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Original question:

BQ24650: suddenly can't not charge

BQ24650: Stops Charging after low light

user4646623
Prodigy 175 points
Part Number: BQ24650

Hello, we designed a LiFePO4 charger with the BQ24650, and we use a 12 cell 1Wp solar panel.

Most of the times it works very good!

We have set the MPP to 5.3 Volts, and we find that the system is indeed regulating the input voltage to this voltage.

Sometimes, after the solar panel has low power, the system doesn't work, of course. I measured an inputvoltage of approx 4 Volts... that is too low, I know.

But when the sun is back, and the solar panel starts working good again, the IC won't charge. I measured the input voltage to rise to fare above MPP. And the STAT1 indicator was OFF ( NO CHARGE) The battery was pretty empty. (2.8V . 4.2 Volt is considered FULL), so it should be charging

To correct the operation I can do 2 things to make it charge again:

- Reconnect the battery

- Cover the solar panel with my hand and release.

After this, It starts working again immideately.While nothing but the "reset"has happended.

It looks like the IC is Stuck in a sleep-mode where it never comes out.

Can someone help me?

  • 0
    TI__Mastermind 24075 points

    Hi,

      For the IC to charge, it not only has to satisfy the sleep condition, but the voltage on the solar panel should also rise above the MPPT point of the charger to start charging.

  • 0 in reply to Kedar Manishankar
    Prodigy 175 points

    Thank you for repliying.

    I measured the voltage on the solar panel, it was far above MPP point again.

    But it didn't charge.

    When I shortly darkened the panel, all started working again.

    During the "fault"status, the circuit was hardly drawing current, from the solar panel. That's why the voltage was far above mpp.

    It went back to mpp after the "reset"

  • 0 in reply to user4646623
    TI__Mastermind 24075 points

    Hi,

     What are your solar panel details, MPP, VOC, ISC? I am assuming this is for 1 cell Li-ion?

  • 0 in reply to Kedar Manishankar
    Prodigy 175 points

    It is a 12 cell solar panel of 1Watt peak

    - Voc= 7.2 V

    - Mpp= 5.8 V ( now set to 5.3 V, because of low light capabilities

    - ISC=200 mA

    It works OK for multiple days, but now and then I find it Non-charging, when it should.

  • 0 in reply to user4646623
    Prodigy 175 points

    Aha....

    I think what the problem might be...

    I think I ran into this: 

    On power-up, if the battery voltage is below the VLOWV threshold, the BQ24650 applies the precharge current to the battery. This feature is intended to revive deeply discharged cells. If the VLOWV threshold is not reached within 30 minutes of initiating precharge, the charger turns off and a FAULT is indicated on the status pins.


    Now, my power source is a 1Wp solar panel.. and I always started tesing with a completely empty battery. ( discharged to 2.5 Volts)

    The Pre-charge current is set to 20 mA only. ( 200 mA fast charge). I think it takes longer than 30 minutes to reach the VLOWV threshold. So, the charger will stop and never will start again ( if not resetted by one of the  2 ways described above)

    I tested a battery which was discharged to 2.5 Volts and it took  more than 1 hour to reach VLOWV.

    So, now I have to think about a fix for this problem.

    I mentioned that it works OK for days... that could be when the battery voltage during startup was a little higher, due to temperature, chemical change.

    I wil try to reproduce this fault.

  • 0 in reply to user4646623
    TI__Mastermind 24075 points

    Hi,

       The 30 minute inbuilt timer is fixed and cannot be modified. However a POR or toggling of the MPPSET pin, will initiate a new charge cycle and reset the 30 minute precharge safety timer.