SOC vs Charge rate

[pkeller]

I am somewhat new to the world of charging and range anxiety so please be gentle with your response.

As I understand it, as the batteries reach a higher SOC the charge rate decreases. This is done to prevent over charging and overheating. I assume that the charge rate is relatively flat for most of the charge, and then dropping at some point. What I am trying to determine is at what SOC does the charge rate begin to drop? I am asking that so that I can plan trips where I utilize the Fast Chargers most efficiently (IE for shortest amount of time). For around town and charging at home I have the max set to 75%. For trips I am planning on starting at 100% and then at the Fast Chargers, charge them to the knee of the curve. This should minimize the stops while also minimizing the amount of time at the chargers.

I understand that there are tools that do some of this but I would like to get a better understanding of the process before I turn the job over to the software.

Pointers?

Thanks.

 

[AlexHung]

The curve isn't flat as far as I can see. I've just done a shortish road trip last week and super charged as we went.

Here I charged from 26% to 63% in 13 min and you can see the curve isn't flat and doesn't have a elbow/hockey stick change. The charge rate also depends on many factors (temperature, SOC, etc.) so no two curves would look the same.

 

[jcanoe]

On a road trip you will want to follow a similar charging protocol to what you do at home. Feel free to charge to 100% just before leaving on the trip but in most cases there is no need to charge beyond 90%. The goal is not to drive as far as possible but to drive approximately 2 hours, stop at a Tesla Supercharger. The optimum way to charge at a Supercharger is to start with the Tesla vehicle's battery SOC somewhere around 20% (could be lower) and set the charging limit to no more than 70% or 80%. This will minimize the time your Tesla vehicle is charging to ~25 minutes. Unless you need to charge beyond 80% to reach the next charging location or your destination for the day don't waste time charging beyond 80%.

Become familiar with A Better Route Planner (ABRP). ABRP is a web-based app and also a phone app. ABRP will help you plan your charging stops along the way. ABRP accounts for temperature, speed, road conditions, elevation, wind, vehicle load and traffic.

 

[Johnny Vector]

On a road trip you will want to follow a similar charging protocol to what you do at home. Feel free to charge to 100% just before leaving on the trip but in most cases there is no need to charge beyond 90%. The goal is not to drive as far as possible but to drive approximately 2 hours, stop at a Tesla Supercharger. The optimum way to charge at a Supercharger is to start with the Tesla vehicle's battery SOC somewhere around 20% (could be lower) and set the charging limit to no more than 70% or 80%. This will minimize the time your Tesla vehicle is charging to ~25 minutes. Unless you need to charge beyond 80% to reach the next charging location or your destination for the day don't waste time charging beyond 80%.

Become familiar with A Better Route Planner (ABRP). ABRP is a web-based app and also a phone app. ABRP will help you plan your charging stops along the way. ABRP accounts for temperature, speed, road conditions, elevation, wind, vehicle load and traffic.

Personally, I take jcanoe's approach even further. My travels so far have been along I-95 on the Eastern Seaboard, where there are enough Superchargers that you can easily choose from many. I aim to arrive at one with 10-20%, and in many cases charge only to ~50%, because that takes maybe 8 minutes, which is time I've already spent using the restroom and grabbing a bite. Depending on traffic, that's enough for 1.5 to 2 hours of driving, and then I stop again. About twice as many stops as I used to make, but the total time is only a few percent longer than I used to take in a gasser (an extra 30 minutes at most over the course of a 12 hour drive; really I think it's closer to 15 minutes). And at least so far I find I arrive much more rested than I ever did driving an ICE.

Fewer, longer stops work better for some people, e.g. a family for whom it takes 20 minutes to wrangle the kids back in the car any time you stop. More, shorter stops make more sense for us older folks who need to stretch and use facilities more often than in our storied youth. In either case, jcanoe's advice is correct: charging above 80% is not worth the time in most use cases. (The only counterexample I can think of offhand is if you're towing a camper and thus have a much lower range, and you're in the wilds of the Rockies with fewer Superchargers available. There may be others, of course!)

