High resistance cell

Resolving the issue:

Step 1. Check the busbars to ensure they are tight.

Most of the high resistance issues turn out to be a loose connection or faulty crimps (if applicable), so it is worth checking closely. High impedance from a loose connection will usually show up in one of the adjacent cells, so that is a good thing to check first.

Step 2. Check the BMS configuration to ensure no busbar compensation has been enabled for the high resistance cell (unless the cell includes resistance from a high impedance busbar, in which case it is important to verify that the correct amount of busbar compensation has been applied).

Open the Orion BMS utility, download the profile from the BMS if necessary, go to the cell settings tab, click cell population settings button and find the cell in question. Look in the last column and verify the busbar compensation setting in the last column. Incorrect settings here can artificially cause the cell to appear as if it has a high resistance when the cell is under load.

Step 3. Verify that the cell voltage and the surrounding cells (ideally from the whole group of 12) are reporting correct voltages through the BMS.

Keep in mind that the voltmeter and the BMS do not share the same calibration, but it should give a good idea if the voltage is significantly higher or lower than it should be. If voltages are incorrect, check the BMS for open wire fault codes, and check the continuity of cell voltage tap wires in the cell group. Also verify that the minimum number of cells in a cell group are populated and are correctly wired.

Step 4. If the measured voltages are correct, the next thing to check would be if the resistance of the cell is in fact high.

The easiest way to do that is to manually check the voltage across the cell with a voltmeter (measuring with one probe at the physical location of the next cell lower’s tap and the physical location of high resistance cell’s voltage tap). Apply a constant load to the pack, calculate the resistance of the cell, and compare the manually measured voltage against the BMS reported voltage. If the voltages that the BMS and the voltmeter are reporting are consistent, look for a high impedance connection between the cells.

Copyright (C) 2015 Ewert Energy Systems

Ewert Energy Systems, Inc
120 Easy St. Suite #14
Carol Stream, IL 60188

Phone: (630) 868-3173
Fax: (866) 657-5667

Find us:
Facebook Twitter