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Let's talk about charging on long distance travel?

DucRider

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The newest CCS charging stations featuring 150-350kW capacities is neat but at what rate does your BEV charge at? There is a charging curve with the highest levels usually between 10-35% SOC and then it drops. Tesla Model 3 owners frequently report on an average 87kW charge for their rate. What is the Rivian charging curve going to look like?
Most BEVs with a decent sized battery sustain the highest charge rate at far above your quoted 10-35%. Probably the best is currently the Audi e tron. It charges at its maximum 150 kW rate up until 70% SOC, and over 100 kW at 80% (at which point most people stop DCFC sessions).

I expect Rivian will allow its max charge rate to at least 60% SOC and probably higher.
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Billyk24

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Billyk24

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Here is audi:
Rivian R1T R1S Let's talk about charging on long distance travel? audi charging curve
 

Billyk24

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Here is Jag verse Tesla:
Rivian R1T R1S Let's talk about charging on long distance travel? Jag charging curve

Makes one realize Tesla is not years ago of "others"
 

ajdelange

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As the handful of taper curves in the preceding posts show there are several approaches to tapering during DC fast charging. Tesla's is, clearly, the most conservative and will result in greater battery longevity than the other manufacturers will realize. Fast charging is not good for the battery and is particularly detrimental at high charge levels. Tesla makes no bones about this. They advise against using fast charging at all except when Level 2 charging is not available (as, for example, on a road trip). And they have reduced the charging rates available at Level 2 down to 11.5 kW in their current crop of vehicles.

Now let's be clear that the detriment spoken of above does not mean the battery will fall out of your car at 20,000 miles if you fast charge it. What it means is that the battery will degrade faster. Tesla warrents that the battery will retain 80% of it's capacity for 7 years or 50,000 miles. A driver using SCs all the time can expect to see his battery deliver at least that. A driver that never uses a fast charger might see less degradation (to 95% for example).

A manufacturer who tapers less can advertise that he charges faster than one who tapers more. In the early days of BEVs charging rate was at least as important to the potential buyer as range anxiety and thus fast charging was pushed hard. And it still is. But Tesla now has sold a million cars and in so doing dealt with lots of grumbling about rapid battery degradation. You can see dozens of posts about this on the Tesla boards. With range anxiety more or less a thing of the past and most people charging at home I think Tesla has now decided to do whatever they can to increase battery longevity. Of course the much anticipated Battery Day announcements are expected to emphasize the "million mile battery" which may change the picture appreciably. Tesla may feel that they can accommodate a more aggressive taper.

But you asked about Rivian. It should be clear that I don't have the foggiest idea what kind of taper Rivian will use. It depends on whether they want to be able to claim longevity or fast charging rate.
 

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DucRider

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As the handful of taper curves in the preceding posts show there are several approaches to tapering during DC fast charging. Tesla's is, clearly, the most conservative and will result in greater battery longevity than the other manufacturers will realize. Fast charging is not good for the battery and is particularly detrimental at high charge levels. Tesla makes no bones about this. They advise against using fast charging at all except when Level 2 charging is not available (as, for example, on a road trip). And they have reduced the charging rates available at Level 2 down to 11.5 kW in their current crop of vehicles.

Now let's be clear that the detriment spoken of above does not mean the battery will fall out of your car at 20,000 miles if you fast charge it. What it means is that the battery will degrade faster. Tesla warrents that the battery will retain 80% of it's capacity for 7 years or 50,000 miles. A driver using SCs all the time can expect to see his battery deliver at least that. A driver that never uses a fast charger might see less degradation (to 95% for example).

A manufacturer who tapers less can advertise that he charges faster than one who tapers more. In the early days of BEVs charging rate was at least as important to the potential buyer as range anxiety and thus fast charging was pushed hard. And it still is. But Tesla now has sold a million cars and in so doing dealt with lots of grumbling about rapid battery degradation. You can see dozens of posts about this on the Tesla boards. With range anxiety more or less a thing of the past and most people charging at home I think Tesla has now decided to do whatever they can to increase battery longevity. Of course the much anticipated Battery Day announcements are expected to emphasize the "million mile battery" which may change the picture appreciably. Tesla may feel that they can accommodate a more aggressive taper.

