SLUUB65B May 2015 – December 2022
Resistance measurements are conducted over the course of a discharge cycle and are constantly stored in RAM. The actual resistance value in data flash is updated if certain conditions are met. Resistance update qualifications are:
Res V Drop is used during battery discharge to qualify sufficient conditions for measuring and storing resistance values. It is useful in applications with low-rate discharge or frequent cold temperature usage that typically have trouble achieving consistent resistance updates. Even with low current, the voltage drop requirement can still be met if enough cell resistance is evident.
The Resistance values that are calculated are subject to additional checks to prevent sudden changes or drops.
This is a weighting factor that takes a certain percentage of the previous Ra table value and the remaining percentage comes from the newest calculated Ra value. This is to prevent resistances in the Ra table from changing quickly. Ra Filter is a filter constant used to calculate the filtered Ra value that is stored into data flash from the old Ra value.
Ra = (Ra_old × Ra Filter + Ra_new × (1000 – Ra Filter)) ÷ 1000
It is normally set to 800 (80% previous Ra value plus 20% learned Ra value to form new Ra value).
During the update of Ra values a filtering process is performed to eliminate unexpected fluctuations in the updated Ra values. Ra Max Delta limits the change in Ra values to an absolute magnitude per Ra update. This value should be set to 15% of the Ra[4] value. The value needs to be manually adjusted after a chemistry change.
After this filter has been applied, there is a final check to make sure that the new resistances satisfy both Max Res Factor and Min Res Factor.
Max Res Factor is the maximum allowable cumulative percentage (ratio) increase for impedance values stored in the Ra table (over 15 gridpoint updates).
For Ra_new > Ra_old,
New Ra = min(Ra_new, Ra_old × Max Res Factor ÷ 10)
The default setting is 15. The algorithm divides the value of this parameter by 10. The upper bound is determined by multiplying (Max Res Factor/10) by the impedance value stored in the Ra table. Therefore, a value of 15 indicates resistance can only change by 50% from the current resistance value in the positive direction.
Min Res Factor is the maximum allowable cumulative percentage (ratio) decrease for impedance values stored in the Ra table (over 15 gridpoint updates).
For Ra_new < Ra_old
New Ra = max(Ra_new, Ra_old × Min Res Factor ÷ 10)
The default setting is 5. The algorithm divides the value of this parameter by 10. The lower bound is determined by multiplying (Min Res Factor/10) by the impedance value stored in the Ra table. Therefore, a value of 5 indicates resistance can only change by 50% from the current resistance value n the negative direction.
Transient modelling is used during resistance measurements. Res Relax Time or resistance relaxation time represents the time it takes for the internal resistance to be fully saturated. The resistance increases from 0 to the final value determined by the Ra table, as defined by the exponent with time constant Res Relax Time during discharge simulation. This way, the gauge will not simulate immediate large IR drops when it calculates the instantaneous voltage from the battery under load. The default value is 500 seconds, which is sufficient for most applications.
Subclass ID | Subclass | Offset | Name | Data Type | Value | Unit | ||
---|---|---|---|---|---|---|---|---|
Min | Max | Default | ||||||
80 | IT Cfg | 17 | Max Res Factor | U1 | 0 | 255 | 15 | num |
18 | Min Res Factor | U1 | 0 | 255 | 5 | num | ||
20 | Ra Filter | U2 | 0 | 1000 | 800 | num | ||
22 | Res V Drop | I2 | 0 | 32767 | 50 | mV | ||
69 | ResRelax Time | U2 | 0 | 65535 | 500 | s | ||
90 | Ra Max Delta | I2 | 0 | 32767 | 54 | mΩ |