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solar charge controller float mode issue

BALKRISHNA TULSYAN
Intellectual 850 points
Other Parts Discussed in Thread: MSP430G2553, BQ24650

Hi,
I have 12 volt /10 amps solar charge controller.
As per design it will bulk charge at 14.4, absorb charge is between 14.4 to 14.6 and after that it will enter into float mode.
when charge controller enters into float mode its voltage will step down to 13.7 volt and led will starts blinking.

I observed that, when i put power supply (to simulate solar panel) voltage above 14.6 volt, led is blinking which is normal but when i measured voltage across battery terminal using multi-meter then voltage is fluctuating between 14.7 to 13.7 and also between these range.
Is this normal or it require a fix.

NOTE: All this observation is while charging.
power supply and battery is connected to the charge controller.
Load is switched off.
I observed the same when i connect solar panel instead of power supply.

Microcontroller used is MSP430G2553


Can anyone guide me on this???

  • 0
    TI__Genius 11480 points
    Hi Amit,

    Which charging IC are you using?

    If you are using the bq24650, have you followed the app note to modify for lead acid batteries (found here: www.ti.com/.../slva437a.pdf )?
  • 0 in reply to David Wiest Jr
    Intellectual 850 points

    Hi,

    I am NOT using any charging IC for this. This is PWM charger where i am changing the duty cycle for varying the voltage.

    I want to know whether this behaviour (voltage fluctuation at float mode) is expected or it require a fix.

    Thank you..!!

  • 0 in reply to BALKRISHNA TULSYAN
    TI__Genius 11480 points
    Amit,

    So you are using a normal DC-DC converter to charge the lead acid?

    I would suspect that the voltage fluctuation at float mode is due to the self-discharge of the lead-acid battery. If you look over the app note I referred you too, this is why we pulse-charge the battery after it reaches the float voltage.
  • 0 in reply to David Wiest Jr
    Intellectual 850 points

    Hi,

    I can send the schematic used for charging to your mail id in case you require ..!!

    I am just using a MOSFET which is driven by BJT and BJT is controlled by PWM pulse generated by microcontroller. Therefore i am generating variable duty cycle to control the voltage at the output. During Bulk charging MOSFET is always ON while in absorbtion and float mode , i am feeding a veriable duty cycle based on battery current status and set point.

    Can you please explain in brief as how to implement pulse charging through code in float mode. Do you have any application note for that? Moreover i have gone through the application note, but i didn't find the reason to implement pulse charging (why pulse charging is required??). It only says about the components need to be added for charging lead acid battery instead of lithium ion with "bq" IC.

    Is the problem experienced by me is normal and seen by you??

    Is there any other method to avoid fluctuation other then pulse charging??

    Thank you

  • 0 in reply to BALKRISHNA TULSYAN
    TI__Genius 11480 points

    Feel free to send me a schematic at d-wiest@ti.com.

    Unfortunately, my software skills are not good enough to help you with code. Writing firmware is well outside of my comfort zone :)

    So, are you using any DC-DC conversion, or just connecting the battery to a voltage source with a FET? Any feedback network to regulate your output?

  • 0 in reply to David Wiest Jr
    Intellectual 850 points
    Hi,

    Please find the attachment in mail.
    I am just connecting the battery to a voltage source with a FET.
    NO DC-DC Converter is used.

    Regards:
    Amit