All electric vehicles experience losses during the charging process. We recently posted a couple of articles explaining why there are charging losses and where they are incurred, but we continue to get questions and comments about it so I decided to record my 2021 Tesla Model 3 charging on an Electrify America DC fast charger in an effort to further explore the topic.
I plugged my Model 3 into the station using a CHAdeMO adapter and recorded the charging session, both the in-car screen and the charging station screen, from 7% to 57% state of charge. In the end, the Electrify America charging station showed 39 kWh dispensed, and the Model 3's display screen showed 35 kWh received, for a difference of 4 kWh.
However, since the car's screen rounds up to the nearest whole number, I couldn't determine how much over 35 kWh was received, so I rounded it up to 35.5 kWh, giving the 50% charging session a loss of 3.5 kWh. Doubling that to achieve a 100% charging session, I would have experienced a loss of 7 kWh.
However, we explain that every charging session is different, and factors like the charging power and battery temperature play a big role in determining how much energy will be lost during the charging process.
But the biggest energy thief is usually the thermal management system, which is working hard to cool or heat the battery during DC fast charging for maximum charging performance. In the picture above, I took two snapshots of the charging session that were only about 30 seconds apart.
Both pictures show the Electrify America screen as well as the in-car display. The Electrify America screen shows 42 kW being delivered to the Model 3 in both pictures. However, the lower picture shows the car stating that it was accepting 30 kW and the upper picture, only seconds later shows the car is taking in 38 kW.
That's because up until the point of the first picture, I could hear the fans and the thermal management system working. They shut off right about when the vehicle reached 20% state of charge. I note in the video that the TMS was working to cool the battery, but it may have been doing the opposite, warming the battery. However, that's really not germane to the discussion.
The point is the act of heating or cooling the battery and components during DC fast charging uses energy, and that energy that the charging station dispenses never makes it into the battery and is considered charging loss.
Additionally, since I was using a CHAdeMO adapter and charging at such a low rate there was less energy loss due to heat. If I were charging at 150 kW at a V2 Supercharger or 250 kW at a V3 Supercharger, there would have been a lot more energy loss in the form of heat.
My model 3 has a 78 kWh battery pack and of that, about 74-75 kWh was usable when the vehicle was new. I have 17,000 miles on it now and like all EVs, my car has experienced capacity loss. I believe I currently have between 70 kWh and 71 kWh usable energy, based on my 100% to 0% driving tests, so a 7 kWh loss during DC fast charging would equate to about a 10% loss, which is relatively normal for DC fast charging.
However, most of the losses in this were incurred early on during the charging session while the TMS was running. I don't know if the system would have turned back on if I had done a true 0 to 100% charging session. But that also goes back to the fact that I was charging at less than 50 kW - very slow for Tesla DC fast charging. When I Supercharge, I typically hear the TMS working for the majority of the time until the state of charge hit 80% and the charging rate slows down.
Therefore, this isn't a scientific experiment aimed at showing precisely how much charging losses I incurred during this charging session. The purpose was to demonstrate the discrepancy in the amount of energy a charging station dispenses, and what Tesla vehicles display in the vehicle. Tesla's don't show you the energy lost during the charging session, only the energy that makes it into the battery pack. This leads many Tesla owners to falsy believe the vehicles are nearly 100% efficient, and that's not the case.
Bjorn Nyland has some good videos on Tesla charging losses so we encourage you to check out his Youtube channel if you would like to learn more about EV charging losses.
So check out the video and let us know your thoughts in the comment section below.