Technical Deep Dive

How the Charger Works

From mains AC power to a fully-charged battery - a complete walkthrough of every stage inside the Solterra on-board charger, including PFC, DC conversion, protection systems, and thermal management.

System Overview

The Solterra on-board charger (OBC) is a sealed, high-efficiency power converter that takes single-phase or three-phase AC from a wall outlet and delivers regulated DC to the vehicle's battery pack through the BMS.

It operates in two broad configurations: CAN-enabled (communicating with the BMS via CAN bus) and Non-CAN (voltage-based termination only). CAN-enabled operation provides closed-loop control and full fault visibility.

Product Family

MB Series	1.35 kW
SC Series	1.5 kW
LC/LD/LE Series	2.0 kW
B/BB Series	3.3 kW

Z = On-board P = Portable L suffix = Li-ion

Power Flow Architecture

Inside the Charger Power Path

A stage-by-stage view of how mains AC is filtered, corrected, isolated, and delivered to the battery, with BMS feedback shown as the control loop.

AC input pathPower conversion stagesBattery-side deliveryBMS feedback path

Rendering graph...

View Mermaid Code

flowchart TD
    AC["AC INPUT<br/>230V / 380V<br/>50 / 60 Hz"]
    EMI["EMI FILTER + INRUSH<br/>X/Y caps, choke, fuse, NTC"]
    PFC["PFC STAGE<br/>Boost PFC<br/>~400V DC bus | PF > 0.98"]
    DCDC["DC-DC STAGE<br/>LLC resonant isolated SMPS<br/>Galvanic isolation"]
    OUT["OUTPUT FILTER + RELAY<br/>LC filter | OVP | OCP"]
    BAT["BATTERY PACK<br/>via BMS<br/>CC / CV mode"]
    CAN["CAN BUS / BMS FEEDBACK<br/>Battery status, voltage, current, stop-charge"]
    ISO["ISOLATION BARRIER<br/>Battery pack remains separated from mains potential"]

    AC --> EMI --> PFC --> DCDC --> OUT --> BAT
    BAT -. Pack status and charge requests .-> CAN
    CAN -. Charger setpoints and stop commands .-> DCDC
    ISO -. Safety-critical separation .-> DCDC

    class AC,EMI state-idle
    class PFC state-activation
    class DCDC state-listen
    class OUT state-charge
    class BAT state-handshake
    class CAN,ISO state-note

    linkStyle 0 stroke:#6f665b,stroke-width:2.2px;
    linkStyle 1 stroke:#6f665b,stroke-width:2.2px;
    linkStyle 2 stroke:#fa913c,stroke-width:2.4px;
    linkStyle 3 stroke:#7cb3ff,stroke-width:2.4px;
    linkStyle 4 stroke:#37d67a,stroke-width:2.4px;
    linkStyle 5 stroke:#7cb3ff,stroke-width:1.8px;
    linkStyle 6 stroke:#7cb3ff,stroke-width:1.8px;
    linkStyle 7 stroke:#8b96a9,stroke-width:1.8px;

Daily Operation

These are the practical operating rules pulled into one place for field use.

Input Window

170-270 Vac

Single phase L+N+E | 50 Hz | 16A max input

Thermal Window

45 C -> 50 C

Full output to 45 C, then derates until shutdown above 50 C

Daily Charge Order

DC -> AC

Connect the vehicle side first, then the wall socket and switch on

Charge Complete

Green steady

Safe to disconnect; automatic top-up restarts are normal maintenance mode

Standard Charge Procedure

Connect the charger output DC connector to the vehicle inlet.

Connect the charger input plug to the supply socket.

Switch on the socket power supply.

Confirm charging status in the vehicle app, battery display, or LED panel.

At end of charge, switch off the socket power supply first.

Remove the DC connector from the vehicle inlet.

Wrap the cables carefully and store the charger in a dry, clean place.

Operating Limits

AC supply	170-270 Vac L-N \| 50 Hz \| Single phase L+N+E	Use a dedicated, properly earthed outlet sized for the charger current.
Environment	-30 C to 50 C \| 5%-95% RH \| below 2000 m altitude	For best performance, keep ambient below 45 C.
Ventilation	Minimum 10 cm clearance on all sides	Never cover vents or place the charger on heat-trapping surfaces.
Handling	Pins clean, cables undamaged, minimum 60 mm bend radius	Do not drag, sharply bend, crush, or lift by the cable.

Normal behavior: when the green LED is steady, charge is complete. Periodic restart after full charge can still be normal maintenance mode as the charger tops up self-discharge.

Stage-by-Stage Breakdown

EMI Filter & Inrush Protection

AC Side

The first thing mains power encounters is an EMI (electromagnetic interference) filter - a combination of X/Y capacitors and common-mode chokes that suppresses high-frequency noise from propagating back onto the grid or into the charger. An NTC thermistor (negative temperature coefficient) limits inrush current at power-on, protecting both the charger and the supply fuse. A fuse on the input provides overcurrent protection.

Protects: grid + chargerNTC inrush limiterX/Y cap filter

PFC Stage - Power Factor Correction

Critical Stage

The PFC (Power Factor Correction) stage is an active boost converter that converts the rectified AC (which has a sinusoidal shape) into a stable high-voltage DC bus, typically around 400V. It simultaneously shapes the input current to be sinusoidal and in-phase with the input voltage, achieving a power factor >0.98. This minimises reactive power draw from the grid.

