OVMS User Manual page 12

OVMS: Renault Twizy User Guide 2019/05/02 RT3.9.1
SOC
The SOC output includes the current SOC and the current SOC usage range (lowest & highest
SOC). The SOC range reflects your last battery usage or charging cycle.
As mentioned above, the SOC is a model based estimation of the Twizy. So it's quite normal it will
sometimes be wrong. To protect the battery from over-discharging, it will normally tend to show
you a SOC lower than real. There's currently nothing the OVMS can do about that.
Grid energy estimation (V3.6)
Prior to V3.6, the energy use was derived from the battery current. That also applied to the Wh sum
for charging. Beginning with V3.6, the real battery power is calculated from the battery current and
voltage.
This now allows to measure how much energy really is stored in the battery and later available for
traction. The data observed from this measurement and power meter readings shows the typical grid
to battery efficiency for the Twizy is ~88.1% for the main charge and ~86.4% including a full 12V
charge cycle.
The grid energy estimation shown by the STAT message calculates from the battery energy with the
mean efficiency of 87.2%. Real grid usage is normally quite close to this for typical charges, but
keep in mind this is an estimation, don't expect this to be as exact as a physical power meter.
Battery capacity estimation (V3.6)
The STAT output displays the battery capacity in percent and absolute Ah.
100% capacity is assumed to be equivalent to 108 Ah. The nominal Ah capacity of the battery is
unknown up to now, the best assumption matching the available data is 120 Ah, with 90% usable
capacity at 108 Ah.
Note: we now know the battery cells are rated at 43 Ah, adding to 129 Ah if new and leaving ~115
Ah usable. The 100% reference of 108 Ah thus is now to be seen as a bit on the "optimistic" side (in
terms of percentage). As it does no harm it has not been changed to not disrupt user statistics. As
the Ah capacity is the real measured value you can simply calculate a second percentage based on
115 Ah.
The capacity estimation is updated every time charging from below 40% to 100%.
Estimation is the more precise the lower the SOC at charge start. To smooth out SOC and
measurement errors, the estimation builds the mean value over the last 10 charges with sufficient
discharge depth. So to calculate a single measurement from the mean values, do...
value
=10×mean −9×mean
new new old
Be aware of SOC jumps: the BMS will occasionally correct it's SOC estimation some minutes
after a drive. If you miss an SOC jump by charging immediately after driving, this will affect your
capacity estimation. SOC jumps can be as high as 5%, check your trip reports or RT-PWR-Log. If
you've got frequent jumps, it may be a good idea to let the Twizy rest for some minutes before
charging.
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