Total charge kWh being consumed

[dafish]

Bottom Line:

I tend to see just under 7% total loss.

I could screw with this for the rest of my life and change it by less than 2% if I could change it at all, and there's no ROI in a change that small. If I was looking to tweak it I would run 60 amp capable wiring and test various total efficiencies. I could no doubt reduce "awake" time and, if using a down-rated charge rate like 32 amps or perhaps 40 amps reduce circuit loss. What would the OBC do? Unknown.

Details:
I have two energy monitoring systems in the home. An Enphase monitoring the solar system and energy consumed, and an Emporia Energy Vue Gen 2 again monitoring energy consumed and also individual circuits. For the latter I've evaluated the CT's used and am using only those reporting within .1%. That said any CT system has errors. We can hypothesize, but reaching hard conclusions within a few percent should be taken with some reservation. At the same time considerable time has been spent challenging the monitoring system and I'm pretty confident these are very accurate. Data for your consideration:

1 month old MY3LR.
3-10 charge using Wall Charger@ 24 amp/240v for 75 min
Garage Temp 47f

Tessie reported power consumed: 4.16KW​

Panel CT Monitor reported: 4.321KW​

Tessie reported added to battery: 4.03KW​

Tessie reported efficiency: 97%​

Actual: 96.9%​

Overall Efficiency: 93.3%​

Loss to Wiring/EVSE, etc 3.6%​

Line Voltage Variance: 235V - 243V​

​

During this time the doors were open for 10-15 minutes and as I recall the heat pump started. Finally, line voltage variance was a bit high, with a low of 235V.​

​

3-10 charge for 170 min

Garage temp 57f​

Tessie reported power consumed: 16.34kw​

Panel CT Monitor reported: 17.05kw​

Tessie reported added to battery: 15.91kw​

Tessie reported efficiency: 97%​

Actual: 97.3%​

Overall Efficiency: 93.3%​

Loss to Wiring/EVSE, etc 4%​

Line Voltage Variance: 239V - 243V​

​

This final (170 minute) charge terminated at 63%, so the BMS was not limiting anything. Cabin preconditioning would have run during this time for a brief period as well. Is this reported accurately? In other conversation with JCannoe I've been led to believe all conditioning circuits are driven by the HV system and would be captured by the OBC as "delivered to the battery". Meaning "yes, data reported by the BMS/OBC will remain accurate".

Wiring loss for the panel to WC circuit is calculated to be 1.04% The Wall Charger has to have its own consumption, and it's own cable loss, but an additional ~2% - 3% seems high to me. I suppose I'm not too pleased overall efficiency is ~7% to the battery, but is what it is, and at least the power has no cost to me.

Finally, how accurate is the power delivered to the cells? No idea, but aside from some small resistance loss it should be very accurate. Will that always translate to matching range? Mostly, but less healthy battery systems should have more pack resistance and therefor less energy actually absorbed by the battery.

Noob though, so WTF do I know?

 

[NewbieT]

So I decided not to put the home in darkness and use the granny charger with a Tapo P111 energy monitor to monitor the actual energy supplied to the charger. The results are;

Charged for 3hrs 58 mins (3.966hrs) and Tapo recorded 7.075kWh
TeslaFi recorder Used: 6.83 kWh Added: 6.16 kWh
Tesla recorded 6kWh (added)

Tesla is only showing charge added to the battery (rounded down) to 6 kWh. Not very accurate!
And TeslaFi is 7.07 / 6.83 ~ is 3.5% reading low (as per my other data)
And Tapo recorded what was actually used (7.075 kWh)

So if you are like me, you need to be adding an additional 3.5% when calculating actual energy supplied to the car when using data from TeslaFi. So for example, since I have owned the car TeslaFi says I spent £ 307.71 charging, but in reality I've actually spent £ 318.48 for 15,700 miles. Not such a big difference...

Sanity check;

Energy supplied = Energy added to the battery + Energy used to operate the computer + other losses. The computer takes ~ 233 watts when running.
Therefore 7.075 kWh supplied = 6.16 kWh to the battery + (3.996 hrs x 0.233 kW computer) = 0.931 kwh + other losses

Therefore other losses = 7.075 - 6.16 - 0.931 = 0.016 kwh. So it seems that other losses (ac to dc conversion) is very low!



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Just to second this. Yesterday’s 2.49kW added (as reported by the car) measured 2.604kW from the smart meter (no other draw). In my case, 4.5% loss but the principle applies.

 

[ajmorr.is]

Thanks for all the detailed replies. I guess what I didn’t think about was that the figure recorded by Tesla can only be what the car receives, and might also be only what is put into the battery (assuming the AC-DC charger itself, and other in car devices will use some power).

I still don’t quite follow why IO is reporting a totally different lower figure out of all the numbers in my case though.