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

[45thParallel]

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.

 

[gfunkdave]

No, you set the charging rate in the car itself. The wall connector should be configured in line with the circuit breaker it's connected to.

 

[45thParallel]

No, you set the charging rate in the car itself. The wall connector should be configured in line with the circuit breaker it's connected to.

Thanks very much. As long as I can set the charging rate from the car that is really good. My intent is to go for the 60 Amp breaker switch if possible based on capacity. I will know after the electrician's visit.

 

[gfunkdave]

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.

 

[45thParallel]

I agree, in the big scheme of things it is peanuts. I have nothing to do for 4 months while waiting!
I do a maximum of 500 miles/month on my current vehicle. To charge 500 miles it would cost me $11 at off peak rate, without having to sign up to any EV plans offered by my Electric Coop. One such "plan" offers unlimited charging for $50 per month! Nice business they have.
But I did find it interesting that above 40 Amps, the efficiency of charging goes down for the 240 volts supply.

 

[Stevedore]

When you install & commission the wall connector, you set the maximum charging rate according to the circuit it’s on. There’s nothing to stop you from setting it to a lower rate if you prefer, as far as I can tell.

 

[45thParallel]

I see. I have downloaded the installation manual. I will read through it. If it is easy to change, only then I will go for that option. Otherwise not worth it if I am locked into a permanent low charge rate that would need the electrician back to change it.

 

[ATPMSD]

I think your analysis, while interesting, is perhaps flawed as the kW and Miles Per Hour numbers on the table are rounded. Also, if we accept your data as is, the difference is negligible, but it takes longer to charge at 40-amps.

Example,
40-amps: adding 50 kWh at 3.77 miles per kW is 188.50 miles
60-amps: adding 50 kWh at 3.65 miles per kW is 182.50 miles, difference is just 6 miles

 

[TomServo]

As others said configure the Gen 3 Wall Charger to the BREAKER that protects the entire circuit, i.e. 50 amps. The car will do the rest and set the maximum charging rate based on that. Again a 50 amp break will charge at 40 amps. But you can always manually adjust the charging rate from the charging screen if you want or need to. But if your circuit and equipment are operating normally just let the car do all the work.

 

[45thParallel]

I think your analysis, while interesting, is perhaps flawed as the kW and Miles Per Hour numbers on the table are rounded. Also, if we accept your data as is, the difference is negligible, but it takes longer to charge at 40-amps.

Example,
40-amps: adding 50 kWh at 3.77 miles per kW is 188.50 miles
60-amps: adding 50 kWh at 3.65 miles per kW is 182.50 miles, difference is just 6 miles

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.

 

[ATPMSD]

I was referring to Tesla’s table, not yours. For example:

240v x 48a = 11.5 kW divided by 44 mph (M3) = 261 wH/mi
240v x 32a = 7.7 kW divided by 30 mph = 256 wH/mi

 

[45thParallel]

I was referring to Tesla’s table, not yours. For example:

240v x 48a = 11.5 kW divided by 44 mph (M3) = 261 wH/mi
240v x 32a = 7.7 kW divided by 30 mph = 256 wH/mi

Both your calculation and mine are correct. We are using a different model and a different metric. To explain further:
1. I calculated for Model Y, you are showing a calculation for Modely 3.
2. I used charging rate/power to indicate efficiency in mph/kwh. If you invert my data and multiply by 1000 W you will get the same metric but as you but for Model Y.
Makes sense?

 

[ATPMSD]

I appreciate the point you are trying to make but at least to me, the efficiency difference is minimal, as opposed to it taking 50% longer to charge, which is significant.

 

[MikeHolliday]

If you are using a 60 Amp circuit and 4 gauge wire (I used a 2 Conductor 4 gauge MC Cable with is MUCH easier to pull than Romex.) I don't think that the efficiency will go down. I have seen individuals using 6 gauge wire and over a long charging period get very warm on hot days. Any load 54 amps of greater require a 4 gauge wire. There is much less resistance and therefore much less warming of the wire. As a cable warms and resistance increases your efficiency will decrease.

 

[jm404]

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.

 

[MikeHolliday]

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.

Call either Loeb Electric or City Electric, they either have it in stock or can get it in one day...

 

[MikeHolliday]

Stop calling big box stores and call a local electrical supply house.
- City Electric Supply Midtown Atlanta
- Lade-Danler Lighting and Electrical Distribution
- etc.

Instead of trying to purchase THHN, just call a supply house, tell them that you want X number of feet 2 Conductor 4 gauge MC Cable. It will contain 2 Hots (L1 & L2 red and black conductors) and a ground. The Ground is not considered a conductor. If you are using a a Gen3 or other 240 volt wall adaptor you will not have a neutral (white) cable. They will have it in stock or can have it in a day or two...

If you need to also have a 120 volt line off of this circuit then you will need a neutral. If you need 120 volts on the circuit then you will need a 3 conductor cable (L1,L2, N). Each leg of a 240 volt circuit is 120 volts, but 240 volt circuit does not use a neutral. Any 120V or 120/240V equipment must be supplied with a neutral conductor. In a 240V-only circuit, there is no neutral, and the ground can be either insulated or uninsulated

​

 

[StkTNk]

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.

If it's a Gen3 charger, I guess you could provision it to think it's on a smaller circuit, and force it to charge at the rate you choose. Basically just lie to it, and make it think it can only do 7.7kW charging?

 

[MikeHolliday]

When you are setting up the Gen3 Wall Connector you actually tell it the size of the circuit breaker that is on the line. But why would you want to lower the output on a need installation. That essentially defeats the purpose of the Gen3 which is to have a faster charge speed than the Mobile Connector.

I love the MC cable for all above ground use if you are going below ground you cannot use THHN as it is not rated for below ground use. If the cable is going below ground use can use THWN Cable in a solid galvanized conduit.

And DO NOT use an SO or SJ Cable they are basically extension cord cables. They are used for power cables for appliances and tools, they are not oil, water or chemical resistant.

 

[StkTNk]

When you are setting up the Gen3 Wall Connector you actually tell it the size of the circuit breaker that is on the line. But why would you want to lower the output on a need installation. That essentially defeats the purpose of the Gen3 which is to have a faster charge speed than the Mobile Connector.

I just offered it as a practical solution for the "problem".
He seems more focused on system efficiency, not rate.

In all likelihood, the minimal thermal loss from the higher rate of charging would equate to fractions of cents, but I suppose system-efficiency is system-efficiency.