Charging SR+ Model 3

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bwilson4web

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Huntsville, AL
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#1
On recent +700 mi trips from Huntsville AL to Coffeyville KS and later Huntsville to Richardson TX (aka., Dallas,) I got a lot of cross country charging experience and began to wonder about charging strategies. For example, which makes more sense:
  • $0.26/min - tier 2 above 60 kw, short and fast for shortest range
  • $0.13/min - tier 1 below 60 kw, long and slower for maximum range
Tier 2 is the most expensive per minute but also adds miles the fastest. But to use it, the battery has to be run down to a minimum reserve battery range, 0-30 miles. "Tickling the dragon," this requires close monitoring and adjusting speed, usually downward, to reach the next SuperCharger. But what happens in tier 1 charging?

This is what my earliest SuperCharger session looked like:


So I blew up the tier 2 session to get:

The initial charging is slow, probably to measure the battery state. Then it reaches a peak of 101 kW. I then digitized the profile to make this table:
Code:
min    kW    kWh    total kWh    $/kWh    Total $
1      65    1.08    1.08        $0.24    $0.26
2      73    1.22    2.30        $0.21    $0.52
3      80    1.33    3.63        $0.20    $0.78
4      90    1.50    5.13        $0.17    $1.04
5      97    1.62    6.75        $0.16    $1.30
6     101    1.68    8.43        $0.15    $1.56
6     101    1.68    10.12       $0.15    $1.82
7     101    1.68    11.80       $0.15    $2.08
8     101    1.68    13.48       $0.15    $2.34
9     101    1.68    15.17       $0.15    $2.60
10    101    1.68    16.85       $0.15    $2.86
11    101    1.68    18.53       $0.15    $3.12
12    101    1.68    20.22       $0.15    $3.38
13    101    1.68    21.90       $0.15    $3.64
14     94    1.57    23.47       $0.17    $3.90
15     75    1.25    24.72       $0.21    $4.16
16     54    0.90    25.62       $0.29    $4.42
Domestic charge rates in Huntsville are $0.11/kWh so the peak charging rate on the road is just 50% higher and quite affordable. So here are the actual SuperCharger costs on the Huntsville to Richardson and back trip:
Code:
date time    Tier 2    Tier 1    mi (PS)    location
05/18 15:30       0    0           0        Huntsville AL
05/18 19:30      16    50        206        Memphis TN (1)
05/19 01:12      16    23        163        Little Rock AR
05/19 04:30      14    20        133        Texarkana TX
05/19 06:50       6    19         98        Sulphur Springs TX (2)
05/19 10:00                       81        LaQuinta
05/19 17:22      12    99                   Plano TX (3)
05/21 13:13       4    16        101        Lindale TX
05/21 16:00       0     0        103        Shreveport LA (4)
05/21 17:59       6    34        104        Monroe LA
05/22 00:38      12    17                   Pearl MS (5)
05/22 09:36      12     7        118        Pearl MS
05/22 11:41      13     11        91        Meridian MS
05/22 18:16      16     8        144        Birmingham AL (6)
05/22 20:50                      106        Huntsville AL
  1. Huntsville-to-Memphis exceeds the 80% range, 192 mi. This suggests the longest segments should start with a non-SuperCharger charge session using a distribution, J1772, or NEMA 14-50 EVSE overnight.
  2. Sulphur Springs was more of a biology break to get out of reserve range management. The rest of the trip was normal car behavior.
  3. The distribution and J1772 ESVEs at the hotel/motel were powered off and this was Sunday. We weren't sure we'd get them turned on Monday so I drove downtown to use the Plano SuperCharger. Sunday afternoon it was very busy and I picked up a quick charge but by 7PM it was all but empty and there were restaurants calling my name. Open question, if you use the phone app to stop charging before reaching the car, do you still get idle or other tier 1 charges?
  4. Shreveport never charged for our session ... Thanks TESLA.
  5. We stopped at Vicksburg and put the portable kennel up on a nearby RV park but we didn't have the right electrical plug for 30A service. Using 12A, 120VAC it was obvious we were losing charge and it wasn't clear we'd have enough to reach Perl MS the next morning. So I took a midnight trip to Perl to put on a strong charge, 144 mi battery range at the RV park and left the kennel in operation. I visited the casino and left with an extra $79 and took at nap in the room. With unusual speed, my wife got ready quickly to see her dogs and we were on the road by 8AM.
  6. We didn't realize how bad the I-20 backup would be so we took a detour and in the heat, AC was necessary. Then about 20 miles beyond the construction, another backup as a truck had rolled off the road and a fire truck was blocking lanes. Autopilot worked great and someone in a tall work truck rolled down their window to ask if I was driving without using my hands . . . he was impressed. We barely found the Birmingham SuperChargers which due to construction was accessible by only one road. The battery was so low we initially lost AC. Once we had enough to reach home, we were off. I used the map to take short-cuts in Birmingham and Huntsville.
LESSONS LEARNED

