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Lithium battery protection to meet dangerous goods regulations

Aaron Burnie
Prodigy 140 points
Other Parts Discussed in Thread: BQ24040, BQ24232

Hello all,

I am in the process of trying to design our Li-Ion batteries so that they pass all the requirements necessary to pass the IATA Dangerous Goods Regulations.
Specifically the Lithium Batteries 3.9.2.6 Clause.

The issue I have is for batteries which are setup in a 1S/2P (1 series, 2 parallel) configuration and ensuring that  dangerous reverse current flow is prevented. This would mean that there would need to be some protection against each battery charging each other.
I wanted to avoid the use of using diodes on each of the batteries if possible.

I know there are protection IC's for batteries in series which would be perfect however there does not seem to be any protection devices which address the safety issues with batteries in parallel.

Can anyone suggest a protection mechanism for batteries in parallel?

regards

Aaron

  • 0
    TI__Expert 7730 points
    If you want to prevent the reverse current from the OUT pin to VBUS pin of our IC, you don't need extra diodes. Most of our chargers have internal blocking FET to prevent the reverse current flow. BQ24040, BQ24232, etc.

    If you want to protect against the wrong battery polarity, you will need add external FETs. Please let me know where case are you talking about.

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 140 points

    Thanks for the reply Wenjia,

    Our rechargeable Li-Ion 1S2P battery is connected like battery 3 & 4 in the image below. In the dangerous goods regulations this parallel battery connection is not allowed because it is possible that battery 3 can charge battery 4 with uncontrolled currents. this is also the same with battery 4 charging battery 3.

    The reason the batteries were connected in parallel was to keep the voltage at an acceptable level so that a real time clock could be powered always while maintaining battery equalization.

    For rechargeable batteries the image with battery 1 and battery 2 will not work.

    For the 3rd image which contains mosfets perhaps there is something which could disconnect battery 3 from battery 4 if the voltage different between them is too large, hence one battery will charge the other.

    The other alternative to meet dangerous goods regulations is that the batteries may just have to be connected in series and then tap off ~3.7V for the real time clock from one of the cells. This means that battery discharging is not even.

    Hope this makes sense...

  • 0 in reply to Aaron Burnie
    Expert 1375 points
    Hi Aaron,
    To my knowledge if Your battery is excepted from Class 9 you do not need a protection diode in serie With each cells Connected in parallel. Please ref Packing Instruction 965-965.

    Regards
    Kjell Ramberg
  • 0 in reply to Kjell Ramberg
    Expert 1375 points
    Sorry - I got a typo in my previous post, - it should be Packing Instruction 965 - 970

    Kjell