Battery Fuel Gauge

1. They are single cell gauges and there are multicell gauges. They are not limited to the coin cell batteries. In fact, any Li-ion cell can be used with the gauge, from LiCoO2 to LiFePO4 and everything in between. The only real limitation is maximum capacity of the cell, but for your application it won't be a problem.

2. A good IC for you to look into would be with the bq20z65 or bq20z45. The main difference between the two is that the z65 provides support for LEDs and the z45 does not.

3. Yes, it does. The z45/z65 measures the impedance of each cell in the stack and uses this for modeling the Remaining Capacity. In addition to this, many of the safety parameters are based on either the highest or lowest cell voltage.

4. The gauge is designed to built into the battery pack, so this situation would not be encountered.

5. Current measurement occurs about every 250ms. Four points are averaged to create one measurement. So the Current register will update about once a second.

6. I'm not sure what you mean here, but the gauge can physically operate down to 4.5V. The gauging algorithm is designed to handle situations in which there are sudden load spikes.

For more information, please visit the following product folders. You might want to start with the datasheets and continue from there. We do have EVMs you can order as well if you would like to evaluate one.

bq20z45: http://focus.ti.com/docs/prod/folders/print/bq20z45-r1.html

bq20z65: http://focus.ti.com/docs/prod/folders/print/bq20z65-r1.html

Hi Chase,

Thanks for a quick reply.

I just want to add few more things about my application.

We get the batteries from outside,so for me there is no way I can put circuit inside the battery pack.Some times I want user to replace them on its own as 3 cells LiPOs are widely available.

1.Is there any fuel gauge which can be outside the battery?

2.We need to replace the battery frequently,so every time a new battery will come in my application.What I understood from overall the bq series is,it maintains the charge history inside the flash and then compares it with the discharge status and produces result.Is this assumption some what correct?What happens when a new battery comes? will the bq series automatically work for it?I read in one of the articles is one bq series is invented to be outside the battery pack (bq27510),will this work for me?So that We need not reprogram the IC for new battery.

3.In my application there will be external charger charging the battery and then putting it inside the unit.In such a situation can any of these bq chips work properly?

Pls give your excellent expert opinions so that I can narrow down my search and reduce my selection process.

1. That type of gauge is called host or system side gauge. Unfortunately, there are no multicell host side gauges. You may be able to make a single cell gauge, such as bq27510, work with a multi-cell gauge and just divide down the voltage to one cell. I don't support those gauges, however, so I don't know the details of how to make that work correctly.

2. For a pack-side gauge, it won't support the replacement of the battery. When the battery is old, the battery and the gauge are thrown away. In a host side gauge, it will support replacement of the battery. It is able to detect when the battery is replaced. The gauge monitors temperature, current and voltage and contains a model of your particular cell in memory. The algorithm uses this model and the measured data to predict the remaining capacity and run time.

3. Again, for host side gauge this will work fine, but not for a pack side gauge.

Hi,

Thanks Chase.

Few last doubts,

1.Are these bq chips are more targeted for the battery manufacturers and less for the Embedded System manufacturer's?

2.Suppose I intend to use 1 fuel gauge to be given with one battery.Now here I don't understand what to do?Do I have to open the batteries and get access to individual cells?

3.In that case I have 3 cell battery,does that mean I have to use 3 bq chips to monitor the cells?As most of them  are single cell bq series chips!

4.At the first time you have suggested to use bq20z45 .Do you think I can connect this as an external to whole battery pack without opening it?Just Positive to Pack+ and Negative to the Pack- or to the current shunt, will this work without opening the battery?I can make the whole system as a unit and the bq in series with the battery so that the charger current will always passes through the shunt.

5.Usually is there any learning process associated with these chips?Like one full discharge of battery is must before the bq chips gets an idea about the nature of the battery?

6.My question is how exactly pack side battery generates the "battery model" mentioned by you?especially in bq20z45 where it will not have access to individual cells.

7.Do you recommend any Charger for this ?I can put the charger and gauge along with battery inside the unit and just give the power supply adapter as an external unit.

8.Does the small bq29xx shown in the corner of the bq20z45 data sheet block diagram is intended for such a charging application or it is a balancer ?

1. Most of the orders do come from pack manufacturers, but there are plenty of end system manufacturers that use these devices as well.

2. Yes, you will need to get access to the cells to use the bq20z45 gauge. You may be able to divide down the full pack voltage and use that with the bq27510, since it only has one cell input.

3. No, you will only need one chip. They are actually just as many multi-cell gauges as there are single cell gauges. You just need to have access to all of the cells to use the multi-cell gauges.

4.  Again, you will need to have access to the individual cell taps.

5. Yes, there is a learning cycle required. That can be done on one pack, though, to generate the golden image. The golden image can be programmed into the rest of your packs. There are documents discussing this process in detail located at the product folder links I posted earlier.

6. You need to have access to individual cells to use bq20z45. You can read more about how the battery model is generated and what the gauging algorithm entails in the attached document (Chapter 6 and 11)

7. There are many chargers available. You can narrow down you search depending on your needs at the following link:

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=411&uiTemplateId=NODE_STRY_PGE_T

8. The bq29xxx is a second-level voltage protector. It is a simple voltage comparator that can be used to blow a fuse or open a FET if one of the cell inputs surpasses a fixed threshold. There are many different thresholds available, depending on what you need. 4.35V seems to be the most common, though.

I know that this is a forum from many years ago.  However, I have a similar issue.

Chase7071949597 said:

2. Yes, you will need to get access to the cells to use the bq20z45 gauge. You may be able to divide down the full pack voltage and use that with the bq27510, since it only has one cell input.

Are there any fuel gauging ICs now which can handle a battery pack voltage up to 15V?  Or would I still have to divide down.  Also, can you recommend a newer chip, to the bq27510?

We also don't have access to individual cells to connect just the overall PACK+ and PACK- but still want fuel gauging.

Many thanks!

Jason