One or more cells or entire banks are not reporting

• Turn off any strong source of electrical noise (motor driver, especially when accelerating or braking, high frequency charger, DC-DC converter) and see if the problem persists (you may have to power the BMS controller with some other 12 V source during this test)
  • The problem only occurs if a source of electrical noise is on

    • Just a single bank is sensitive to noise:

    • Noise: a number of banks

  • The problem persists even with no noise sources:

    • Missing battery: no banks are reporting

    • Alternating missing banks: banks toggle between reporting and not reporting

    • Permanently missing bank: an entire bank is not reporting (no communications)

    • Missing cell: just one or some of the cells in a bank are not reporting (but the bank is reporting)

    • Positive only: only the Positive end cell board blinks

In the presence of electrical noise, just 1 bank stops reporting

This could be due to wiring problems with the harness of that one bank, such as missing shield , ungrounded shield or shield ungrounded at multiple points. See the Noise section for more information.

But, we have seen it also due to a damaged BMS controller, damaged by connecting a grounded battery pack voltage to that bank's communication harness' shield, which blows a trace on the BMS controller's PCB (see picture below, left detail).

Rear of BMS controller PCB assembly, showing the rear of the 5-pin bank connectors. The ground trace for the middle pin of the 3rd connector (bank 2) was fused by a large current.

You can easily test the bank inputs of a BMS controller:

• Use an Ohmmeter, in the Beep mode, with the black lead to the ground of the BMS controller (such as pin 1 of the Control connector), and measure continuity to ground of pins 2, 3 and 4 of all the bank connectors: it should be 0 ohm. If on a pin there is no continuity to ground, the ground trace to that pin is blown.
• Use an Ohmmeter, in the 200 Ohm range, with the black lead to the ground of the BMS controller (such as pin 1 of the Control connector), and measure the resistance to ground of pins 5 (farthest from the edge) of all the bank connectors: it should be 100 ohm
• Use an Ohmmeter, in the 2 kOhm range, Measure the resistance between pin 1 (closest to the edge) of any bank connector, and the pin 1 of all other bank connectors: it should be 200 ohm

In that case, you may attempt repair yourself, by placing a solder bridge between the pad that has lost its ground trace, and an adjacent pad that still has its ground trace (see picture above, right detail).

In the presence of electrical noise, some cells or banks stop reporting

There are two approaches to handle noise susceptibility:

• Reduce the level of noise at the source
• Reduce the sensitivity to the noise

It is beyond the scope of this troubleshooting guide to deal with noise reduction at the source. Instead, we will focus of how to minimize the effect of noise on the BMS.

Typical ways in which noise disturbs the BMS are:

• Communication harness shielding
  • The communication harness between the BMS controller and the banks is not shielded
    • Both section of the harness must be shielded: the one to the negative end cell board, and the one to the positive end cell board
    • At most 1 inch (2.5 cm) of wire can be unshielded at the ends of the communication harness
  • The communication harness' shield is not connected
    • The shield must be connected only in one spot: at the 5-pin connector on the BMS controller
  • The communication harness' shield is connected in more than one place
    • The shield must not be connected to chassis or to other shields
• Noise coupling
  • Inductive coupling: communication wire routing
    • The area enclosed by the communication wire, the B+ wire (red wire in prismatic cell boards) and the power conductor (bus bar, power wire) forms a loop antenna, that picks-up electrical noise
      • Minimize that area by running the communication wire as close as possible to the B+ wire, and the power conductor, to the next cell board
      • Make the power conductor as short as possible: a short bus bar is ideal, a power cable that is more than a few inches in length is totally not appropriate
        • If you cannot make the power conductor short, split the bank into 2 banks at that point
      • Secure the communication wire to the B+ wire and the power conductor, but don't twist them around each other
  • Capacitive coupling
    • Electrically, the battery may be "shaken up and down" by the source or the load, at a frequency of 5 to 50 kHz, and a level that can be as high as 100s of volts
    • As long as the cell boards are allowed to "jump up and down" together with the cells, they are fine
    • Any capacity between a cell board and ground will keep the cell boards from "jumping up and down" together with the cells
    • The idea is to maximize the capacity between the cell board and the cell, and minimize the capacity between the cell board and the chassis ground
    • All that is true not only for the cell board, but also for the communication wire between cell boards
      • A metal case surrounding the battery
        • Face the cell boards so that its components face the cells, and its ground plane side face the metal case
        • Cover a cell board with metal shielding that is electrically connected to the B- of the cell it (make sure it doesn't make electrical contact with the cell board)
        • Use shielded cable in place of the communication wire, with the shielded connected only in one place: the B- pad of the more positive cell board
      • Low voltage wiring routed next to the cell boards (such as the communication harness)
        • Reroute the wiring so that it's away from the cell boards

No banks are reporting

All banks may be missing because:

• The BMS controller is misprogrammed,
• There truly are problems with each and every bank

First:

• Make sure that all banks missing, and not just some banks; if the latter, see the Missing bank section