First segment should be from a non-SuperCharger source, a hotel/motel or RV park, where a full charge can be put on the car. This avoids the 80% SuperCharger range limit.

Always leave with a 30 mi reserve range to the next SuperCharger but have handy the PlugShare map of RV parks, J1772, and distribution chargers along the route. If the reserve range reaches 10 mi, divert to these alternate charging sources.

If using an RV park, make sure you have a set of 30A plugs and/or adapters. There are different styles.

Bob Wilson
 
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bwilson4web

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#2
Hi,

We're still keeping our 2014 BMW i3-REx as backup for our 2019 Tesla Model 3 but after some cross country trips, +700 mi each way, we have a better idea of the relative EV costs:
  • 60-101 kW -> $0.26/min Model 3
  • 15-60 kW -> $0.13/min Model 3
  • 0-50 kW -> $0.30/min BMW i3-REx
The Model 3 supports twice the maximum charge, 101 kW, rate on a SuperCharger as the BMW i3-REx at 50 kW. The SuperCharger cost $0.26/min at 60-100 kW versus $0.30 flat rate at an Electrify America charger.

At 15-60 kW, the SuperCharger rate falls to $0.13/minute. Meanwhile, the BMW is still paying $0.30/min and it can only charge at 0-50 kW. EVgo is even more expensive than Electrify America, $0.35/min.

In summary, the BMW i3-REx charges at half the rate of the Model 3 yet at any rate, pays a high cost per minute. Neither Electrify America nor EVgo have charge-rate pricing so the slower, taper charge costs as much as the initial, high-rate charge.

Bob Wilson
 

Frully

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#3
Sanity check- is that an SR model 3?

unless you're referring to average charge rate from empty to full...Model 3 LR can supercharge realistically at 150kw, and soon to be 250kw depending on the site...giving 5x the charge rate of the i3

I also wonder if they're going to change the pricing model for 'over 60kw', perhaps moving to a 3 tier system.

I really wish the 'energy retailer' regulations weren't in place so Tesla could just charge by kWh instead of 'time for a charging service' to skirt the rules. 75kWh battery, 95% efficiency, uses 80kWh...costs between 8-20 dollars depending on the local electricity rate. The math is much simpler that way.
 

Frully

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#5
I've thought about this a bit but never done the math - specifically working the calculus backwards to sum under the curve. Since it's nonlinear the intuitive answer might not be immediately obvious: Try to use supercharging in the top half of each tier...in my case only use T2 from 90-120kw and only use T1 from 30-59kw to get the highest bang for buck...likewise minimize time in the low end of each tier unless absolutely necessary.

My last intuition is that supercharger start charging slowly dependent on whether they have battery storage on site. Our local supercharger, Rockyview/Calgary I think doesn't. Seems to always tick up from 0>150kw in 1-3kw/second increments. I suspect this is to prevent hitting the grid with a fractional megawatt-class load too abruptly, which I'm confident would surely piss off the local utility providers.
 

