Range, charging, 2WD questions

[just_jim]

I just started paying attention to Rivian again since it looks like customer deliveries are imminent. I have a few questions/concerns regarding what's been disseminated in the last week or so regarding range, charging and a "magical" 2wd drive mode that will somehow increase range:

1. A screenshot I saw two days ago from the R1T display showed Trip 301 mile, Extended 252 miles and Daily 200 miles. Assuming that the Trip is 135kWh, why is the Daily SoC only 66% of that? Compare this to my Model Y which has an advertised range of 326 miles, but recommended for 85-90% SoC for daily usage. Nearly 18 months in this gives me a range of 250-270 miles (@85-90% SoC). What is going on with the batteries/BMS that the Daily range is 66% of the max and how much battery degradation is expected at higher SoC?

2. Another screenshot I saw showed charging at 48A (level 2 I assume, so 240V) and 15 miles/hr charge rate. At the 11.5kW charge rate this gives 768 Wh/mile. When I read that, it talked about AC and other accessories running contributing to that number. Comparing this to my Teslas when charging at home (240V @ 48A) with AC on max (playing games, etc) as a test, I charge at 38 miles/hour for 303 wH/mile. Considering the size/weight of the R1T I have problems believing that AC and all accessories going while the truck is parked and charging is drawing more than 1.5x the power it takes to drive 1 mile (~490Wh). Am I missing something here ?

3. This 2WD "economy" mode. I haven't seen this on the Rivian site, but it is mentioned elsewhere. I have a problem seeing how shutting off any number of motors while maintaining any speed will make a significant (>5%) difference in range. Basic physics says that for two identical objects (mass, Cd, atmospheric conditions, etc) x number of watts is required to move that object at y speed. The reason 4WD/AWD is less fuel efficient on ICE vehicles is due to added weight (driveshaft, differential, etc) of the components as well as frictional/rotational losses when the 4WD/AWD system is engaged (the ICE has to move more mass). For the R1T/R1S this isn't the case, so I fail to see how shutting down any motors will increase range. If it takes 490Wh/mile, how does that matter if those 490Wh are split between 2 or 4 motors? Additionally if this is really a "feature" it means that there is a clutch (or other mechanism) that disengages the motors from the wheels (added complexity) or some sort of circuit to handle stray voltage generated by a free-spinning PM motor (which by nature would also induce a small amount of opposite torque). I'm not sure what I'm missing that demonstrates how shutting off motors would increase range, but I would love to hear what I'm missing from an EE/ME who works in motors/electro-mechanicals.

FYI I'm an LE reservation holder from Feb '19.

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[ThatOneGuy]

3. This 2WD "economy" mode. I haven't seen this on the Rivian site, but it is mentioned elsewhere. I have a problem seeing how shutting off any number of motors while maintaining any speed will make a significant (>5%) difference in range. Basic physics says that for two identical objects (mass, Cd, atmospheric conditions, etc) x number of watts is required to move that object at y speed. The reason 4WD/AWD is less fuel efficient on ICE vehicles is due to added weight (driveshaft, differential, etc) of the components as well as frictional/rotational losses when the 4WD/AWD system is engaged (the ICE has to move more mass). For the R1T/R1S this isn't the case, so I fail to see how shutting down any motors will increase range. If it takes 490Wh/mile, how does that matter if those 490Wh are split between 2 or 4 motors? Additionally if this is really a "feature" it means that there is a clutch (or other mechanism) that disengages the motors from the wheels (added complexity) or some sort of circuit to handle stray voltage generated by a free-spinning PM motor (which by nature would also induce a small amount of opposite torque). I'm not sure what I'm missing that demonstrates how shutting off motors would increase range, but I would love to hear what I'm missing from an EE/ME who works in motors/electro-mechanicals.

FYI I'm an LE reservation holder from Feb '19.

Hey Jim. Welcome to the forums!

I can't speak to your first two questions, but regarding the last, I think the two front motors are different than the two rear motors. It's possible that the front two motors are more efficient and that's where they're getting power savings.

 

[ajdelange]

1. A screenshot I saw two days ago from the R1T display showed Trip 301 mile, Extended 252 miles and Daily 200 miles. Assuming that the Trip is 135kWh, why is the Daily SoC only 66% of that?

This is the SoC that Rivian has determined is best for extending the life of the battery as they understand their battery at this point.

