Other Parts Discussed in Thread: LM61495RPHEVM, BQ24650, BQ25756E
Tool/software:
Hi,
I am choosing the BQ24650EVM kit for charging LiFePO4 lithium-ion phosphate ANR26650M1 batteries. The battery pack connected to the BQ24650EVM, VOUT is 10.8V, composed of three 'ANR26650M1' cells in series, each with a maximum charging voltage of 3.6V and a capacity of 2.5Ah. The total battery bank capacity is 10.8V and 2.5Ah.
I have two different input sources from the truck (automotive) coming, where I want to use this charger. We have two types of trucks: Truck 1 with an input voltage range of 11V to 14V maximum, and Truck 2 with an input voltage range of 24V to 28V maximum. This BQ24650 charger should be compatible with both types of trucks. We aim to design a single hardware solution that can connect to any truck without needing separate designs for 12V and 24V systems. The charging requirements for the battery bank will be the same for both trucks. On the Vsystem of the BQ24650 connector, I have connected a TI: LM61495RPHEVM Buck converter (5V-10A) to run my load (5V-6A-30W). I want to connect my load directly to the output Vsystem of the BQ24650. When the truck power is available (ignition on), the load should run on truck input power. I have reviewed the BQ24650EVM kit circuit, which implements power ORing to manage the source for the load (Vsystem). This means the load will initially run on truck power when available and switch to battery power when truck power is off.
I have set the battery output voltage to 10.8V to charge my LiFePO4 batteries, with a maximum charging current of 8A for the battery pack. I plan to make the following changes to the BQ24650EVM kit to achieve my desired results: change R6 to 5mOhms and use a 3.3uH inductor (L1).
I am confused about what MPPT voltage to set because of the two different input conditions (11V to 14V and 24V to 28V). The datasheet mentions that the charger will turn on only when the selected VOUT battery bank voltage plus 1V is reached. For my selected battery pack voltage of 10.8V, the charger will turn on at 11.8V, which is fine. However, I am unsure what MPPT voltage to set for both conditions. I plan to choose an MPPT voltage of 12.0V for both input ranges (11V to 14V and 24V to 28V). The MPPT will try to achieve maximum power tracking (12.0V), and the battery pack will charge at 10.8V and 8A, reducing the charging current as the batteries reach full charge.
I plan to change the following components of the kit to charge my battery pack without issues:
* R6 = 5mOhms
* L1 = 3.3uH (IHLP2525EZER3R3M01) (Current Rating Amps= 8A, Tolerance= ±20%, Isat=8A)
* R13 = 499kOhms
* R15 = 120kOhms to achieve 10.8V for the battery pack
* For MPPTSET: R17 = 499kOhms and R19 55kOhms to achieve 12.0V
* C7 and C8 both 22 µF ±10% 25V Ceramic Capacitor X7R 1210
Question-1:Could you please confirm, the above selected values are suitable for MPPTSET and VOUT, or should I consider other values? Also, will the charging current automatically reduce as the batteries fully charged?
Question-2: Since my circuit has 3 batteries of 3.6V, the final bank voltage will be 10.8V. I have added a battery balancer circuit so each cell is charged efficiently. Is this the correct approach?
I am choosing the BQ24650EVM kit for charging LiFePO4 lithium-ion phosphate ANR26650M1 batteries. The battery pack connected to the BQ24650EVM, VOUT is 10.8V, composed of three 'ANR26650M1' cells in series, each with a maximum charging voltage of 3.6V and a capacity of 2.5Ah. The total battery bank capacity is 10.8V and 2.5Ah.
