After charging, the screen reported 15 KW used. Is this the total power pulled from the socket?

[pjensen]

I have a standard range M3 (2020). After finishing the charge, the car reported 15 KW used. I use 240 volts at 32 amps to charge. Went from 48% to 80%.

So I took my last electric bill total, divided by the total KW used for the month and came up with $0.14 per KW. This includes taxes, transmission charges and municipal fees. The cost to charge was $2.10 (using this math).

Does this 15 KW number include the electrical conversion losses? Or is it just the amount that went into the battery?

 

[pipp]

When I was charging with 120 volts (12 amps), my meter showed 31 kwh went into the car, which, showed that it received 20 kwh. That was the biggest reason why I switched to 240 volts, which my meter can’t measure. But my understanding is that the car receives something around 88% of the electricity output through the 240 volt plug…

 

[pjensen]

But my understanding is that the car receives something around 88% of the electricity output through the 240 volt plug…

That makes sense. At 88% efficiency, the power from the wall socket would be 17 KW. So the total cost to charge was $2.38. Seems cheaper than gas...

 

[RayK]

With gas going for over $5/gal for regular unleaded here in the Bay Area, $0.42/kWh Supercharger rate doesn't seem all that bad.

 

[pjensen]

A small correction - I'm seeing the charge total on the tesla app on my phone, not on the car screen.

Today I charged from 28% to 81%, (25 KW shown on the app). So this charge cost $3.98 and took 3.5 hours. Not bad....

 

[rejedejo]

I think it’s how much went into the batteries. Ancillary power is not tracked, converter losses, heat etc

 

[AlanSubie4Life]

Does this 15 KW number include the electrical conversion losses?

No.

Or is it just the amount that went into the battery?

No. It’s the number of rated miles added to the battery * 52.5kWh/250rmi in your case. Somewhat decoupled from actual energy into the battery though it correlates fairly well. My point is that it is not a measurement, it’s the output of a formula.

This value is thus about 4.5% higher than the energy actually added to the battery (each displayed rated mile does not include buffer energy of 4.5%).

I use 240 volts at 32 amps to charge.

Your charging efficiency is probably about 87%. The best possible for Model 3 appears to be 88-89%, as outlined precisely in the documents Tesla provides to the EPA.

Went from 48% to 80%.

If you provide your rated miles at 100% and exactly time the duration of the charging event (along with voltage at the car and the current), we can calculate your charging efficiency. Or we can assume the charging efficiency is 87% and predict the charge time. You also have to switch to miles so we can see the miles added rather than the kWh added in the charge event (less rounding error).

This stuff is all really easy to calculate within a couple %, since we know the constant.

I would guess you have:

15kWh/(52.5kWh/250rmi) /0.32 = 223rmi at 100% but the rounding error means it could be anywhere from 216rmi to 231rmi.


(One thing I haven’t checked recently is if the kWh number reflects energy used (say you have the heater on full blast) by the car while charging. I think it does not, but easy enough to do an experiment to check. Add 10 rated miles in a charging event with heater blasting and then add 10 rated with it off and see if the number of rated miles and kWh on the screen is different in the two cases. So if not different, as I think, this number (kWh or rmi) is just a formula based on net energy added to the pack for the current charging event and does not include accessory use. But as I said I don’t know. Important for supercharger billing and such, how this is managed, but I conveniently don’t pay for supercharging, so I don’t pay attention. It could also be managed and counted and displayed differently during DC charging but last time I checked a couple years ago it appeared to be the simple net energy - but may not have had enough accessory use on the charge to notice any discrepancy.)