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Can we manually set the charging speed to a lower rate in a Tesla Wall Connector?

thecavalry

Member
Aug 27, 2021
195
250
Utah
I found 4/3 MC locally. Holy crap it's huge. 1" actual diameter. The electrical shop didn't have the correct connectors. All of the metal boxes only have 3/4" knockouts. I need to find a connector that has a 3/4" threaded side that will accept 1" MC
Get a step bit and make a bigger hole, then use the correct size fitting for 1”.
 
The calculations are not rounded, only the data on the chart was shown rounded to 2 decimal places. Not sure one would call rounding to 2 decimal places as flawed. Anyway here is a snap shot rounded to 5 decimal places instead of 2 decimal places if that makes better sense to you. Regardless the conclusions remain the same on the efficiency of charging at various Kwh rate as determined by the Circuit breaker current rating.


View attachment 711041
Here is what I came up with using Tesla's Published Charge Rate for the Model Y and the second charge rate shows what would happen if you adjusted 3 of the numbers down to account for Tesla's rounding of the Charge Rates. I find it very interesting that based on Tesla's numbers 3 of the Amperage draws produce the exact Miles Gained/KWh Used and in the second chart it shows that if 3 of the numbers are adjusted to account for Tesla's possible rounding. every scenario then uses exactly to a hundredth of a KW burned to yield the same Mileage Gained.
Model Y Using Tesla Gen3 Wall Connector with Published Miles per Hour Charge Rate
Current DrawKWh Drawn/HourMiles Gained/hr.KWh burned/Mile of Charge
48 Amps1.152420.27428
40 Amps0.960360.26667
32 Amps0.768290.26489
24 Amps0.576210.27428
16 Amps0.384140.27428
12 Amps0.288100.288
Model Y Kilowatts Used, but Changing Published Charge Rates Down by 0.5 Miles of Range
48 Amps1.152420.27428
40 Amps0.960350.27428
32 Amps0.768280.27428
24 Amps0.576210.27428
16 Amps0.384140.27428
12 Amps0.28810.50.27428
Only the following were adjusted by a 1 Mile Range 12 Amps, 32 Amps, 40 Amps. To account for possible rounding of the Charge Rate by Tesla.
The Range was arrived at by simply dividing the Watts (Kilowatts multiplied by one thousand) used by the Miles Gained
 

45thParallel

Member
Sep 5, 2021
570
534
Minnesota
Here is what I came up with using Tesla's Published Charge Rate for the Model Y and the second charge rate shows what would happen if you adjusted 3 of the numbers down to account for Tesla's rounding of the Charge Rates. I find it very interesting that based on Tesla's numbers 3 of the Amperage draws produce the exact Miles Gained/KWh Used and in the second chart it shows that if 3 of the numbers are adjusted to account for Tesla's possible rounding. every scenario then uses exactly to a hundredth of a KW burned to yield the same Mileage Gained.
Model Y Using Tesla Gen3 Wall Connector with Published Miles per Hour Charge Rate
Current DrawKWh Drawn/HourMiles Gained/hr.KWh burned/Mile of Charge
48 Amps1.152420.27428
40 Amps0.960360.26667
32 Amps0.768290.26489
24 Amps0.576210.27428
16 Amps0.384140.27428
12 Amps0.288100.288
Model Y Kilowatts Used, but Changing Published Charge Rates Down by 0.5 Miles of Range
48 Amps1.152420.27428
40 Amps0.960350.27428
32 Amps0.768280.27428
24 Amps0.576210.27428
16 Amps0.384140.27428
12 Amps0.28810.50.27428
Only the following were adjusted by a 1 Mile Range 12 Amps, 32 Amps, 40 Amps. To account for possible rounding of the Charge Rate by Tesla.
The Range was arrived at by simply dividing the Watts (Kilowatts multiplied by one thousand) used by the Miles Gained
your calculations are in line with my finding the most efficient charging is at 40 Amp circuit breaker, then 50 Amp, followed by 20/30 and then 60 Amp. But the cost of charging at home is low, so it is not going to make a significant impact. I am expecting my Tesla next month and I do plan to test this out for a month each and check the power consumption. More of a curiosity than anything.
 