• Make sure that all banks missing, and not just some cells; if the latter, see the Missing cell section

• Make sure that the problem is not due to electrical noise; if so, see the Noise section

Procedures

• Check that the BMS controller does expect to see banks
  • On the terminal, do Home / Set-up / More... / Battery arrangement / Number of cells in each bank / Set manually
  • If the number of cells in bank 0 is 0, that's the problem, or at least part of the problem
    • Press ESC, then Learn Automatically / Enter
    • If the problem persists, then the problem is that all banks have problems communicating: proceed as below
      • With the BMS power on, see if any cell boards are blinking
      • For each bank, proceed with the test depending on which cells blink:

        • None blink: No cell board is blinking

        • All blink: All cell boards blink

        • Part: From the positive end board up to a certain point they blink, then the rest don't blink

        • Random: Some blink, some don't, with no apparent pattern

Banks alternate between reporting and not reporting

Cause

• There is a short across one of the bank outputs (white and green wires), or
• One of the banks has a cell board that whose output is always on

Discovery procedure

Determine which bank is causing the problem:

Method 1:

• Disconnect one RJ45 connector at a time from the Master, until you see that the other banks report fine
• If that RJ45 cable goes to only one bank, that's the bank that has the problem
• If that RJ45 cable goes to two banks:
  • Reconnect the RJ45 cable
  • Identify the two banks that use that RJ45 cable (one yellow, one green)
  • Disconnect the yellow cable from the negative end cell board; if the other banks now report fine, that's the bad bank
  • Else, reconnect the yellow cable, disconnect the green cable from the negative end cell board; if the other banks now report fine, that's the bad bank

Method 2:

• In the GUI, press Control T; the terminal screen appears
• Click on the left pane, to activate it
• Press H, 6, 3
• In the last row of the "Bank Status" section ("Discrimination values"), note the 8 hex values, one for each bank (A through H)
• See which value is the lowest; that's the value for the bad bank

Troubleshooting procedure

• Follow the Permanently missing bank procedure.

A bank is not reporting

A bank may be missing because:

• it is misprogrammed,
• there's an open or shorted connection,
• it is misconnected,
• the communication cable from the BMS is too long
• it picks up too much electrical noise.
• the cell boards are in the wrong order (positive end on most negative cell, and vice-versa)

First:

• Make sure that the entire bank is missing, and not just some cells; if the latter, see the Missing cell section

• Make sure that the problem is not due to electrical noise; if so, see the Noise section

See also:

• Cell Board testing

Procedures

• With the BMS power on, see if any cell boards are blinking
• Proceed with the test depending on which cells blink:

  • None blink: No cell board is blinking

  • All blink: All cell boards blink 1/s

  • Part: From the positive end board up to a certain point they blink 1/s, then the rest don't blink

  • One: Only the positive end board blinks 1/s

  • Random: Some blink 1/s, some don't, with no apparent pattern

  • 2 blinks: A cell board blinks 2 times / second

A cell is not reporting (its bank is reporting)

First:

• Make sure that just some cells are missing, and not the entire bank; if the latter, see the Missing banks section

• Make sure that the problem is not due to electrical noise; if so, see the Noise section

See also:

• Cell Board testing

IMPORTANT NOTE

If a bank reports that its negative end board is missing, that's probably not true: all that means is that one of the boards in the bank is missing, and we don't yet know which one.

All banks reporting, no cells reporting

Rev 1.14 and above.

The "CELL DATA READ AND REPORT RATE" setting (H 4 8 5 5) is 0. Change it to 10 (one report every 1 second).

Only N cells in each bank reporting

Rev 1.14 and above. Exactly 5 cells report in each bank, or some such number.

The "CELL DATA READ AND REPORT RATE" setting (H 4 8 5 5) is too low (reporting is too fast, and there's not enough time to do all the cells). Increase the value (reduce the reporting rate).

Introduction

The BMS assigns IDs to the cell boards on the fly, starting from 0 for the cell board at the most positive end of the bank. If a cell board is not responding, the BMS skips it and assigns its ID to the following (more negative) cell board. Therefore, the non-responsive cell board gets no ID, and the following cell boards will have a lower ID than they should.

For example, if a bank has 5 cell board, the BMS will assign IDs 0 through 4 to them.

However, if the mid-bank cell board is not responding, the BMS will see 4 cell boards instead, and assign IDs 0 through 3 to them, skipping the cell board that doesn't report.

The BMS controller knows that a cell board is not reporting, but it has no idea which one. It just sees 4 cell boards, but it doesn't know which 4 they are. If it were the second cell board that was missing, that appears exactly the same to the BMS controller.

The BMS controller will report that cell board #4 is missing, but that simply means that it was not able to assign ID 4 to any cell board; it doesn't necessarily mean that the cell board that is not reporting is the last one in the bank. To know which cell board is not reporting, one must physically look at the cell boards.

