I am an engineering student and have been designing a power management system for a unmanned aerial vehicle. I am using a 11.1V 3200mAh 25C 3 cell Li-Po battery pack and want to be able to monitor the capacity level of the battery over the duration of the flight.
I have been looking at the BQ range of battery monitors, fuel gauges and gas gauges but am unsure what would be best for my need. The majority of these seem too over-engineered for the function I require. Literally all I want to do is monitor the level of capacity of the battery and send this back to a microcontroller as a percentage.
Any thoughts on the best IC for this? Any advice would be appreciated.
Thanks in advance!
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.
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.
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.
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.
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?
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.
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,
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.