Graph of amperage draw over time for Model S and Tesla wall charger?

[Crager5]

I’m trying to find a graph of amperage draw over time for a 60 amp circuit breaker to the Tesla wall charger for the current Model S. I know there are a bunch of variables in play, but hoping to find something. An electrical engineer told me to run #4 gauge cable instead of #6, as it will pay for itself over time if and when running at high amperage draws.

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[JBee]

How long is your cable run? What Voltage?

 

[GnarlyDudeLive]

I would run 4 gauge anyhow in anticipation that one could be charging 2 vehicles at the same time in the future. Look at it this way, you wont be saying in the future I wish I ran 6 gauge instead, whereas the opposite is likely to be more true. Obviously if the expense is the issue then you are bound by that limitation.

 

[electricAK]

How is it saving money to run the 4AWG? Surely not the power lost in resistance.

I just ran the math based on the following assumptions:
- on an average day, you charge at 40amps for a half hour. (obviously there would be variation on this in real life, but average it over 365 days and maybe this is close enough)
- power costs $0.24/kWh
- your length of cable is 10ft from the breaker box to the wall charger (obviously you want this to be as short as possible)

P = I^2 * R, so at 40amps your 4AWG cable is losing 3.98W of power per 10ft length
while the 6AWG cable is losing 6.32W due to resistance. That's a difference of 2.34 W per 10ft of cable.

At $0.24/kWh and charging 30mins/day, you only save 10 cents per year by using the 4AWG cable.

You can modify the assumptions, but unless you're running a very long cable it's not going to change the result by much....and then you're paying way more for the cable anyway!

 

[Crager5]

38’ cable run, 60 amp breaker, 220-240 vAC

 

[Crager5]

Thanks electricAK

 

[Crissa]

It saves money to not have to do it again! Labor is expensive.

-Crissa

 

[Crager5]

After 3 electricians scheduled multiple visits and never show, I did it myself. Fortunately, I had good advice from Chris Wilson of C.M.Wilson, Inc out of western North Carolina. A father and son team that designs and installs solar/battery projects. thanks guys!

 

[SwampNut]

All of that is overkill unless you're running a taxi service. There is almost never a reason to home charge above 25 amps or so (about 6kW or enough to fill the car easily overnight). Your batteries will last longer being at a lower rate. If you live in a place with a demand charge, like we do, then you'll pay a "fine" for fast charging every month. All of this stuff about installing the fastest charger is a huge waste. Every charger I've helped install for my friends and their friends is a UMC connected to a 14-30 and #10 wire. The effective charge rate for a M3 is about 26 MPH. Who needs more than that at home? Even a person using one for a full time Uber service says she has at last 12 hours between being "on."

 

[Bill906]

All of that is overkill unless you're running a taxi service. There is almost never a reason to home charge above 25 amps or so (about 6kW or enough to fill the car easily overnight). Your batteries will last longer being at a lower rate. If you live in a place with a demand charge, like we do, then you'll pay a "fine" for fast charging every month. All of this stuff about installing the fastest charger is a huge waste. Every charger I've helped install for my friends and their friends is a UMC connected to a 14-30 and #10 wire. The effective charge rate for a M3 is about 26 MPH. Who needs more than that at home? Even a person using one for a full time Uber service says she has at last 12 hours between being "on."

What you say is true for existing cars (S3XY). But I suspect the CT tri-motor (and/or Quad motor) will have significantly larger batteries and guessing they will require significantly more watt*hrs per mile. If the effective charge rate for a Model 3 is 26MPH on a 30A charger, it will be less on the CT (maybe 13MPH? we don't know). And if the battery is larger than the Model 3 (300 mile battery vs 500 mile), there will be more "miles" to charge.

I plan on driving my CT to my parents house 290 miles away. I plan on getting the 500 mile tri-motor. Now, I don't drive slow or efficiently and many trips will be in winter with snow covered roads and the heater on high. So that 500 mile will probably be closer to 300 miles on bad drives. I expect to make the trip without stopping to charge. When I get there I'll most likely have a pretty low battery. I asked my dad to install a 50A (~11kW) outlet for me. I suspect an 8 hour overnight charge will not bring me up to 80% with either 30A or 50A plug, but 50A will bring it closer. At least the first few trips I expect to be driving the CT a lot when I go there. It will be quite the bummer if I'm trying to show it off to my friends and family there and have to stop to charge. So that's my plan A. If it ends up not working, my plan B is, there's a super charger in route to my parents house about 60 miles before I get there. I may have to do a 10 or 15 minute stop just to give myself some buffer.

Also, I don't think charging at 11kW is significantly different than charging at 6kW as far as battery life is concerned. It's the superchargers charging at 150kW, 250kW (someday higher ?) that may have significant effect on the battery life.

 

[Crissa]

Your batteries will last longer being at a lower rate.

While you are quite correct that very few need a quick turn-around time at home, there is no evidence that charging slower (aside for avoiding frequent high-heat situation Supercharging) will extend the battery life. Tesla has active cooling for the battery and even so, this level of charging is very small compared to pack size. Also, a Tesla will choose when to charge based upon your set leaving time and the station available current, so won't leave it sitting at full charge unnecessarily.

-Crissa

 

[SwampNut]

There is no evidence that it WON'T affect a Tesla, as it affects every other battery. Temperature is only one factor, and cooling is a complex situation that still creates heat disparities inside each cell. We know for sure that charge rate affects all non-Tesla batteries.

Nearly nobody needs faster than 20-30A charging, and only bad can come of it, not good.

 

[Crissa]

There is no evidence that it WON'T affect a Tesla, as it affects every other battery.

No, there is no evidence that it does at these power levels.

Remember, charging is relative to the kWh of the total pack it is spread across.

11kW is 150% of my battery pack but it's only 15% of a Model 3. Charging a Model 3 at 11kW is like charging my battery at 70% my Level 1 charger puts out.

-Crissa

 

[SwampNut]

What's the advantage of spending more to charge faster?

I just spent the morning reading Panasonic data sheets in order to reprogram one of our bikes. Stupid me changed the battery manager parameters accidentally. I'm quite aware that at ALL measurable levels, those batteries are affected by charge rate. Even just going from .1 amp to .3 amp per cell. I have no evidence that Tesla's are not.

 

[Crissa]

What size cells do you have?

A 2170 stores from 3.5-5 amp-hours in a cell. Going from 0.1 to 0.3 would be changing charge time from (at best) 35 hours to 10 hours. Which is, well, a massive change, but also... Really a huge amount of time to dissipate the heat from it. 0.1 amps at wall current is the same as a 100-watt bulb. That's alot of potential heat.

It really does matter the size of the entire battery pack and the ambient temperature and its ability to actively cool or heat the pack. And any active temperature control is coming from the power supplied, so you have to subtract it off the amount the EVSE supplies.

Having a more capable station means:

• Being able to charge better during inclement weather.
• Being able to charge at all when it's too cold or too hot for the battery.
• Being able to charge during the limited low-price hours.
• Being able to charge from solar in the limited time panels are active.
• Being able to charge more than one vehicle.
• Being able to have a quicker turn-around time.
• Lowering the total time the pack spends at the highest charging states.

-Crissa

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