8 Cell Battery testing

Leethal

Other Parts Discussed in Thread: BQ27010, BQ27210, BQ27510-G2

Hi,

I use 8 cell Li-Ion batteries(29.6V) with only the 2 power leads avalilable. I would like some feedback as to the best way to monitor the AH capacity. I can, I imagine use a small value series resistor with a load and monitor this with an ADC, log the data and calculate the area under the curve.

Is there a better way than this, perhaps using one of TI's components to check the state of the battery. Note that I have no access or data from individual cells.

Regards,

Lee.

over 14 years ago

0 Neil Kurzman over 14 years ago

Prodigy 30 points

If that is all you have look at the coulomb counter ICs

0 Leethal over 14 years ago in reply to Neil Kurzman

Intellectual 695 points

Hi Neil,

They seem to be limited to 1 or 2 cells, but I imagine I could work around that by powering the device independant of the battery and just using the shunt resistor????

Regards,

Lee.

0 dMax over 14 years ago in reply to Leethal

TI__Genius 14985 points

You could use an LDO to power the monitor. For only coulomb-counting (what we call a battery monitor, not battery gauge), the best IC to use is a bqJunior as per this app note:

SLUA347: Building a Superior Battery Monitor with the bq27x00

A battery monitor doesn't account for changes to actual usable capacity due to internal impedance. This means your host will need to compensate for temperature, aging, and different load rates. By using the bqJunior as a battery monitor you are basically ignoring its gauging functions that do this for you (after proper configuration). If you have a relatively light load and/or use it in a pretty stable environment this might be fine.

This app note explains the difference between a battery monitor and a gauge: http://www.ti.com/litv/pdf/slua358

Another option that is theoretically possible is to use an 8:1 voltage divider with a single-cell gauge, either a bqJunior (bq27010/bq27210) or an Impedance Track gauge like bq27510-G2:

SLUA387: Multicell Li-Ion and Li-Pol Battery Gas-Gauge Application Using the bqJunior

SLUA496: Multicell Li-Ion and Li-Polymer Battery Gas-Gauge Host Side Application (Rev. A) (with IT gauges, example shows 2S pack)

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8 Cell Battery testing