How efficient is charging?

[jmueller065]

It just dawned on me today (LOL after I've had the car for over a year!) that its really easy to figure out how efficient the charger in the car is:
http://jamiegeek.myevblog.com/2014/08/08/how-efficient-is-charging/

TL;DR version: Using Chargepoints usage reporting, and MFM's trip and charge log I calculated that the internal charger in the car is 85% efficient (basically: amount consumed/amount charged). I'm going to do the calculation again using the trip meter's value vs the Juicebox's reported value with a deeper discharge than 20% to see if there is much of a difference (I would expect the efficiency value to be higher with a deeper discharge).

 

[hybridbear]

Good thinking! I look forward to seeing any more results you get. Perhaps other owners could also post their results from using ChargePoint stations, etc. Since MFM only reports kWh used to one decimal place the data isn't super accurate so many measurements will be needed to get reasonably accurate data. It's too bad that Torque Pro doesn't work with the FFE. The computers in the Fusion Energi/C-Max Energi actually track kWh down to 8 decimal places. When you have access to that level of data you can get much more accurate measurements.

 

[mcowger]

It just dawned on me today (LOL after I've had the car for over a year!) that its really easy to figure out how efficient the charger in the car is:
http://jamiegeek.myevblog.com/2014/08/08/how-efficient-is-charging/

TL;DR version: Using Chargepoints usage reporting, and MFM's trip and charge log I calculated that the internal charger in the car is 85% efficient (basically: amount consumed/amount charged). I'm going to do the calculation again using the trip meter's value vs the Juicebox's reported value with a deeper discharge than 20% to see if there is much of a difference (I would expect the efficiency value to be higher with a deeper discharge).

I just realized I have a pretty accurate way to gauge this too. I use a system from PowerhouseDynamics that attaches to each breaker on my main panel and measures current, voltage, etc at 1Hz. My EVSE (JuiceBox Basic) also has a dedicated circuit, and the PHD system understands how to deal with 240V dual pole circuits.

Here's a charge from 7% to 100%

Using the integral of that, as well as the fact that the car is rated for 6.6kW and the circuit was delivering 7.160kW during charging, my estimate is the car is about 85.9% efficient from the wall....note that this includes any losses introduced by the EVSE.

 

[jmueller065]

Keep in mind it also includes any power consumed by the TMS. Thus the efficiency may change from time to time because the TMS runs sometimes and doesn't other times.

Cool plot.

 

[dmen]

Keep in mind it also includes any power consumed by the TMS. Thus the efficiency may change from time to time because the TMS runs sometimes and doesn't other times.

That was the exact thought that came to mind reading your initial post. I'd appreciate it if you could update this thread with measurements of nearly full charge efficiencies over a range of ambient temps. I would guess it's most inefficient at very warm temps, then at very cold temps, and most efficient at 70-80.

 

[mcowger]

Keep in mind it also includes any power consumed by the TMS. Thus the efficiency may change from time to time because the TMS runs sometimes and doesn't other times.

Cool plot.

Thats true, although my FFE is garaged and during this time of year it maintains about 58* throughout the night....so its unlikely the TMS is having to do that much work.

 

[jmueller065]

Update:
I've updated the blog post with a few more data points. Short form: So far I haven't seen the car charge at anything more efficient than 85% and change (including last nights charge: 11.1 kWh consumed vs 13 kWh to charge it back up--so far the deepest discharge since I've been calculating this figure).