What We Do Not Know - Important Information Still Needed to Make an Informed Decision

[davrow_R1T]

Nope. I'm saying they will set their prices however they want without regard to your particular feelings on the matter.

This is not true at all. No company will price a product without an understanding of what the consumer will pay.

I'm sorry. Headingly, that I was not clear that I was speaking to Coast2Coast. You actually reinforce what I was trying to say. Companies price according to their criteria of what people will buy and for how much.

What one person wants is immaterial, it is what the company hears the market saying.

Sponsored

 

[ajdelange]

In battery parlance 'c' is the 'capacity' of the battery i.e. how many ampere hours of current it takes to 'charge' it. Charge is in quotes because it refers to the Ah that must be put in to bring the battery from 'empty' to 'full' and those two terms can be defined rather arbitrarily. To charge or discharge a battery at the rate 1.5c simply means that if it's cpacity c = 100 Ampere hours you will be charging or discharging at 1.5*100 = 150 Amperes and that means that it will go from full to empty or empty to full in 1/1.5 = 2/3 hours = 40 minutes. That's the formal definition. When speaking as we often do here of cars C is often expressed in kW hours (energy) rather than Ampere hours (current). As the two are related it conveys the same information. A 135 kWh battery charged or discharged at 1.5C is fully charged or discharged in 1/1.5 = 2/3 of an hour and power is taken from it or put into it at 1.5*135 = 202.5 kW.

It should be clear that batteries are happiest if charged and discharged at a sloe rate. We think the RITs are going to use about 450 Wh/mi so cruising at 60 mph the power consumption is going to be .450 (kwh/mi)*60 (mi/hr) = 27 kW. Using the three capacities in the table in No. 29 that means a discharge rate of 27/105 = 0.257C for the smallest pack, 27/135 = 0.2C for the medium and 27/180 = 0.15C for the largest. Thus another advantage of a large pack is that the charge and discharge rates are lower and the battery should have an easier life. Maximum Level 2 charging (11.52 k51W) amounts to, respectively, 0.11C, 0.087C and 0.0651C for the three pack sizes. Fast DC charging at 300 kW means 2.86C, 2.22C or 1.657C. This might lead us to conclude that the OEMS like to keep charge and discharge to below 3C (and once again causes us to shake our heads in disbelief at Rivins decison to release the mid sized battery first).

Thus far we are talking about the nominal conditions of cruise and charging. What about acceleration? There are three factors determining the power demand of the inertial load during acceleration:

1)Rate of acceleration
2)Current speed
3)Mass

In fact the required power for the inertial load is P = m*v*a in which m is the mass, v the speed and a the acceleration. We can get a rough idea as to how much power will be taken from the battery during a 0 - 60 mph run by observing that 60 mph is 26.82 m/s and assuming that we are in the torque limited part of the motor characteristic and that the acceleration is, therefore, uniform up to 60 mph. According to the formula the greatest demand on the battery is then at 60 mph. From the power data in the table we can estimate the mass of the vehicle by assuming that the powers in the table represent the power at 60 mph which, we again, assume is the transition between torque limited and power limited portions of the vehicle characteristic. This gives weights of, respectively, 4495, 5155 and 5107 lbs for the three variants. Clearly not consistent (how could the truck with the 180 kWh pack weigh less than the one with the 135 kWh pack?) but it's not unreasonable to think these vehicles are going to weigh something over 5000 lbs.

The specified gearbox input powers (resp. 300, 562 and 522 kw) represent discharge at, respectively, 2.86C, 4.16C and 2.9C. Now 4.16C may seem like a pretty heavy discharge rate and it is but look again at the power formula. With it's 0 - 60 time of 3 seconds the truck is below 20 mph with a discharge rate of less than (4.16/3)C for the first second and less than (2*4.16/3)C = 2.77C for the second. It only tops 3C in the last second. Discharge at such a high rate but for short duration will not harm the battery.

Now can you operate the trucks at their maxium (power limited) discharge rates estimated to be 2.86C, 4.16C and 2.9C? Sure can. Haul a big trailer up a long steep hill. Will the trucks' BMS do something to prevent damaging the battery if you try to do something like that? I think we can be sure it will but it will not prevent us from driving or charging our trucks in ways that are hard on the batteries within limits.

All the usual caveats with respect to assumptions, relevance of what is in the old table relative to what Rivian will deliver tomorrow etc. apply.

 

[protamine]

I would like to know the range, performance and handling difference between the 3 sets of tires.

 

[azbill]

The power output, however, is usually regulated by a power control module so that it only outputs as much power as other components such as wiring and drivetrain can handle. But you are correct that it would take more power to make a heavier truck accelerate at the same rate.

My assumption is that all wiring and components support the largest battery output capability. The control module would only try to limit for the particular battery size.