I think that you are missing my point. Look at the second chart. I find it literally impossible that I can change 3 of the charge rates by either .5 or 1 mile difference and they all end up having the exact wattage consumption. I think that if you look at Tesla's exact numbers you will find that they all have the exact efficiency.
 

MachAF

Member
Feb 3, 2020
32
20
CZI
your calculations are in line with my finding the most efficient charging is at 40 Amp circuit breaker, then 50 Amp, followed by 20/30 and then 60 Amp. But the cost of charging at home is low, so it is not going to make a significant impact. I am expecting my Tesla next month and I do plan to test this out for a month each and check the power consumption. More of a curiosity than anything.
I don't think you have type of equipment/controlled environment required to calculate the minuscule difference (a few watts maybe?)
 
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I just used Tesla’s published data. I am sure they would be averages and not exact numbers. but they are a good basis for comparison.
So, if you looked at Tesla's numbers, then your errors are caused by you using the breaker size and not the true amperage draw. Ohm's Law = Voltage X Amperage = Watts, 1,000 Watts=1 Kilowatt. If you follow my numbers you will see how the much more accurate, because they are usi g the wattage (or Kilowatts) that you are actually using and paying for in this situation.
 

jm404

Member
May 27, 2021
181
391
Atlanta
You can buy 4/3 MC Cable for about $6.25/ft. at Wire and Cable Your Way -- 4/3 MC Cable w/ Ground

I have been buying 95% of my cable here for the last 10 years. They have great service...

Hard wiring is the only way to go. NEMA 14-50 outlets are not designed to be Plugged and Unplugged on a regular basis. They will fail.

Just going to tack on here for anyone reading this in the future. MC is heavy and difficult to work with. I had a 60 foot run, the beginning of which was fairly complicated (I had to start at the panel since I wanted to use every inch of cable available). This meant the first part of the run, in my basement over ductwork and plumbing, required moving the entire 60' roll. The further I got the less cable and it was easier. In hindsight I probably would've looked into EMT or some other conduit, where I could hang the relatively lightweight conduit then run XHHW or THHN through it.

Also terminating the 4/3 in a box was something else... it's shocking how difficult this stuff is to work with compared to 12/2 or even 10/2

And finally, my plan was to run MC in the garage all the way to the charger. It's XHHW so wet rated. But I'm going to go ahead and run EMT so I can get it tucked tight into the corners
 

MachAF

Member
Feb 3, 2020
32
20
CZI
Just going to tack on here for anyone reading this in the future. MC is heavy and difficult to work with. I had a 60 foot run, the beginning of which was fairly complicated (I had to start at the panel since I wanted to use every inch of cable available). This meant the first part of the run, in my basement over ductwork and plumbing, required moving the entire 60' roll. The further I got the less cable and it was easier. In hindsight I probably would've looked into EMT or some other conduit, where I could hang the relatively lightweight conduit then run XHHW or THHN through it.

Also terminating the 4/3 in a box was something else... it's shocking how difficult this stuff is to work with compared to 12/2 or even 10/2

And finally, my plan was to run MC in the garage all the way to the charger. It's XHHW so wet rated. But I'm going to go ahead and run EMT so I can get it tucked tight into the corners
Exactly why certain folks here recommended 6/2 MC....
 
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Though to be clear, you don't need to set the charging rate. The car will talk to whatever you plug into it and determine the max power it can draw, and will draw up to that, varying as it charges, to balance charge rate, battery life, battery condition, etc.

