L1 vs L2 charging efficiency

[dakhlkt22]

Wondering what kind of charging efficiency folks are measuring on their L1 or L2 home charging setup.

I was expecting under 80% efficiency for L1 based on some posts I've seen, but TeslaFi shows:
USED 13.46 kWh
ADDED 11.59 kWh
Efficiency 86.1%
12:00 AM - 7:45 AM
AVG 116 V
MAX 118 V
AVG 15 A
MAX 15 A
Miles Added 52.81

I limited charging to 15A. I am using the 5-20 adapter on the mobile connector.

I'm surprised we are getting such high efficiency and am wondering if L2 would be much more efficient. I don't anticipate needing to add more than 50 miles per night. In addition to the safety of a hardwired connector, my reason for considering L2 is to get higher efficiency, but I don't know how much more efficient L2 would be if we are already getting 86% on L1.

Wondering why we are getting 86% on L1. Do newer wires and connectors have higher efficiency? This is a new 120V 20A circuit we installed in our garage this year and it runs to a new 200A panel.

 

[fhteagle]

Do newer wires and connectors have higher efficiency?

Not that I know of, unless your old wires and connections are starting to suffer corrosion, in which case they should be replaced anyway.

Haven't tried it on the Tesla, but on my Volt delivered energy went down about 0.3 kWh out of about 11.6 used for a full charge when I switched from 120 to 240. This was measured by the OpenEVSE itself, which is not perfectly accurate but the CT inaccuracy should be the same in both cases.

The other thing to do consider is the Tesla keeps a lot of things powered on during charging, to the tune of maybe 200 to 300W of parasitic losses. If you can increase the charging power used from the wall, you reduce the time that the onboard charger is doing its thing, you get less losses too.

So, 240V should be marginally more efficient. Not incredibly different, but measurably different.

 

[Cosmacelf]

Wondering what kind of charging efficiency folks are measuring on their L1 or L2 home charging setup.

I was expecting under 80% efficiency for L1 based on some posts I've seen, but TeslaFi shows:
USED 13.46 kWh
ADDED 11.59 kWh
Efficiency 86.1%
12:00 AM - 7:45 AM
AVG 116 V
MAX 118 V
AVG 15 A
MAX 15 A
Miles Added 52.81

I limited charging to 15A. I am using the 5-20 adapter on the mobile connector.

I'm surprised we are getting such high efficiency and am wondering if L2 would be much more efficient. I don't anticipate needing to add more than 50 miles per night. In addition to the safety of a hardwired connector, my reason for considering L2 is to get higher efficiency, but I don't know how much more efficient L2 would be if we are already getting 86% on L1.

Wondering why we are getting 86% on L1. Do newer wires and connectors have higher efficiency? This is a new 120V 20A circuit we installed in our garage this year and it runs to a new 200A panel.

How did you measure your “used” electricity? Was it simply the volts x amps being measured while charging?

And yes, based on forum research, I was using 78% efficiency for 120V charging vs 90% for 240v in my calculator, so these results are indeed interesting. CarCharging.us

 

[dakhlkt22]

How did you measure your “used” electricity? Was it simply the volts x amps being measured while charging?

And yes, based on forum research, I was using 78% efficiency for 120V charging vs 90% for 240v in my calculator, so these results are indeed interesting. CarCharging.us

These are measurements from TeslaFi which I have authorized to connect to my car. Not sure how they measure it all.

 

[Mark57]

am wondering if L2 would be much more efficient.

If you can afford it, run, don't stop to a high quality 14-50 plug and breaker. Don't cheap out on parts quality at either end. Again . . . . don't cheap out on these parts. They're going to pull more current for longer non-stop times than anything else in the house. Most electricians have no clue about this even though they will tell you otherwise. It gets VERY hot in Oklahoma. We hit 109° this week and my garage was 100°. Cheap crap parts get hot and fry and fail badly. Don't do it. Sermon over. Sorry.

I charged 2 Model 3's @ 120v for 1.5 years with a NEMA 5-15 plug and 20A breaker. I then upgraded the plug only to NEMA 5-20 plugs, same 20A breaker. We then installed two (2 cars) NEMA 14-50 industrial quality Hubbell receptacles with 6 AWG copper and industrial quality breakers. 120V charging was OK since we didn't have a commute, but a quality 14-50 is superior. You can preheat or cool without using the battery which you can't do @ 120v.

