG for MPPT; ferrules on small conductors. Heat-shrink every lug.
- Fuse: mount Class-T within ~20 cm of BAT+; land to BUS+. Shunt on the negative—battery on “BAT” side, everything else on “SYS”.
- Land MultiPlus DC to BUS via breaker. Mount GFCI. Add L5-30 outlet linked to your exterior inlet → transfer equipment.
- Wire MPPT BAT+/− to BUS (fused). Add PV disconnect and MC4 pigtails.
- SB50: panel-mount; tie to BUS through breaker for safe in/out power.
- Program MultiPlus & MPPT for LiFePO₄ (values above). Verify with your battery datasheet.
- Bring-up: meter polarity → close main DC → power MultiPlus (no loads) → connect battery to MPPT → connect PV → test small AC load.
Variant B — EG4 3000EHV-48 (All-in-one)
Heads-up: This inverter is for 48 V battery banks only. Use 16s LiFePO₄ (51.2 V nominal). If you need 24 V DC loads, add a 48→24 V buck.
Specs
| Battery | 48 V (16s) LiFePO₄, 100–200 Ah |
|---|---|
| Inverter/Charger | EG4 3000EHV-48 (3 kW, 120 V AC) |
| MPPT (built-in) | PV operating 120–450 V, max 500 V; up to ~5 kW PV |
| Quick-swap | SB50 on the 48 V bus (or manufacturer DC lugs with breaker) |
LiFePO₄ charge (48 V)
| Absorb | ~56–58.4 V (per battery datasheet; many use 56.8–57.6 V) |
|---|---|
| Float | ~54–57 V (or lower for longevity; some disable float) |
| Low-V shut | ~44–48 V (per datasheet/BMS) |
Program in the EG4 menu: battery type “User/Li”, set bulk/absorb/float, and charge current limits.
AC I/O
- Local GFCI duplex
- L5-30 (or unit’s hardwire) → inlet → transfer switch/interlock
Wiring (DC backbone)
48V BAT+ → [Class-T 150–200 A] → BUS+ → EG4 + / Distro / (optional) DC-DC 48→24V
48V BAT− → [Shunt BAT side] → [Shunt SYS side] → BUS− → EG4 − / Distro −
SB50 ↔ BUS via breaker (for external pack or DC tools)
Wiring (PV — high voltage)
PV strings in series → PV DC switch → EG4 PV+
Respect PV VOC cold! Keep ≤ 500 V max. Set PV/AC charge priority in menu.
Sequence: connect battery first, then PV per manual.
Settings — EG4 3000EHV-48 (quick start)
- Battery type: User/Lithium. Bulk/Absorb e.g. 56.8–57.6 V; Float 54.0–56.0 V (or disabled); charge current ≤ battery spec.
- AC input current limit: set to your branch rating.
- Charger priority: choose PV priority by day; AC charger for night/top-off.
- Low-V cut: ~46–48 V; restart 50–52 V (or follow battery/BMS guidance).
Step-by-Step (build)
- Layout: 48 V battery bank, Class-T fuse, shunt, EG4 unit, PV disconnect, bus bars, SB50, transfer-safe inlet.
- Crimp & land: 2/0–1/0 AWG DC to EG4; Class-T near battery; shunt on negative; torque to spec.
- PV: build series strings for 120–450 V operating; verify cold-weather VOC stays < 500 V.
- Program EG4 battery & PV settings above. Limit charge amps to battery spec.
- Bring-up: meter polarity → close DC → power EG4 (no loads) → connect PV → test small AC load → verify charge behavior.
Runtime & Solar Helpers
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Total Use / Day | 0 Wh | ||
Runtime (100%) ≈ (Capacity × Eff) / Total_Watts. Solar harvest extends runtime.
Solar Size
| Harvest (kWh/day) | — |
|---|---|
| Charge amps @ 28 V (24 V sys) | — |
| Charge amps @ 56 V (48 V sys) | — |
Rule: Wh/day ≈ PV_W × SunHours × 0.75. Check your controller & wire limits.
Quick Start (print this)
- Close main DC breaker; inverter on; test GFCI.
- Transfer: connect L5-30 to inlet → operate transfer switch/interlock only.
- Solar: connect battery to MPPT/all-in-one; connect PV last. Watch charge current.
- Shutdown: PV off → open DC → AC off.
Sources & Standards
- NEC Article 702 (transfer equipment, no backfeed): EC&M explainers 2020–2024. Ref 1, Ref 2.
- Generator hazards (context): OSHA & CPSC fact sheets. OSHA, CPSC.
- Victron MultiPlus 24/2000 (120 V) docs: Manual & config pages. Manual, Config. Lithium charge guidance (28.4/27.0): Victron.
- MPPT sequence: Battery first, PV last (SmartSolar manuals). 150/60–250/70, 100/30–100/50.
- EG4 3000EHV-48: Manual/specs and PV window. Manual, Docs hub, Spec snapshot.
- 48 V LiFePO₄ charge ranges: RELiON/Battle Born. RELiON, Battle Born.