Chapter 3: Corrective Maintenance SOP (Corrective Maintenance SOP)
This chapter stipulates the physical disassembly and repair standards when P1/P2 level hardware failure occurs in the energy storage system. All operations must be performed by a CoreTect certified engineer holding a low voltage/high voltage electrician's license. Before performing any disassembly actions, engineers must have system-level topological troubleshooting thinking.
3.1 Hybrid inverter topology and fault determination foundation (System Topology & Triage Foundation)
CoreTect engineers strictly prohibit blind replacement of accessories without identifying the root cause (Root Cause). It is necessary to be familiar with the "five core circuit modules" inside the inverter and their energy flow, which will serve as the fundamental basis for determining liability for on-site faults and disclaiming legal liability.
3.1.1 Core anatomy of the inverter (Hardware Topology)
(Note: Engineers need to memorize this diagram, and on-site troubleshooting must strictly follow this energy flow direction)
3.1.2 Function definition and fatal fault mapping of each module
1. MPPT photovoltaic boost circuit: responsible for extracting solar energy.
High frequency fault: PV insulation resistance too low (Error 201 / F24).
Criteria for determining liability: Most cases are caused by broken roof cables and leakage during rainy seasons. If the alarm disappears after unplugging the PV cable, it is judged that the inverter is intact and it is the responsibility of external engineering construction.
2. Bidirectional battery charging and discharging circuit (Buck-Boost): responsible for the step-up and step-down conversion between the battery and the high-voltage bus.
High frequency fault: Passive alarm / unable to charge and discharge.
Criteria for determining liability: Check the underlying communication status of the BMS. If the cell voltage difference is too large and causes the BMS to lock up, it will be judged as improper battery maintenance and a cell reconstruction work order will be entered.
3. DC high-voltage bus (DC Bus): the energy accumulation reservoir of the whole machine (high-voltage danger zone).
High frequency fault: Bus soft start failed (Fault 09).
Liability determination standard: If a busbar failure is reported when the machine is turned on, accompanied by a burning smell, it will be judged as a serious internal short circuit and the machine will be shut down immediately.
4. Inverter bridge circuit (DC-AC Inverter): converts DC into household AC sine wave. The most vulnerable core of the entire machine.
High frequency fault: AC/DC hardware overcurrent (F18), IGBT short circuit.
Criteria for determining liability: Use a multimeter to measure the output end of the diode. If the resistance is zero, the IGBT has broken down. 90% of the cases are caused by the high-power inductive load (deep well water pump/old compressor) generated by the customer's private connection, which is an illegal use and the original manufacturer refuses to insure it.
5. AC output and grid-connected control circuit: manages and controls grid entry and exit and off-grid switching.
High-frequency faults: relay fault (Error 117), grid undervoltage/overvoltage protection.
Liability determination standard: If the grid voltage exceeds the limit, enter the menu to relax the wide voltage range; if the power outage cannot be switched, it is likely that the relay contacts are sintered, and board-level replacement needs to be performed.
3.1.3 Golden Rule of Troubleshooting
External first, then internal; communication first, then strong electricity.
For any fault that causes motherboard breakdown (IGBT explosion), engineers are absolutely prohibited from using a soldering iron for chip-level repairs on site. A "Hardware Damage RCA Report" must be issued and the customer is required to pay for a board-level swap to avoid joint legal liability for fires caused by secondary explosions.
3.2 BMS motherboard burnt/locked replacement procedure (BMS Replacement)
Applicable scenarios: Cloud monitoring shows BMS offline, MOS tube breakdown and short circuit, or serious faults that cannot be resolved through remote commands.
Fatal safety warning: The BMS connects the high-voltage cell cluster to the inverter grid. Once the order of disassembly and assembly of the wiring harness is reversed, it will cause an instant short circuit of the collection line, secondary burnout of the motherboard, and even cause arc burns!
3.2.1 Disassembly preparation and safe isolation
System complete power outage (LOTO): follow the standards in Section 2.2, disconnect the AC and DC main gate, and hang the safety lock. Use a multimeter to confirm bus voltage < 36V DC.
Physical isolation: Use high-voltage insulating tape to wrap all exposed external cable terminals (connected to the inverter end) to prevent them from touching the metal shell of the cabinet.
