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

I fully agree... I am of the old school, KISS (Keep It Simple Stupid). Most of the big box stores know less about the cable you are buying than you know. Also, there is no reason that the car should be more or less efficient at different charge rates as long as the Cable & Circuit were designed to handle the load. I can see if you had an undersized cable and attempted to draw a heavier load than the cable could carry that you might into an efficiency issue.
 
I fully agree... I am of the old school, KISS (Keep It Simple Stupid). Most of the big box stores know less about the cable you are buying than you know. Also, there is no reason that the car should be more or less efficient at different charge rates as long as the Cable & Circuit were designed to handle the load. I can see if you had an undersized cable and attempted to draw a heavier load than the cable could carry that you might into an efficiency issue.
The resistive capacity of the various gauges and carrying-ampacity of systems would cause variations in the efficiency of the charger as a system, but in such a small amount it's hardly worth doing the math.
I'd just go with the manufacturer specs for cable/breaker and let the cars battery management system do the heavy lifting on the decision-making for charge rate.
 

MachAF

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Feb 3, 2020
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Lord. 50A vs 60A?

I'm still spinning around trying to decide the best path. FYI 4/3 romex is very hard to find. An electrical supply shop can get it in 5-6 days "maybe no promises". However, they have the choice of "SO" or "SJ". Apparently SO is 600v, SJ 300v and easier to pull? So I'm assuming SJ is fine

All 3 Home Depots near me are basically out of THHN.

My install is fairly frustrating and I don't want to have to upgrade down the road, so I want to run a 60 amp circuit rather than cave for a 50A, but really, I'm almost at the point of just running two runs of 6/3 rather than jump through the hoops of tracking down 4/3.
SO and SJ cable? For what?...and two runs of 6/3 vs one run of 4/3? What are you trying to do? You don't need a */3 cable, what you going to do with the neutral wire?

You'll quickly realize 40 or 48 amp charge rate isn't as big of deal everyone makes it out to be.

The different between charing at 40amps (50amp breaker) and 48 amps (60 breaker) are very minimal. You won't be charging your car 0%-100% every day. At most you'll charge it 50%-90% ( depending on your commute of course). That will only take a few hours.

Does it really matter if you charge up in 2:05 vs 2:00?
 
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drtimhill

Active Member
Apr 25, 2019
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Seattle
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.
Generally you set the wall connector to 80% of the circuit capacity (max safe charing rate) and then choose your rate in the car. As for efficiency, since the car takes a fixed amount to drive the various systems while charging the rule of thumb is to use higher current (power), since this minimizes the effect of this fixed overhead (and is part of the reason 120V charging is so slow).

And unless you have very unusual driving patterns, any 240V charging rate will get you fully charged overnight, so that really isnt a concern.
 
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jm404

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May 27, 2021
199
404
Atlanta
SO and SJ cable? For what?...and two runs of 6/3 vs one run of 4/3? What are you trying to do? You don't need a */3 cable, what you going to do with the neutral wire?

You'll quickly realize 40 or 48 amp charge rate isn't as big of deal everyone makes it out to be.

The different between charing at 40amps (50amp breaker) and 48 amps (60 breaker) are very minimal. You won't be charging your car 0%-100% every day. At most you'll charge it 50%-90% ( depending on your commute of course). That will only take a few hours.

Does it really matter if you charge up in 2:05 vs 2:00?

I want /3 in case I ever need to change to a 240v outlet if I end up with a non tesla. I'm considering two runs of 6/3 because it's a PITA to run the cabling, and if my wife gets an EV I don't want to have to go through it all again
 
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
I hope that you are not doing your calculations based on the breaker size the breaker size has no effect on the amount of power used. If I have a 15 Amp 120 volt circuit and run a 50 watt light bulb or a 100 watt light bulb there is a great deal of difference in the power consumed. Remember that when using a Continuous Load (That is a device that is anticipated to pull a load 3 hours or longer) that a 120 volt 15 Amp Circuit can only draw 12 Amps or 1,440 watts, a 120 volt 20 Amp circuit can only draw 16 Amps or 1,920 watts, a 240 volt 30 Amp circuit can only draw 24 Amps or 5,760 watts, a 240 volt 40 Amp circuit can only draw 32 Amps or 7,680 watts, a 240 volt 50 Amp circuit can only draw 40 Amps or 9,600 watts and a 60 Amp circuit can only draw 48 Amps or 11,520 watts... You should do your calculations based on the actual load on the circuit and Watts/Mile of range calculations. When you calculate the kilowatts burned/Mile of Range the 60 Amp circuit is by far the most efficient charge rate which must be credited to the efficiency of the on-board charger.
 
