Battery¶
OVES Electric Mobility Battery Charging Strategy and Maximum Discharge Current Values at Different SOC States¶
Charging Strategy¶
1. Classification¶
OVES electric mobility batteries typically have two charging methods: slow charging and fast charging.
2. Normal (Slow) Charging¶
A 10A charger is used, and the battery is designed with a three-vertical pin (with the middle pin horizontal to prevent AC insertion). The charging mode is the standard CC to CV mode, where the CC to CV voltage is 1V lower than the full charge voltage.
3. Fast Charging¶
A 25A charger is used, and the battery BMS (Battery Management System) is designed with a common port for charging and discharging, meaning the same connector is used for fast charging and discharging. The BMS applies for charging voltage and current from the charger via the CAN bus based on the cell chemistry of the battery pack, combined with the battery pack capacity and temperature.
4. 32140 Cylinder Cell Charging Parameters¶
5 32140 Cylinder Battery Pack Charging Parameters¶
Take a 73.6V/45Ah(3.31KWh) battery pack as an example, with a designed capacity of 45Ah:
- When the temperature is -10~5°C, the charging current is 45*0.2=9A.
- When the temperature is 5~10°C, the charging current is 45*0.33=15A.
- When the temperature is 10~20°C, the charging current is 45*0.5=20A.
- When the temperature is 20~45°C, the charging current is 45*1=45A, but since the maximum output current of the charger is 25A, it will only charge at 30A even if 45A is requested.
- When the temperature is 45~50°C, the charging current is 45*0.5=20A.
- When the temperature is 50~55°C, the charging current is 45*0.2=9A.
The above only limits the charging current based on temperature. The SOC value of the battery itself also affects the charging current:
- When SOC is 0~5%, the charging current is reduced by 50% based on the temperature condition.
- When SOC is 5~15%, the charging current is reduced by 30%.
- When SOC is 15~30%, the charging current is reduced by 20%.
- When SOC is 30~80%, the charging current remains unchanged based on the temperature condition.
- When SOC is 80~90%, the charging current is reduced by 25%.
- When SOC is 90~100%, the charging current is reduced by 50%.
As the number of battery cycles increases, the battery's storage capacity will decrease, so the charging current should be calculated based on the fully charged capacity (FCC).
The following table is made based on the above conditions, and the BMS can obtain the charging current through look-up and broadcast it via the CAN bus (0x1806E611):
| SOC Temp | 0~5% | 5~15% | 15~30% | 30~80% | 80~90% | 90~100% |
|---|---|---|---|---|---|---|
| -10~5℃ | FCC0.20.5 | FCC0.20.7 | FCC0.20.8 | FCC0.21.0 | FCC0.20.75 | FCC0.20.5 |
| 5~10℃ | FCC0.330.5 | FCC0.330.7 | FCC0.330.8 | FCC0.331.0 | FCC0.330.75 | FCC0.330.5 |
| 10~20℃ | FCC0.50.5 | FCC0.50.7 | FCC0.50.8 | FCC0.51.0 | FCC0.50.75 | FCC0.50.5 |
| 20~45℃ | FCC10.5 | FCC10.7 | FCC10.8 | FCC11.0 | FCC10.75 | FCC10.5 |
| 45~50℃ | FCC0.50.5 | FCC0.50.7 | FCC0.50.8 | FCC0.51.0 | FCC0.50.75 | FCC0.50.5 |
| 50~55℃ | FCC0.20.5 | FCC0.20.7 | FCC0.20.8 | FCC0.21.0 | FCC0.20.75 | FCC0.20.5 |
| 55~60℃ | FCC00.5 | FCC00.7 | FCC00.8 | FCC01.0 | FCC00.75 | FCC00.5 |
6. Square Aluminum Shell (PH) Cell Charging Parameters¶
7 Square Aluminum Shell (PH) Battery Pack Charging Parameters¶
| SOC Temp | 0~5% | 5~15% | 15~30% | 30~80% | 80~90% | 90~100% |
|---|---|---|---|---|---|---|
| -10~5℃ | FCC00.5 | FCC00.7 | FCC00.8 | FCC01.0 | FCC00.75 | FCC00.5 |
| 5~10℃ | FCC0.20.5 | FCC0.20.7 | FCC0.20.8 | FCC0.21.0 | FCC0.20.75 | FCC0.20.5 |
| 10~20℃ | FCC0.50.5 | FCC0.50.7 | FCC0.50.8 | FCC0.51.0 | FCC0.50.75 | FCC0.50.5 |
| 20~45℃ | FCC10.5 | FCC10.7 | FCC10.8 | FCC11.0 | FCC10.75 | FCC10.5 |
| 45~50℃ | FCC0.50.5 | FCC0.50.7 | FCC0.50.8 | FCC0.51.0 | FCC0.50.75 | FCC0.50.5 |
| 50~55℃ | FCC0.20.5 | FCC0.20.7 | FCC0.20.8 | FCC0.21.0 | FCC0.20.75 | FCC0.20.5 |
| 55~60℃ | FCC00.5 | FCC00.7 | FCC00.8 | FCC01.0 | FCC00.75 | FCC00.5 |
Maximum Discharge Current Values¶
Close cooperation between the controller and the battery is required to prevent the battery from stopping discharge first, causing sudden power failure of the vehicle. To address this, discharge tests were conducted on the battery to determine its maximum discharge current at different SOC states. The BMS broadcasts the maximum discharge current value of the battery in real time via the CAN bus based on the SOC value, and the controller performs power limitation after receiving it. According to the discharge test results, the following table is made, and the BMS can broadcast the maximum discharge current value of the battery via the CAN bus (ID 0x1806E611) through look-up:
1. 32140 Cylinder 45Ah Battery¶
| Serial Number | SOC (%) | Corresponding Voltage (V) | Maximum Discharge Current (A) |
|---|---|---|---|
| 1 | 60~100 | Above 76.1 | 120 |
| 2 | 50 | 76.1 | 100 |
| 3 | 45 | 75.55 | 100 |
| 4 | 40 | 75.34 | 100 |
| 5 | 35 | 74.83 | 100 |
| 6 | 30 | 74.55 | 80 |
| 7 | 25 | 74.06 | 80 |
| 8 | 20 | 73.55 | 60 |
| 9 | 15 | 73.06 | 40 |
| 10 | 10 | 68.04 | 20 |
| 11 | 5 | 66.5 | 10 |
| 12 | 0 | 64 | 5 |
2. 32140 Cylinder 30Ah Battery¶
| Serial Number | SOC (%) | Corresponding Voltage (V) | Maximum Discharge Current (A) |
|---|---|---|---|
| 1 | 60~100 | Above 76.1 | 80 |
| 2 | 50 | 76.1 | 60 |
| 3 | 45 | 75.55 | 60 |
| 4 | 40 | 75.34 | 60 |
| 5 | 35 | 74.83 | 60 |
| 6 | 30 | 74.55 | 50 |
| 7 | 25 | 74.06 | 50 |
| 8 | 20 | 73.55 | 40 |
| 9 | 15 | 73.06 | 25 |
| 10 | 10 | 68.04 | 15 |
| 11 | 5 | 66.5 | 5 |
| 12 | 0 | 64 | 3 |
3. Square Aluminum Shell (PH) 100Ah Battery¶
| Serial Number | SOC (%) | Corresponding Voltage (V) | Maximum Discharge Current (A) |
|---|---|---|---|
| 1 | 30~100 | Above 75.10 | 100 |
| 2 | 25 | 74.77 | 90 |
| 3 | 20 | 74.30 | 80 |
| 4 | 15 | 73.75 | 70 |
| 5 | 10 | 73.59 | 60 |
| 6 | 5 | 69.97 | 50 |
| 7 | 0 | 66.7 | 0 |
OVES Electric Mobility Battery Cycle Counting Method¶
1. Cycle Count vs. Charge Count¶
A charge-discharge cycle of a lithium battery refers to the process of completing a 100% full discharge and subsequent full charge.
For example, if a battery starts at 100% charge, is discharged to 0%, and then recharged to 100%, this constitutes one charge-discharge cycle. Here, the cycle count is 1, and the charge count is 1.
Another example: a battery at 100% charge is first discharged to 40% and recharged to 100%, then discharged to 60% and recharged to 100%. These two uses combined form one full cycle. The cycle count is 1, but the charge count is 2.
Thus, a complete 100% discharge-charge cycle can involve 1, 3, 4, or even 5 charges. However, the lifespan of a lithium battery is determined by the cycle count, not the charge count.
Understanding this clarifies a common misconception: EV batteries and mobile phone batteries have different degradation rates. EV batteries typically complete one cycle per week, while mobile phone batteries can complete one cycle per day.
2. Factors Affecting Cycle Count¶
a. Battery Capacity Degradation: Over time and with use, a battery’s energy storage capacity degrades. The degradation rate is closely related to the battery’s chemical system and operating conditions. Therefore, the discharged capacity is always calculated based on the current full charge capacity (FCC), not the design capacity.
b. Battery Usage Patterns: There is a correlation between discharge depth (DOD) and cycle count. Generally, a deeper DOD leads to fewer cycles. This is because deeper discharges intensify internal chemical reactions, accelerating material wear and structural aging. Specifically, material structures change during each discharge, with some active materials converting to irreversible products, reducing storage capacity. Increased DOD amplifies irreversible reactions, decreasing available energy and cycle life.
c. Battery Management Strategies: To balance available energy and lifespan, optimization strategies are used to control DOD and cycle count, including:
- Defining a reasonable DOD range
- Controlling cycle frequency
- Implementing temperature control and thermal management
d. Cycle Counting Methods: To make cycle life appear longer or align with warranty terms, some manufacturers equate charge counts to cycle counts, while others count a cycle when discharged capacity reaches 80% of FCC. Under the same control strategy, different counting methods only affect the recorded cycle count, not the actual cycle life.
3. OVES Battery Cycle Counting Method¶
OVES electric mobility batteries use an ampere-hour (Ah) integration method: a cycle is counted when the discharged capacity reaches 90% of the full charge capacity (FCC).
- Example for a new 3.31KWh battery with an FCC of 45Ah:A cycle is counted when the discharged capacity reaches 40.5Ah (45Ah × 90%).
- Example after 2 years of use, when the FCC drops to 40Ah:A cycle is counted when the discharged capacity reaches 36Ah (40Ah × 90%).