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Different kWh readings: public charger vs. [charge_energy_added]

rponte 3 years ago updated 3 years ago 5

When I charge at a public charger, the kWh consumed reported by (i) the charging station is always lower than (ii) the "kWh Used" mentioned in Teslafi. The difference is about 10%.

I was expecting the 2 to be (exactly) the same.


Do you have any obvious explanation for this difference?

It could be that the public charger isn't measuring correctly the energy provided to the car. Or are the Tesla Model S readings known to incorrectly measure the kWh used?

Answer

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Answered

You may need to adjust your kWh factor in the settings page on TeslaFi.  After completing a trip 20+ miles or more look at the the trip meter in the car and compare it to the trip on TeslaFi.  Adjust the kWh factor accordingly.


kWh is not provided by the Tesla API so it has to be calculated.  Still with adjusting the factor it can get very close.  Longer drives will have more accuracy.

Answer
Answered

You may need to adjust your kWh factor in the settings page on TeslaFi.  After completing a trip 20+ miles or more look at the the trip meter in the car and compare it to the trip on TeslaFi.  Adjust the kWh factor accordingly.


kWh is not provided by the Tesla API so it has to be calculated.  Still with adjusting the factor it can get very close.  Longer drives will have more accuracy.

Thanks, I will try that and report back over the weekend.


But just to double check with you, the difference I'm getting is not while driving, but while charging (kWh mentioned by the public charger vs. [charge_energy_added] field).


Sorry, I need to catch up on sleep.


That is separate from what I mentioned.  But again, the kWh used is not provided by the API.  It's a calculation based on a per minute sample of the amperage and voltage coming in from the charge on a per minute bases and extrapolated over the time of the charge.  It's not perfect but when I and others were testing it in the past it was much more accurate than +-10%.  Usually within a percent or two of electrical meters.

Is Teslafi taking into consideration the Power Factor, when calculating the kWh used?

If it isn't (maybe it's not even possible / there is not enough data for this), the problem is that the "Charge Efficiency" is also including the grid's difference between Apparent Power (kVA) and Active Power (kW). That is, it's underestimating the Charge Efficiency calculation.


If Teslafi isn't currently using the Active Power to calculate the Charge Efficiency, do you envision any way to do it?

Hi


Any news on this?

If there's no better way to measure the Energy Used, at least it would be advisable to update the definition of "Charge efficiency (%)", to clearly state that it drops with the amount of reactive energy in the grid, which ISN'T charged to the user.