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Original question:

EMB1428Q: How To Resolve Fault Code 0b1001

EM1402EVM: Active Cell Balancing

SAURABH SHAH36
Prodigy 240 points
Part Number: EM1402EVM
Other Parts Discussed in Thread: EMB1499Q

Hello,

I am working on EM1402EVM Active Cell Balancing Module. I have written a code that says, continue balancing until the cell deviation comes below the threshold limit. I want to ask, is it necessary to stop balancing after some fixed period just for relaxing the EM1402EVM board or I can continue balancing process?

Thanks,

Saurabh Shah

  • 0
    TI__Genius 11480 points
    Hi Saurabh,

    I think you may run into two things

    1: The internal watchdog of the EMB14xx chipset. It expires automatically after 8 seconds. If you want to continuously balance you must re-issue the balance command for that cell.

    2: If switching between cells, you will need to let the converter ramp down before enabling the next balancing command.
  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    Hi David,

    Thanks for your reply. But I have seen the schematic of EM1402EVM, which shows the watchdog timer is permanently disabled by grounding WDOR terminal of EMB1499Q IC. So balancing continues. But I want to ask during balancing the cell data that i am acquiring is not correct. Can you tell what might be the reason?

    Thanks and regards,

    Saurabh Shah

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points

    Hi Saurabh,

    Could you provide more details please? What is not correct - the cell voltage?

  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    Hi David,

    Cell voltages are not correct (Variation upto +/- 500 mV). What might be the reason? I believe it depends on cell chemistry. I am using 3.7 V, 1800 mAH Li ion battery. 

    I would like to tell you one scenario...

    I discharged one cell completely to 3.024 V on Saturday i.e 26/05/2018 and left it open (Isolated). Today i.e 28/05/2018 its OCV is 3.394 V. I could not understand the reason. 

    Thanks and regards

    Saurabh Shah

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points

    Hi Saurabh,

    You may be seeing a long "relaxation" period of the cell. I am no cell chemist, but this may be something that you can check with your cell supplier.

    Is your cell measurement not correct sitting at idle (no load on cells), or do you have a load on the cells? How large is the load, and what does your noise profile look like? Are you balancing?

    There are a few different things that you may be seeing. Without knowing more, I can only guess unfortunately,

    If you have any load, you may be measuring the internal impedance of the cell & connections used to put cells in series. If a dynamic load, you may be measuring noise on the cell. If balancing, it could be the I*R drop from the balancing current. It is likely a current path somewhere, it is just a matter of finding where.

  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    Hi David,

    Thanks for your reply. Yes you are right the cells are seeing a long relaxation time. The cell voltage measurement is correct when the cells are not balancing even if the cells are not relaxed. The battery pack (I have used 16 cells connected in series) is not connected to any load. I am just doing active cell balancing. 

    How to get more information on cell relaxation period?

    Thanks and regards,

    Saurabh Shah

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points
    Hi Saurabh,

    Then you will also be measuring any I*R drop from the balancing current, with any resistance (parasitics included) in the path. This is why you will see an offset.

    For questions about your cells, I would refer to your vender.
  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    Hi David,

    While checking the voltage levels on multi meter, it varies from 3.623 V to 3.644 for the same cell. I am not getting the reason for this. Is there any such thing like cell dynamics during charging or discharging? 

    Another thing I want to ask is, I am not getting information about turns ratio of the forward transformer that is used in EM1402EVM. The reference document shows, turns ratio are calculated by the formula 0.25*n, where n is number of cells. But I downloaded the datasheet of pulse electronics PA3856.005NL, it is showing different turns ratio. I am confused. 

    Because logically thinking, while discharging overcharged cell in auxiliary battery, the overcharged cell voltage shall be greater than (auxiliary battery voltage)/(turns ratio). How shall I justify this. 

    Thanks and regards,

    Saurabh Shah

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points
    Hi Saurabh,

    I recommend using a scope rather than a multi-meter. A meter will only give you the RMS information of the signal, whereas a scope will let you see (almost) everything.

    It depends, if you are loading the cell at all you could be measuring the impedance of the cell or impedance of the connections.

    Unfortunately, I am not sure what the logic behind the selection on the EM1402 transformer selection was, as the original designer is no longer with the company. One important thing to note is that the turns ratio mostly dictates the duty cycle of the converter, because the EMB1499 regulates current into/out of the cell being balanced. It does not really care what the cell voltage is.
  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    HI David,

    I tried to monitor cell voltage using scope but could not get the data as I expected. It showed approximately zero reading with lot of noise. 

    No David the cells are not connected to any load.

    For the turns ratio part, can you tell me why the formula for calculating turns ratio is given in the reference document? Is there any significance? Also can you tell me how the frequency of switching in forward converter decided?

    Thanks and regards, 

    Saurabh Shah

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points
    Hi Saurabh,

    Is your scope AC coupled?

    Also pay close attention to the grounding of the scope.

    I can share an additional document with you that should go into more insight into the circuit design.

    As far as the switching frequency, I am unsure.Unfortunately, I do not have the history for the device definition.
  • 0 in reply to David Wiest Jr
    Prodigy 240 points

    Hi David,

    Sorry for the delayed reply. The scope is DC coupled as I am measuring DC voltage. I am grounding the scope to the battery pack. 

    Yes, David kindly share the document. That will be very helpful for me.

    Thanks and regards,

    saurabh

  • 0 in reply to SAURABH SHAH36
    TI__Genius 11480 points

    Hi Saurabh,

    Please contact me at d-wiest@ti.com....I will share it with you offline.