BQ25895: Charging and using 8 18650 cell in parallel

Mayur Prajapati1

Part Number: BQ25895

Hi,

We need to use 8 18650 cells in parallel in one of our project. This 8 cells will be replaceable and will be connected to each other in parallel creating a 3.7V 20.8Ah battery capacity.

Below are my queries related to the use case:

1) Can we use a single cell charger IC (e.g: bq25895) for 8 cells in parallel?

2) DO we have to use a BMS for parallel cell options?

3) Our use case is similar to the power bank. But, the User will have an option to replace the cells if needed. Could you let us know if we need to take care of any extra protection?

4) We are going to design a customer PCM circuit for the OCD, OVP and other needed protection for all 8 cells together. Let us know if we need to add anything else too.

Regards,

Mayur

over 3 years ago

0 Ning T over 3 years ago

TI__Guru 51571 points

Mayur,

How much charger current is needed to charge 8 cells in parallel?

Thanks,

Ning.

0 Mayur Prajapati1 over 3 years ago in reply to Ning T

Prodigy 70 points

Hi Ning,

We need to charge the cells at a maximum of 2A/3A in parallel. 2A /3A for all 8 cells combined.

Regards,

Mayur

0 Ning T over 3 years ago in reply to Mayur Prajapati1

TI__Guru 51571 points

Mayur,

The total charge current is only up to 3A for 8 cells combined? You mentioned it is 20.8Ah battery capacity.

Thanks,

Ning.

0 Mayur Prajapati1 over 3 years ago in reply to Ning T

Prodigy 70 points

Hi Ning,

The total capacity of the battery is 20.8Ah by combining the 8 cells of 2600mAH ( 8*2.6Ah= 20.8Ah).

Regards,

Mayur

0 Ning T over 3 years ago in reply to Mayur Prajapati1

TI__Guru 51571 points

Mayur,

The BQ25895 is a 5-A single-cell charger. With 8 cells in parallel, it could be hard for a single-cell charger to balance each cell effectively. And what if one or more of the 8 cells fails in the middle of charging? It is not recommended to use a single-cell charger for this case.

Thanks,

Ning.

0 Mayur Prajapati1 over 3 years ago in reply to Ning T

Prodigy 70 points

Hi Ning,

Please let me know if I should use a multicell charger IC?. if so please suggest a suitable part number and method to connect the multicell IC for parallel configuration.

Also, It would be helpful to us if you can suggest a design or reference for our use case.

Regards,

Mayur

0 Ning T over 3 years ago in reply to Mayur Prajapati1

TI__Guru 51571 points

Mayur,

This is single-cell charger support. Please submit a new thread for multi-cell charger recommendation. The right support team will help you further.

Thank you very much,

Ning.

0 Mayur Prajapati1 over 3 years ago in reply to Ning T

Prodigy 70 points

Hi Ning,

AS per the below E2E link it seems even if i use 8 cells in parallel it will work as a single cell.

e2e.ti.com/.../945156

We are going to use the cell with inbuilt PCM, thus if the cell goes bad it will disconnect itself.

I believe we cannot use multiple cell configuration for the cells in parallel. Please confirm.

Regards,

Mayur

0 Mayur Prajapati1 over 3 years ago in reply to Ning T

Prodigy 70 points

Hi Ning,

AS per the below E2E link it seems even if i use 8 cells in parallel it will work as a single cell.

e2e.ti.com/.../945156

We are going to use the cell with inbuilt PCM, thus if the cell goes bad it will disconnect itself.

I believe we cannot use multiple cell configuration for the cells in parallel. Please confirm.

Regards,

Mayur

0 Ning T over 3 years ago in reply to Mayur Prajapati1

TI__Guru 51571 points

Mayur,

It is ok to use the BQ25895 to charge the 8 cells in parallel as long as the cells have built-in protection and may disconnect bad cells automatically.

Thanks,

Ning.

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BQ25895: Charging and using 8 18650 cell in parallel