Compare this to my Model Y which has an advertised range of 326 miles, but recommended for 85-90% SoC for daily usage.

Are you sure that number is attached to a claim of best battery life? Or is it that they are saying charge up to 90% for daily use and above that for trips?

What is going on with the batteries/BMS that the Daily range is 66% of the max and how much battery degradation is expected at higher SoC?

Tesla's battery, BMS and battery management philosophy are not the same as Rivian's. There are many nuances to batteries and thus many approaches to managing them. This is just a manifestation of that fact of life.

2. Another screenshot I saw showed charging at 48A (level 2 I assume, so 240V) and 15 miles/hr charge rate. At the 11.5kW charge rate this gives 768 Wh/mile.

That was noticed by others too. The EPA numbers are out not and evidently rated consumption is around 490 Wh/mi.

Comparing this to my Teslas when charging at home (240V @ 48A) with AC on max (playing games, etc) as a test, I charge at 38 miles/hour for 303 wH/mile. Considering the size/weight of the R1T I have problems believing that AC and all accessories going while the truck is parked and charging is drawing more than 1.5x the power it takes to drive 1 mile (~490Wh). Am I missing something here ?

I think that Tesla uses the rated consumption in it's display of miles added. But we don't know at this point whether Rivian is doing that same thing or using realized Wh/mi over the last x = ? miles. This is one of the reasons I don't look at miles added but rather % SoC added and kWh added.

3. This 2WD "economy" mode. I haven't seen this on the Rivian site...

I doubt the motors are different but it could be that they are geared differently. This means that at the same vehicle speed the motors would be operating at different shaft speeds. While the max efficiency plateau (in torque/speed space) is amazingly flat on top it is not, in fact, flat. You can gain a bit of extra efficiency by operating at a more optimal point in this space. Thus while rolling resistance, drag and slip might be the same if one switches those loads to the more efficienct of 2 pairs of motors he might save a smidge on heat loss. All this is pure speculation. I've never heard of this "economy mode". Note that the Tesla has its "range mode" in which they limit HVAC, accelleration etc.

 

[SeaGeo]

Welcome Jim. I'll give it a shot to at least give you some of the potential answers. Obviously we'll benefit from getting official answers from Rivian, which should come soon enough.

A screenshot I saw two days ago from the R1T display showed Trip 301 mile, Extended 252 miles and Daily 200 miles. Assuming that the Trip is 135kWh, why is the Daily SoC only 66% of that? Compare this to my Model Y which has an advertised range of 326 miles, but recommended for 85-90% SoC for daily usage. Nearly 18 months in this gives me a range of 250-270 miles (@85-90% SoC). What is going on with the batteries/BMS that the Daily range is 66% of the max and how much battery degradation is expected at higher SoC?

Tesla recommends staying between 20% and 90%. So your net battery is 70% there. In the past Elon has suggested staying between 30 and 80% as well. VW recommends charging the ID.4 to 80%. The assumption here is Rivian is trying to provide a simple tool to keep people in the 15 to 80 or 20 to 85% range to help limit degradation. It's really just a risk reduction tool to minimize potential degradation at the margins.

nother screenshot I saw showed charging at 48A (level 2 I assume, so 240V) and 15 miles/hr charge rate. At the 11.5kW charge rate this gives 768 Wh/mile. When I read that, it talked about AC and other accessories running contributing to that number. Comparing this to my Teslas when charging at home (240V @ 48A) with AC on max (playing games, etc) as a test, I charge at 38 miles/hour for 303 wH/mile. Considering the size/weight of the R1T I have problems believing that AC and all accessories going while the truck is parked and charging is drawing more than 1.5x the power it takes to drive 1 mile (~490Wh). Am I missing something here ?

I worked through some potential numbers in the larger thread, so I'll be a little briefer here. Basically, we don't necessarily know what sort of outlet the vehicle was plugged into. There's some energy loss when charging (say 5 to 10%) so the effective charge gained is 11.5kw, it's say... 10.7 kw. The 25 mph may have been based off the 315 range (or more?), and that specific car was showing 301 miles. Tossing in 2 or 3 kw overhead when heating the car, and maybe more for preconditioning if that was happening and you could get down to 15 mph. The charging location may have been providing less than 240 volts. They may have been using a charger that's not giving the full 48 amps as well. There's just two many variables there to say for sure what was going on.

But realistically, no, I don't expect that AC and accessories will suck down what... 7 kWh?