The numbers are hard to present here but I have copied charge data out of Tesla-Fi for the 3 charging scenarios. 120v 5-15 plug & 5-20 plug, and 240v NEMA 14-50. The same original mobile charger that came with the car and a different plug adapter was used for each senario.

4/6/22
NEMA 120v 5-15 amp plug & 20A breaker
21 Hours 37 Minutes 49% - 85%
USED 30.17 kWh
ADDED 25.56 kWh
Efficiency 84.7%
AVG 117.5 V
AVG 12 A
AVG 5.2 mph
Miles Added 34.26

5/9/22
NEMA 120v 5-20 amp plug & 20A breaker
15 Hours 11 Minutes 37% - 70%
USED 28.01 kWh
ADDED 23.68 kWh
Efficiency 84.6%
AVG 115.3 V
AVG 16 A
AVG 6.9 mph
Miles Added 107.62

5/28/23
NEMA 14-50 outlet w/mobile charger, 50A breaker
4 Hours 36 Minutes 43% - 90%
USED 34.56 kWh
ADDED 33.78 kWh
Efficiency 97.7%
AVG 234.9V
AVG 32A
AVG 32.3 mph
Miles added 153.55

 

[dakhlkt22]

If you can afford it, run, don't stop to a high quality 14-50 plug and breaker. Don't cheap out on parts quality at either end. Again . . . . don't cheap out on these parts. They're going to pull more current for longer non-stop times than anything else in the house. Most electricians have no clue about this even though they will tell you otherwise. It gets VERY hot in Oklahoma. We hit 109° this week and my garage was 100°. Cheap crap parts get hot and fry and fail badly. Don't do it. Sermon over. Sorry.

I charged 2 Model 3's @ 120v for 1.5 years with a NEMA 5-15 plug and 20A breaker. I then upgraded the plug only to NEMA 5-20 plugs, same 20A breaker. We then installed two (2 cars) NEMA 14-50 industrial quality Hubbell receptacles with 6 AWG copper and high quality breakers. 120V charging was OK since we didn't have a commute, but a quality 14-50 is superior. You can preheat or cool without using the battery which you can't do @ 120v.

The numbers are hard to present here but I have copied charge data out of Tesla-Fi for the 3 charging scenarios. 120v 5-15 plug & 5-20 plug, and 240v NEMA 14-50. The same original mobile charger that came with the car and a different plug adapter was used for each senario.

4/6/22
NEMA 120v 5-15 amp plug & 20A breaker
21 Hours 37 Minutes 49% - 85%
USED 30.17 kWh
ADDED 25.56 kWh
Efficiency 84.7%
AVG 117.5 V
AVG 12 A
AVG 5.2 mph
Miles Added 34.26

5/9/22
NEMA 120v 5-20 amp plug & 20A breaker
15 Hours 11 Minutes 37% - 70%
USED 28.01 kWh
ADDED 23.68 kWh
Efficiency 84.6%
AVG 115.3 V
AVG 16 A
AVG 6.9 mph
Miles Added 107.62

5/28/23
NEMA 14-50 outlet w/mobile charger, 50A breaker
4 Hours 36 Minutes 43% - 90%
USED 34.56 kWh
ADDED 33.78 kWh
Efficiency 97.7%
AVG 234.9V
AVG 32A
AVG 32.3 mph
Miles added 153.55

Wow, 98% efficiency? I didn't even think that was possible. I suppose it's possible TeslaFi is missing some of the charging losses.

Regardless, those charging numbers suggest L2 will allow me to be at an efficiency level that is 13 points higher than L1 as whatever TeslaFi is missing is probably missed in the data from both types of charging. So I guess it makes sense to still do L2.

I think I'm not going to do a 14-50 though, I'm going to do the wall connector. I bought the old version that is for Tesla and doesn't have the built in adapter for other vehicles. Bought it a month too early I guess.

 

[Mark57]

I think I'm not going to do a 14-50 though

I went with 14-50 since I needed 2 and it did everything I needed, provided flexibility, and was cheaper than the big Tesla wall connector, much less two of them.

I routinely see efficiency between 96% to 99.4%. in the stats. Short 1% - 3% charges will often show 100%.

 

[father_of_6]

120V charging was OK since we didn't have a commute, but a quality 14-50 is superior.

I think I'm not going to do a 14-50 though, I'm going to do the wall connector.