 

[azbill]

In battery parlance 'c' is the 'capacity' of the battery i.e. how many ampere hours of current it takes to 'charge' it. Charge is in quotes because it refers to the Ah that must be put in to bring the battery from 'empty' to 'full' and those two terms can be defined rather arbitrarily. To charge or discharge a battery at the rate 1.5c simply means that if it's cpacity c = 100 Ampere hours you will be charging or discharging at 1.5*100 = 150 Amperes and that means that it will go from full to empty or empty to full in 1/1.5 = 2/3 hours = 40 minutes. That's the formal definition. When speaking as we often do here of cars C is often expressed in kW hours (energy) rather than Ampere hours (current). As the two are related it conveys the same information. A 135 kWh battery charged or discharged at 1.5C is fully charged or discharged in 1/1.5 = 2/3 of an hour and power is taken from it or put into it at 1.5*135 = 202.5 kW.

It should be clear that batteries are happiest if charged and discharged at a sloe rate. We think the RITs are going to use about 450 Wh/mi so cruising at 60 mph the power consumption is going to be .450 (kwh/mi)*60 (mi/hr) = 27 kW. Using the three capacities in the table in No. 29 that means a discharge rate of 27/105 = 0.257C for the smallest pack, 27/135 = 0.2C for the medium and 27/180 = 0.15C for the largest. Thus another advantage of a large pack is that the charge and discharge rates are lower and the battery should have an easier life. Maximum Level 2 charging (11.52 k51W) amounts to, respectively, 0.11C, 0.087C and 0.0651C for the three pack sizes. Fast DC charging at 300 kW means 2.86C, 2.22C or 1.657C. This might lead us to conclude that the OEMS like to keep charge and discharge to below 3C (and once again causes us to shake our heads in disbelief at Rivins decison to release the mid sized battery first).

Thus far we are talking about the nominal conditions of cruise and charging. What about acceleration? There are three factors determining the power demand of the inertial load during acceleration:

1)Rate of acceleration
2)Current speed
3)Mass

In fact the required power for the inertial load is P = m*v*a in which m is the mass, v the speed and a the acceleration. We can get a rough idea as to how much power will be taken from the battery during a 0 - 60 mph run by observing that 60 mph is 26.82 m/s and assuming that we are in the torque limited part of the motor characteristic and that the acceleration is, therefore, uniform up to 60 mph. According to the formula the greatest demand on the battery is then at 60 mph. From the power data in the table we can estimate the mass of the vehicle by assuming that the powers in the table represent the power at 60 mph which, we again, assume is the transition between torque limited and power limited portions of the vehicle characteristic. This gives weights of, respectively, 4495, 5155 and 5107 lbs for the three variants. Clearly not consistent (how could the truck with the 180 kWh pack weigh less than the one with the 135 kWh pack?) but it's not unreasonable to think these vehicles are going to weigh something over 5000 lbs.

The specified gearbox input powers (resp. 300, 562 and 522 kw) represent discharge at, respectively, 2.86C, 4.16C and 2.9C. Now 4.16C may seem like a pretty heavy discharge rate and it is but look again at the power formula. With it's 0 - 60 time of 3 seconds the truck is below 20 mph with a discharge rate of less than (4.16/3)C for the first second and less than (2*4.16/3)C = 2.77C for the second. It only tops 3C in the last second. Discharge at such a high rate but for short duration will not harm the battery.

Now can you operate the trucks at their maxium (power limited) discharge rates estimated to be 2.86C, 4.16C and 2.9C? Sure can. Haul a big trailer up a long steep hill. Will the trucks' BMS do something to prevent damaging the battery if you try to do something like that? I think we can be sure it will but it will not prevent us from driving or charging our trucks in ways that are hard on the batteries within limits.

All the usual caveats with respect to assumptions, relevance of what is in the old table relative to what Rivian will deliver tomorrow etc. apply.

I was only discussing discharge C rating which can be quite different than charging. I have RC batteries that are capable of 5C charging, but 100C short term discharge rating.

 

[Coast2Coast]

I'm sorry. Headingly, that I was not clear that I was speaking to Coast2Coast. You actually reinforce what I was trying to say. Companies price according to their criteria of what people will buy and for how much.

What one person wants is immaterial, it is what the company hears the market saying.

So, we agree @davrow_R1T. Companies price according to their costs and feedback from customers or, more generally, the market. If costs decline, prices should drop unless other costs are incurred.

 

[ajdelange]

The "power control module" is a lot more sophisticated that I think you guys appreciate. It's function is to put the magnetic field where it wants it to be to satisfy the driver's pedal input IOW to set the motor flux and torque at the levels that make the car do what the driver wants it to do subject to certain limitations. That means that in the torque limited region it will not respond to a command that would develop more torque than the drive train can handle. In the power limited region it will not implement commands that would require more power than is programmed. Note that the torque and power limits may change with conditions. If, for example, a lot of current has been drawn over the last few minutes (the leaky integral of i^2 is high) it may limit commands that require a lot of current. If the battery is cold it will definitely limit the amount of current the "motors" can put into the battery and may also limit the amount they can take out.

