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BQ24450: 24V / 24Ah sealed lead acid battery charger

Luis Conrado Teixeira
Prodigy 40 points
Part Number: BQ24450
Other Parts Discussed in Thread: BQ24610

Hello,

I need to develop a sealed lead acid battery charger which will be incorporated to an UPS module of a medical device. The charger will charge two 12V/12Ah batteries connected in series. Each battery has 6 cells.

The maximum charging voltage is 28,5V and the charging current is 4,8A (maximum).

I was wondering if I can use the BQ24450 in this design. Is it possible?

If no, what TI component should I use?

Thanks in advance,
Luis

  • 0
    TI__Mastermind 19195 points

    Hi Luis,

    Charging current is high, heating from the pass element would be an issue with BQ24450. 

    BQ24610 would be a better choice here.

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 40 points

    Hi Nick, 

    Thanks for answering.

    Just to understand your point:

    • Still regarding the BQ24450, according to its page (https://www.ti.com/product/BQ24450), this IC can charge up to 16 lead acid cells, with charging voltage of 20V (max). I'd like to understand why the maximum charging voltage is 20V. I used to think that the current and voltage limits were mainly imposed by the external transistor. Are there some other heating element in the IC itself? 
    • Now regarding BQ24610. It is suitable for Li-Ion/Li-Polymer batteries with charge voltage of 26V (max). Considering that I need to charge lead acid battery with charge voltage of 28V (max), is the BQ24610 still the best option?

    Thanks in advance,

    Best regards,

    Luis

  • 0 in reply to Luis Conrado Teixeira
    TI__Mastermind 19195 points

    Hi Luis,

    The max charging voltage is limited by the max input voltage of 40 V.

    You are correct, the pass transistor is the main heating element. With a 30V input and battery at 24V you can calculate the heat dissipation (30-24)*5A = 30 W.

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 40 points

    Hi Nick, 

    Thanks again.

    Just to conclude, considering that the circuit will charge 12 lead acid battery cells of 2V each one which a maximum charging voltage of 27,6V and 4,8A (charging current), can I use the BQ24450 with no problem?

    In case of using the BQ24610, can it be used with lead acid batteries even if it's indicated for other kind of chemical?

    Best Regards,

    Luis

  • 0 in reply to Luis Conrado Teixeira
    TI__Mastermind 19195 points

    Hi Luis,

    BQ24450 in the External Quasi-Darlington configuration can be used here. 

    For the BQ24610, the max charging voltage is 26V. We do have an app note showing how it can be configured for lead acid here: 

    https://www.ti.com/lit/pdf/slua992

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 40 points

    Hello Nick,

    Thanks again for you help. 

    I'm going to use BQ24450 with a N-channel MOSFET pass transistor. 

    Best regards,

    Luis