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Help with bqEasy chemistry test

Nicholas Alunni
Prodigy 170 points
Other Parts Discussed in Thread: BQEVSW

Hello,

I'm trying to determine my batteries chemistry to calibrate the bq20z65EVM but I'm running into quite a few problems.  I was hoping someone here might be able to help me.  I'll do my best to describe what I've done so far and the problems I'm facing.

Process:

I've fully connected the bq20z65EVM to the EV2300 module, and both are able to communicate to the computer.

I've successfully started it up and can read all teh SMB registers.

Using bqEasy I've setup the board, configured, and calibrated it all successfully.

I then edit some of the values that the configure sets incorrectly (such as the temperature splits for charging) and write the Data Flash to the board.

I've build and tested the discharge circuit and I am quite posative that it is working correctly.

Then I start the chemistry test.

Problems:

When the chemistry test reaches the discharge part of the test, the board never starts discharging automatically.  I checked the voltage across the Pack+ and Pack- terminals during the discharge test and there was nothing.  I then tried manually turning the discharge FET on and there was a voltage across the terminals.  I also checked putting the PRES and Pack- pins together to see if that was the problem but it would not start discharging automatically.  As of now it appears to me that the only way to get it to discharge is to manually turn the discharge FET on, which does not seem to me what I should have to do.  As far as I can tell the process should be entirely automatic.

The chemistry test states that the batteries should be charged to 4.2 Volts each before I begin the test.  Each time I've charged them to that voltage before beginning the test but I believe due to keeping the board alive as well as communicating with the EV2300 module by the time the chemistry test reaches the discharge phase, each battery is only at approximately 3.9V.  I'm not sure if this is intentional or if the batteries should not be that low by the time the discharge test is beginning. 

Any help solving either of these problems would be greatly appreciated.

Notes:

I'm using a Pack of 2 batteries in series.  The batteries are LiFePO4 batteries rated for 4.2V and 4400mAh each.  The pack is therefore 8.4V and has a capacity of 4400mAh.  This chemistry is not present in the most recent release of the chemistry table or update for the bqSoftware and while there are a few LiFePO4 batteries there aren't any that are close to 4400mAh.

bqEVSW Version: 0.9.64
bqEasy Version: 1.87

Any help would be greatly appreciated.

Thanks,

Nick

  • 0
    Prodigy 170 points

    Update:

    Instead of using the chemistry test instead I've opted to manually log the bq20z65EVM and then hopefully someone here can figure out what type of battery it is for me.  I've seen on a bunch of other forums posts TI Employees letting people know which battery chemistry they're using so hopefully someone can help me!

    I didn't log all the fields, only what I thought were the important ones.  Hopefully that isn't an issue, as I really do not want to have to re-run the test right now.

    Log: 1512.Chem Test 2011-06-07 03.log

    Image of Output Graph:

  • 0 in reply to Nicholas Alunni
    TI__Expert 3865 points

    There is no discharge cycle in the log file. We will not be able to match any ChemID by just have relaxation data.

    You should use bqEASY to try matching the best chemistry for your battery pack. To do it you will need to build the switch and load circuit and connect the control to the VOUT port of EV2300. Click on the picture of step 4C in bqEASY. The picture shows the connection of the switch & load circuit to the EVM and to EV2300.

     

    Once you have the circuit built, you can apply a small current across PACK+/-, and use the ON/OFF buttons on screen Step 4C to test the switch (when press on, you should see current reporting in the SBS screen; when you press OFF, the current will be 0). Now follow the Step 4C in bqEASY to start the test.

  • 0 in reply to Jackie Hui
    Prodigy 170 points

    Hi Jackie,

    Here's a bit of an update.

    That actually was a battery discharge, not just the relaxation data.  The issue was that the current calibration was set incorrectly such that the cc gain and cc offsets were zero.  This causes a lot of things to not work for the most part.  I've just set the calibration correctly and I'm re-running the auto-chemistry to see if it comes up with an answer on its own.  If it doesn't I'll post the log here.

    Thanks,

    Nick