But you asked about Rivian. It should be clear that I don't have the foggiest idea what kind of taper Rivian will use. It depends on whether they want to be able to claim longevity or fast charging rate.
You make a lot of assumptions without sufficient facts to back them up. Lots of "everybody knows that" contained above, which often turns out not to be the case.
One reason Tesla needs to taper the curve faster because they either (dpending on how you want to phrase it):
a) don't protect the battery with a top end buffer
b) make more of the battery available for occasional use.
Tesla recommends not charging the battery to "100%" on a daily basis, where most (all?) other manufacturers don't have that recommendation and very few even have a means to set a lower charge level.

There is no scientific evidence I have seen that fast charging from 20-80% on a regular basis creates, in and of itself, faster battery degradation. Lots of anecdotal stories, but there are many Tesla owners that only fast charge (no option to charge at home or work), and that portion of the market is growing. Tesla salespeople starting pushing that as an option pretty heavily with the Model 3.
 

ajdelange

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Assumptions without facts. Well if one has facts it isn't necessary to make assumptions, is it? The "facts" here are that Tesla is definitely promoting charging at slower rates. If you understand the charge/discharge process at all you will have some inclination as to why this is probably advantageous but being able to give a detailed explanation would require detailed knowledge of the particular cells Tesla is using currently. Tesla has that, they know how their cells perform and they have implemented slower charging both in the home chargers they sell and SCs (through taper).

As noted in the previous post, the differences do no mean the difference between a 500,000 mile battery and a 20,000 mile battery but more probably the difference beteen a 500,000 mile battery and a 400,000 mile one. Thus this realization is not really that much of a bummer for those who cannot charge at home for whatever reason. If I couldn't charge at home a BEV would be a hard sell as that is one of BEVs greatest advantages relative to ICE but you can't blame Tesla for trying to sell them to those folks. In any case degradation information is available to users and is noted by them. That I believe is the reason for the current emphasis on lower charging rate but that is speculation. And, also as noted in #20 the whole thing may be mooted by newer battery technology in which, for example, lithium capture by the SEI is appreciably reduced relative to what it is now. This I am assuming is going to feature big on Battery Day.
 
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DucRider

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Yes Tesla is promoting minimal use of Supercharging - but it is very likely, at least in part, in order to reduce congestion and mitigate the need to greatly expand the number of stations.

What Tesla does and needs to do may or may not be be what Rivian will do and/or need to do to preserve battery life. Bigger top and bottom buffers would go a long way towards preserving battery life, but at the expense of range. Tesla chooses to make more range available but is clear that using that capability on a regular basis is not good for battery health. There are a bumch of owners more than a little ticked off that Tesla did an over the air "update" that reduced the available battery capacity of their vehicles. Tesla is claiming for "safety reasons", but many owners suspect it is to avoid warranty claims.
 

ajdelange

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Yes Tesla is promoting minimal use of Supercharging - but it is very likely, at least in part, in order to reduce congestion and mitigate the need to greatly expand the number of stations.
If you want to generate jejune arguments I think you can do better than that. They operate the Super Charger network at a loss, Elon says, and so by keeping people away from them and limiting the amount of electricity they can take on at an SC they limit that loss. I can understand why they would want to discourage me because I get Super Charging free. But were the motivation to reduce congestion they would do the opposite of what they do. They would taper less gradually or not at all as the manufacturers who have put "fast" charging before battery longevity have done. They have also reduced the charging rate at non Tesla DC chargers and in Level II charging by putting smaller rectifiers in their products. This strongly suggests to me that there is some benefit to slower charging and the chemistry suggests that there is but that it could have nothing to do with this is a possibility I have to accept because I have no personal communication from Elon Musk that Occam's razor applies here.

