BQ25713: NiMh cell charging

Jonathan Navor

Part Number: BQ25713
Other Parts Discussed in Thread: , BQ25798, BQ24650

Hi Experts,

We need your confirmation with these two devices. BQ25713 and BQ25713B.

Could we connect a photovoltaic panel (Vtyp:3.6V Ityp:50mA 180mW - Voc:4.9V Vocmax:5.5V Isc: 64mA) directly on the input of the BQ25713?

Could we recharge up to 4 NiMh cells (series) with the same photovoltaic panel?

Thank you in advance for your support.

Best regards,

Jonathan

over 2 years ago

+1 Ethan Galloway over 2 years ago

TI__Mastermind 32285 points

Hello Jonathan,

I would recommend using a TI part has better MPPT. I think the BQ25798 might better suit this application.

Yes, it is possible to charge a NiMh battery with the charger. However, It will not be easy to do because NiMh has a different charging profile than Li-Ion. The customer will need to monitor the charging voltage closely to determine when to stop charging.

Best Regards,
Ethan Galloway

0 Jonathan Navor over 2 years ago in reply to Ethan Galloway

TI__Genius 9475 points

Hi Ethan,

Thank you.

We need further assistance with this query. Compared to the typical application shown in the datasheet what should we change and/or add?

The customer would like to try 2 cells and 4 cells NiMH and the BQ25798 is not available in stock.
Is there an alternative?

Best regards,

Jonathan

0 Ethan Galloway over 2 years ago in reply to Jonathan Navor

TI__Mastermind 32285 points

Hi Jonathan,

You should be able to follow the design procedure in the datasheet.

Keep in mind to perform MPPT with the BQ25713, you need to use the VINDPM feature. You'll need to find the open circuit voltage and then set the appropriate VINDPM setting.

If you are still looking for alternative parts, the customer could also use the BQ24650.

Best Regards,
Ethan Galloway

0 Jonathan Navor over 2 years ago in reply to Ethan Galloway

TI__Genius 9475 points

Hi Ethan,

Here is the customer's feedback.

Does the BQ24650 also work for NiMh batteries?

I think it is better to use the BQ25713 component. Is the open circuit voltage (VINDPM setting) that of the photovoltaic panel?

Best regards,

Jonathan

0 Ethan Galloway over 2 years ago in reply to Jonathan Navor

TI__Mastermind 32285 points

Hello Jonathan,

Thanks for checking. The BQ24650 does not support NiMh. It's a standalone charger.

When I said open circuit voltage, I was referring to the open circuit voltage of the solar panel.

VINDPM is a setting of the charger.

Best Regards,
Ethan Galloway

0 Jonathan Navor over 2 years ago in reply to Ethan Galloway

TI__Genius 9475 points

Hi Ethan,

Therefore:
1) We can use BQ25713 to charge from 1 to 4 NiMH cells.
2) We have to set Vindpm equal to the open circuit voltage of the solar panel.

But can I recharge 4 NiMh cells with a panel with a 3.6V output voltage?

Best regards,

Jonathan

0 Ethan Galloway over 2 years ago in reply to Jonathan Navor

TI__Mastermind 32285 points

Hi Jonathan,

Thanks for working with me and being patient with this. I had something come up today. I will get back to you tomorrow.

Best Regards,
Ethan Galloway

0 Ethan Galloway over 2 years ago in reply to Jonathan Navor

TI__Mastermind 32285 points

Hi Jonathan,

For MPPT, you set the input voltage limit to some fraction (usually 80%) of the Voc of the solar panel.

Yes, you can recharge 4 NiMh cells from a 3.6 V adapter. I recommend the adapter/solar panel be able to sink greater than 300 mA to charge the battery pack.

Best Regards,
Ethan Galloway

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BQ25713: NiMh cell charging