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Charging 2 LiFe cells using the bq24630 chip at 10 amps each

Sandeep Kuthyar
Prodigy 80 points
Other Parts Discussed in Thread: BQ24630, BQ24630EVM

Hi All,

This is my first time posting here and I am an amateur  electronics enthusiast. Please forgive if I get some of the lingo wrong.

I am trying to fast charge 2 LiFE cells at 3.6 volts and 10 amps each using dual bq24630 chips.

1) How do I accomplish this? Do I have to set up 2 boards with 1 bq24630 chip each and duplicte the associated components(Inductors,MOSFETs, capacitors etc) ? and monitor the overall charging process by using a MCU?

2) How much does it cost to implement the above  solution? what would be the bill of materials for the charging circuit only (not including power supply and cells) ? Please also provide a bulk cost if possible.

3) Are there any components that can be shared in the 2 channel charger mentioned above or is it best to isolate the 2 circuits?

4) How will I accomplish cell balancing? I can put some login in the MCU to wait till I get the "Charge Complete" signal from both bq24630 chips, is this the best way?

Thanks

  • 0
    TI__Expert 8690 points
    Hi Sandeep,

    What is the capacity of each battery? Do you have a datasheet for the battery?
    How much is the average system load and peak system load?

    To answer your questions:
    1. You can design one board with the two ICs. You can use the EVM user guide to help you design the PCB. Also you can look at our recommendations at the datasheet page 30. The IC comes as a standalone, but if you want to control "charge enable" (or any other functionality) and monitor the status pins, then you can include an MCU as well.
    2. You can look into the user guide of our EVM and estimate the cost.
    3. You will have to isolate both circuits separately. You may have to use ferrite beads at the input of each converter to minimize the noise on the input voltage line.
    4. You can use logic to connect one battery at a time, when one battery goes below a certain voltage, disconnect it from the system line and connect the next battery.

    Thanks,
    Steven
  • 0 in reply to Steven Bangdiwala
    Prodigy 80 points

    Hi Steven,

    Thanks for taking the time.

    The cells each have a capacity of 2500mah. The data sheet says it can fast charge at 10 amps at 3.6 charging voltage. I only care mostly about the contant current charging and will terminate charging once the current starts dropping maybe once it reduces to 1 amp.
    I would expect the peak system load to be at 36 watts * 2 = 72 watts. I will be using a 20 volt 4 amps power supply.
    I expect the avg load to stay the same since the current does not really drop till the battery is charged to 80%.

    I can email you the data sheet as needed. or you can look up cell (2.5Ah).
    I need to fast charge 2 cells parallley so I need an external circuit (MCU) to monitor them both.

    Question: The evaluation board BQ24630EVM allows a max of 8 amps only even though the chip can charge at 10 amps. How will I be able to use the evaluation board and charge at 10 amps?
    Do I need to duplicate components in both circuits, are there any components that can be used in common? even though both chips are running parallely.

  • 0 in reply to Sandeep Kuthyar
    TI__Expert 8690 points
    Sandeep,

    I have one question. Is this just to charge the battery or do you plan on connecting the batteries to a system in the same board? I was under the assumption that you will be connecting the batteries to another system after charging them. Will you be connecting them in series after charging them? A block diagram may explain things better.

    You also need to take into account the efficiency. 80W for 72W charging is cutting it close assuming 90% efficiency. For ACSET use 4A so that your input power does not crash. Make sure your PCB has enough copper pour to dissipate heat that will be generated from 20A charging.

    In the EVM you will have to change ISET1 according to datasheet section 8.3.2 and look at table 4 on page 28 to make the appropriate adjustments for 10A. Duplicate components, there are no components that can be used in common.

    Regards,
    Steven
  • 0 in reply to Steven Bangdiwala
    Prodigy 80 points
    Hi Stven, Yes I will be discharging the batteries in series in the same circuit board(Assuming everyhing will be in one board). I will be "switching off" the charging circuit when it is in discharge more and vise versa. the discharge circuit board will contain a DC to DC converter to maintain a contant discharge voltage and it will also provide discharge protection to the cells. All processes will be controlled by a micro controller.
    Regarding cost, I looked at the bill of materials in the evaluation board, will I need all the components ?
    You are right about the 80 watt charger I will probably end up using 90 watt power supply.

    Thanks
    Sandeep
  • 0 in reply to Sandeep Kuthyar
    TI__Expert 8690 points

    Sandeep,

    You need necessary components for the charger to work, you don't need to add all of them. Our EVM is designed to be tested on and used as reference, not as a final design. Make your own schematic based on your system's needs with the necessary components and then add those for your estimated cost.

    You should look into the gauges for cell balancing, post at the gauge forum and see if someone can help you out. Although it sounds like charging both batteries to the same voltage before connecting them in series will be the reasonable approach. The gauges I've seen work with both of the batteries connected in series to one charger.

    Regards,
    Steven