Note that Tesla has mechanisms for limiting conjeStion. They will, when a charger is busy, limit the reachable SoC to 80% and in addition impose "idle fees" for staying beyond that.

What Tesla does and needs to do may or may not be be what Rivian will do and/or need to do to preserve battery life.
That was the whole point of No. 20! There is a trade space here between longevity, charge/discharge depth, charge rate and SoC.

Bigger top and bottom buffers would go a long way towards preserving battery life, but at the expense of range. Tesla chooses to make more range available but is clear that using that capability on a regular basis is not good for battery health. There are a bumch of owners more than a little ticked off that Tesla did an over the air "update" that reduced the available battery capacity of their vehicles. Tesla is claiming for "safety reasons", but many owners suspect it is to avoid warranty claims.
So you are suggesting that Tesla narrowed the spread between Voc(min) and Voc(max) in order to improve battery life but cannot accept that lowering the charge rate would do the same?
 

DucRider

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So you are suggesting that Tesla narrowed the spread between Voc(min) and Voc(max) in order to improve battery life but cannot accept that lowering the charge rate would do the same?
This is the first mention of charge rate. The discussion was about taper.
Tesla Superchargers will start at ~3C on a LR M3. The Rivian announced specs will put DCFC at 1.2C on the 135 kWh version and .9C on the 180.
This is another reason Tesla needs to taper the charge where Rivian will not be as compelled to do so.
 

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bajadahl

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I wanted to take a moment to thank you all for the continued discussion... As a person completely new to BEV's I am learning a bunch about what to look for and how to understand the different aspects to consider when talking about vehicle range and charge rates..... When doing long distance travel I often go 350 miles between stops, driving between 70-80 miles per hour. (Think about those long stretches of IH10 or IH40 between Texas and California...) anyway... It sure sounds like I might need to temper my expectations about driving those same stretches of highway even with the 400+ version of the R1S. Especially if I want to take proper care of the battery.
 

Billyk24

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Here is another charging graph:
Rivian R1T R1S Let's talk about charging on long distance travel? charging curves multiple vehicles

Looking for the link for Rivian's charging curve.
 

ajdelange

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This is the first mention of charge rate. The discussion was about taper.
Perhaps you are confused, as so many are, while learning about BEVs, about the distinction between kW and kWh. The latter is a measure of energy i.e. an amout of work. A kW is a measure of power which is the RATE at which energy (work or potential work) is done or transferred. Thus when we speak of taper we are speaking of how the RATE of charge is programmed. IOW we, or some of us at any rate, have been talking about RATE throughout,

Tesla Superchargers will start at ~3C on a LR M3.
Well no. I was at one in a Raven X yesterday and it started at 1.41C. You may be confused about the meaning of C too. C is the capacity of the battery in ampere hours. My X battery has a charge capacity of about 100 kWh. Noting that Watts are just volts times amps I hope you will be able to understand if express C in KWh rather than ampere hours to avoid having to deal with the voltage. The LR M3 has esentially the same battery capacity as the X AFAIK.

I assume you took the LR M3 data from the curve in No. 17 above. That curve shows an initial rate of 2.5C but the overall rate for that curve from 0 to 100 % is 0.86C (assuming, again, the battery has a charge capacity of 100 kWh),

The Rivian announced specs will put DCFC at 1.2C on the 135 kWh version and .9C on the 180.
Yes, and so?

This is another reason Tesla needs to taper the charge where Rivian will not be as compelled to do so.
Tesla doesn't "need" to taper any more or less than Rivian does. But Tesla has determined that if it tapers, it's batteries last longer and that they can put that longevity improving taper into their cars and still get a reasonably "fast" charging time. The curve shown in No. 17 indicates a 100 kWh battery will charge from 0 to 100% in 1 hr and 9 minutes (from a charger that can deliver 250 kW at start) and charge from 20% to 60% in 13 minutes or from 20% to 70% in 18. The latter two figures are typical of how we Tesla drivers operate our cars. IOW we stay in the low SoC region which is, in itself, good for the battery and where we get the fastest charging rates too, Perhaps Tesla tapers as much as they do to try to keep us in that region. It's for our own good and keeps the number of "my battery is degrading too fast" service calls down. There are, of course, exceptions and let me again make it clear that charging the battery to 90 or even 100% as when departing on a road trip is specifically noted as being OK as long as it is done occasionally.