 

[ajdelange]

I was only discussing discharge C rating which can be quite different than charging. I have RC batteries that are capable of 5C charging, but 100C short term discharge rating.

We are talking automobiles here. The application is dramatically different. We have no need to discharge at 100C. It seems 4C is adequate. Nor do we charge at 5C. The way the packs are constructed we wouldn't be able to get the heat out nor do we really want to go above 3C, charge or discharge, except briefly. We want our batteries to last years and years.

 

[Gshenderson]

The "power control module" is a lot more sophisticated that I think you guys appreciate. It's function is to put the magnetic field where it wants it to be to satisfy the driver's pedal input IOW to set the motor flux and torque at the levels that make the car do what the driver wants it to do subject to certain limitations. That means that in the torque limited region it will not respond to a command that would develop more torque than the drive train would require. In the power limited region it will not implement commands that would require more power than is programmed. Note that the torque and power limits may change with conditions. If, for example, a lot of current has been drawn over the last few minutes (the leaky integral of i^2 is high) it may limit commands that require a lot of current. If the battery is cold it will definitely limit the amount of current the "motors" can put into the battery and may also limit the amount they can take out.

Agree. My point was that simply assuming a larger battery = more max power output to the wheels is not necessarily true. Often bigger batteries are more about range - same power to the wheels, but over longer period of time.

 

[ajdelange]

Agree. My point was that simply assuming a larger battery = more max power output to the wheels is not necessarily true.

If the numbers in the table in No 29 pertain it is definitely not true. They show considerably more power being taken from the 135 kWh pack than from the 180. I confess to some puzzlement over this though.

Often bigger batteries are more about range - same power to the wheels, but over longer period of time.

Bigger batteries do mean more stored energy, of course, and that translates into more range if you want it to. But it also means more current and power at lower C rates which means more torque which means better 0 - 60 times and it also means better towing capacity/performance. The big battery option in the CT is there for trailering. Given that the extra range comes as 'frosting on the cake'. Rivian seems to want to use the extra battery for extended rang only even sacrificing 0 - 60 performance (limiting maxiumum power draw) to get it.

 

[Eager2own]

So, we agree @davrow_R1T. Companies price according to their costs and feedback from customers or, more generally, the market. If costs decline, prices should drop unless other costs are incurred.

I would change your last sentence to “prices may drop.” Rivian may price this like other OEMs who do charge more for adding a third row vs. a vehicle with only two rows.
Or they may take the approach that 3 rows is the standard configuration and a customer can elect “third row deletion” at no extra charge (but also no discount). Many manufacturers take this approach on some standard equipment even if the customer deletion is a lower cost to the OEM. For example, you can buy a 911 with PDK or opt for just a manual transmission at no extra charge (or discount) although the 911 with manual is lower cost to Porsche than one with a PDK.

 

[Eager2own]

A previous article made mention of the Rivian being towed and its capability for recharging while towed. I would love to know more about this. Will the production models be approved for being towed?
More a wishlist item than a question, but I would love if the R1T has the capability to hook up to towing vehicle’s 7-pin connector for brake light signals and — better yet — to activate regen parking in the towed R1T. This (along with capability to recharge when towed and with ability to provide 15A power in emergencies) would make this a much more appealing dinghy than the thousands of Wranglers currently towed behind RVs.

 

[Bobthebuilder352]

A previous article made mention of the Rivian being towed and its capability for recharging while towed. I would love to know more about this. Will the production models be approved for being towed?
More a wishlist item than a question, but I would love if the R1T has the capability to hook up to towing vehicle’s 7-pin connector for brake light signals and — better yet — to activate regen parking in the towed R1T. This (along with capability to recharge when towed and with ability to provide 15A power in emergencies) would make this a much more appealing dinghy than the thousands of Wranglers currently towed behind RVs.

This seems like more trouble than it’s worth because how often it is going be towed? RV’s pull jeeps and small cars adding resistance doesn’t seem like a great idea. Besides, I’ve been behind enough RV’s to notice how slow they already are. Seems like a feature 5% of owners would use about 1% of the time.

 

[jjwolf120]

Rivian being towed and its capability for recharging while towed.

It's only something you would do in an emergency, but usefull if you need it.

 

[Eager2own]

This seems like more trouble than it’s worth because how often it is going be towed? RV’s pull jeeps and small cars adding resistance doesn’t seem like a great idea. Besides, I’ve been behind enough RV’s to notice how slow they already are. Seems like a feature 5% of owners would use about 1% of the time.

You’re very likely right and, in fact, the number who use it may be less than 5% (although for those who do, it will be much more than 1% of the time — for me it would be once or twice a month).
The benefit to Rivian is that folks with those expensive diesel rigs often have lots of money, and the RV community talks a lot. If a vehicle captures a niche for literally being plug-and-play and also providing back-up power, it could capture a huge share (although of a relatively small market). This is clearly not for you (and I won't address that you don't like the idea of RVs towing vehicles... but for those of us who do it, it's worth the "resistance" for a number of reasons), but it could create a unique target group.

Sponsored