(Been a while since I started a thread here! ) I recently finished some efficiency testing on the Model S Gen2 chargers (pre-refresh, but VIN > ~20k). Tests were done at 240V single phase. 5 amps, 82.77% 10 amps, 89.53% 15 amps, 89.06% 20 amps, 90.04% 25 amps, 91.03% 30 amps, 90.37% 35 amps, 90.75% 40 amps, 91.75% 45 amps, 90.81% 50 amps, 90.88% 55 amps, 90.55% 60 amps, 90.32% 65 amps, 90.21% 70 amps, 90.55% 75 amps, 90.77% 80 amps, 91.63% Keep in mind that the gen2 chargers are actually three smaller chargers in one, and that dual chargers would be six smaller chargers. So, during the current ramp up different numbers of these are online which explains the dips and jumps at say, for example, 25->30A. The data was collected over several days from two different vehicles with dual gen2 chargers and averaged. The number represents overall system efficiency (actual power into the battery pack while charging vs actual power into the charge port) which would include coolant pumps and other items needed for charging. Tests done at room temperature (~70F/21C) This doesn't take into account losses through the EVSE cabling and such, which will vary depending on design and other factors, but shouldn't be appreciable enough to matter when pitted against charger system efficiency. TLDR: For highest charger efficiency, charge at 40 or 80A.

So you're saying that car's above VIN ~20k came with gen2 mobile chargers and 80A HPWC's purchased in that timeframe are also gen2?

I'm referring to the chargers that are built into the car under the rear seats which actually do the AC to DC work, not the EVSE (HPWC/mobile connector) which is basically just a glorified "smart" extension cord.

It would be interesting to contrast these results with the newest 48A/72A chargers in the current cars. A methodology question. Are these numbers instantaneous numbers gathered after a set time after charging starts, like 5 minutes, or are they session averages, or session averages after a set time, or ??

Yes. The superchargers use 12 of these. The newest ones may use something newer, but I'm not sure. I had a script do the following: Car parked/off/locked/untouched for 15 minutes. Reading taken of idle/non-charging DC power usage average over 30 second period. Charge input current set to current test setting and charge started. 5 minutes into charging a 5 second average taken on input and output power as measured by the chargers and BMS. Repeated a 5 second average every minute for 25 minutes. Charge stopped. Subtract initial idle/non-charging power usage from all DC side numbers. Repeat for different amperages. Repeat entire routine again. Repeat on second vehicle. Initial preliminary findings revealed output current had virtually no impact on the efficiency, so SoC was not a sufficient factor to bother controlling for testing, although the tests were performed between ~20% and ~90%. Lots of things end up being factored in due the methodology, which is why I say it is a system efficiency. For example, 80A charging is slightly less efficient than 40A charging because pumps/fans would run slightly more at the higher rate, resulting in slightly less power getting to the battery per unit of input power.

Very nice. Are you noticing any degradation in capacity of your tesla modules after one year of solar operation?

Interesting. Does anyone have any pointers to where I could learn more about the differences between the gen 1 vs. gen 2? I imagine my 78xx car w/ dual chargers has gen 1, but I would learn for sure after reading more.

Very nice work. Thanks for sharing as always. Speaking from a European framework; Initial euro Model S' (with the gen2 charger in question) would not have charge single phase 32 amps, 7kW because a charger used 3 different charging modules as you said and each could carry 16 amps per phase. So they shipped every Model S with dual chargers, except the second one was software locked if you didn't buy the option. Second charger was used when charging 32amps (7kW). To make this possible they designed the UMC blue connector (single phase 32amps) so that CP of the Type 2 connector would signal 32amps total available to the car, only just a total of 32amps. 16 on both L1s of each charger. Someone plugged this UMC blue connector into a ZOE and ZOE interpreted this as having 32 amps available each phase, meaning 96 amps on the neutral wire. This fried up both ZOE and UMC. Later on they, via software, made it split the 32 amps to L1 - L2 - L3 of a single charger so it was resolved. Why they went with the complicated way first is beyond me. Moreover, later after the facelift, why they went for a single 72 amp charger with the initial option locked to 48 amps via software is beyond me. They reduced max AC charge from 22kW to 16.5kW. This doesn't matter that much for markets with a lot of Superchargers but for under developed Tesla markets in europe this is a bad thing.

I am one of those readers who is very interested by this, has limited understanding of engineering, and missed this when initially posted. I too miss what used to be the preponderance of intelligent conversations. A simple question: shouldn't the most efficient charging amperage be evenly divisible by 3 (assuming the 3 divisions of each charger are essentially the same)? Feel like trying this again at 39, 42, 45, 48, and 78 amps? Someone (maybe FlasherZ?) posted a similar but less thorough analysis back in ~ 2013-2014, and suggested that 48 amps was the most efficient charging level, IIRC.

Thanks for this, wk057. I missed it the first time around. This is very good information. I've been trying to understand the overhead losses from cooling pumps, fans, etc when charging and it seems there might be a clue here. If you look at the 5 amp efficiency of 82.77 and the jump to 10 amp efficiency of 89.53, would it be reasonable to assume that the 7% difference in efficiency (about 90 watts) is due to the pumps, fans, etc. which do not change much between 5 and 10 amps?

You know, I had thought to try this with increments of 3 but decided against it for simplicity. If I have a schedule that fits with doing this testing again some time in the near future (it takes a significant amount of time, actually, and I need to have driven a decent amount prior) I will rerun from 6A to 78A by 3 and see if there are any noticeable differences. Edit: Actually, the differences shouldn't be too noticeable. Once all three charger modules are online the load is split among them evenly at 0.1A increments if I recall correctly. I should try to force debug output and log the operation of the individual modules when I test again. That is a valid estimate, yeah. The MCU, all modules, charger itself, BMS/contactors, pumps, fans, etc. The overhead definitely varies quite a bit during a charge, though, and you're calculating what would be the average overhead.