• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 790 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ2004: Battery not being fully charged.

Peter Buncle
Prodigy 40 points
Part Number: BQ2004

I am using the BQ2004 development kit to evaluate it's ability to charge our cell pack (10 cell NiMH, 1.2V per cell, 4.5Ah capacity). I have the board set up as follows: TM1=Low, TM2=High, VSEL=High, DSEL=High, INH=High. Power to the board is 15V (limited to 4A).

I have tried different charging times but even if I allow the batteries to charge overnight can't reach the same capacity as an off the shelf charger. The capacity in use is just over half what I'm expecting!

Can you suggest what might be wrong / different please?

  • 0
    TI__Guru 56650 points
    What is the fast charge timer setting (TM1 and TM2)? Could you double the timer setting or make the fast charge timer even longer? I got a feedback recently: the timer is half of the spec table number.
  • 0 in reply to Wang5577
    Prodigy 40 points

    Hi,

    With TM1 = Low and TM2 = High the fast charge time should be 90 minutes according to the datasheet. This appears to be about right although the current only starts at ~2A which I assume is 0.5C. I think that this setting should give 1C charge current which I believe in this case is 4.5A. Is that right?

    After the fast charge time has expired the current drops to ~0.02A. Not sure how much the board takes for itself but pretty sure that doesn't leave much for a charging current.

  • 0 in reply to Peter Buncle
    TI__Guru 56650 points
    Yes. 90minutes is not enough to charge up a battery with 0.5C rate. if So, set 90minutes timer, we should use 1C rate.
    If the timer has expired, the charger current should be stopped.
  • 0 in reply to Wang5577
    Prodigy 40 points

    In that case can you suggest how I need to set the board up to charge the battery? Do you know if the board can supply up to 4.5A and if so why the charge current is so much lower? Should the supply voltage be higher? Also, after the fast charge period I thought it continued to charge at  a much lower rate?

  • 0 in reply to Peter Buncle
    TI__Guru 56650 points
    bq2004 is a not synchronized buck converter. All freewheeling inductor current goes through a diode. So, I don't think supplying 4.5A is a good idea. Yes, if you want to push the output current higher, the supply voltage should be higher.
    Or, you can increase the fast charger timer with a lower charging current.
  • 0 in reply to Wang5577
    Prodigy 40 points

    The problem I have is that the battery is NOT charged after the fast charge period no matter what time I select. However instead of continuing to charge at a lower rate it appears to stop charging completely. Is this what you would expect?

  • 0 in reply to Peter Buncle
    TI__Guru 56650 points

    Yes. For some TM1 and TM2 settings, the top off charge is disabled.