Even more superior is the wall connector. It costs less to install and is safer, plus has the potential to provide 48 amps to cars that can take it.

The mobile connector with a NEMA 14-50 has a higher potential for safety issues plus caps out at 32 amps.

About the only time it makes sense to me to use a NEMA 14-50 is if you already have one, but even then the wall connector is an upgrade.

 

[johnny_cakes]

A few weeks ago I had the chance to charge with L1, L2, and Supercharger all in 1 week. These are the efficiencies as reported by Tessie:

 

[AlanSubie4Life]

Be careful about measuring efficiencies with TeslaFi & other apps. Read up on their FAQ about what this number means exactly.

Anyway, as is fairly evident, you need to look at energy added to the battery, and you need to look at energy from the wall.

To measure wall energy, you can get reasonably close by looking at the voltage displayed in the car for a given charging current (once the current ramps up - can't measure before!), and timing the charge carefully. That's for energy from the wall (and does not account for any wiring losses up to the car, of course). V*I*t. There's potentially substantial rounding error here (for 12A/120V you have to trust that it is not 11.5A or 12.5A - that the car is correctly limiting exactly to the set current), though, so an actual separate wall meter would possibly be more accurate).

For actual energy to the battery, without something like SMT, you first need to determine the energy per displayed rated mile for your vehicle (this is extremely easy to determine, as described elsewhere), and look at the delta for a given charging session. This will give you a good idea of actual usable energy added to the pack. The value in the car displayed on the screen for a charging session (in kWh when energy display is set to %) is not correct, as everyone knows (it's 4.7% too high (1/0.955)), in addition to having potential substantial rounding error (it's rounded to the nearest kWh so the error will be huge except for very long charge sessions).

Best case efficiency for 11.5kW charging is something around 91-92% I think, give or take a couple %. Haven't measured it for a while.

120V/12A is something around 80%, maybe a bit less depending on overhead (may depend on vehicle model year too).

These are just approximate. Have to measure for yourself.

 

[dakhlkt22]

12:01 AM - 4:33 AM 4 Hours 32 Minutes

10% 90% - 100%

USED 7.81 kWh ADDED 5.98 kWh

Efficiency 76.6%

AVG 115.3 V MAX 117 V AVG 15 A MAX 15 A

Only got 76.6% efficiency last night charging half the night to top off the battery.

Is an 8 hour charging night more efficient than a 4.5 hour charging session? Or is it the fact that my battery was almost full and you get lower efficiency near a full battery?

 

[davewill]

Only got 76.6% efficiency last night charging half the night to top off the battery.

Is an 8 hour charging night more efficient than a 4.5 hour charging session? Or is it the fact that my battery was almost full and you get lower efficiency near a full battery?

There's two issues that cause L1 efficiency to be lower than L2. One is that there is a fixed overhead (approx 3-400w) to run the car while charging. So, an 8hr charging session will be less efficient than a 4.5hr one that fills the battery by the same amount. If you're charging at 120V/12a (1440w) a significant percentage of your charging power is wasted on the overhead. Charging does slow down when the battery is almost full, but even at full L2 amperage, it doesn't slow down until the last few percent, so it's usually not a big factor, but since you charged from 90-100%, yes, it might explain part of the low efficiency you measured.

The second issue is that the conversion from 120V AC to battery voltage (400V DC) is less efficient than the conversion from 240V to battery voltage. I don't have a good feel for how much that accounts for.

 

[AlanSubie4Life]

Only got 76.6% efficiency last night charging half the night to top off the battery.

While this is around what I would expect for L1, I’d just measure it myself as described above. That way you don’t have to look at an app, and you don’t have it doing the work for you (never a good idea!). TeslaFi has some sort of pseudo-integration of the input voltage & current parameters - I think. No idea how reliable it is.

As mentioned, it is possible the very top part of the charge might be slightly less efficient (probably not for LFP vehicles which don’t seem to have much taper). Not really relevant most of the time, so a side issue.

 

[ucmndd]

As mentioned, it is possible the very top part of the charge might be slightly less efficient (probably not for LFP vehicles which don’t seem to have much taper). Not really relevant most of the time, so a side issue.

Recently switching from an old Model S to a new LFP Model 3, I’m amazed at the lack of taper. I haven’t been able to catch my Model 3 charging at anything less than 32 amps, even at 99% SoC.