 

[pkeller]

Thanks for the suggestions. Sounds like I should keep my 75% charge limit, and shoot for an SOC of 20% for the lower limit.

Doing some very quick and crude calculations:
- Using a maximum (conservative) range of 250 miles
-- Using 75% >> 20% SOC is 55% battery usage which is about 140 miles or 2 hours at 70mph.

I like it. It's simple and makes sense

Now for the follow on question (ever watch the show Columbo?)

Is it possible to estimate the amount of time required for a charge while in the 20<>75% SOC range? Is it as 'simple' as
60 *(Battery Cap*55%)/(charger kW) = Estimated time
for MY 60*(75*0.55) = 2475 (rounding up to 2500)
Thus on a 250kW charger it would take about 10 minutes
And on a 150kW charger it would take about 17 minutes

Does this come close?

Thanks again.

 

[jcanoe]

It is not as simple as charging using Level 1/2 that you already use at home. When using a Supercharger there are multiple factors in play. The state of charge of the battery pack (a lower SOC is better for faster charging.) The temperature of the cells within the battery pack (higher is better, up to a point, for fastest charging.) That is why when you select a Supercharger as your next destination in the Tesla's navigation system the Tesla vehicle may start to warm the battery as you get closer to the Supercharger. The Tesla battery management system even tracks the age of the battery pack and how much Supercharging has been performed over the life of the pack.

Then there is tapering. Tapering is what happens when you are charging at a high charge rate as when Supercharging. The Tesla battery management system will initially ramp up the charging rate to a maximum charge rate that can approach the theoretical maximum for the V2, V3 Supercharger station. Within a short time, less than 10 minutes, as the battery state of charge increases the charging rate (kW) starts to fall as the Tesla controls both the maximum charging voltage and the charging amperage. There are several obvious charging thresholds. The first is at ~40% to 50%. Then charging will remain fairly constant until ~70%. Above 70% the charging rate significantly tapers off. This is why it is rarely a good practice to charge above ~80% when using a Supercharger.

That V3 Supercharger that can approach 250kW can only deliver maximum charging rate for perhaps 6 minutes, then the rate starts to taper. The net benefit can be that you reduce the time to charge by 10 minutes due to that initial ~250kW rate.

At the other end of the current Supercharging spectrum is the Urban Supercharger. These require a smaller infrastructure (the high voltage transformers and other electronics that you don't see as these are usually behind an enclosure.) The part of the Supercharger station that looks like a gas pump, that is just a small part of what it takes to have a Supercharger station. Urban Superchargers are limited to 72kW, resulting in a much slower charge rate than the V2 and V3 Supercharger. While on a road trip in may make sense to skip an Urban Supercharger if there is a V2 or V3 Supercharger within your driving range. If you are stopping for a meal then an Urban Supercharger might fit your travel schedule. Tesla has very sophisticated software to ensure that the battery in the Tesla vehicle is always protected from charging at too high a rate. That said, charging at up to 72kW that the Urban Supercharger can perform is less stressful to the battery pack than charging at a higher rate.

Battery/electrical engineers refer to the optimum charge rate (also discharge rate) for a lithium battery as being 1X the Capacity of the battery or 1C. For the Long Range Tesla Model Y 1C would be up to ~82kW (for the 2021 MY.) If you use an Urban Supercharger without first warming the battery pack or if the battery is already at 50% SOC you may only be able to charge at 36kW rate, (approximately 0.5C.) All things being equal charging at 0.5C up to 1C is less stressful on the battery than charging at or above 2C.

 

[Fourdoor]

Personally, I take jcanoe's approach even further. My travels so far have been along I-95 on the Eastern Seaboard, where there are enough Superchargers that you can easily choose from many. I aim to arrive at one with 10-20%, and in many cases charge only to ~50%, because that takes maybe 8 minutes, which is time I've already spent using the restroom and grabbing a bite. Depending on traffic, that's enough for 1.5 to 2 hours of driving, and then I stop again. About twice as many stops as I used to make, but the total time is only a few percent longer than I used to take in a gasser (an extra 30 minutes at most over the course of a 12 hour drive; really I think it's closer to 15 minutes). And at least so far I find I arrive much more rested than I ever did driving an ICE.

