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UC3906 charging current problem

Anantha Shayana
Prodigy 10 points
Other Parts Discussed in Thread: UC3906

Hi All

I am using UC3906 for charging my SLA battery 6V 4.5Ah battery with the following specifications.

Voc = 7.5 V,  Vf = 7V,  Imax = 500mA (C/5) Vin = ~10.5V,  V31 (float to bulk transition) = 6.3 V

The problem I am facing is, the charging time is too slow. it takes more than 24 hrs to full charge the battery and reach float voltage ( I am getting a float volatge of 7.1V practically). As my Imax is 500mA for a 4.5Ah battery it should take 9 hrs to fully charge the battery. By the way, the transformer used is a 9-0-9 1A rating which would be sufficient to provide the 500mA as dictated by using the resistor Rs=0.5ohm

All other parameters are matching my design, except this. Is there anything else I am missing. Please let me know what could be done to resolve this problem

Regards

Ananthu

 

 

  • 0
    TI__Guru**** 150730 points

    There could be several things that extend the charge time.  Do you have a load or any other circuitry connected to the battery?  Have you measured the current into the battery over the charge process?  Note that this is not equal to the input current as some of that current is lost in the drive of the pass element.

    Could you describe what the C/S Out, State Level Control, and Over-charge Indicate outputs are doing as the battery is charging?  Specifically, what times are you measuring in each of the following states:

    1. C/S Out high, OC Indicate high, State Level low (trickle charge)

    2. C/S low, OC Indicate high, State Level low (constant current charge)

    3. C/S low, OC Indicate low, State Level low (constant voltage charge)

    4. C/S high, OC Indicate high, State Level high (float charge = charge done)