Charge efficiency, 20A vs 40A vs 48A?

[balefire]

I miss the days of my MS which allowed home charging of 80A or my MX AP1 which allowed 72A charging.

With our refresh MX, what is the most efficient Amp to charge our MX? Current max is 48A.

Model S Gen2 Charger Efficiency Testing

(Been a while since I started a thread here! :P) 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...

teslamotorsclub.com

Per this old post for MS, it looked like the sweet spot was 25A or 40A. I used 25A on my old MS and MX for that reason. Just curious if its the same with the refresh battery. Thanks

 

[DCGOO]

I miss the days of my MS which allowed home charging of 80A or my MX AP1 which allowed 72A charging.

With our refresh MX, what is the most efficient Amp to charge our MX? Current max is 48A.

Per this old post for MS, it looked like the sweet spot was 25A or 40A. I used 25A on my old MS and MX for that reason. Just curious if its the same with the refresh battery. Thanks

The answer is, it depends. How much time do you have to get to your desired state of charge? Frankly, 48 amps is so far below what the battery can actually handle, there is nothing to be gained by any value lower than the maximum possible. Remember, if the vehicle is doing anything else, that is taken off the top, with the remainder going to charging. At very low levels of current (like trying to charge from a 120V outlet), it is possible the battery will not charge at all. IOW the maximum possible rate is the most efficient.

In today's models, 48 amps if you have the required equipment. If you have a vehicle that supports 72 or 80 amps, those values would be great. However installing any circuit over 60 amps (required for 48 amp charging) is significantly more complex, requiring much larger cable and cutoff switches at the wall connector location. But if you already have one, go for the max. Back when I had an 80 amp and 72 amp capable vehicle, I only went to the trouble of installing a 60 amp circuit at home. I could charge from 0 to 100 kw, in less than ten hours. Of course no one needs really charge to that extreme. More typically I only need to add in around 20 kWh for daily use, which only takes a couple of hours to get to, pulling 48 amps.

 

[Rocky_H]

Per this old post for MS, it looked like the sweet spot was 25A or 40A. I used 25A on my old MS and MX for that reason. Just curious if its the same with the refresh battery.

It doesn't have anything to do with the battery. That's not where the efficiency differences are. The efficiency differences are in the onboard charger, which is doing the conversion from the circuit's 240V AC to what the battery needs as 400V DC. Those processes of rectifying and voltage boosting are where the chargers can have different efficiencies.

But anyway, it's all pretty much splitting hairs as the results are going to be things like 92% here or 94% there. It's just not enough of a difference to worry about.

 

[Joer293]

Typically the max rate will be most efficient. Unless parked outdoors in 100+ heat. There is always the flat overhead tax, the smaller % of total power control circuits and coolant pumps consume , the more efficiency you get. Also, temperature can really impact efficiency too. I’ve noticed my battery is most efficient around internally 90 degrees. Outdoors may be 75-80F. In cold temps, Lower current will never heat the battery to optimal temperature, that heat lowers internal resistance. That resistance works against efficiency at lower amps.

 

[dafish]

It doesn't have anything to do with the battery. That's not where the efficiency differences are. The efficiency differences are in the onboard charger, which is doing the conversion from the circuit's 240V AC to what the battery needs as 400V DC. Those processes of rectifying and voltage boosting are where the chargers can have different efficiencies.

But anyway, it's all pretty much splitting hairs as the results are going to be things like 92% here or 94% there. It's just not enough of a difference to worry about.

I would add heat loss over the breaker to evse increases as amps increase.

I did test all this. I still use 48a, but 40a was overall more efficient

Most efficient charging level

Sorry for the TL;DR Over the last few months, I've been curious about charging efficiency for my Model 3P and so I decided to do a small test: My wife has a very consistent driving schedule with it and so if you tracked from day to day and week to week, the charge level of the car (as well as...

teslamotorsclub.com

 

[Joer293]

I would add heat loss over the breaker to evse increases as amps increase.

I did test all this. I still use 48a, but 40a was overall more efficient

Most efficient charging level

Sorry for the TL;DR Over the last few months, I've been curious about charging efficiency for my Model 3P and so I decided to do a small test: My wife has a very consistent driving schedule with it and so if you tracked from day to day and week to week, the charge level of the car (as well as...

teslamotorsclub.com

How much is your breaker heat loss? My 100amp breaker with the 2guage thhn when charging the Model S at full 80 amps, only reaches maybe 80F max usually lower. My tankless water heater breaker heats up more, probably because that's only 8 gauge. (pic 172 is the tankless, pic 282 is the HPWC with the cover off the panel. Yes in the picture there is no conduit around the THHN, I wanted testing pictures. After I took the pics, I rewired through conduit. )

The cord to the car is hotter, but still only 90F or so at 80 amps near the handle. Those Gen 1 HPWC's wore out and I can see heat from the loosening connections inside the handles.

 

[dafish]

Breaker to evse loss is in the table linked and varies by amperage. Breaker itself? Unknown

 

[DCGOO]

Breaker to evse loss is in the table linked and varies by amperage. Breaker itself? Unknown

First off, the breaker is SUPPOSED to get warm. When it gets too hot, it trips. It would be malfunctioning if it did not get warm with 80% of rated flowing through it.

 

[dafish]

yes…. I don’t worry, or even think about, the breaker. there Is loss over that entire circuit, by and large the wire, and that’s what I measured.