Fewer, longer stops work better for some people, e.g. a family for whom it takes 20 minutes to wrangle the kids back in the car any time you stop. More, shorter stops make more sense for us older folks who need to stretch and use facilities more often than in our storied youth. In either case, jcanoe's advice is correct: charging above 80% is not worth the time in most use cases. (The only counterexample I can think of offhand is if you're towing a camper and thus have a much lower range, and you're in the wilds of the Rockies with fewer Superchargers available. There may be others, of course!)

You don't go far enough! Adopt the Kyle Conner method, arrive at 2% SOC and charge to 50% while standing next to the car filming with the door hanging open

Keith

PS: Anyone get a chance to meet him, ask why he leaves the damn door open all the time I met him in Feb 2020 before I noticed the habit of leaving his door open all the time.

 

[Johnny Vector]

You don't go far enough! Adopt the Kyle Conner method, arrive at 2% SOC and charge to 50% while standing next to the car filming with the door hanging open

Keith

PS: Anyone get a chance to meet him, ask why he leaves the damn door open all the time I met him in Feb 2020 before I noticed the habit of leaving his door open all the time.

Don't be ridiculous! My way is exactly perfect. Anyone who arrives at a higher SOC than me is an idiot, and anyone who arrives at a lower SOC than me is a maniac!

(Apologies to George Carlin)

 

[pkeller]

It is not as simple as charging using Level 1/2 that you already use at home. When using a Supercharger there are multiple factors in play. The state of charge of the battery pack (a lower SOC is better for faster charging.) The temperature of the cells within the battery pack (higher is better, up to a point, for fastest charging.) That is why when you select a Supercharger as your next destination in the Tesla's navigation system the Tesla vehicle may start to warm the battery as you get closer to the Supercharger. The Tesla battery management system even tracks the age of the battery pack and how much Supercharging has been performed over the life of the pack.

Then there is tapering. Tapering is what happens when you are charging at a high charge rate as when Supercharging. The Tesla battery management system will initially ramp up the charging rate to a maximum charge rate that can approach the theoretical maximum for the V2, V3 Supercharger station. Within a short time, less than 10 minutes, as the battery state of charge increases the charging rate (kW) starts to fall as the Tesla controls both the maximum charging voltage and the charging amperage. There are several obvious charging thresholds. The first is at ~40% to 50%. Then charging will remain fairly constant until ~70%. Above 70% the charging rate significantly tapers off. This is why it is rarely a good practice to charge above ~80% when using a Supercharger.

That V3 Supercharger that can approach 250kW can only deliver maximum charging rate for perhaps 6 minutes, then the rate starts to taper. The net benefit can be that you reduce the time to charge by 10 minutes due to that initial ~250kW rate.

At the other end of the current Supercharging spectrum is the Urban Supercharger. These require a smaller infrastructure (the high voltage transformers and other electronics that you don't see as these are usually behind an enclosure.) The part of the Supercharger station that looks like a gas pump, that is just a small part of what it takes to have a Supercharger station. Urban Superchargers are limited to 72kW, resulting in a much slower charge rate than the V2 and V3 Supercharger. While on a road trip in may make sense to skip an Urban Supercharger if there is a V2 or V3 Supercharger within your driving range. If you are stopping for a meal then an Urban Supercharger might fit your travel schedule. Tesla has very sophisticated software to ensure that the battery in the Tesla vehicle is always protected from charging at too high a rate. That said, charging at up to 72kW that the Urban Supercharger can perform is less stressful to the battery pack than charging at a higher rate.

Battery/electrical engineers refer to the optimum charge rate (also discharge rate) for a lithium battery as being 1X the Capacity of the battery or 1C. For the Long Range Tesla Model Y 1C would be up to ~82kW (for the 2021 MY.) If you use an Urban Supercharger without first warming the battery pack or if the battery is already at 50% SOC you may only be able to charge at 36kW rate, (approximately 0.5C.) All things being equal charging at 0.5C up to 1C is less stressful on the battery than charging at or above 2C.