This 2WD "economy" mode. I haven't seen this on the Rivian site, but it is mentioned elsewhere. I have a problem seeing how shutting off any number of motors while maintaining any speed will make a significant (>5%) difference in range. Basic physics says that for two identical objects (mass, Cd, atmospheric conditions, etc) x number of watts is required to move that object at y speed. The reason 4WD/AWD is less fuel efficient on ICE vehicles is due to added weight (driveshaft, differential, etc) of the components as well as frictional/rotational losses when the 4WD/AWD system is engaged (the ICE has to move more mass). For the R1T/R1S this isn't the case, so I fail to see how shutting down any motors will increase range. If it takes 490Wh/mile, how does that matter if those 490Wh are split between 2 or 4 motors? Additionally if this is really a "feature" it means that there is a clutch (or other mechanism) that disengages the motors from the wheels (added complexity) or some sort of circuit to handle stray voltage generated by a free-spinning PM motor (which by nature would also induce a small amount of opposite torque). I'm not sure what I'm missing that demonstrates how shutting off motors would increase range, but I would love to hear what I'm missing from an EE/ME who works in motors/electro-mechanicals.

This is an outstanding question for all of us at the moment. The real-world frame of reference we have is that you see Porsche using a clutch to disconnect their motors permanent magnet motors as part of the range mode. Porsche also has a two speed transmission, but that would come into play with range mode or not. I totally agree with your ICE logic and the basic physics to start. Except that lugging around added weight at a constant speed has a really small impact on efficiency. At the end of the day, the Porsche engineers are obviously not stupid, so there's something that they saw there.

An interesting little observation is that AWD variants of the same model BEV are consistently less efficient on the EPA highway cycle, to a degree that I really can't imagine it's due to weight only. For example with the MME the EPA highway efficiency is significantly more impacted by going from AWD to RWD than by going from the weight of the extended battery pack to the weight of the standard battery pack. It saves about 2 to 4 kW/100 mi dropping down to AWD and the associated 200 lbs, but only .7 to 1.2 kW/100 mi dropping the 333 lbs going from the extended to standard range battery. Dropping from AWD to RWD saved about 1.6 kWh/100 mi with the 2020 model 3 as well. So those two models both saw between 5 and 10% more consumption going from 2WD to AWD.

It does seem counter intuitive that you'd see much much energy loss from adding the 3rd and 4th motors, unless there's more loss than we realize from trying to have the same motor produce the same RPM for each wheel. I would be surprised if the benefit is more than 5 to 10%, but if a conserve/trip mode drops the air suspension a few inches and effectively reduces Cd*A say... 5% and then disengaging the rear motor saves 5%, you're suddenly close to 300 miles of range after taking a 10 to 15% hit for the A/T tires.

It's also entirely possible that MT botched their article and the CS rep I chatted with didn't have all of the info and this mode doesn't exist.

 

[just_jim]

Thanks for the thoughtful reply!

I doubt the motors are different but it could be that they are geared differently. This means that at the same vehicle speed the motors would be operating at different shaft speeds. While the max efficiency plateau (in torque/speed space) is amazingly flat on top it is not, in fact, flat. You can gain a bit of extra efficiency by operating at a more optimal point in this space. Thus while rolling resistance, drag and slip might be the same if one switches those loads to the more efficienct of 2 pairs of motors he might save a smidge on heat loss. All this is pure speculation. I've never heard of this "economy mode". Note that the Tesla has its "range mode" in which they limit HVAC, accelleration etc.

The range mode must be a Model X thing (just checked my Y and not a thing), but after reading the replies here and thinking a bit more on it, I'm guessing that while cruising, only 1 (maybe 2...) motors are actually turning a wheel. I seem to remember someone who monitored their Tesla via OBD2 saying something about their rear motor only getting used during acceleration. If that's the case keeping the circuits open at the non-powered motors with some sort of voltage protection circuit makes more sense.

 

[just_jim]

An interesting little observation is that AWD variants of the same model BEV are consistently less efficient on the EPA highway cycle, to a degree that I really can't imagine it's due to weight only. For example with the MME the EPA highway efficiency is significantly more impacted by going from AWD to RWD than by going from the weight of the extended battery pack to the weight of the standard battery pack. It saves about 2 to 4 kW/100 mi dropping down to AWD and the associated 200 lbs, but only .7 to 1.2 kW/100 mi dropping the 333 lbs going from the extended to standard range battery. Dropping from AWD to RWD saved about 1.6 kWh/100 mi with the 2020 model 3 as well. So those two models both saw between 5 and 10% more consumption going from 2WD to AWD.

