Set battery limit to 60 kW

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bwilson4web

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#1
Hi,

The two-tier charge rates occur above and below 60 kW. By setting my Standard Range Plus Model 3 battery charge limit to 63%, 150 mi, any time I visit a SuperCharger, the car will be in the fastest and most affordable range. The results:
  • fastest charge rates
  • lowest costs
Charging sessions are in the 17-18 minutes, barely enough for a biology break. Of course for an first drive in the morning, go for 100% but for the rest of the trip, use the shorter limit and you'll make maximum block-to-block speed and lowest cost.

On the first SuperCharger session, monitor the rate of charge. When it reaches 60 kW, set the limit to what is shown and the problem is solved.

Bob Wilson
 

garsh

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#2
That doesn't seem right. Charging at 59kW at $x/kW is going to be almost as fast and about half the cost of charging at 61kW at 2 * $x/kW.
 

garsh

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#5
If possible, you want to only charge on the top half of each half...
I understand the idea behind this kind of statement, but I can't think of any way to mathematically state why this would be true or false.

The only guidelines that I can explain with any kind of rationale are:
  • Try to arrive at a supercharger with as low a SOC as you feel comfortable. This allows the car to charge more quickly.
  • Only charge long enough to make it to your next planned supercharger stop with low SOC.
This both minimizes your charging time and minimizes the price you pay at two-tier superchargers.

Even then, you can still argue over whether it's better to perform longer charging sessions at superchargers spaced farther apart, or if instead you should perform short charging sessions at superchargers that are closer to each other.

And the downside to the "arriving with low SOC" approach is if a supercharger happens to be offline/down/broken/occupied when you arrive. It's not like a gas station where you'll find another one on the other corner of the same intersection. So I don't blame people who choose to keep the battery at higher SOC for doing so.
 
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Ed Woodrick

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#6
If you care about costs, then a Supercharger isn't where you charge at.
It also doesn't factor in my time. While it minimizes the time at the Supercharger, there's the time to get to/from the Supercharger that needs to be factored in. 5 minutes out of the way is probably a decent number, so 10 minutes total.

My time is worth more than a few cents per hour.
 

bwilson4web

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#7
I first saw this effect during a 700 mi trip each way to Detroit and back. I was getting faster SuperCharger-to-SuperCharger speeds by charging to just what was needed and back on the road again. What I was looking for was a simple 'rule of thumb' that anyone could identify and apply:
  • set the battery charge limit to the 60 kW boundary
  • maximum charge at night before the first segment
The math model actually uses early principles taught in basic calculus, how to integrate the rate of charge over time with the rate of discharge at any speed. With a spreadsheet, one can model trips to maximize the speed and moderate the charging costs. But even a graph can be confusing if you don't know here it came from. So I've been looking for a simpler, rule of thumb.

That doesn't seem right. Charging at 59kW at $x/kW is going to be almost as fast and about half the cost of charging at 61kW at 2 * $x/kW.
At first blush, correct until we look at the whole charging charging curve:

At around 20-21 minutes, the rate of charge has fallen 'off the cliff'. Further time on the SuperCharger is significantly slower but meanwhile, the car is parked and not making progress.

An easy trick is to bring up a second, smaller window over the graph. You can use the top and left edge of the smaller window to read out either Y-axis and the time equivalent X-axis.

Bob Wilson
 

victor

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#8
At first blush, correct until we look at the whole charging charging curve:

At around 20-21 minutes, the rate of charge has fallen 'off the cliff'. Further time on the SuperCharger is significantly slower but meanwhile, the car is parked and not making progress.

An easy trick is to bring up a second, smaller window over the graph. You can use the top and left edge of the smaller window to read out either Y-axis and the time equivalent X-axis.

Bob Wilson
Why did you align 240 mi (red scale) against 120 kW (blue scale) and not against 80 kW or 105 kW or 240 kW?
It would draw a total different picture, you know.
 

garsh

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#9
What I was looking for was a simple 'rule of thumb' that anyone could identify and apply:
  • set the battery charge limit to the 60 kW boundary
That seems like an arbitrary point at which to stop charging. Wouldn't it make more sense to simply stop charging when the car has enough energy to make it to the next supercharger?

If you add the next supercharger as your destination in the car's navigation (and be sure to tell the car to "remove supercharging stops" along the way if it suggests any), the car will tell you how much battery it expects you to have when you arrive. It will start off as a negative amount, and once it goes positive (by some buffer that you're comfortable with), you can stop charging and continue on your way.
 

bwilson4web

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#10
If you care about costs, then a Supercharger isn't where you charge at.
I'm finding a SuperCharger is 2x to 3x cheaper and faster than a CHAdeMO. Using a maximum rated L2, I only get 31-32 miles of charge per hour. Just curious what alternative to the SuperCharger do you use on cross country trips?

It also doesn't factor in my time. While it minimizes the time at the Supercharger, there's the time to get to/from the Supercharger that needs to be factored in. 5 minutes out of the way is probably a decent number, so 10 minutes total.

