But these values in the BMS are misleading.
They do not represent the capacity you are working with and for what you are “charged” for in your contract.
As much as we figured, they are total arbitrary and only a placeholder.
That figure would put the Capacity of the battery to about 129Ah!!!
Realistically we work with ca 116-118Ah.(108Ah used)
Just have a look at what the cells are labeled with!
A cell has 966Wh.(there are 7 cells in a Twizy battery)
That´s 6762Wh total capacity.
Renault says you can use up to 6100kWh.
Its more like 6000kWh.
The charge end voltage is set a bit lowerby Renault so the BMS only charges to about 88-90%
The SoH deals somewhat with this values.
The best method still is to measure how much you can charge the battery.
With a bit empiric data you can figure out what losses you get from the charger.
A normal full charge with the OVMS looks like this.
(The OVMS continuously measures the power intake during the charge)
CHG: 5648 (~6477) Wh
Range: 79 - 68 km
SOC: 100.00% (5.04%…100.00%)
ODO: 15311.0 km
CAP: 99.4% 107.4 Ah
The charger only reports the power used in the primary circuit ( AC before the DC)
With a bit of above mentioned data collection you can assume and calculate the efficiency of the charger.
This will bring you to the second value 5648Ah for a 95% charge.
At the end of the lifespan(100tkm) %CAP (Measured by the OVMS) and %SoH (Set in the BMS) will meet again.
I only can assume that Renault does this on purpose to calm the minds of users.
In conclusion, relying on the SoH in the first years and the Capacity in the BMS does not help you when you try to figure out how much you really lost in range.
It´s not that easy. There is a bit of calculating to do!
BTW: With that numbers the OVMS calculates the Range independently(and temperature compensated) to the range displays by the UCH.
And that this range calculation is mostly spot on (other than the Renault values) says a little bit about the method and the data it´s based on