I have two different input sources from the truck (automotive) coming, where I want to use this charger. We have two types of trucks: Truck 1 with an input voltage range of 11V to 14V maximum, and Truck 2 with an input voltage range of 24V to 28V maximum. This BQ24650 charger should be compatible with both types of trucks. We aim to design a single hardware solution that can connect to any truck without needing separate designs for 12V and 24V systems. The charging requirements for the battery bank will be the same for both trucks. On the Vsystem of the BQ24650 connector, I have connected a TI: LM61495RPHEVM Buck converter (5V-10A) to run my load (5V-6A-30W). I want to connect my load directly to the output Vsystem of the BQ24650. When the truck power is available (ignition on), the load should run on truck input power. I have reviewed the BQ24650EVM kit circuit, which implements power ORing to manage the source for the load (Vsystem). This means the load will initially run on truck power when available and switch to battery power when truck power is off.
I have set the battery output voltage to 10.8V to charge my LiFePO4 batteries, with a maximum charging current of 8A for the battery pack. I plan to make the following changes to the BQ24650EVM kit to achieve my desired results: change R6 to 5mOhms and use a 3.3uH inductor (L1).
I am confused about what MPPT voltage to set because of the two different input conditions (11V to 14V and 24V to 28V). The datasheet mentions that the charger will turn on only when the selected VOUT battery bank voltage plus 1V is reached. For my selected battery pack voltage of 10.8V, the charger will turn on at 11.8V, which is fine. However, I am unsure what MPPT voltage to set for both conditions. I plan to choose an MPPT voltage of 12.0V for both input ranges (11V to 14V and 24V to 28V). The MPPT will try to achieve maximum power tracking (12.0V), and the battery pack will charge at 10.8V and 8A, reducing the charging current as the batteries reach full charge.
I plan to change the following components of the kit to charge my battery pack without issues:
* R6 = 5mOhms
* L1 = 3.3uH (IHLP2525EZER3R3M01) (Current Rating Amps= 8A, Tolerance= ±20%, Isat=8A)
* R13 = 499kOhms
* R15 = 120kOhms to achieve 10.8V for the battery pack
* For MPPTSET: R17 = 499kOhms and R19 55kOhms to achieve 12.0V
* C7 and C8 both 22 µF ±10% 25V Ceramic Capacitor X7R 1210
Question-1:Could you please confirm, the above selected values are suitable for MPPTSET and VOUT, or should I consider other values? Also, will the charging current automatically reduce as the batteries fully charged?
Question-2: Since my circuit has 3 batteries of 3.6V, the final bank voltage will be 10.8V. I have added a battery balancer circuit so each cell is charged efficiently. Is this the correct approach?
Question-3: What MMPT Voltages should I set for both cases (12v and 24v)
Question-4: Since the BQ24650 uses a buck topology, is it possible for my charger to start charging when the input is 11V or greater, given that the Vout (battery bank) is 10.8V maximum?
Question-5: If the BQ24650 is designed to start charging or kit turn on at 11.8V (10.8V + 1V), what changes should I make to allow it to start charging at 11V?
Question-4: Since the BQ24650 uses a buck topology, is it possible for my charger to start charging when the input is 11V or greater, given that the Vout (battery bank) is 10.8V maximum?
Question-5: If the BQ24650 is designed to start charging or kit turn on at 11.8V (10.8V + 1V), what changes should I make to allow it to start charging at 11V?
Question-6: The maximum battery pack voltage is 10.8V, but the resistor combination (499k and 120k) results in a maximum of 10.83V. Is this acceptable, or should the resistors be adjusted to achieve exactly 10.80V?
Question-7: To maintain stability according to datasheet section 8.3.19, the best stability occurs when the LC resonant frequency, fo, is approximately 12 kHz – 17 kHz. I am planning to connect two 22uF capacitors in parallel, C7 and C8, resulting in a final capacitance of 44uF. This yields a fo of 13.20 kHz, which meets the stability criteria. Is this approach correct?
Thank you.
Question-7: To maintain stability according to datasheet section 8.3.19, the best stability occurs when the LC resonant frequency, fo, is approximately 12 kHz – 17 kHz. I am planning to connect two 22uF capacitors in parallel, C7 and C8, resulting in a final capacitance of 44uF. This yields a fo of 13.20 kHz, which meets the stability criteria. Is this approach correct?
Thank you.
