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Very urgent Support request bq24650 Solar SLA charger

paulo onofre1
Prodigy 10 points
Other Parts Discussed in Thread: BQ24650

Hi

My application requires charge a SLA battery  12V / 40Ah from a Solar panel.

The charger should allow solar panel from 22W to 100W ( panel Optimun operating voltage (Vmp)= 17V  ) 

i itend to use  the next circuit,  ( reference:  doc SLVA437A )

vmppt set=17v   vbat=14.59 v  i charge=8A

My questions?

- what is the  the charge current in a pre-conditioning mode ? 1/10 of  fast charge? what is the time?

- Is possible reduce de Precharge region time  in this circuit?

- What is the charge current when a voltage in the solar panel drops below the mppt set voltage (17V ) ?    What is the Min voltage necessary  in the Input, to charge the battery?

I await your observations and suggestions to optimize the circuit

Thanks

Regards

  • 0
    TI__Expert 5565 points
    First, a few comments on the circuit:
    1. The purpose of D3 is to get a little bit better efficiency from the battery when there is no input voltage present. If D3 is not present, then the battery current has to go through R6, L1, and the body diode of Q1:A to reach the VCC pin of the IC. With D3 present (preferably a Schottky diode), the voltage that reaches the VCC of the BQ24650 is a little higher, thus better efficiency.
    2. The datasheet states (page 21) that the resonant frequency of the output LC filter should be between 12kHz and 17kHz for optimal loop stability. With this, a better value for L1 would be 10uH.

    Answer to your questions:
    1. Yes, pre-charge current is 1/10th of the fast charge current setting. This is also the same for the termination current. The fault timer for pre-charge is 30 minutes. If within 30 minutes the battery voltage does not reach VLOWV, then the charger turns off and a fault is indicated on the STAT1/STAT2 pins.
    2. No, it is not possible to change the pre-charge time. It is a fixed timer in the BQ24650.
    3. If the input voltage drops below 17V while the battery is charging, then the BQ24650 will reduce the charging current so that the MPPSET voltage does not drop below 1.2V. The BQ24650 will continue to reduce the charging current to zero in order to maintain the MPPSET voltage equal to or greater than 1.2V.