Cell connecting problem with LTC6813-1

Hi, 

A 18S board design with LTC6813-1, but mounting for 14S use.

The circuit for cell connecting is as below. Because for 14S only, some 0 ohm/0603 are used to configure. 

Bn for actual battery cell connect input through CON2 and CON1.

In board test stage using power supply to simulate cell voltage input, everything is  OK.

But when connecting actual battery cell stack, R7 (0 ohm/0603) may be damage (Hi-R, open ~3 out of 40 DUT). 

Could you please review the circuit and give me advice.

Thank you!


Sean


circuit upload
[edited by: altis0510 at 8:08 AM (GMT 0) on 21 Dec 2018]
  • Hi Sean, 

    What we understand from this schematic is the 0 Ohm resistor is coming in series to 2 cells which may be of different voltages and the low voltage cell may be drawing more current through the resistor which may lead to damage of resistor.

    We suggest to short the first 4 cells or the bottom 4 cells .This should avoid the damage of the resistor.

    Please let us know if you still face any issue after doing this way.

    Best Regards, 

    Phani

  • Hi, Phani

    Thanks for reply. I hope I didn’t misunderstand what you mean.

    Let me explain the 0 ohm connection. It is used for connecting unused cell inputs of LTC6813 to cell stack

    It does not connect to 2 cells. B0~B14 are actually 14 cell connections. (V0~V18 is net name only)

    What we understand from this schematic is the 0 Ohm resistor is coming in series to 2 cells which may be of different voltages

    The board layout is for 18S, if we use it for 18S, then no 0 ohm will be mounted.

    This time we use the board for 14S, so five 0 ohm resistors (C1, R1, R2, R7, R49) are mounted.

    This just follows the data sheet of LTC6813 page 82:

    If the number of cells being measured is not a multiple of three, the top MUX(es) should have fewer cells connected. The unused cell inputs should be tied to the other unused inputs on the same MUX and then connected to the battery stack through a 100Ω resistor.

    In my 14S case, unused cell inputs of LTC6813 (C17 C18 C12 C6):

    1. Cell input  LTC6813 pin C17 tied to pin C18 by 0Ω(C1) then connected to the battery stack (B14) through 100Ω + bead +0Ω + 0Ω  (R37+bead+R1+R2)

    2. Cell input  LTC6813 pin C12 connected to the battery stack (B10) through 100Ω +bead + 0Ω (R43+bead+R7).

    3. Cell input  LTC6813 pin C6   connected to the battery stack (B5  ) through 100Ω + bead+ 0Ω + 0Ω (R85+bead+R49).

    The same connection method was used before for the LTC6811, and no problem occurs. It may cause by other problem(such as crack by PCB bending), but I still hope to make sure my connection is correct or not.

    Thanks!

    Sean

     

  • Hi Sean, 

    Thanks for your detailed explanation. Schematic looks fine as per the data sheet if the unused cell are connected back to the battery stack using 100 Ohm resistor. But as the resistor is getting opened( damaged) is it possible to measure the current flowing through R7 and R49 just to confirm that it is not happening because of any high current drawn through them

    Thanks

    Phani