Discrepency Between MS and Chargepoing on Energy Used.

[AWDtsla]

LOL..... yeah if the car's actually drawing 26A when you've set 25A, and 39A when you've set 40, I can see how 25A setting might seem more efficient. It's not.

 

[cmorgan]

On the trip meter inside my model S it says I have used a total of 444 kWh for the entire time I have owned the car. About 90% of my charging happens at work through a ChargePoint station. ChargePoint says I have charged through them for a total of 500 kWh. How do I reconcile these numbers? When I got the S it was already 90% charged plus I do some charging at home and my current battery is only at 40%. I can't think of any reason the ChargePoint number should be higher.

The charger is free at work so I am not worried about getting ripped off. I am just curious to understand what I am missing here. Some sort of electricity loss between the charger and my battery?

With a Neurio and an rough average of the cars reported consumption numbers I've calculated about 82% efficiency with my home HPWC setup. It looks like you are looking at 444/500 = ~89% efficiency which is much higher. Makes me think the number I'm using for the cars consumption may be too high, I should recalculate after using trip numbers.

 

[hacer]

LOL..... yeah if the car's actually drawing 26A when you've set 25A, and 39A when you've set 40, I can see how 25A setting might seem more efficient. It's not.

You don't seem to understand. In my plot I am computing the ratio of the ending "charge_energy_added" from the REST API which is an internal integration by the Tesla of energy entering the battery to the difference between the ending reading and starting reading of the dedicated utility meter. Thus I'm using only 3 numbers, 1 provided by the car at the end of charging, and two from my power meter. My X-axis variable is the user setting on the charge screen, which is the targeted wall current.

If the reported current fluctuates slight during charging (which the actual current surely does) it has no effect on my calculation. If you don't trust Tesla's battery current or battery voltage readings (which when their product sampled every 3 seconds and time-integrated closely match the "charge_energy_added") to be accurate then you have no means to measure the charger efficiency without tearing down and introducing your own instrumentation.

Finally, based on when you joined TMC, I suspect you have an older car that has a different charger from mine which likely has different efficieny. The OP would have the same charger that I do.