Now I will again mention that Tesla's taper curve is what Tesla has determined is best for their batteries. As one can plainly see from the new set of curves kindly posted by Billyk24 other manufacturers use other tapers; presumably ones that give them an acceptable trade between charge rate and battery life. Rivian's curve may or may not resemble any of them.
 

DucRider

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Perhaps you are confused, as so many are, while learning about BEVs, about the distinction between kW and kWh. The latter is a measure of energy i.e. an amout of work. A kW is a measure of power which is the RATE at which energy (work or potential work) is done or transferred. Thus when we speak of taper we are speaking of how the RATE of charge is programmed. IOW we, or some of us at any rate, have been talking about RATE throughout,

Well no. I was at one in a Raven X yesterday and it started at 1.41C. You may be confused about the meaning of C too. C is the capacity of the battery in ampere hours. My X battery has a charge capacity of about 100 kWh. Noting that Watts are just volts times amps I hope you will be able to understand if express C in KWh rather than ampere hours to avoid having to deal with the voltage. The LR M3 has esentially the same battery capacity as the X AFAIK.

I assume you took the LR M3 data from the curve in No. 17 above. That curve shows an initial rate of 2.5C but the overall rate for that curve from 0 to 100 % is 0.86C (assuming, again, the battery has a charge capacity of 100 kWh),

Yes, and so?

Tesla doesn't "need" to taper any more or less than Rivian does. But Tesla has determined that if it tapers, it's batteries last longer and that they can put that longevity improving taper into their cars and still get a reasonably "fast" charging time. The curve shown in No. 17 indicates a 100 kWh battery will charge from 0 to 100% in 1 hr and 9 minutes (from a charger that can deliver 250 kW at start) and charge from 20% to 60% in 13 minutes or from 20% to 70% in 18. The latter two figures are typical of how we Tesla drivers operate our cars. IOW we stay in the low SoC region which is, in itself, good for the battery and where we get the fastest charging rates too, Perhaps Tesla tapers as much as they do to try to keep us in that region. It's for our own good and keeps the number of "my battery is degrading too fast" service calls down. There are, of course, exceptions and let me again make it clear that charging the battery to 90 or even 100% as when departing on a road trip is specifically noted as being OK as long as it is done occasionally.

Now I will again mention that Tesla's taper curve is what Tesla has determined is best for their batteries. As one can plainly see from the new set of curves kindly posted by Billyk24 other manufacturers use other tapers; presumably ones that give them an acceptable trade between charge rate and battery life. Rivian's curve may or may not resemble any of them.
The Model 3 LR will charge at 250 kW, the curves and data you are looking at are out of date.
An 85 kWh battery charging at 250 kW is ~3C.
C is not the battery capacity, but is a measure of the discharge/charge rate relative to it's maximum capacity. A 100 kWh battery charging at 100 kW would be a 1C rate.
The Model 3 LR has ~85% of the X's battery capacity, but utilizes different cells, chemistry, and can accept higher charge rates, The LR can charge at 250 kW, the SR+ at 170, and a new S or X at 200.
I am very familiar with the difference between kW and kWh, and am far from new to BEVs, have organized NDEW (and other) events for many years.
The graph you show above for the M3 is limited by the Supercharger and/or is an older vehicle. V3 Superchargers will deliver 250 kW to a LR M3
Rivian R1T R1S Let's talk about charging on long distance travel? Tesla-Model-3-LR-on-Supercharger-V3-June-2019-Data
 

