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    How to charge an empty 6V VRLA battery?

    Hi guys,

    I need help here to top up the charge on a 6V 1.3Ah empty VRLA battery.

    Whats the voltage & current i should be using to charge the battery?

    Here's the battery information:

    Constant voltage charge

    Boost/equalize: 7.2 - 7.5V

    Float: 6.75 - 6.9V

    Max charging current :0.39A

    I am using an LM317 adjustable voltage regulator to set the charging voltage.

    Thanks,
    Sunny55.

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  2. #2
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    Re: How to charge an empty 6V VRLA battery?

    A state machine with flip flops is simple to control these 3 states. plus Vbat present.

    Use a current sense R such as 75~ 100mV at max current.
    Use a band gap ref for controlling current , voltage and shutdown float, which is included in LM317, but using a linear regulator is very inefficient with heat sink required.

    Measure average current with a comparator to turn on MOSFET for CC mode with series storage inductor and clamp diode to make a buck regulator. This will make it oscillate, so inductor must be able to handle DC current. ( e.g. 50~100uH)

    Voltage feedback also feedback to prevent over voltage with small filter.

    When CC reaches 7.2V it goes into CV mode and a few seconds after CV mode, it checks if current is less than ~ 10% of max rated current, then can go into Float mode.

    Generally VRLA's use a thermistor to compensate target voltages to prevent gassing according to Mfg specs.

    Or look for a ASIC to reduce component count.
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



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