3.2.2 Strict Disassembly Sequence
The first step (disconnect weak current): First unplug all "cell voltage/temperature sampling cables (white multi-core cables)" on the BMS! Never remove the main power cord while the sampling line is plugged in, otherwise the floating voltage will breakdown the motherboard chip.
Step 2 (disconnect communication): Unplug the RS485/CAN communication network cable connecting the 4G DTU gateway and the inverter, as well as the screen cable.
Step 3 (Disconnect the main negative output): Use an insulated socket wrench to remove the black main negative wire connected to the BMS P- (or C-/load terminal).
Step 4 (Disconnect the negative input of the battery): Finally, remove the total negative input line connected to B- (battery terminal) of the BMS.
3.2.3 Strict installation sequence (Installation Sequence)
(Principle: completely opposite to the disassembly sequence)
Step one (connecting the battery terminal): Firmly connect the battery negative copper bar to the B- terminal of the new BMS. Mark the standard torque of 12 N·m and draw the red and blue anti-loosening lines.
Step 2 (connecting the output terminal): Connect the negative pole of the external output to the P- terminal of the BMS.
The third step (weak current verification and access - key!): Before plugging in the sampling cable, you must use the black test lead of the multimeter to ground, and the red test lead to measure each pin of the cable plug in sequence. Confirm that the voltage increases step by step from 3.2V, 6.4V, and 9.6V. After confirming that there is no disconnection or disorder, firmly insert the sampling cable into the new BMS mainboard and hear a "click" sound to confirm that it is locked.
Step 4 (Restore communication): Plug back the 4G DTU network cable and temperature measurement NTC probe.
3.2.4 Software burning and closed loop
Turn on the DC circuit breaker and power on the system.
Connect the laptop via USB to RS485 cable and open the BMS host computer software. Load the factory configuration file (Profile): Import CoreTect's exclusive parameter package for this model of battery (overvoltage 3.65V, undervoltage 2.70V, maximum charging current, etc.). Confirm that the equipment is back online in the Coretect cloud backend, complete the trial run for 15 minutes, and submit the replacement SN code for entry into the spare parts library.
3.3 "Cell Top-Balancing & Replacement" procedures for serious voltage differences in single cells (Cell Top-Balancing & Replacement)
Applicable scenarios: Cloud alarm cell voltage difference (Delta-V) > 100mV, or the internal resistance of a certain string of cells becomes abnormally large, resulting in a sudden drop in the package capacity.
3.3.1 Diagnosis and physical extraction
Cloud positioning: Before emergency repair, use the CoreTect Cloud historical curve to accurately locate the backward cell number (such as Cell #14).
Safe removal: Use an insulated ratchet wrench to remove the battery pack top cover. Since the 314Ah battery cell is extremely heavy (about 5.5kg), you must use a professional suction cup or handle to pull it out vertically. It is strictly prohibited to hold the pole to lift the battery cell!
3.3.2 Cell depth charge and discharge (Top-Balancing)
(If the battery core is not physically damaged, it is just severe starvation and imbalance)
Equipment preparation: Place the Coretect-2050 battery capacity tester on an anti-static workbench.
Parameter setting (no errors allowed): Set the tester mode to "Constant current and constant voltage charging (CC-CV)". The voltage cutoff upper limit is strictly set to 3.60V (the absolute safety upper limit of lithium iron phosphate). Current setting is 20A - 50A depending on the situation.
Execution operation: Use the Kelvin test clip to clamp the positive and negative poles of the outdated battery cell, start recharging until the charging current drops below 0.5A, and determine that the battery cell is fully charged.
3.3.3 Battery core replacement and torque control
(If the internal resistance tester shows that the internal resistance of the battery cell is > 0.5mΩ, it is determined that the internal physical damage is caused and must be replaced with a new one)
Get new batteries of the same batch and internal resistance (with M6 studs pre-welded) from the spare parts warehouse.
In-line assembly: Put the new battery core into the module, and a 1mm-thick FR4 epoxy resin insulation board must be inserted in the middle to prevent the expansion and friction of the battery core from causing short circuit.
Connect the copper bar: Put on the flexible connecting copper bar and flange anti-slip nut.
Torque Control (Core Red Line): Use an insulated torque wrench, set strictly to 6 N·m (for M6 studs). Excessive torque will twist off the internal tabs of the battery core and cause a fire; too small torque will cause excessive contact resistance and heat generation. After tightening, use a red marker to draw a "single line" across the nut and copper bar.