Charging and Energy Management Systems
AC charging
Level 1 is 120 V and Level 2 is 208–240 V; both pass through the on-board charger. The J1772 connector carries line, neutral, protective earth, control pilot (CP), and proximity pilot (PP). The EVSE places a 1 kHz PWM signal on CP; the duty cycle advertises available current, and the vehicle signals readiness by shifting the voltage on that pin. The PP resistor tells the vehicle the cable rating. DC fast charging adds dedicated DC contacts, bypasses the OBC, and feeds the pack through its own contactors.
Energy management
The BMS tapers current as SOC rises and as cell temperature leaves the ideal band. Preconditioning warms or cools the pack before a fast charge. The DC-DC converter keeps the 12 V system alive during charging, and scheduled charging or cabin preconditioning draws from the EVSE rather than the pack when plugged in.
Traps
Assuming a no-charge complaint means a failed OBC - an open CP or PP circuit, tripped GFCI, or ungrounded EVSE stops the session first. Assuming 100% charge is healthiest, when on NMC packs it accelerates aging. Expecting full DC fast-charge rate into a cold pack. Overlooking that a Level 2 station on a shared circuit may deliberately reduce current.
Rule of thumb
On J1772, available amps ≈ duty cycle percent × 0.6. A 40% duty cycle advertises 24 A.
Worked example: customer reports only 3 kW at a 40 A Level 2 station. 24 A × 240 V ≈ 5.8 kW is expected. Check the pilot duty cycle and the vehicle's commanded current before replacing the OBC.