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Charges to 84% when charge set to 80%
- Thread starter Jerryr
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There are plenty of threads around here on that topic. Short answer: yes it's normal. Charge percentage is an estimate, not a fully precise value. BMS recalibrates after charge and value can change, temperature affects it etc...
This is normal; sometimes charging will stop at X - 1% or overshoot the charging limit X + by a couple of percent. The Tesla Model Y battery management system can't always exactly determine the state of charge of the battery. The state of charge will vary at different battery temperatures. When the battery management systems performes cell balancing right after charging the state of charge may be lower by a couple of percent after cell balancing has been completed as this bleeds off energy from some of the cells so overall the cells are once again balanced.
The charging level is calculated by using current SOC, target SOC and the estimated capacity.
The SOC can not be measured during the charge so it will be a estimate.
A overestimation of the battery capacity will lead to a overshoot of the target SOC and a underestimate will lead to a undershoot.
Of course, if the BMS has not gotten the chance to measure the real SOC before the charge commence the initial SOC can be wrong, up or down leading to a over or undershoot.
The SOC can not be measured during the charge so it will be a estimate.
A overestimation of the battery capacity will lead to a overshoot of the target SOC and a underestimate will lead to a undershoot.
Of course, if the BMS has not gotten the chance to measure the real SOC before the charge commence the initial SOC can be wrong, up or down leading to a over or undershoot.
gtae07
Member
I've found I often lose 1-2% in the morning after the battery cools off, and I then gain a percent or two late in the afternoon when it's hot out. Today I went from 49% when I got home from dropping my son off at school, to 52% when it was time to go get him.
The car (BMS) can not measure the real SOC during a charging session.
(Each SOC number corresponds to a specific voltage and as current is “pushed” into the battery the supply voltage is higher than the battery voltage.)
So the charge energy is calculated before the charging starts by the current SOC and the target set SOC together with the estimated capacity.
For example, slightly simplificated:
A battery of 80kWh estimated capacity is to be charged from 30-80%.
This is 50% of the estimated capacity to be charged, so 40kWh.
The battery is charged with 40 kWh energy and the charging stops.
If the capacity was overestimated, and the battery capacity in fact is only 76 kWh, the estimation will still charge for 40 kWh so it will end up with 22.8+40 kWh = 62.8 kWh which is 82.6%.
It is possible that your overshoot coms from overestimation. Easiest to see if it is that, is by checking the SOC direct at arrival after a longer drive, and then let that car stand/sleep for 30-60 minutes. If the SOC reduces during this time, it is probably that.
A correct capacity estimate by the BMS should mean the SOC stays the same.
bo3bdar
Member
Model 3 SR. This is the type of thing I don't really understand. It's not a serious problem, but unexpected behavior makes it harder to predict, especially when low on charge.
Normal idle, sleep loss. Starts charge at 9%.
Drift up in charge by 4%. 13% to 17% when it woke to charge. Top is 22%, then drifts down 1 to 21%.
4% seems like a lot, especially when compared to starting state of 13%. That's 25% of that state.
Normal idle, sleep loss. Starts charge at 9%.
Drift up in charge by 4%. 13% to 17% when it woke to charge. Top is 22%, then drifts down 1 to 21%.
4% seems like a lot, especially when compared to starting state of 13%. That's 25% of that state.
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