State of Charge
From Unofficial Zero Manual
- SoC is a porportional representation; a percentage (fraction), so it is only applicable with a known total or max.
- Riders all have experienced different ranges under different temperatures, various environmental conditions etc.
- So full is really a subjective term, like asking When is a balloon full? Before it pops? But if you fill it with cold air then move to a warm environment, it pops.
- Paraphrase of ElectricZen's explanation
- SoC is most easily calibrated using the battery pack's voltage at rest or near rest.
This is a rough guide to correlating at rest battery voltage to the state of charge.
- There is respectable unofficial guidance that this curve varies as the pack ages over its lifetime.
- These figures are determined from some selection of owners with logs, with minimal experimental controls.
|Warning:||Your mileage may literally vary!|
- (Obsolete) SoC Indications per protomech
- Before Zero removed pack capacity readout from the mobile app, there were some corroborating indications available:
- The app appeared to simply show kWh using Zero's max capacity rating, i.e. present voltage times present amp hours.
- The voltage and amp-hours were likely to be correct, but the kWh readout was a rough guide at best.
- The percentage reading adjusted to the estimated pack maximum over time, so as the pack aged, the reported Ah and kWh readout would decrease, but not the maximum percentage.
- Variance across Battery Pack Years
- The sensor equipment measuring current and temperature for the battery pack improve over the years, impacting SoC indication.
- 2017 model year bikes appear to have an increased range of current sensor calibration quality, improving that year's estimations.
- Cell behavior also varies over the years, generally improving in robustness.
- One can find multiple complaints of going into limp-home mode at 5-15% from 2014 SR owners, for example.
- Variance by riding conditions
- Cell discharge is an electrochemical process that depends on the cells' physical conditions.
- The resistance of the cell (which should be low) increases with environmental factors like temperature.
- This results in reduced performance, since the resistance lowers the terminal voltage of the cells and the overall battery pack.
- At low SoC values, SoC might drop considerably once the BMS observes low terminal voltage as an indirect result of low temperatures or a cell imbalance.
- The lowest-performing cell becomes the limiting factor in pack performance at low voltage / SoC, and Zero does not provide indications to help you anticipate or diagnose this.