Li-Po battery pack monitoring

Hi Matthew,

The bq20z65-R1 is the latest mass market device with the best accuracy but the bq3060 is a simpler device to configure and use but there is some trade off in accuracy, especially over the life of the battery as they use two different gas gauging algorithms The EVMs for both come configured by default in a way that will get you up and running quickly although some minor tweaks may be needed to change the configuration for different cell size/count values and protection. The bqEVSW available in the EVM tool folder will help enable these changes.

Both provide the RelativeStateOfCharge( ) command that reports the % of capacity available that can be read via an SMBus or I2C master.

Best regards

Garry

Hi Garry,

Thanks for the reply. On the BQ3060, does it matter if I don't have access to the individual cell terminals within the battery pack? As far as I can see these are just used for the overvoltage protection and not the battery capacity.

Many thanks,

Matt

Hi Matt,

  For most solutions we do use the cell connections for OV but also cell balancing and Impedance Track algorithm. If you don't have access to the cell nodes then the bq2060 may be another option as it just looks across the stack and has no balancing or protection features, essentially its just a gauge. It does have the same RSOC( ) % read out as the others.

Best regards

Garry

If you just want to coulomb count and you will be using the battery across a relatively narrow range of loads and temperatures so that the capacity extracted is pretty constant, you might use something like the bq27210 with a scheme shown in application note SLUA387 to divide the voltage down.  Refer to SLUA347 if you want to just use the bq27210 as a coulomb counter instead of bothering to configure all the gauging parameters to match your battery profile.

Hi Garry,

I have taken a look at the BQ2060/BQ2060a but it still seems like these require connections to the individual cell electrodes. Maybe I'm not reading this right though and they are not required for the SOC function?

Also, it doesn't say that this particular gas gauge is compliant with Li-Po batteries, it just mentions Li-I. Would the device still work with LiPo cells?

Many thanks,

Matt

Hey dMax,

Thanks for letting me know about the BQ27210. Using a voltage divider is a good idea! I'll be in touch if I need more advice on this device.

Cheers,

Matt

dMax,

I have looked more closely at the BQ27210 and am concerned that it is necessary for the battery to be connected to the monitor during every charge/discharge cycle. The battery will be connected during discharge but will be charged externally to the circuit. Another concern is that different batteries will be used interchangeably. When one battery is completely discharged it will be replaced with a fully charged battery, in this case it doesn't seem possible that we will be able to have compensated capacity registers.This is ok and I would be happy to simply use the non-compensated capacities but these seem to also require a connection to the battery during charging.

I simply want the SOC (%) output but the calculation for this uses all the compensated values. I looked at SLUA347 which does state in the abstract that it is possible to read the capacity of the battery even if the battery is externally charged or replaced. However, it doesn't discuss this topic in the document itself. Also, the SLUA347 is for BQ27x00 battery monitors although it is probably still applicable for the BQ27210...?

Any advice would be greatly appreciated dMax,

Cheers,

Matt