OVMS User Manual page 21

OVMS: Renault Twizy User Guide
General SEVCON power cutbacks
The SEVCON cuts back recuperation at the upper and drive power at the lower SOC end. The
recuperation cutback point is configured in SDO 0x2872.02 and defaults to -35 A (CFG WRITE
needs this 16 bit encoded, so this is 65536 - 35 = 65501). 35 A is normally available below ~97%
SOC (around 2000 W charge pwr / ~57.2 V battery voltage). If you set this to e.g. -20 A, you will
get recuperation earlier. Take care not to overcharge your battery (i.e. if you live up a high hill...).
The drive power cutback is configurable as well. The default map begins cutback at 15% SOC
with 100% power and ends at 0% SOC with 15% power left. That's more a psychological trick than
a technical necessity, as the BMS itself will also lower the discharge power level to protect the
battery. If you don't need the cutback you may change the map using CFG WRITE:
Cutback start SOC:
Final power level:
Using the battery monitor
The battery monitoring needs no configuration. It's enabled by default and works automatically in
the background and normally will only alert you about critical conditions.
Critical (=alert) conditions are:
– Single cell voltage offset from mean value >= 30 mV
– Standard deviation of cell voltages >= 25 mV
– Single module temperature offset from mean value >= 3 °C
– Standard deviation of module temperatures >= 3 °C
In addition to critical conditions, the monitoring will also set a "watch" flag if the voltage or
temperate has an offset from the mean value that is higher than the current standard deviation of all
cells / modules, or if the standard deviations higher than normal. You may want to keep an eye on
these cells, if the deviations tend to raise over time, these may be the source of performance loss or
even become the part that breaks.
Standard deviations are a measurement of the overall cell drift = overall pack health. A healthy pack
will have a maximum voltage standard deviation of 5-10 mV and a maximum temperature standard
deviation of 1-2 °C. Standard deviation "watch" status is triggered at voltage deviations from 15
mV and temperature deviations from 2 °C.
All battery statistics and alert flags are automatically reset each time you start the Twizy. So if an
alert occurs, you can easily see if it was a temporary stress issue or if it persists with the next drives.
Remember, the CAN bus is offline while the car is switched off, so temperatures and voltages are
not updated while the car is off. The last values read from the bus will be kept by the OVMS.
SDO 0x3813.13 = <SOC%> * 50
SDO 0x3813.12 = <Power%> * 50
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2019/05/02 RT3.9.1
Default=15%
Default=15%