External balancing BQ40Z60

Karol,

The typical internal cell balancing current is 10mA. You can add external resistors and FETs to enable more aggressive cell balancing. I attached a document with a schematic example. (The same will apply to the bq40z60.) I used 1 kohm series resistors, but we have seen cases where the higher resistance can affect cell voltage accuracy. It would be better to reduce the series resistor and use a FET with a lower Vgs threshold.

Tom

0167.6180.bq40z cell balancing equations.pdf

Dear Tom ,

Hi , i recently join this blog..
I am planing to use bq40z60 in my application where we solar module to charge the battery bank ? should we require external charger or Bq40z60 Have inbuilt charger .

Sachin

Tom, many thanks for this information. With additional PMOS FET at the lowest cell, it all makes sense now.

In all datasheets that I saw, there was only NMOS FETs everywhere and I thought that couldn't work this way.

Thanks again,

Karol

The bq40z60 does have an integrated charger and I have used the gauge to charge cells with a solar panel. The panel just has to supply adequate voltage and current to run the charger.

/cfs-file/__key/communityserver-discussions-components-files/196/2703.6180.bq40z-cell-balancing-equations.pdf

I am using 3 Cell Battery in my circuit. Because of Cell Balancing issues, with your reference, I have connected External FET between 3P and Cell2 alone and tested with 3rd cell with lower voltage(1.4V) and other 2 good working cells(full charged) . I didn't used NFET and PFET between 2P--1P and 1P--1S cells respectively. I have used 100 Ohm Series Resistor instead of Cell Balancing having NMOSFET Part CSD17308Q3. But Cell Balancing not happened. Kindly help with a solution

Sorry for dealy in reaply..
Is it possible to share resolve this issue schematic...

As per the schematic, we tried with Cell1 and Cell2 with 3.7V and Cell3 alone at 1.4V with FET control to check whether balancing happens or not. Also if any one of the Cells reaching full charge of 4.1V, then too charging and balancing doesn't occurs.
Kindly provide a solution for this External Cell Balancing.

There are a few issues that could cause your cell balancing experiment to not work.

1) Cell balancing is disabled until Update Status = 0E.
2) Make sure that cell balancing is enabled in the Balancing Configuration register. Set to 03 or 07, if you want to balance while at rest.
3) The device uses capacity based balancing, so a good DOD point must be set to allow the gauge to update the balancing times. Qmax and the Ra tables also have to be optimized, but this will have been done, if Update Status = 0E. A good DOD point will be set, if you allow the pack to rest until the REST flag sets.