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BQ25185: Can BQ25185 be used as a solar charger for 3S NiMH battery?

qAtmoman
Prodigy 10 points
Part Number: BQ25185
Other Parts Discussed in Thread: BQ25172,

We are looking for a stand-alone IC solution for a low power 3S NiMH battery solar charger and from the looks of it, out of 300+ ICs that TI is offering, only very few are tailored for NiMH chemistry (BQ25172 in particular) and none of those supports any MPPT-like or VINDPM functionality. 

Since 3-cell in series NiMH battery is very close in charge profile and voltage requirements of 1S LiIon/LiPo cell, can we use BQ25185 for this purpose? 

Our plan is to create a Solar Charge Controller that would charge ~1000mAh battery at around 100mA, and best we found so far is this IC. Assuming we set proper voltage cut-off and charge current limit, are there any cons of using this IC for this application? We plan on using 1-3W 6V solar panels.  


Thank you in advance!

  • 0
    TI__Genius 13905 points

    Hi,

    The BQ25185 should be suited for your solar application. It should be able to handle 100mA charging and BATTRACK VINDPM should allow you to maximize current from solar panel charging.

    With regards to charging a 3S NiMH battery, can you share your expected regulation voltage, pre-charge voltage, and BUVLO voltages?

    Best Regards.

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    In our application 3S NiMH is supposed to be a replacement for 1s Li Ion type cell as we do not need high current output of lithium battery and want to benefit from lower fire hazard of NiMH.  

    Output to the application will be regulated 3.3v and 5v with maximum of 50mA current (6mA typical) for which we plan on using buck-boost regulators attached to Sys out pin. 

    If I understand correctly, BUVLO is fixed at 3v for BQ25185, which would automatically cut-off output to system when battery reaches that level, which is perfectly fine for us. 

    In terms of pre-charge voltage, we actually do not need it, and would want the 3S NiMH to charge at available current from the Solar output up to ICHG limit of 100mA. If I read the datasheet correctly, pre-charge state also should transition to "fast charge" (100mA in our case ) at around 3V, so we should generally avoid this pre-charge state altogether.   

    If all my assumptions are correct, sounds like BQ25185 should be ideal for our scenario of charging 3S NiMH even if it was not designed for this chemistry. Would you confirm?

  • +1 in reply to qAtmoman
    TI__Genius 13905 points

    Hi,

    Yes, if there is no issue with the pre-charge state then the BQ25185 should work well for your charging scenario.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    Thank you for confirming!