BQ21040: Can we charge multiple cells in parallel with this?

Matt Roybal

Part Number: BQ21040

Hello, we have a circuit that accepts a lithium ion/polymer voltage of 2.7v to 4.2v, and boosts it up to 6 volts. We are currently using the BQ21040 to charge the cell. In an effort to get more battery capacity, can we connect multiple cells in parallel? I am understanding that its important for the batteries to be matching voltages before connecting them in parallel, but after this is done, would there be anything wrong with the BQ21040 to charge them both simultaneously in parallel? Thanks and any help/advice is greatly appreciated.

over 4 years ago

0 Bill Johns over 4 years ago

TI__Guru 65846 points

Hello

From a BQ21040 standpoint the parallel cells will look like a larger battery, potential problems with a larger battery would be longer charge time. Note that Precharge is 30min and Fast Charge is 10 hours.

Other possible issues related to the battery:

1.) Does each cell have a protector that could trip

2.) Are the cells matched so they will track each other on charge and discharge

3.) Thermal protection TS pin. does each cell have an NTC resistor

0 Matt Roybal over 4 years ago in reply to Bill Johns

Intellectual 345 points

Hi Bill, thanks for the response!

I have the option of using cells that have internal protection, and cells that do not. I wanted to go with the cells that have internal protection just for that extra protection.

Yes the cells will be brand new, same lot, and installed at the exact same time. After years of use or degraded battery performance, all cells would be swapped out at the exact same time for new ones.

The cells are 14500 so they just have a positive and negative. I was wondering if I could put the single NTC resistor as close to the negative or positive battery as possible?

I suppose I could use part # "RL0503-5820-97-MS" for the NTC, this would allow me to get a NTC closer to the center of the batteries. Its an expensive through hole component, so if putting a surface mount NTC close to the battery contacts would work that would be preferable:

https://www.digikey.com/product-detail/en/amphenol-advanced-sensors/RL0503-5820-97-MS/KC003T-ND/136365?utm_adgroup=Temperature%20Sensors%20-%20NTC%20Thermistors&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Sensors%2C%20Transducers&utm_term=&utm_content=Temperature%20Sensors%20-%20NTC%20Thermistors&gclid=Cj0KCQiAyKrxBRDHARIsAKCzn8yeaitqZz1v-79IFayeZcA2e-RuM-4Vetqf8kYFKrH7QaKJWsUTLl8aAuoVEALw_wcB

Thanks again!

0 Bill Johns over 4 years ago in reply to Matt Roybal

TI__Guru 65846 points

Hello

It would be best to check with the battery manufacture on paralleling the two cell and any cautions you should take.

From the charger side adjust charge current to meet your desired charge current and time for the combined cells.

NTC looks promising, what charge temp range are you looking for?

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BQ21040: Can we charge multiple cells in parallel with this?