Introduction: Power battery management system (BMS) plays an important role in ensuring the safety and service life of electric vehicle battery packs and maximizing the performance of the battery system. Usually, the individual voltage, total voltage, total current and temperature are monitored and sampled in real time, and the real-time parameters are fed back to the vehicle controller.
If the power battery management system fails, the monitoring of the battery will be lost, and the state of charge of the battery cannot be estimated. even driving safety.
The following lists the common fault types of electric vehicle power battery management systems, and briefly analyzes their possible causes, and provides common analysis ideas and processing methods for reference.
Common fault types and treatment methods of power battery management system
Common fault types of power battery management system (BMS) include: CAN system communication fault, BMS not working properly, abnormal voltage acquisition, abnormal temperature acquisition, insulation fault, total internal and external voltage measurement fault, pre-charging fault, unable to charge, abnormal current display fault , high voltage interlock failure, etc.
1. CAN communication failure
If the CAN cable or power cable is disconnected, or the terminal is withdrawn, it will cause a communication failure. In the state of ensuring the normal power supply of the BMS, adjust the multimeter to the DC voltage gear, touch the red test lead to the internal CANH, and the black test lead to touch the internal CANL, and measure the output voltage of the communication line, that is, the voltage between CANH and CANL inside the communication line. The normal voltage value is about 1 to 5V. If the voltage value is abnormal, it can be judged that the BMS hardware is faulty and needs to be replaced.
2. BMS is not working properly
When this phenomenon occurs, the following aspects can be mainly considered:
(1) Power supply voltage of BMS: First, measure whether the power supply voltage of the vehicle to the BMS has a stable output at the connector of the vehicle.
(2) Unreliable connection of CAN line or low-voltage power line: Unreliable connection of CAN line or power output line will cause communication failure. The communication line and power line from the main board to the slave board or high-voltage board should be checked. If the disconnected wiring harness is found, it should be replaced or reconnected.
(3) Retraction or damage of the connector: The retraction of the low-voltage communication aviation plug will cause the slave board to have no power or the data from the slave board to be unable to be transmitted to the main board. The plug and connector should be checked and replaced if found to be retracted or damaged.
(4) Control the main board: replace the board for monitoring, and after the replacement, the fault is eliminated and it is determined that there is a problem with the main board.
3. Abnormal voltage acquisition
When abnormal voltage acquisition occurs, the following situations should be considered:
(1) The battery itself is under voltage: compare the monitoring voltage value with the voltage value actually measured by the multimeter, and replace the battery after confirmation.
(2) Loose tightening bolts of the terminals of the collection line or poor contact between the collection line and the terminals: Loose bolts or poor contact between the terminals will lead to inaccurate voltage collection of the single cell. At this time, shake the collection terminals gently, and after confirming the poor contact, tighten or replace the collection terminals. Wire.
(3) The fuse of the collection line is damaged: measure the resistance of the fuse, if it is above l S2, it needs to be replaced.
(4) Slave board detection problem: Confirm that the collected voltage is inconsistent with the actual voltage. If the collected voltage of other slave boards is consistent with the battery voltage, it is necessary to replace the slave board and collect on-site data, read historical fault data, and analyze.
4. Abnormal temperature collection
When abnormal temperature collection occurs, focus on the following situations:
(1) Failure of the temperature sensor: If a single temperature data is missing, check the intermediate butt plug. If there is no abnormal connection, it can be determined that the sensor is damaged and can be replaced.
(2) The connection of the temperature sensor wiring harness is unreliable: Check the intermediate butt plug or the temperature sensor wiring harness of the control port, if it is found to be loose or fall off, the wiring harness should be replaced.
(3) There is a hardware failure in the BMS: The monitoring finds that the BMS cannot collect the temperature of the whole port, and confirms that the wiring harness from the control harness to the adapter to the temperature sensor probe is normally connected, then it can be determined as a BMS hardware problem, and the corresponding slave board should be replaced.
(4) Whether to reload the power supply after replacing the slave board: Reload the power supply after replacing the faulty slave board, otherwise the monitoring value will show abnormality.
5. Insulation failure
In the power battery management system, the inner core of the connector of the working wiring harness is short-circuited with the outer casing, and the high-voltage line is damaged and the vehicle body is short-circuited, which will lead to insulation failure. In view of this situation, the following methods are used to analyze the diagnosis and maintenance:
(1) Leakage of high-voltage load: Disconnect DC/DC, PCU, charger, air conditioner, etc. in sequence until the fault is resolved, and then replace the faulty parts.
(2) Damaged high-voltage lines or connectors: use a megohmmeter to measure, and replace after checking and confirming.
(3) Water in the battery box or battery leakage: Dispose of the inside of the battery box or replace the battery.
(4) Damaged voltage collection line: Check the collection line after confirming the leakage inside the battery box, and replace it if any damage is found.
(5) High-voltage board detection false alarm: replace the high-voltage board, and after the replacement, the fault is removed, and the high-voltage board detection fault is determined.