Determining which cell board is not reporting

• Turn off the BMS controller
• Note that the LEDs on all the cell boards are off
  • If a cell board's LED stays on, replace that cell board (do so immediately: or it will kill the cell)
• Turn on the BMS controller
• Look for blinking LEDs in the cell boards
  • If a cell board's LED stays on, it could be that the cell is full and needs to be balanced, but it could also be that the cell board is measuring too high a voltage
    • Check if the BMS is balancing, with the terminal: Home / Status / Pack, then look at the "Loads On" line
    • If the terminal says that there is no balancing, the cell board is bad: it is measuring the wrong voltage; replace it

    • If the terminal says "balancing if > x V", note x as the Balancing Voltage

    • Measure that cell's voltage
      • If the voltage is less than the Balancing Voltage, the cell board is bad: it measuring the wrong voltage; replace it
• If a cell board's LED doesn't blink, the cell board is not running
  • Check the cell voltage; if it's less than 2.0 V, that's not enough to power the cell board
  • Try resetting the cell board
    • Disconnect one end of the cell board from the cell
    • Reconnect it (this will reset the program)
    • Check what the LED does as soon as the cell board is connected
      • If the LED blinks twice, and repeats that 3 times, then goes off, the cell board may be OK
        • If that fixes the problem, do let us know
      • If the LED doesn't come on, the cell board is bad: replace it
• If all cell boards have a blinking LED, see which cell board doesn't respond to heat, using a "binary search" method
  • Find a cell board in the middle of the bank
  • Touch it with your finger (or some other medium heat source), to heat it
  • On the terminal, see which cell board's temperature starts rising, if any
    • If none, that cell board is not reporting: replace the cell board
    • If you're heating the cell whose ID should be N, and the BMS controller reports correctly that cell board N is getting hot, the problem is in a cell board that has a higher ID (more negative)
      • Repeat with a cell board mid way between the one you just did, and the negative end board
    • If you're heating the cell whose ID should be N, but the BMS controller reports it's cell board N+1 that is getting hot, the problem is in a cell board that has a lower ID (more positive)
      • Repeat with a cell board mid way between the one you just did, and the positive end board
  • Continue recursively through the "binary search", until you find the cell board that is not responding
    • Allow enough time for one cell board to cool off before starting to heat another cell board

Only the Positive end cell board blinks

In order of likelihood:

• The Positive End cell board was mounted on the most negative cell instead of on the most positive cell
• The communication wire between the Positive End cell board and the following cell board is open
• Either the Positive End cell board or the following cell board is bad
  • Check the following board:
  • Disconnect the B+ wire in the following cell board from its cell
  • Wait 5 seconds
  • Reconnect it
  • If the cell board does not blink, it's bad
  • Check the communication lines of the Positive End cell board (#0)
    • Turn off the power to the BMS master
    • Measure the voltage of the C- wire of the Positive End cell board (red probe) with respect to its B- terminal (black probe)
    • The voltage should be about -3 V (the voltage of the following cell, but negative)
    • If the voltage is 0 V, there's a short between the C- line and the B- terminal of the Positive End cell board
    • If the voltage is lightly positive, the Positive End cell board is bad
  • Check the communication lines of the following cell board (#1)
    • Measure the voltage of the C- wire of cell board #1 (red probe) with respect to its B- terminal (black probe)
    • If the voltage is 0 V, there's a short between the C- line and the B- terminal of the #1 cell board
    • If the voltage is lightly positive, the the #1 cell board is bad

A bank is seeing more cells than it expects

This can be due to 3 things:

• Some bank plugs are interchanged on the BMS controller
• The BMS controller was programmed by hand, and a mistake was made
• A cell was missing when the BMS learned automatically the number of cells, but the cell board is now reporting

Procedure

• Check that the bank plugs are connected in the proper order to the BMS controller
• Set the correct number of cells in series for that bank
  • On the terminal, do Home / Set-up / More... / Battery arrangement / Number of cells in each bank / Set manually

  • Use the '>' or '<' keys to go to that bank

  • Enter the number of cells in series in that bank and press Enter

Cell numbering mismatch

The number of cells is different than expected.

Incorrect bank connections

• There is confusion on which bank is plugged into which port in the BMS master
  • Regardless of how the GUI is set-up, connect the most positive bank to bank 0
• The most positive bank is not plugged into bank 0 in the BMS master
  • Regardless of how the GUI is set-up, connect the most positive bank to bank 0

For the sake of the installer, THE MOST POSITIVE BANK MUST BE CONNECTED TO BANK 0, regardless of GUI settings, or you'll be confused.

Electrically, it makes on difference to the BMS. but YOU, the installer, will get confused is you connect the banks any other way.

Here is an actual example from one of our clients, who connected the most negative bank to bank 0, and then called to report that the software was buggy (it isn't).

Incorrect GUI configuration

• The GUI is set to start at cell #1 when you expect the 1st cell to be numbered #0, or vice versa
• The GUI is set to start from the most positive cell when you expect the 1st cell to be the most negative, or vice versa