I'm also surprised by the MME numbers you posted, I'm going to try and track down a motors guy to explain why AWD vs 2WD in a BEV would have more of a penalty than just weight.

It does seem counter intuitive that you'd see much much energy loss from adding the 3rd and 4th motors, unless there's more loss than we realize from trying to have the same motor produce the same RPM for each wheel. I would be surprised if the benefit is more than 5 to 10%, but if a conserve/trip mode drops the air suspension a few inches and effectively reduces Cd*A say... 5% and then disengaging the rear motor saves 5%, you're suddenly close to 300 miles of range after taking a 10 to 15% hit for the A/T tires.

It's also entirely possible that MT botched their article and the CS rep I chatted with didn't have all of the info and this mode doesn't exist.

I hadn't taken into consideration any suspension lowering in Trip mode, though it makes a lot of sense.

 

[ajdelange]

The range mode must be a Model X thing (just checked my Y and not a thing),

Could be.

but after reading the replies here and thinking a bit more on it, I'm guessing that while cruising, only 1 (maybe 2...) motors are actually turning a wheel. I seem to remember someone who monitored their Tesla via OBD2 saying something about their rear motor only getting used during acceleration.

It is widely believed that in the Teslas that use one synchronous and one induction motor the one or the other is preferred depending on the driving circumstances because the synchronous motors are more efficient (no rotor copper loss).

If that's the case keeping the circuits open at the non-powered motors with some sort of voltage protection circuit makes more sense.

I don't think they would take one or the other out of the circuit but rather "blend" them by asking for the optimum (in terms of efficiency) amount of torque from each dependent on speed, load... This would be done by controlling the stator fields.

 

[DucRider]

I just started paying attention to Rivian again since it looks like customer deliveries are imminent. I have a few questions/concerns regarding what's been disseminated in the last week or so regarding range, charging and a "magical" 2wd drive mode that will somehow increase range:

1. A screenshot I saw two days ago from the R1T display showed Trip 301 mile, Extended 252 miles and Daily 200 miles. Assuming that the Trip is 135kWh, why is the Daily SoC only 66% of that? Compare this to my Model Y which has an advertised range of 326 miles, but recommended for 85-90% SoC for daily usage. Nearly 18 months in this gives me a range of 250-270 miles (@85-90% SoC). What is going on with the batteries/BMS that the Daily range is 66% of the max and how much battery degradation is expected at higher SoC?

2. Another screenshot I saw showed charging at 48A (level 2 I assume, so 240V) and 15 miles/hr charge rate. At the 11.5kW charge rate this gives 768 Wh/mile. When I read that, it talked about AC and other accessories running contributing to that number. Comparing this to my Teslas when charging at home (240V @ 48A) with AC on max (playing games, etc) as a test, I charge at 38 miles/hour for 303 wH/mile. Considering the size/weight of the R1T I have problems believing that AC and all accessories going while the truck is parked and charging is drawing more than 1.5x the power it takes to drive 1 mile (~490Wh). Am I missing something here ?

3. This 2WD "economy" mode. I haven't seen this on the Rivian site, but it is mentioned elsewhere. I have a problem seeing how shutting off any number of motors while maintaining any speed will make a significant (>5%) difference in range. Basic physics says that for two identical objects (mass, Cd, atmospheric conditions, etc) x number of watts is required to move that object at y speed. The reason 4WD/AWD is less fuel efficient on ICE vehicles is due to added weight (driveshaft, differential, etc) of the components as well as frictional/rotational losses when the 4WD/AWD system is engaged (the ICE has to move more mass). For the R1T/R1S this isn't the case, so I fail to see how shutting down any motors will increase range. If it takes 490Wh/mile, how does that matter if those 490Wh are split between 2 or 4 motors? Additionally if this is really a "feature" it means that there is a clutch (or other mechanism) that disengages the motors from the wheels (added complexity) or some sort of circuit to handle stray voltage generated by a free-spinning PM motor (which by nature would also induce a small amount of opposite torque). I'm not sure what I'm missing that demonstrates how shutting off motors would increase range, but I would love to hear what I'm missing from an EE/ME who works in motors/electro-mechanicals.

