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Original question:

BQ25505 - charging battery with piezoelectric

BQ25504: Missed the MPPT update frequency

Fredrik Tarnell
Intellectual 385 points
Part Number: BQ25504
Other Parts Discussed in Thread: BQ25505, , BQ25100

Hi.

Used the BQ25505 to harvest energy from small solar panel mounted on a moving object. Problem is that object constantly gets the panel under different lighting situations.

For this I created a dome type of setup mounting 5 panels facing "all potential" angles so that at least on panel is faacing the the sun +- 15 degrees...

What I totally missed is that I will never get a proper MPPT sample. I guess using MPPT is not in scope for the use case. Then came across the following thread.

Recommending to change to bq25504 to be able to eliminate MPPT all together.

Because of my panel arrangement I have needed to go for 5 separate bq25504 since either serial or parallel arrangements works since no panels are alike from a mounting perspective.

This will cause 5 battery chargers to operate on the same cell. Would a better option be to use 5 separate boost-converters and get them to convert to let's say 5volt and from there connect it to a charger  instead to cut down the price of my BOM?? Could you please recommend parts? I guess a really low input voltage is given.

Any benefits of sticking with 5x bq25504??

Thanks!

  • 0
    Intellectual 385 points

    Could the bq25100 be used as the charger if going for a boost converter with separate charger?

    But it looks like it's difficult to find a boost converter with an input voltage lower than 0.2v ...  

  • 0 in reply to Fredrik Tarnell
    TI__Genius 10385 points

    Fredrik, 

    I do not think using multiple boost converters would be to feed into a single charger would be a good idea. As you have said, boost converter with low operation voltages are not easy to find. Economically, I cannot speak to the price of the ICs as I do not know what volumes you are considering and this isn't the place for that conversation, but I can tell you that connecting multiple DC/DC converters in parallel requires additional hardware. This is because the converters would not share the load evenly and try to regulate each other. This can be resolved a variety of ways such as using external current sense circuitry to help split the load evenly, using a diode OR to only allow one converter to provide current at a given moment, or using a power switch in higher current applications.

    If you would like to disable the MPPT circuitry, you will have to move to BQ25504. Please we aware of the differences between BQ25504 and BQ25505 recommended operating conditions. Generally, BQ25504 has a more reduced operating range than BQ25505. If your solar panel's output voltage exceeds the rating for the input voltage pin, you may have to use a zener diode to clamp the input voltage.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    TI__Genius 10385 points

    Hello,

     

    I have not heard back from you in a while. Please let us know if you have any further questions, otherwise I will be closing this thread.

     

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 385 points

    Hello Ricardo,

    Sorry for not replying back sooner.

    Connecting multiple chargecontroller in larger solar installation having different "lighting situations" seems to be a viable option. In fact the only option when I look around. Searched for "mppt charge controllers in parallel" and as soon as you have multiple conditions to different sets of panels this seems to apply.

    The thing that differs here is that I think (think) MPPT might be in the way in my setup since panels are constantly moving in and out of sun/cloud/facing wrong way and so on. Think of an object spinning around from time to time. My understanding is that MPPT would be even worse than not using MPPT in such situations.

    Looking at the TI productline I cannot find much else than BQ25504, BQ25505 and BQ25570. But only BQ25504 can be configured without MPPT as I understand it. Thing is that BQ25504  has been marked "not for use in new designs".

    The range of the BQ25504 suits me fine. And since the charge-profile would be the same for all five BQ25504 working in parallel I was hoping that voltage would be the same but current would increase in total.




  • 0 in reply to Fredrik Tarnell
    TI__Genius 10385 points

    Fredrik,

    BQ25504 is actually active. the NRND label on the datasheet is a mistake. Thank you for bringing this to our attention. Based on this, I recommend you use BQ25504 for your design to be able to disable the MPPT feature.

    Thanks,

    Ricardo