Vethy VS02 PRO BMS calibration and cell balancing procedure

• Table of Contents

1. BMS diagnostic readouts via Vethy Service App
2. Cell voltage divergence analysis
3. Calibration after deep-discharge event
4. Telematics data interpretation and fleet service decision framework

The Vethy VS02 PRO 200 Ah LFP pack includes an active Battery Management System (BMS) that continuously monitors cell voltage, current and temperature, and performs background cell balancing to maintain pack health. Under normal operation, BMS calibration is automatic and requires no service intervention. However, certain events — extended deep discharge (pack left at <10% SOC for >30 days), cell voltage divergence beyond automatic balancing capability, or telematics-flagged anomalies — trigger requirement for diagnostic BMS calibration. This procedure documents the service workflow.

BMS diagnostic readouts via Vethy Service App

Connect to VS02 PRO V-FMSG-24 via Vethy Service App (iOS/Android Bluetooth pairing or LTE remote access). Navigate to Battery Diagnostics → Pack Health. Service App reports: (1) Pack state-of-charge (SOC) %. (2) Individual cell voltages (8 cells, displayed as graph). (3) Cell voltage divergence — difference between highest and lowest cell voltage (normal <0.05V, balancing engagement >0.05V, replacement-flag threshold >0.15V). (4) Pack state-of-health (SOH) % — calculated usable capacity vs nameplate (200 Ah). (5) Cycle count since installation. (6) Internal pack temperature (each cell + ambient). (7) Recent fault codes (any over-temperature, over-voltage, under-voltage events in past 90 days). Healthy pack: SOC reading consistent with last charge, all cells within ±0.02V, SOH >85%, no recent fault codes.

Cell voltage divergence analysis

Cell voltage divergence is normal aging phenomenon. LFP cells age slightly differently due to manufacturing tolerance and operating history. BMS active balancing automatically engages when divergence exceeds 0.05V — redistributing charge from highest cells to lowest cells via shunt resistors during charging phases. (1) Divergence <0.05V: normal, no action required. (2) Divergence 0.05-0.10V: BMS automatically balancing — verify balancing is engaging during charge cycles (Service App → Cell Balancing → Activity Log). If balancing not engaging, run BMS Reset (Service App → Maintenance → BMS Reset) to clear stuck state. (3) Divergence 0.10-0.15V: BMS balancing capacity may be insufficient — run manual extended balancing cycle (Service App → Maintenance → Extended Balancing — runs 12-24 hour balanced charging). (4) Divergence >0.15V persistent: indicates one or more cells degrading beyond balance capability — flag for pack replacement under warranty (if within 5-year window) or scheduled replacement.

Calibration after deep-discharge event

Extended deep discharge (pack at <10% SOC for >30 days) can de-calibrate BMS state-of-charge accuracy. Symptoms: SOC reading inconsistent with actual capacity (e.g., reports 80% SOC but compressor stops at apparent SOC because actual is 5%). Calibration procedure: (1) Connect pack to shore power or external charger via Vethy Calibration Adapter (part VS02-CAL-24). (2) Run Vethy Service App → Maintenance → SOC Calibration → starts calibration cycle. (3) Calibration cycle: charge pack to 100% SOC + balance + discharge to 5% SOC under controlled current + recharge to 100% SOC. Total elapsed time 20-24 hours. (4) BMS automatically recalibrates internal SOC algorithm from observed Ah throughput. (5) Verify recalibration: SOC reading should now match expected capacity within ±3%. SOC calibration is generally not needed unless deep-discharge event has occurred — normal fleet operation does not require periodic recalibration.

Telematics data interpretation and fleet service decision framework

V-FMSG-24 sends BMS data to fleet telematics platform (Geotab, Samsara, Vethy Fleet Dashboard, etc.). Fleet operations should monitor: (1) Per-tractor SOH % trending — flag any tractor showing >2% SOH decline per quarter (faster than expected degradation). (2) Cell divergence trending — flag any tractor showing >0.05V divergence increase per month. (3) Charging anomalies — failure to charge to >95% SOC after extended driving phase indicates either alternator issue or pack degradation. (4) Service decision framework: SOH <70% triggers planned pack replacement scheduling. Cell divergence >0.15V persistent triggers warranty investigation. Charging anomalies trigger alternator + pack joint diagnostic. Vethy Fleet Dashboard automates this monitoring with rule-based alerts.

Frequently asked questions

Does BMS calibration require pack removal from VS02 PRO?

No — BMS calibration is performed with pack installed and connected. Calibration is software-driven via BMS controller, requires only shore power or external charger connection (for SOC calibration procedure).

How often should BMS calibration be performed proactively?

Not required under normal operation. BMS self-monitors and self-balances. Calibration is event-driven: deep-discharge events, cell divergence beyond auto-balance, telematics anomalies. For most fleet operations, no scheduled calibration is performed.

What causes deep-discharge events that require SOC recalibration?

Most common: tractor parked for extended period (30+ days) without driving phase to recharge — e.g., decommissioned tractors awaiting sale, seasonal fleet (RV-style operations), tractors in extended maintenance bay. Prevention: connect to shore power during extended idle periods, or perform monthly drive-cycle to recharge.

Can BMS calibration recover SOH on degraded packs?

No — BMS calibration restores SOC accuracy but does not recover lost capacity (SOH). LFP cell capacity loss is electrochemical aging, not reversible by software calibration. Calibration ensures BMS reports accurate SOC against actual current capacity, not theoretical nameplate capacity.