Charging Efficiency and Cost Question

[Wolfpacker83]

I use the standard wall outlet and can only charge at 8A due to my circuit. My efficiency (according to optiwatt) is always between 70-80%. Is this normal?
Does the charging cost that optiwatt displays take into account the efficiency or does the cost assume a 100% efficiency? (I searched the optiwatt site but couldn't find the answer)

 

[Sophias_dad]

Yes. It takes a decent amount of power just to keep the car awake so charging at low speeds takes a hit. It gets even worse when you intentionally slow it down.

Charging table - time to charge at 120/240V considering efficiency+

Tesla's official charging rates are estimates, but I think they make NEMA 5-15 charging seem really bad (3 miles/hour for a model 3?). I've plugged some data into a spreadsheet to calculate charging times for various volts and amps. volts amps (continuous) kW efficiency kW actual hours to...

teslamotorsclub.com

 

[Wolfpacker83]

Still trying to find this answer:
Does the charging cost that optiwatt displays take into account the efficiency or does the cost assume a 100% efficiency? (I searched the optiwatt site but couldn't find the answer)

 

[jcanoe]

Does Optiwatt know what is plugged into the Optiwatt tracking device? I don't think so. 120V and 8A is 960W (roughly 1kW.) Optiwatt will report kilowatts used. The cost is based on what you currently pay for a kWh. If you pay $0.15 per kWh then it costs you $0.15 per hour to charge your Tesla vehicle. After charging for 10 hours you will have spent $1.50. The Tesla vehicle can display the total kWh for the charging session (should be 10kWh). The battery state of charge will have increased by 10kWh X .80 (assuming 80% charging efficiency) or 8kWh (~10% of the battery capacity.)

In this example you consumed 10kWh to add 8kWh to the Tesla's battery. The Optiwatt should indicate that 10kWh was used over the 10 hour charging session. Your utility company will charge you for the 10kWh at the current rate. The remaining 2kWh was lost, mostly dissipated as heat energy, during the charging session.