Battery fuel gauge characterization

[yamanoorsai]

I am using DS2782 as a battery fuel gauge in my project. I have interfaced it to a microcontroller and I am able to interface and read something. This application note explains a characterization process where they suggest varying the temperatures and loads to characterize the battery used in the project. I don't have the necessary equipment to do so. I am currently charging the battery and discharging it in cycles.

I am charging the battery completely and discharging until the voltage read by the DS2782 is less than 3V(based on the suggestion by the application note). The parameters like Active remaining capacity are still close to zero(values read are close to 7).


Is the simple  charge and discharge cycle sufficient to characterize the battery?

[minime72706]

Is the "current accumulation" register behaving in an expected way?

I remember sampling this chip back in 2010 for my undergraduate senior project, but I scrapped the idea. I was too busy writing pages and pages of code and trying to perfect my toner-transfer PCB etching process.

[yamanoorsai]

I am able to read a number from the MSB and LSB from the accumulated current register. My status register always reads '39' which means the battery is actually not full. But my charging circuit indicates that the battery is full and stops charging.

Sai

[ohmineer]

I am using DS2782 as a battery fuel gauge in my project. I have interfaced it to a microcontroller and I am able to interface and read something. This application note explains a characterization process where they suggest varying the temperatures and loads to characterize the battery used in the project. I don't have the necessary equipment to do so. I am currently charging the battery and discharging it in cycles.

I am charging the battery completely and discharging until the voltage read by the DS2782 is less than 3V(based on the suggestion by the application note). The parameters like Active remaining capacity are still close to zero(values read are close to 7).


Is the simple  charge and discharge cycle sufficient to characterize the battery?

I don't know whether you have already finished PCB design but I would recommend to you to capture charge and discharge cycle data using an external data logger. In that way, you can compare offsets that you have to configure later on in DS2782 memory. Furthermore, you can not consider ACR readings accurate if you have not model your current sense resistor.

Battery characterization in temperature is important:
- Usually you will not have problems at high temperature because there is a small difference of capacity in the 20ºC to 40ºC range.
- However, at low temperatures capacity available is reduced almost explonentially due to internal resistance increase. If you don't model your cell, capacity reported will be higher than capacity available and your system will turn off (Due to low voltage or circuit protection trigger) before ACR has reached 0 mAh.

[ohmineer]

I am able to read a number from the MSB and LSB from the accumulated current register. My status register always reads '39' which means the battery is actually not full. But my charging circuit indicates that the battery is full and stops charging.

Sai

In order to read a logic 1 in the Full Charge Flag within the status register VCHG and IMIN parameters must be configured.

[yamanoorsai]

I am using a 110mAh Li-Po battery that I bought off the shelf. The application has a very light current load (in the order of few mA). It is powering up a microcontroller, accelerometer, op-amp and a bluetooth UART transmitter. It would be operated at normal room temperatures and all I need is a rough estimate to plug in the USB cable to recharge the battery

[minime72706]

I do hope you get that fuel gauge IC working, but if it becomes too much of a pain, this is what I would do:
Just monitor the voltage of the battery and have some sort of indicator turn on when it hits about 3.0V (people may disagree with this number).
Use a MAX1555 or something similar (but this chip is pretty damn simple) to charge the battery.?

This may be useless advice if PCB design has already been completed.