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Charging a 12V 26Ah battery

Cameron Foss
Prodigy 20 points
Other Parts Discussed in Thread: BQ24450

I am looking to charge a 12V 26Ah VRLA battery with a max charge current of about 3.5 Amps and max input voltage of 16V.

From looking at the data sheet, it appears that the diagrams shown are for charging 6V batteries, so I was wondering what are the significant(if any) changes that need to be made in order to charge my battery?

I have already tried building the circuit the datasheet suggest, but I ran into errors with the pass transistor. I was using a PNP power transistor(2N5876), but I found that the DRVC pin doesn't supply a high enough voltage to put the pass transistor into the saturation mode.(ie Veb maxed at 5V for the transistor, but I have 16-2 = 14V that is required.

Is there a way to design around this restriction?

  • 0
    Prodigy 20 points

    Sorry Im using the bq24450 LA battery charger manager.

    One more question, what is the maximum power that the chip can safely manage? That is, if I charge the battery with an input of about 16V at say 3.5Amps that's 56W. Is this chip suitable for this amount of power?

  • 0 in reply to Cameron Foss
    TI__Mastermind 31120 points

    This is a controller IC so the heat dissipated is the voltage drop from the input to the battery times the current.

    There are different configurations of drives explained in the data sheet on page 13.

    If you have the proper heat sink and enviornment to get rid of the heat without too much temperature rise, then the circuit should work.  You are probably talking a maximum of 12W of dissipation.