Why two fault types? The charger distinguishes between PFC Internal Fault (failure inside the PFC controller, gate drivers, or MOSFET) and PFC External Fault (bad AC input voltage - too high, too low, wrong frequency, or poor plug contact). External faults are field-fixable; internal faults require factory service.

PFC Internal -> return to factoryPFC External -> check AC input

DC-DC Stage - Isolated Converter

Galvanic Isolation

The DC-DC stage takes the ~400V PFC bus and converts it to the battery's required voltage (typically 48-96V for two-wheeler packs) using a high-frequency LLC resonant converter with a transformer providing galvanic isolation. This isolation is safety-critical - it means the battery pack is never directly connected to mains potential.

Charging follows a CC/CV (Constant Current / Constant Voltage) profile: the charger pushes a regulated constant current until the battery reaches its target voltage (CV phase), then holds the voltage while current tapers to zero. For CAN-enabled chargers, the BMS dictates exact current and voltage setpoints in real time.

LLC resonant topologyHigh-freq transformerCC -> CV charging profile

Output Filter, Relay & Protections

Battery Side

Before output voltage reaches the connector, it passes through LC output filtering to reduce ripple, then through an internal relay. The relay opens instantly on any fault condition - overvoltage, overcurrent, short circuit, or overtemperature. Output voltage ripple is kept below 0.5% of full load at nominal conditions.

Relay Fault: If the internal relay fails to open or close correctly, the charger enters Relay Fault mode (LED: Yellow-Red-Green-Red-Green-Red-Green). This requires factory service - the output path is compromised.

Thermal Management

The charger uses active fan cooling and three independent thermal sensors to protect both internal stages and the surrounding environment.

TEMP

External Temperature Sensor

Monitors ambient temperature at the charger's intake. If ambient exceeds the rated limit, the charger triggers an External Temperature Fault and shuts down output to prevent thermal damage to surroundings or the battery.

DC Stage Thermal Sensor

Monitors the DC-DC converter heatsink temperature. The charger operates at full rated current up to 45C ambient, then linearly derates output current as temperature rises toward 50C, then shuts down.

PFC

PFC Stage Thermal Sensor

Monitors the PFC section. Overtemperature here indicates high ambient, blocked vents, or excessive input-side losses. Clear dust from vents every 3-6 months to prevent this fault.

Derating behaviour: When ambient temperature is between 45C and 50C, output current is automatically reduced to keep junction temperatures safe. Charging continues at reduced rate rather than stopping entirely - unless the temperature exceeds the upper limit.

Protection Systems

Multiple layers of protection are active simultaneously during operation.

Protection Type	Trigger Condition	Response	User Action
Overcurrent (AC)	Input current exceeds rated limit	PFC shuts down; NTC thermistor absorbs inrush	Check supply fuse and wiring gauge
Overvoltage (DC Out)	Output voltage exceeds setpoint + margin	Output relay opens; fault LED	Check battery voltage and BMS setpoints
Short Circuit (DC)	Near-zero impedance at DC output	Immediate relay open; fault mode	Not protected in Activation Mode (see Activation page)
Under-voltage (Battery)	Battery voltage below minimum threshold	Output withheld; UV fault LED	See Activation Function
Overtemperature	Any of 3 thermal sensors exceed limit	Output derates then shuts down	Improve ventilation; reduce ambient temp
Precharge Timeout	Output current = 0 for extended period	Fault mode after timeout	Check battery and connections; may need replacement
Reverse Polarity	DC output connected backwards	Not protected in Activation Mode	Verify connector polarity before plugging in

Activation Mode Risk: During the activation (wakeup) pulse, the charger produces a forced output with no reverse polarity or short circuit protection. Always verify connector orientation before connecting to a deeply discharged battery. Reverse polarity damage during activation is excluded from warranty.

Preventive Maintenance

Most repeated field faults come from airflow restriction, damaged cables, or poor connector condition rather than charger hardware failure.

Interval	Task	What To Do
Every charge	Visual inspection	Check the AC plug, DC connector, and both cables for damage, corrosion, fraying, or heat marks before connecting.
Monthly	Connector check	Inspect for loose pins, heat discoloration, or corrosion at all accessible connectors.
Every 3-6 months	Vent cleaning	Clear cooling fins and ventilation slots using a dry cloth, dry brush, or gentle compressed air.
Every 3-6 months	Cable inspection	Check strain-relief points and the full cable run for cracks, chafing, or crush damage.
Every 6 months	Battery health test	Run a capacity or discharge test so weak packs are found before they become field failures.
Annually	Torque check	Re-torque mounting and battery-side connections to the specified values.

Dust accumulation in cooling fins and vents is one of the biggest causes of repeated thermal faults. A dry cleaning every 3 to 6 months has outsized impact on reliability.

Non-CAN Charger: Important Risks

Non-CAN chargers use only voltage-based termination. There is no communication loop with the BMS. This creates uncontrollable risks that Solterra users should understand:

BMS Protection Failure: If the battery protection board fails, the charger has no feedback mechanism. If the stop-charge condition is never met, the charger will continue delivering power indefinitely - potential overcharge or thermal event.

MOSFET Damage Scenario: If a BMS MOSFET is damaged and the protection board issues a cut-off command, the command cannot execute. The charger continues charging - cannot receive the stop instruction from a non-communicating battery.

Solterra Technologies Pvt Ltd accepts no liability for property or personal injury resulting from these Non-CAN scenarios. CAN-enabled operation is strongly recommended for all new deployments.

Next: CAN Bus Communication