Wow I think I may have over simplified it just a little. I expected it to be more complex than a linear solution but not as complex as it is. . Looks like I'll learn by experience how to guesstimate our rest time and then add a fudge factor.

Thanks for the education.
-Phil-

 

[ATPMSD]

A lot of good advice! Here is a chart that perhaps addresses your question

 

[pkeller]

A lot of good advice! Here is a chart that perhaps addresses your question

View attachment 682006

Very useful chart. My "back of the napkin" calculations yield
- From 20% >> 40% about 6.5 minutes
- From 40% >> 75% about 16.5 minutes

So (as has been mentioned before, but now I understand the reasoning)
** Using 20%<>75% as operating SOC
- Drive for 2 hours (avg 70mph)
- Rest/charge for about 25 minutes (rounded). 150kW @ 'room' temperature

Thanks to all for the education.

-Phil-

 

[jcanoe]

Very useful chart. My "back of the napkin" calculations yield
- From 20% >> 40% about 6.5 minutes
- From 40% >> 75% about 16.5 minutes

So (as has been mentioned before, but now I understand the reasoning)
** Using 20%<>75% as operating SOC
- Drive for 2 hours (avg 70mph)
- Rest/charge for about 25 minutes (rounded). 150kW @ 'room' temperature

Thanks to all for the education.

-Phil-

Create an account on A Better Route Planner web site. Plan a few trips. Variables such as your speed, Supercharger arrival SOC, Destination arrival SOC will have the greatest impact on the number of charging stops and their duration. (If you create a basic account you can save your trip planner for future reference.)

 

[kavyboy]

Maybe things have changed, but it used to be that SOC + kWh = a constant plus/minus a small amount. Right now my constant is about 100 on my 2015 S70. That is a close-enough number that I can tell if there is a problem with the current charger, and lets me guess how much longer I have to wait.
As for trips, I do what the nav tells me plus a little bit extra unless there's unusual weather. If I'm under-charged for a leg, I slow down. Speed is the biggest controllable variable.
No need to overthink things.

 

[pkeller]

Create an account on A Better Route Planner web site. Plan a few trips. Variables such as your speed, Supercharger arrival SOC, Destination arrival SOC will have the greatest impact on the number of charging stops and their duration. (If you create a basic account you can save your trip planner for future reference.)

I have an ABRP account and I have played with it for a trip from the bay area to Las Vegas. BUT I like to understand a bit about the magic that the planner uses so that I can do a little preplanning and estimation. Then I can see if the planner is correct

 

[Rocky_H]

Maybe things have changed, but it used to be that SOC + kWh = a constant plus/minus a small amount. Right now my constant is about 100 on my 2015 S70. That is a close-enough number that I can tell if there is a problem with the current charger,

Yes, the old "rule of thumb". That was very consistent and helpful with the Model S. And the reason why that worked so well was with how the Supercharger power and the battery sizes in the cars were pretty closely matched so it could keep that almost linear relationship.

But what changed was that the Model 3/Y can charge much faster for a very short time, and the V3 Superchargers can supply much higher power, so there is more variability that throws things off some, so you get those weird charging curve graphs with big flat areas and then angles and sharp drop offs.

 

[Fourdoor]

I think the charts earlier in this thread were from Ionity CCS chargers in the EU compared to V1 and V2 Superchargers. Over my vacation time I compiled a bunch of data at Superchargers and came up with the following charts for V2 and V3 supercharging in summer conditions with a warm battery. I really wish the V3 matched the 200 KW charger curve from above, but over several Supercharger sessions, after around 40% SOC the V3 Supercharger curve matches the V2 Supercharger curve pretty darn close.

Later,

Keith

 

[Fourdoor]

You don't go far enough! Adopt the Kyle Conner method, arrive at 2% SOC and charge to 50% while standing next to the car filming with the door hanging open

Keith

PS: Anyone get a chance to meet him, ask why he leaves the damn door open all the time I met him in Feb 2020 before I noticed the habit of leaving his door open all the time.

I think I have figured out the "leave the door hanging open" thing. If you open and close the doors the climate control spools up and spools down over and over again when you open / close the doors. I can see this causing audio issues while recording a video

Keith