FYI I'm an LE reservation holder from Feb '19.

The MT truck was a pre production unit, so the numbers and features you see in the UI are likely going to be different on the production vehicles.
In the roundtable discussion (), RJ says they were pushing out a new software update every week, and still getting feedback from users. What the set for the daily limit may change before shipping, and in fact may change from owner to owner depending on how they use the vehicle.
@DuckTruck had conversations with RJ during his visit that indicated that more range would (potentially) be unlocked OTA based on individual usage patterns.

Given that the EPA numbers do not align with the display in the pre production test vehicle, I'm reserving judgment on a lot of these things until we see information from Rivian themselves. I get the feeling that if they are not 100% on the readiness and extensive testing of any feature, it won't be enabled at launch (tank turn, 2WD, etc)

 

[ajdelange]

I'm going to try and track down a motors guy to explain why AWD vs 2WD in a BEV would have more of a penalty than just weight.

I can give you an argument as to why two motors delivering the same power are more efficient that one. If there are two the load is split evenly and thus each need draw only 1/2 the current relative to one alone. This reduced the I^2R loss in each to 1/4 of what it is in the single motor but as there are 2 the total motor I^2R loss is 2*1/4 = 1/2 QED.

But you don't just stick another motor and inverter in there. You also put in another transmission, half shaft's etc. There is then twice as much transmission loss in going to AWD. Hence if the mechanical transmission loss is greater than the I^R loss you will have a net less efficient system.

 

[just_jim]

I can give you an argument as to why two motors delivering the same power are more efficient that one. If there are two the load is split evenly and thus each need draw only 1/2 the current relative to one alone. This reduced the I^2R loss in each to 1/4 of what it is in the single motor but as there are 2 the total motor I^2R loss is 2*1/4 = 1/2 QED.

But you don't just stick another motor and inverter in there. You also put in another transmission, half shaft's etc. There is then twice as much transmission loss in going to AWD. Hence if the mechanical transmission loss is greater than the I^R loss you will have a net less efficient system.

Yes, but doesn't that assume the motors are more efficient at a lower load? Also, I thought with variable frequency drive PM motors there is little efficiency difference at lower loads vs higher.

I think you're spot on regarding R1x motor load being driven by optimum "efficiency" - makes me wish I hadn't dodged feedback & controls.

 

[ajdelange]

Yes, but doesn't that assume the motors are more efficient at a lower load?

It shows why they are, in terms of I^2R losses more efficient at lower loads: they draw less current. But there is more to motor efficiency than just I^2R losses.

Also, I thought with variable frequency drive PM motors there is little efficiency difference at lower loads vs higher.

PM and switched reluctance motors are more efficient as there are no I^2R losses in the rotor as there is no current flow in the rotor. Beyond that the direction of the flux is always the same in the rotors of these designs so hysteresis and eddy losses are reduced.

Both PM/SRM and induction motors use variable frequency drives. The stator field rotates at exactly (synchronous with) the rotor speed in PM/SRM and at close to the rotor speed in an induction motor.

 

[LoneStar]

How does one control or limit the top-end of Percentage of Charge? I mean is there a menu setting or something that automatically ends charging when plugged-in? I cannot believe you have to personally know where charging level stands and go unplug it at some certain time. That's crazy. So is this a factory preset value to preserve battery life or long-term capacity?

 

[Amdolan]

How does one control or limit the top-end of Percentage of Charge? I mean is there a menu setting or something that automatically ends charging when plugged-in? I cannot believe you have to personally know where charging level stands and go unplug it at some certain time. That's crazy. So is this a factory preset value to preserve battery life or long-term capacity?

Although not confirmed, you would likely be able to control the top-end charge via the vehicle interface and the app. Once that state of charge is reached, the vehicle would stop accepting power from the charge source and can remain plugged in without pulling additional energy.

 

[ajdelange]

How does one control or limit the top-end of Percentage of Charge? I mean is there a menu setting or something that automatically ends charging when plugged-in? I cannot believe you have to personally know where charging level stands and go unplug it at some certain time. That's crazy. So is this a factory preset value to preserve battery life or long-term capacity?

Pictures of the truck's displays now indicate that there are 3 preset levels for us to choose from trip, nominal and battery longevity. The last one is 66%, the first presumably 100% and the middle one somewhere in the middle. I cannot believe that we will be restricted to these three choices so that there must be a slider control somewhere. At least I hope so.

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