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bq24450 SLA design

Bornfree
Prodigy 240 points
Other Parts Discussed in Thread: BQ24450

Hi There,

 

I'm very new to design and this is my very first project. I have to use BQ24450 to charge SLA 12V 7Ah battery. the charger need to have LED indicator for charging and full charge. Can someone please help me with calculation the resistor values. I plan to use 2STD2360T4 PNP transistor. Any help would be great.

Thanks for your time

  • 0
    TI__Guru**** 150610 points

    Bornfree,

    I am glad you want to use the bq24450 lead acid charger.  The first thing to do is look through the product page here: http://focus.ti.com/docs/prod/folders/print/bq24450.html Read the datasheet and the application notes there to get a feel for the part.

    There is a design example in the datasheet that you can use to pick your resistor values.  Just decide on what values you would like to use for the battery parameters on page 14.  Your pack manufacturer should be able to help you get those.

  • 0 in reply to Chris Glaser
    Prodigy 240 points

    Hi Chris,

     

    I have managed to make a charger using the BQ24450. Is there any way of showing the charge status using LED's? I only need to show, Charging and Charge complete.

     

    Also for a 12V 7A/h battery, how long will it charge until it goes on Float mode of 13.8V? The charger is supplying 1.2Amps

  • 0 in reply to Bornfree
    TI__Guru**** 150610 points

    Yes, you can use the STAT1 and STAT2 pins to know the charging status.  Please see page 5 of the datasheet.  The IC charges in bulk, then boost, then float mode.  So, STAT1 can be used to sense the difference between the bulk/boost state and float state, when the charge is done.

    For the charge time, it depends on how empty the battery is to begin with, how old the batteries are, if you use pre-charge or not, etc.  Also, the charging efficiency needs to be considered.  The battery pack manufacturer should have a much better idea of the charge time for their batteries with your conditions.

  • 0 in reply to Chris Glaser
    TI__Mastermind 31120 points

    One would have to track the state of charge to estimate the time to full.  Many lead acid cell are not made to discharge very much so make sure you treat the battery according to the manufactures guidelines.