ajdelange

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C is the capacity of the battery in units of ampere-hours. If we charge at 1.5C that expression means that we can load 1.5 times C into the battery in an hour or that it would take 1/1.5 hours to load C Ah into it. The units of the number multiplying C are reciprocal hours. My X has a battery capacity of about 250 Ah. 1.5C for this car means 1.5*250 = 375Ah/h which is a charging rate of 375 A. A rate of 1.0C means 1.0*250 = 250Ah/h = 250 A. Lithium batteries are "coulomb efficient" (an Ampere-hour is 3600 Coulombs) which means that a Coulomb put in can be taken out. This is an idealization and the whole object of battery care is to make sure that it is as true as possible. We hope that each coulomb put in will transfer 1/F (F = the Faraday constant) moles of lithium from cathode to anode but in fact a tiny fraction carry lithium ions into reactions with the SEI or, worse yet, to a dendrite. Being nice to the battery keeps that fraction tiny,

It would obviously be pretty handy if we could just say "Hey, its a 385 V battery so each Ah out delivers 385 Wh and thus the capacity is 250Ah*385 V= 96.25 kWh". So handy that this is in fact what we often do (the guys in the labs wouldn't) but it's an approximation because battery voltage isn't 385 V. Whatever voltage it is depends on temperature, SoC and load and voltage drop across the resistive parts of the battery assembly (cells, wires, switches) represents energy that doesn't get stored in or returned from the battery. Thus more energy must be delivered to the battery than can be recovered from it leading to different apparent capacities for charge and discharge. For my X the charging capacity is about 100 kWh and the discharge capacity about 92 kWh. So when I say "charging at 1.5C" I mean delivering 1.5*100kWh/h = 150 kW.

What I really want to do is revisit the question in light of what some of the postings which followed it have revealed

The newest CCS charging stations featuring 150-350kW capacities is neat but at what rate does your BEV charge at? There is a charging curve with the highest levels usually between 10-35% SOC and then it drops. Tesla Model 3 owners frequently report on an average 87kW charge for their rate. What is the Rivian charging curve going to look like?
The answer is still "who knows" but it might be instructive to review how Tesla fast charging works under the fairly sure assumption that Rivian has learned something from Tesla (and on its own). When the car connects to the terminal it handshakes with it, identifying itself to the network. When the network authorizes charging it informs the car of this and tells it how much is available. The car then takes what it wants. This is not necessarily all the charger has to offer. For example, a new X can only take 200 which is less than some of the new chargers Tesla is rolling out. The car has a charging profile. What happens during a charge depends entirely on the profile. New profiles can be downloaded by the manufacturer any time he wants and the car make make move during charging to protect the battery as when, for example, the battery is too hot or too cold upon arrival at the charging station. As an example, here's what I got at the Strassburg, VA SC the other day.


Rivian R1T R1S Let's talk about charging on long distance travel? StrssCh


Time for this charge was 27 min. Average power taken from the charger was 100 kW.

So the answer to the question is that the Rivian curve can be almost anything with what it is for any particular charge session depending on the chrarger, the truck and the weather. In general you can assume some sort of taper. How steep will depend on the particular battery and how aggressively Rivian wants to treat it. Just to give an idea about the implications of taper here is a set of charge time numbers from a 100 kWh battery capable of charging at 125 kW until 47% SoC after which it tapers linearly to 25 kW at 90 SoC.
From 20% to 30% takes 4.8 min.; Avg Pwr: 125.00 kW; Effective rate: 1.25C
From 20% to 40% takes 9.6 min.; Avg Pwr: 125.00 kW; Effective rate: 1.25C
From 20% to 50% takes 14.4 min.; Avg Pwr: 124.64 kW; Effective rate: 1.25C
From 20% to 60% takes 20.1 min.; Avg Pwr: 119.37 kW; Effective rate: 1.19C
From 20% to 70% takes 27.4 min.; Avg Pwr: 109.62 kW; Effective rate: 1.10C
From 20% to 80% takes 37.5 min.; Avg Pwr: 95.96 kW; Effective rate: 0.96C
From 20% to 90% takes 54.5 min.; Avg Pwr: 77.08 kW; Effective rate: 0.77C
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