6. Nesab total voltage detection failure
The causes of the total voltage detection failure can be divided into: loose or falling off between the acquisition line and the terminal, resulting in the total voltage acquisition failure; loose nut leading to ignition and total voltage acquisition failures; loose high-voltage connectors leading to ignition and total voltage detection failures ;Maintenance switch is pressed to cause total pressure acquisition failure, etc. In the actual inspection process, maintenance can be carried out according to the following methods:
(1) The terminal connection at both ends of the total voltage collection line is unreliable: use a multimeter to measure the total voltage of the detection point and compare it with the total monitoring voltage, and then check the detection circuit to find that the connection is not reliable, and tighten or replace it.
(2) Abnormal connection of high-voltage circuit: use a multimeter to measure the total pressure of the detection point and the total pressure of the monitoring point, and compare them, and then check the maintenance switches, bolts, connectors, insurance, etc. from the detection point in turn, and replace them if any abnormality is found.
(3) High-voltage board detection failure: Compare the actual total pressure with the monitored total pressure. After replacing the high-voltage board, if the total pressure returns to normal, it can be determined that the high-voltage board is faulty and should be replaced.
7. Precharge failure
The reasons for the pre-charging failure can be divided into: the external total voltage collection terminal is loose and falling off, which leads to the pre-charging failure; the main board control line has no 12V voltage, which causes the pre-charging relay to not close; the pre-charging resistance is damaged and the pre-charging fails. Combined with the actual vehicle, inspections can be carried out according to the following categories.
(1) Failure of external high-voltage components: When the BMS reports a pre-charging fault, after disconnecting the total positive and total negative, if the pre-charging is successful, the fault is caused by the external high-voltage components. Check the high-voltage junction box and PCU in sections.
(2) The main board problem cannot close the pre-charging relay: check whether the pre-charging relay has 12V voltage, if not, replace the main board. If the pre-charging is successful after the replacement, it is determined that the main board is faulty.
(3) Damage to the main fuse or pre-charging resistor: measure the continuity and resistance of the pre-charging fuse, and replace if abnormal.
(4) Detection failure of the external total pressure of the high-voltage board: After the high-voltage board is replaced, the pre-charging is successful, and the fault of the high-voltage board can be determined, and it can be replaced.
8. Unable to charge
The phenomenon of inability to charge can be roughly summarized into the following two situations: one is that the terminals of the CAN line at both ends of the connector are withdrawn or dropped, resulting in the failure of communication between the motherboard and the charger, resulting in the inability to charge; the other is that the damage to the charging insurance will cause the charging circuit to fail to form. , charging cannot be completed. If the vehicle cannot be charged during the actual vehicle inspection, you can start from the following aspects to repair the fault:
(1) The charger and the main board do not communicate normally: use the instrument to read the working data of the CAN system of the whole vehicle. If there is no charger or BMS working data, check the CAN communication wiring harness immediately. If the connector is in poor contact or the line is interrupted, proceed immediately. repair.
(2) The fault of the charger or the main board cannot start normally: replace the charger or the main board, and then reload the voltage. If it can be charged after the replacement, it can be determined that the charger or the main board is faulty.
(3) BMS detects a fault and does not allow charging: judge the type of fault through monitoring, and then solve the fault until the charging is successful.
(4) The charging fuse is damaged and cannot form a charging circuit: use a multimeter to detect the continuity of the charging fuse, and replace it immediately if it cannot be turned on.
9. Abnormal current display
The terminal of the power battery management system control wiring harness is dropped or the bolt is loose, and the surface of the terminal or bolt is oxidized, which will lead to current errors. When the current display is abnormal, the installation of the current collection line should be checked completely and in detail.
(1) The current collection line is not properly connected: at this time, the positive and negative currents will be reversed, and the replacement can be done;
(2) The connection of the current collection line is unreliable: first, make sure that the high-voltage circuit has a stable current, and when the monitoring current fluctuates greatly, check the current collection line at both ends of the shunt, and tighten the bolts immediately if they are found to be loose.
(3) Detect the oxidation of the terminal surface: First, make sure that the high-voltage circuit has a stable current, and when the monitoring current is much lower than the actual current, detect whether there is an oxide layer on the surface of the terminal or bolt, and treat the surface if there is.
(4) Abnormal detection of high-voltage board current: After disconnecting the maintenance switch, if the monitoring current value is above 0 or 2A, the current detection of the high-voltage board is abnormal, and the high-voltage board should be replaced.
10. High voltage interlock failure
When the ON gear is turned on, measure whether there is a high voltage input here, check whether the 4 terminals are plugged firmly, and measure whether there is a 12V voltage at the driving end (the thin wire is the voltage driving wire). According to the specific situation, it can be divided into the following three categories:
(1) DC/DC fault: measure the DC/DC high-voltage input air plug to see if there is a short-term high voltage when the ON gear is turned on, if there is, it is determined to be a DC/DC fault and should be replaced.
(2) The terminals of the DC/DC relay are not plugged firmly: check the high and low voltage terminals of the relay, and re-plug the terminals if they are not reliable.
(3) The failure of the main board or the adapter board causes the DC/DC relay not to close: Measure the voltage driving end of the DC/DC relay, open the ON block and there is no 12V voltage for a short time, then replace the main board or the adapter board.
Post time: May-04-2022