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MachAF

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Feb 3, 2020
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I want /3 in case I ever need to change to a 240v outlet if I end up with a non tesla. I'm considering two runs of 6/3 because it's a PITA to run the cabling, and if my wife gets an EV I don't want to have to go through it all again
Pretty much every charger is able to be hardwired. Unless you need the outlet for another purpose such as RV or welding, hard wiring is the way to go. Wiring a outlet has more complications such as its required to be on a GFCI breaker (depending on your local code of course).
 
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MachAF

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Feb 3, 2020
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First, Tesla tell you right in the instruction NOT to use a GFCI Circuit. Secondly, I always use a 4 gauge MC cable due to the Continuous Load. I have already seen issues with wiring at some locations.
Correct. But current code IF wiring an OUTLET a GFCI breaker is required if you want to pass inspection. Just trying to say hardwiring is the way to go.
 
Why? 4/3 NM-B is $12 a foot and it good for 70 amps. 6/3 MC is $5 a foot and good for 75 amps.
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.
 
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Rocky_H

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Feb 19, 2015
7,340
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Boise, ID
I want /3 in case I ever need to change to a 240v outlet if I end up with a non tesla.
That does not yield that conclusion. 240V outlets still don't need that third wire. That is what the 6-XX series of outlets are, like 6-20, 6-30, 6-50. (And you can easily find plenty of generic J1772 charging stations that could plug into a 6-50 outlet.) They are just Hot1, Hot2, and ground and are 240V only. You would only need the /3 with the neutral if you insist you need to have a dual voltage outlet that can support both 120V and 240V, like the 14-30 or 14-50. But I wouldn't go to that trouble just for someone else's future flexibility. Just consider it a car charging circuit, and it will just never have a reason to have the extra neutral wire.
 
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Correct. But current code IF wiring an OUTLET a GFCI breaker is required if you want to pass inspection. Just trying to say hardwiring is the way to go.

That does not yield that conclusion. 240V outlets still don't need that third wire. That is what the 6-XX series of outlets are, like 6-20, 6-30, 6-50. They are just Hot1, Hot2, and ground and are 240V only. You would only need the /3 with the neutral if you insist you need to have a dual voltage outlet that can support both 120V and 240V, like the 14-30 or 14-50. But I wouldn't go to that trouble just for someone else's future flexibility. Just consider it a car charging circuit, and it will just never have a reason to have the extra neutral wire.
The only reason that Ovens etc. have the Neutral is for the Clock, Timing Circuits, etc... that will use 1 leg of the 240 and the Neutral for 120 volts.
 
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jm404

Member
May 27, 2021
199
404
Atlanta
That does not yield that conclusion. 240V outlets still don't need that third wire. That is what the 6-XX series of outlets are, like 6-20, 6-30, 6-50. (And you can easily find plenty of generic J1772 charging stations that could plug into a 6-50 outlet.) They are just Hot1, Hot2, and ground and are 240V only. You would only need the /3 with the neutral if you insist you need to have a dual voltage outlet that can support both 120V and 240V, like the 14-30 or 14-50. But I wouldn't go to that trouble just for someone else's future flexibility. Just consider it a car charging circuit, and it will just never have a reason to have the extra neutral wire.

Over my life I've learned it's better to spend an extra couple bucks, buy once cry once sort of thing. Also if I wanted to use it as a sub panel for generator, who knows. Very very minimal cost for 4/3 over 4/2
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,340
9,042
Boise, ID
Over my life I've learned it's better to spend an extra couple bucks, buy once cry once sort of thing. Also if I wanted to use it as a sub panel for generator, who knows. Very very minimal cost for 4/3 over 4/2
OK, maximum flexibility of use is a good reason. I just didn't want that sitting out there for someone to read later, and think having a 240V outlet means it needs to have a neutral wire.
 
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As others have said, you can "lie" to the WC during commissioning and tell it that it's connected to a smaller breaker, but your savings will most likely be minimal. I'd argue there could be other benefits of running less current through the system (less waste heat, lower peak draw for the house), but again, assuming everything is built to code, these benefits are minimal as well.

If lowering the current still makes sense, I'd recommend that you lower the setting in the car, not the wall connector. That way, you can charge more efficiently when you know you'll be plugged in long enough to get a full charge - even at a 32A draw, which is the most efficient setting your graph shows*, you'll get 200 miles or more on an overnight charge. But if you find the need to charge faster than that at any point, you can always adjust it back up in the car's settings without having to reset your WC.

* Actual amperage drawn is always 80% of breaker rating, so a 40A breaker x .8 = 32A. The actual draw, not the breaker capacity, is what shows up in the car's charging UI.
 
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jm404

Member
May 27, 2021
199
404
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.

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
 

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