My time is worth more than a few cents per hour.
Let me volunteer my recent trip between Huntsville and Ann Arbor using PlugShare:


START 100% (240 mi) FROM HOME
  • Nashville (skip) - arrive battery 139 mi (240 - 101 mi) SOC is too high to get maximum SuperCharger rate
  • Bowling Green (charge) - arrive battery 60 mi (240 - (101+78.5)) SOC is low enough to get maximum rate, charge to 143 mi, with 30 miles reserve, takes ~20 min. (see chart time from 80 mi to 143 mi)
SEGMENT BY SEGMENT
  • Louisville (charge) - arrive with 30 mi reserve; charge to 107+30 mi, takes ~18 min (chart time from 30 mi to 140 mi)
  • Cincinnati (charge) - arrive with 30 mi reserve; charge to 63+30 mi, takes ~13 min (chart time from 30 mi to 93 mi)
  • Dayton (charge) - arrive with 30 mi reserve; charge to 69+30 mi, takes ~13 min (chart time from 30 mi to 99 mi)
  • Lima (charge) - arrive with 30 mi reserve; charge to 88+30 mi, takes ~18 min (chart time from 30 mi to 118 mi)
  • Toledo (charge) - arrive with 30 mi reserve; charge to 82+30 mi, takes ~18 min (chart time from 30 mi to 112 mi)
TOTAL TRIP MILES AND TIME
  • ~704 miles
  • ~13:00 hrs total
    • 11:20 hh:mm - drive time
    • 01:40 hh:mm - charge time
  • 54 mph block-to-block time
So re-run the route using a speed higher than the 65 mph that PlugShare/Google uses for highway speed. My model verified by highway tests indicate cruising at 73 mph will give a block to block speed of 60 mph.

Bob Wilson
 

bwilson4web

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#11
Why did you align 240 mi (red scale) against 120 kW (blue scale) and not against 80 kW or 105 kW or 240 kW?
There are two lines in the graph and each has a different metric. So the blue line, the charge rate, uses the left Y-axis and the red line, the battery range in miles, uses the right Y-axis.
That seems like an arbitrary point at which to stop charging. Wouldn't it make more sense to simply stop charging when the car has enough energy to make it to the next supercharger?
Yes. So when I did my example trip to Ann Arbor, I used the expected charge times.
If you add the next supercharger as your destination in the car's navigation . . .
I do most of my trip planning at home to see the 'big picture.' This allows me to optimize meal breaks and as needed, meal or overnight stops. It also lets me investigate alternatives to "SuperCharger deserts."

Bob Wilson
 

victor

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#12
There are two lines in the graph and each has a different metric. So the blue line, the charge rate, uses the left Y-axis and the red line, the battery range in miles, uses the right Y-axis.
I understand that. And you didn't answer my question. What is a scientific or a non-scientific reason in you decision to align two graphs in such way? I'm asking this because you're trying to make some conclusions based on the point of crossing of these graphs.
 

bwilson4web

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#13
I understand that. And you didn't answer my question. What is a scientific or a non-scientific reason in you decision to align two graphs in such way? I'm asking this because you're trying to make some conclusions based on the point of crossing of these graphs.
Time is the common independent variable shared on the X-axis for both curves. All of us share this same variable ... time.

Bob Wilson
 

garsh

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#14
Time is the common independent variable shared on the X-axis for both curves. All of us share this same variable ... time.
But the Y-axis scales are arbitrarily matched. The crossing-point changes depending on the relative scales. Therefore, the crossing point has no significance.
 

bwilson4web

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#15
I agree that the crossing point has little to no significance. We have to draw horizontal lines to the curve of interest and down to the X-axis, Then we gain insights from the other curve.

Bob Wilson
 

Ed Woodrick

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#16
I'm finding a SuperCharger is 2x to 3x cheaper and faster than a CHAdeMO. Using a maximum rated L2, I only get 31-32 miles of charge per hour. Just curious what alternative to the SuperCharger do you use on cross country trips?
Bob Wilson
I didn't say cross-country trips, neither did you.
 

Ed Woodrick

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#17
Let me volunteer my recent trip between Huntsville and Ann Arbor using PlugShare:

  • ~704 miles
  • ~13:00 hrs total
    • 11:20 hh:mm - drive time
    • 01:40 hh:mm - charge time
  • 54 mph block-to-block time
Bob Wilson
Let me share a recent trip of mine, without the intimate details.

From Atlanta to Fort Lauderdale. App 500 miles. around 10 hours.

0 time spent charging.

Biology and food did require some stops though. But 0 minutes spent sitting at a charger.
 

Ed Woodrick

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#18
Bob, there's a large number of factors that you leave out that make a huge difference and invalidate your hypothesis.

First, you suggest that spending 17-18 minutes. You forgot to add the time from deceleration on the Interstate to back to speed. That number is often over 50% of your suggested time, meaning that the "Supercharger stop" took actually about 30 minutes. By increasing the time that you stay, you decrease the overhead of the stop.

You also seem to suggest that there's an option to choose when you stop. There simply often isn't. Remember, only a few months ago you were fretting about getting to Memphis. How many options did you have? Superchargers are often placed at about 100 mile distance, sometimes less, sometimes a lot more. Your only option is often can you skip one or not.

And no matter what your calculations, the generally acceptable number is around 80% to stop charging. That's the number that is generally accepted as taking too much time if you go beyond and losing too many miles if you go below. That's also combined with real world, including the time to get off and on the road.

Honestly, your calculation really seem to be based on the 60 kW cost factor. Your numbers suggest that for the first 17 minutes, that you fill the battery to about 50%....

Wait a sec, your numbers are inconsistent. You indicate 63% and 150 miles, but your chart shows 63% is about is about 25 minutes!
Just staying 10 more minutes gives you 192 miles at half the cost of the first 20 minutes.

What happens, as it becoming so familiar these days, that you have to charge at a shared pedestal and you are #2? And become #1 after 5 minutes or 15 minutes?

What happens if you find a V3 Supercharger?

What happens if you are in a long range car. Remember your title said 60 kW. (Which was an extremely misleading title, as that terminology is commonly used when charging at home, not Supercharger. Also, you would NEVER want to set your limit to this, as it would ALWAYS be advantageous to be charging while plugged into a Supercharger)
 

bwilson4web

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#19

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#20