Teslafi Charge data: Is it Right?

[Palros]

So I am just shy of 2 month in on my Life with a EV.

I have noticed that the number between my Smart Charger and Teslafi are some what different. I would assume my Charge is probably more accurate as it just doing it job. Here are the number

So we are talking a difference here of about 120kWh which is a reasonably large margin for error. I was expecting some difference , but nothing this large.

The hours are way out and i dont really care.

Anybody else noticed this?

 

[JIBYC]

I've seen something similar although not as great.

I think it's due to losses in the wall connector which TeslaFi can't "see" as it occurs before the energy enters the vehicle. I've crossed check some charging sessions against my meter and I estimate the loss to be about 7%. I haven't seen a way to get TeslaFi to show this loss other than adjusting the price per kWh up by 7%

 

[Palros]

Quick update,
I did just find this.

This bring the Delta to around 100kWh.

 

[NorfolkMustard]

When the car is plugged in, and the car is drawing power from the mains (or heating etc) but at the same time not recording its status as Charging, then it looks like teslafi doesn't record that power as part of a charge - that's where your difference will be.

During each charge period, the car keeps a running total of kWh added - teslafi probably just adds up the final charging record of each charge. the car doesn't update that tally outside of a Charging period, even if the car is drawing power from the mains.

 

[Palros]

When the car is plugged in, and the car is drawing power from the mains (or heating etc) but at the same time not recording its status as Charging, then it looks like teslafi doesn't record that power as part of a charge - that's where your difference will be.

During each charge period, the car keeps a running total of kWh added - teslafi probably just adds up the final charging record of each charge. the car doesn't update that tally outside of a Charging period, even if the car is drawing power from the mains.

Thanks, that makes sense. It would be good to be able to do some kind of correction on Teslafi so your costs are all correct. Oh well. I will just use the lower number to make myself feel better

 

[Jason71]

Thanks, that makes sense. It would be good to be able to do some kind of correction on Teslafi so your costs are all correct. Oh well. I will just use the lower number to make myself feel better

Teslafi can only report what the car tells it from the api's I don't think the car keeps a record of this so there is nothing Teslafi can do about it.
Also the Charger is reporting the energy that arrives in the charger. A lot happens before it gets to the battery. There are losses in the cable and AC/DC conversion in the car and thermal losses during chargin. These can be upto 5% so this will account for a chunk of your missing energy.

The Teslafi figure is accurate in so much as that is the amount of energy that the car is reporting as actually going into the battery so it is the right figure to use in calculating the actual efficiency of the car.
BUT in terms of knowing how much it is actually costing you overall. the higher figure is correct.

Charging an electric car is like filling a car with petrol but spilling some of it during the process every time. No point adding that to the MPG but it still adds to the costs

 

[ramonneke]

It is well known that you have 7-15% loss on kWh's added depending on the charge rate. I've heard 16A and 32A are most efficient on Model S/X.

Then there are losses in the cables too and that is why it is always recommended to use largest diameters for your wires as charging will heat up the cables which is increasing resistance especially over longer distances.

It is recommended to use at least 4mm2 diameter wires. I've seen lots of people go for 2.5mm2 because the specs say that is sufficient. It is, but larger diameter will give less resistance thus more efficient charging.