Larry M

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#6
Hi, I'm new to the forum and was hoping someone could help me with a question I have about charging. Hope I'm not getting too far off subject. I recently test drove a Model 3 and the salesperson sent me a link to the supercharging site. You can enter a trip and get a route to your destination showing where to stop for charging along the way. I entered the model 3 extended range and the trip distance is 659 miles, from Tampa FL to Kinston NC. Almost the entire trip is on I95. The app has me stopping 5 times for charging with a total charging time of 2 hours and 25 minutes and a gas savings of $12.00. The car has a range of 310 miles and the trip is 659 miles. I would think that stopping no more then 3 times for charging would be the recommendation, not 5 times. I checked, and the supercharging stations are approximately 100 miles apart. It just doesn't add up. Am I missing something here? Plus, a savings of $12.00 compared to using a gas vehicle. Not exactly what I would expect. I entered the trip and vehicle information several times but keep getting the same results. I really want to move ahead with this purchase but these numbers are very concerning.
 

bwilson4web

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#7
. . . I recently test drove a Model 3 and the salesperson sent me a link to the supercharging site. You can enter a trip and get a route to your destination showing where to stop for charging along the way. I entered the model 3 extended range and the trip distance is 659 miles, from Tampa FL to Kinston NC.
I'm partial to www.plugshare.com because it allows me to see any mix of charging stations and alternates. It has a good trip planner so this is what I got:
fl_nc-jpg.26469


. . . Almost the entire trip is on I95. The app has me stopping 5 times for charging with a total charging time of 2 hours and 25 minutes and a gas savings of $12.00. The car has a range of 310 miles and the trip is 659 miles. I would think that stopping no more then 3 times for charging would be the recommendation, not 5 times. I checked, and the supercharging stations are approximately 100 miles apart. It just doesn't add up. Am I missing something here?
I prefer Plugshare because it can also show alternate chargers such as distribution and J1772. Found at hotel/motels, they can provide an overnight, full charge for the next day. You can find RV parks with NEMA 14-50 to campout in the car and leave the next day with a full charge.
. . . Plus, a savings of $12.00 compared to using a gas vehicle. Not exactly what I would expect. I entered the trip and vehicle information several times but keep getting the same results. I really want to move ahead with this purchase but these numbers are very concerning.
A Prius Prime would take 666 mi / 56 MPG ~= 12 gal @$2.50 -> $30.00. So $30 - $12 ~= $18 expected SuperCharger cost for 666 mi, sounds a little low. Of course I'm a former Prius Prime owner so the EV advantage was not so great. What was the MPG of your current ride?

I'm typically seeing SuperCharger costs of ~$30 for 750 mile trips.

DRIVING STRATEGIES

Your most important skill is to calculate the battery reserve to the next SuperCharger. This is how many miles the battery icon shows minus the navigation miles. If the reserve miles are going down, slow down early, say 5 mph, and see if holds. If the reserve miles are going up, WHOOPIE.

Arrive with 10-40 mile reserve, short segments

The goal is to arrive at a SuperCharger with a low battery. This allows the SuperCharger to put the fastest rate of miles into the battery which shortens the time spent charging. Use climate control while on the charger.

Arrive with 10-40 mile reserve, long segments

Fully charge the battery which will take the longest time ... say at a long meal break. If the battery charge reaches the maximum, get to the car as quickly as possible to avoid idle fees. Use climate control while on the charger.

J1772, Distribution, or NEMA 14-50 "free" but slow chargers

Best used overnight at a hotel/motel or RV park where you are taking a nap. Start climate control about 30 minutes before leaving.

Bob Wilson
 
Last edited:

Larry M

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#8
Thank you so much for your input! I know there's a lot of charging anxiety for new EV owners. I'll just to work through that.
 

bwilson4web

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#9
Tonight I made some screen shots showing how "reserve mileage" is calculated:

  • set your navigation destination
  • when it shows the miles to go, subtract from the battery miles
  • the result is how many miles should be on the battery when you arrive

This is how it worked for this short trip.

Bob Wilson
 

MelindaV

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#10
Tonight I made some screen shots showing how "reserve mileage" is calculated:

  • set your navigation destination
  • when it shows the miles to go, subtract from the battery miles
  • the result is how many miles should be on the battery when you arrive

This is how it worked for this short trip.

Bob Wilson
That is not entirely true. The number next to the battery icon, and the battery range given in the navigation pane assume you will be driving at the rated efficiency. Ask the folks in the north how this looked last winter vs the remaining range when arriving.
 

bwilson4web

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#11
That is not entirely true. The number next to the battery icon, and the battery range given in the navigation pane assume you will be driving at the rated efficiency. Ask the folks in the north how this looked last winter vs the remaining range when arriving.
Any recommendations of who to ask?