Honestly I wouldn't worry about trying to eke out the maximum charging efficiency (unless you like that sort of thing). Just plug the car in when it's parked in the garage and enjoy the new car.
If the charging rate in amps doesn't matter, why did Tesla put in the ability to change the charging rate in the app?
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,271
8,957
Boise, ID
@SteveF-M3LR I will get to your question in a second, but first, I have to address this.
As far as I know, the Charge Rate was put into the Appp, because when you use a non-Tesla destination charger you need to be able adjustbthe charge rate seeing that the car cannot talk to a non-Tesla Wall Connector...
No. Tesla can communicate the J1772 signaling language just fine. The J1772 stations signal the maximum amount of amps, and the car understands and sets its maximum for that, and it works perfectly, with no user interaction needed.
OK, now back to our regularly scheduled program.
If the charging rate in amps doesn't matter, why did Tesla put in the ability to change the charging rate in the app?
Two things, why did they put it in the app, specifically? Because a bunch of Tesla owners whined about having to go to the car to change it on the touch screen.
But I think you're asking why is this ability to change the amps even there at all. There can be a few reasons for this, but mainly if people need to do something a bit non-standard. Here are a few examples:

1. Some people want to use energy that is coming in directly from their solar panel generation, and their solar panel system may not be generating at a high enough level to keep 40 or 48A continuous to the car, so they will turn it down to some lower level that the solar will be able to provide.

2. If you are charging at a campground site, sometimes the wiring and outlets in those can be pretty old and crummy or the wire runs really long, so pulling the full amp level trips the breaker frequently or causes the voltage to sag too much. So dialing the amps down some will sometimes enable it to keep charging.

3. If you are having to use some long wiring or extension cords. I have done this one. I was traveling several years ago before the city had a Supercharger or much else public charging infrastructure. So I was running a 30 foot extension cord up their driveway and in the side kitchen door and down the steps to the basement to plug into a dryer outlet. With those extra connections and distance, I didn't want to press my luck running it at the most it could go, so I turned it down a few amps.

4. If you are crossing from one Tesla adapter plug to another third party adapter cord that is for a different number of amps. The Tesla adapter you put into the charging cable has a chip that signals what number of amps it should use. That's all fine if you are using the correct plug type for the outlet. But some years ago, Tesla used to have a very small selection of plug types available. So we had to do some hokey stuff, like using the Tesla 14-50 and then using a little 1 foot cord to adapt it to a 14-30 for a dryer plug. The car can't see that it's only a 30A outlet, since it has the Tesla plug for a 50A outlet, so it can draw too much if you don't manually turn it down.

So that feature of letting people turn the amps down is an important option to have available, but if you are doing very standard things like using the proper plug type or an official charging station, you shouldn't need to adjust that.
 
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MY-user

MYLR, 5s, OD9/10, received on Nov. 29.
Sep 15, 2021
321
223
Colorado
I did a quick analysis to see the efficiency of the Tesla wall connector at various charging speeds. It seems most efficient charging happens when you have a circuit breaker at 40 Amps (drawing 7.7 KW output) followed by at 50 Amps (drawing 9.6 KW). So my question is can a Tesla Wall Charger drawing current from a 60 Amp breaker switch be set to run at 7.7 KWH power rate? Or does the system go for the maximum power rate of 11.1 KW which is the second lowest efficiency in terms of bang for your buck. I have ordered a wall charger and a Model YLR so my apologies if the question is stupid. I have attached a graph showing the efficiency at various power levels. Thanks.

I have a NEMA outlet that can charge at 240V 32Amp. I intentionally set 20 amps for slower charging. Why? Let's say it takes 4 hrs to reach the limit. If, for some reason I need to leave home an hour earlier I'm going to be 3/4 way to the limit.
By the way, faster charging might degrade the battery faster. I wonder if it's significant enough to take into account.
 
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drtimhill

Active Member
Apr 25, 2019
2,357
3,073
Seattle
I have a NEMA outlet that can charge at 240V 32Amp. I intentionally set 20 amps for slower charging. Why? Let's say it takes 4 hrs to reach the limit. If, for some reason I need to leave home an hour earlier I'm going to be 3/4 way to the limit.
By the way, faster charging might degrade the battery faster. I wonder if it's significant enough to take into account.
Considering the battery can take 150kW or more when supercharging, the difference between the various L2 rates from a degradation standpoint is almost certainly negligible.
 

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