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For agricultural operations and workshops. Objective: demystify 48–51.2 V lithium packs (2 to 15 kWh) and provide concrete guidelines for sizing, installing, maintaining, and diagnosing safely.

1) 12 V lead vs 48–51.2 V lithium (LFP/NMC)

  • 12 V lead (starting): historical, inexpensive, heavy, limited cycles, sensitive to deep discharges, maintenance (liquid lead). Suitable for thermal engine starting, less so for prolonged traction/electric tool use.
  • 48–51.2 V lithium (traction/tool): more compact/lighter pack, superior efficiency, significantly better cycle life, better sustained power. Requires a BMS and careful installation.

Orders of magnitude (according to products):

  • Mass per kWh: lead ≈ 25–35 kg/kWh; LFP ≈ 10–15 kg/kWh.
  • Useful cycles: lead ≈ 300–600 (at 50% DoD); LFP ≈ 2000–4000 (at 80% DoD).
  • Recommended DoD: lead ≈ 50%; LFP 70–90% (see specs).

2) Useful lithium chemistries: LFP vs NMC

  • LFP (LiFePO4): very good thermal stability, long lifespan, cell voltage ≈ 3.2 V → 16s ≈ 51.2 V nominal (≈ 58.4 V max). Ideal for field use and safety.
  • NMC: higher energy density (lighter pack for the same kWh), cell voltage ≈ 3.6–3.7 V → 13s ≈ 48.1 V nominal (≈ 54.6 V max). Requires rigorous integration.

Quick choice: prioritise LFP for robustness/safety/cycles; choose NMC if compactness is paramount and if thermal/electronic integration is mastered.

3) Actual voltage, SoC, SoH

  • “48 V” = pack ≈ 51.2 V (LFP 16s) or ≈ 48.1 V (NMC 13s) nominal; voltage varies with SoC, current, temperature, ageing (SoH).
  • SoC (State of Charge): charge level estimated by the BMS (voltage + coulomb counting). At rest, the voltage/SoC curve is indicative; under load, the voltage drops.
  • SoH (State of Health): health status (remaining capacity vs nominal, internal resistance). Decreases with age, deep cycles, heat.

3bis) BMS — role, limits, basic configuration

  • Main role: protect and balance the pack; monitor voltage/current/temperature; cut off in case of danger; estimate SoC/SoH; log faults.
  • Key protections: cell/pack overvoltage during charge, undervoltage during discharge, overcurrent (continuous/peak), over/under-temperature (charge/discharge), short circuit.
  • Balancing: passive (dissipation) most common; active on advanced packs. Aims to homogenise cell voltages to preserve useful capacity and safety.
  • Typical configuration (to be adapted to specs): max pack voltage according to chemistry (e.g. LFP 16s ≈ 58.4 V), undervoltage thresholds (beware of cut-off level), continuous/peak current, trigger delays, temperature ranges.
  • Limits: the BMS does not compensate for poor sizing (insufficient current or kWh), faulty wiring, or poor thermal dissipation.
  • Best practices: keep a log of BMS events, note factory parameters, avoid modifications without reason; after intervention, check logs and balancing.

4) Quick sizing (2 to 15 kWh)

Reminders: Wh = V × Ah; autonomy (h) ≈ Useful energy (kWh) / Average power (kW). 
Useful energy ≈ Nominal energy × DoD × η.

Example: 1.2 kW average for 2 h, η ≈ 0.85, DoD 80%.

  • Useful energy ≈ 1.2 × 2 / 0.85 ≈ 2.82 kWh; E_nominal ≈ 2.82 / 0.8 ≈ 3.5 kWh.
  • An LFP pack 51.2 V – 70 Ah ≈ 3.6 kWh is coherent (or 100 Ah for more margin).
  • Average current ≈ 1200 / 51.2 ≈ 23 A; check continuous/peak current of the BMS (margin ≥ 1.25×).

Advice: allow margin for cold (−20% possible capacity), soft ground, slopes, start-up peaks; size fuse, switch, and cables according to current and length.

5) Installation and maintenance (workshop/farm)

  • Mounting: rigid support, vibration damping; suitable IP rating (dust/mud/water).
  • Wiring: short, protected, compliant sections; cable ties; grommets; sheathing.
  • Connections: manufacturer's torque settings; recheck after 50 h, then periodically.
  • Protections: DC fuse near the +, accessible switch; clearly identified polarities.
  • Charging: charger compatible with chemistry/voltage; avoid recharging < 0 °C (unless dedicated preheating).
  • Prolonged storage: 40–60% SoC, dry place 10–25 °C; quarterly check.

6) Basic diagnosis (without opening the pack)

Tools: multimeter (pack voltage), DC clamp meter, BMS interface (if provided).

  • At rest: measure the voltage and compare to nominal ranges (e.g. LFP 16s ~ 51.2 V; max ~ 58.4 V; typical low threshold ~ 44–46 V according to BMS).
  • Under load: note the voltage drop and current; excessive drop may indicate high internal resistance or loose connection.
  • BMS: read SoC, fault codes, temperatures; frequent triggers = sign of poor configuration or overuse.
  • Temperature/hot spots: IR check at terminals/connections.

Common signs:

  • Reduced autonomy: cold, ageing (SoH), higher consumption, SoC calibration to be redone.
  • Cut-offs: overcurrent, undervoltage (pack too discharged), temperature out of range.
  • Unstable voltage: loose terminal, undersized cable, poor contact.

7) Safety and recycling

  • Low voltage ≤ 60 V but high energy: significant arc/short-circuit risks. Insulated tools, no loose metallic objects, PPE.
  • Fire/explosion: more likely with overcurrent, short circuit, out-of-range charging, impact/puncture, assembly fault. Provide: suitable DC fuse, switch, calibrated cables; avoid spark sources; do not cover pack discharge/ventilation openings.
  • Electrolyte leak/unusual smell: isolate area, ventilate, avoid skin/eye contact; gloves/goggles; contain with suitable absorbent; do not dispose of in sink; contact specialised channel.
  • Always disconnect and lock out before intervention; respect torque settings.
  • Compliant transport/securing; avoid shocks/punctures.
  • Recycling: approved channels; LFP (less critical materials), NMC (strategic metals). At end of life (SoH ≤ 70–80%), consider documented stationary reuse.

Quick checklist

  • Sizing validated (Wh, I_cont, I_peak, DoD, η, cold margin)
  • DC protections installed (fuse, switch), polarities and torques identified
  • Short cables and suitable sections; planned re-tightening check
  • Suitable charger; cold storage/charging rules known


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*: The technical information presented in this article is provided for guidance only. It does not replace the official manuals of the manufacturers. Before any installation, handling or use, please consult the product documentation and follow the safety instructions. The Torque.works site cannot be held responsible for inappropriate use or incorrect interpretation of the information provided.