Bob Wilson
 

bwilson4web

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#13
For temperatures in the 65-95F range, these techniques worked for us. The wife AC side was at 76F and the driver, 72F at temperatures above 80-85F.

I'll have to wait six months for freezing weather to work on cold weather calibration factor(s).
 

wackojacko

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#14
Hi, I'm new to the forum and was hoping someone could help me with a question I have about charging. Hope I'm not getting too far off subject. I recently test drove a Model 3 and the salesperson sent me a link to the supercharging site. You can enter a trip and get a route to your destination showing where to stop for charging along the way. I entered the model 3 extended range and the trip distance is 659 miles, from Tampa FL to Kinston NC. Almost the entire trip is on I95. The app has me stopping 5 times for charging with a total charging time of 2 hours and 25 minutes and a gas savings of $12.00. The car has a range of 310 miles and the trip is 659 miles. I would think that stopping no more then 3 times for charging would be the recommendation, not 5 times. I checked, and the supercharging stations are approximately 100 miles apart. It just doesn't add up. Am I missing something here? Plus, a savings of $12.00 compared to using a gas vehicle. Not exactly what I would expect. I entered the trip and vehicle information several times but keep getting the same results. I really want to move ahead with this purchase but these numbers are very concerning.
The Tesla site and the car try to reduce the stopping time. If you only stopped 2 or 3 times you would need to stop longer each time as the charge rate drops as the battery gets full. Therefore Tesla navigates you to stop for quicker chargers at a higher rate. In reality you might stop longer for say lunch or dinner and throw off the navigation calculation.

Don't worry, you can use the Tesla route as a starting point, but always ignore a charging stop if you know you have enough to get to the next supercharger and plan to stop longer to say eat.
 

bwilson4web

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#15
I didn't like the quality of my first report so I repeated it using iPhone, 'TIME-LAPSE' to record the session:

  • Standard Range Plus Model 3, V19.16.2
    • climate control was off
  • 20 mi indicated battery range at start
  • 237 mi stopped recording data in spreadsheet
    • frame numbers to reconstruct true time
    • kW rate
    • mi/hr rate
    • battery mi
    • cost
    • first and last frame times
Here is the battery range in miles during the session:

One goal is resolving the optimum charge session for cost and speed, the green dashed rectangular box:
  • too short duration - the ramp up slows getting back on the road. It is cheapest BUT a slower trip end-to-end speed.
  • too long duration - the battery taper slows getting back on the road. It is also more expensive while giving a slower trip end-to-end speed.
Adding the charge and travel time at 65 mph with the distance covered gives a curve showing the optimum, battery charge:

What this means is attempts to charge to the vehicle maximum range is both expensive and causes the trip to take longer. It is slightly faster and cheaper to go shorter distance, SuperCharger-to-SuperCharge when in SuperCharger mode. This does not apply on the first trip of the day leaving with the car at maximum charge.

This busy chart combines the costs and battery mi level with the X-axis, charge rate:

  • $0.025/mi = $2.50/100 mi - optimum route, expected cost. With gas at $2.50/gal, in effect, 100 MPG equivalent.
  • longer distance legs will give a slower trip time and higher cost but if you have to reach a SuperCharger, there is only one alternative . . . slower speed than 65 mph. But it will be faster than stopped or using an L1 or L2 charger.
On long range trips that require multiple SuperCharger sessions, there may be more than one route. Choose the route with the closest SuperChargers and do multiple, short charges. Avoid routes that have a lot of maximum range segments.

Bob Wilson
 
Last edited:

AmpManNC

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#16
Nifty charts, Bob, thanks for making them up.

I'm a Prius Prime owner who watched you make the transition to M3 SR+. We jumped on the SR+ bandwagon in April, and love the car (my wife's). I still have the Prime, as it's still ideal for my round town drives, and the occasional long trips where we don't have time to deal with charging. Though I must say I prefer to take the M3 on a trip, and enjoy the challenge of working out SC hops. Most road trips these days I'm in no great hurry anyway, as I'm more-or-less retired.

Neil

P.S. We also tend to take the Prime when we carry bikes, as I have a hitch on it. Haven't decided if i'm going to put a hitch on the M3 for such use...