ajdelange

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I'm really curious to see what below freezing temperature does to range as Rivian has chosen not to add a heat pump...
Rivian has a heat pump as do all of these cars. They just don't use it in reverse to draw heat from the air as Tesla (and some others do) but look at the trouble Tesla has been having recently.

...or proper cold weather preconditioning.
How have you concluded that Rivian's preconditioning is inadequate or missing?

Hopefully we can get some more specific range tests, the only accurate ones being from 100% to 5% at a relatively steady speed, no major altitude changes, and temperatures listed. Lots of people improperly math out range.
EPA range numbers are useul for rough comparisons of vehicles because they take out the variability, to the extent that is possible, in realized range on the road but what is really of interest is consumption data (Wh/mi). It is that which you use during a trip to determine your "fuel condition" at any given point and on which you base your determination as to whether you will reach your destination without a supplemental charge. What we want to see reported by people who are actually operating the trucks is the Wh/mi they see in town, the Wh/mi they see on the highway, how many wH/mi are added when the temperature drops below freezing, how much rain adds and, of particular interest to these trucks, how many Wh/mi are added when going off road into, for example, sand.


Photos of the trip computer showing efficiency and mileage is ideal. Unfortunately it's like 0-60 times and people often exaggerate.
What we really hope for is that folks like the people that did TeslaFi and Stats will release similar apps for the Rivians. That would depend, of course, on the existence of an API. Is there one?[/QUOTE]

 
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ajdelange

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I really hope they enable on command both cabin and battery Preconditioning when cold. I'm more worried about impacts of not heating the battery up than heating the cabin.
The battery heats itself when current is drawn from it and the inverters and motors produce more heat when they are propelling the vehicle. These components all sit on cooling loops and, of course, those loops can also contain resistive heaters. The consequence is that the battery will be warm within a few minutes of departure. Regen may be limited until that happens.
 

ajdelange

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this is what rivian said about not having a heat pump


"The R1 vehicles are designed with active battery heating achieved through power electronics in the system, essentially mimicking the behavior of a heat pump," explained a Rivian spokesperson. "This allows for battery temperatures to be maintained to provide appropriate energy output from the battery pack for optimizing range and cabin conditioning. This system supports the R1 vehicles' overall performance in cold weather."
In the previous post I mentioned heat derived from the inverters. This could well be what the quote means by "active battery heating through power electronics". The fascinating thing about this quote in the implication that perhaps they are intentionally fiddling with the transistor gating waveform in order to make the inverter less efficient and thus have it produce more heat than it otherwise would. Ordinarily the want the transistors to switch as fast as possible so they are either in the full on or full off state for as much of the switching cycle as possible. In those states they dissipate little power (still enough that cooling is required, however). It is when the devices are in the intermediate state, i.e. during the transition from on to off or conversely that they produce heat. By prolonging that interval the inverter can, while still inverting, serve as a heater as well obviating the need for a separate electrical heater. I, of course, have no proof that they are doing anything of the sort but it would be devilish clever of them.

This does not, however, "mimick the behavior of a heat pump" in which the heat is derived from the phase change (condenstation) of a refrigerant. This is I^2R loss.
 

ajdelange

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Does the extra weight and tow hooks don't affect the R1T as much?
That depends on the rolling resistance. With tires designed for maximum range on a smooth substrate you can add quite a bit of weight with minimal effect on consumption. With off road tires in sand even a few extra pounds can such a lot of Wh/mi. Rolling resistance can become the largest load. This will be of special interest to those who plan to go off road in desert and on the beachl
 

ajdelange

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...and be really glad they don't have heat pumps. The Model 3s/Ys that have heat pumps have been fixed repeatedly and are now 'waiting on software update' to maybe have them work. Until then, failed cars have no heat at all in or out of cabin.
They clearly haven't doped out the true nature of the problem. It's not a "heat pump" problem. It's a cooling system problem. Tesla's engineers, as does any engineer, knows that "heat pumps" always "fail" when the spread between hot reservoir and cold becomes too great. They must, in their designs, thus provide for a source of backup heat for very cold weather and that S and Y must have those. No heat at all means that the backup isn't kicking in when it should. That's a system problem.

Elon is now saying that the problem is in the expansion valve. It is very probably controlled by software (not just temperature) and if it is not programmed properly the system isn't going to work. Eventually Tesla will dope it out.

I'm not glad Rivian doesn't have two way heat pump capability. Where I live the temperature seldom drops below 30 °F and the modern systems are capable of amazing COP even down to those temperatures. That translates into potentially quite a few extra miles on a chargel
 

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This is from September. I am not sure it was posted here before. I didn’t expect Rivian City efficiency to be that much worse from efficient EVs in the pack with regen and all. I wonder how much accelerating slowly will help.
The average for the R1T is 481 Wh/mi. The EPA range for the RIT is 312 (?) mi. That says its battery is .481*312 = 150 kWh and we know it isn't so the numbers in the table are not on the road consumption numbers. They are "from the wall" numbers which are great for calculating your electric bill but pretty useless for trip planning and fuel state monitoring on the road. Given that charger efficiency is probably about 90% the actual rated consumption is probably about 435 Wh/mi. Common sense says it wouldn't be as bad as 481.

I wonder how much accelerating slowly will help.
When you ask for high acceleration you ask for torque and torque comes from current. Motor speed is low and so, thus is back EMF and you wind up dissipating lots of I^2R power in the rotor resistance. Note it is proportional to the square of the current and hence torque. Regen cannot recover this power - it is dissipated as heat. So yes, slower acceleration does help. How much depends on a lot of things.
 
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ajdelange

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I think having the independent motors reduces efficiency more than people think.
I've argued before that 4 motors is more efficient and it is in terms of I^2R losses especially in town where you are accelerating and decelerating a lot. If you have 2 motors each must supply half the torque and thus draw half the current. The I^2R losses are thus 1/4 unit per motor and there are two motors so the total is 1/2. With 4 motors each produces 1/4 the torque, draws 1/4 the current and develops 1/16 unit of loss. But there are 4 motors so the total loss is 4/16 = 1/4 which is less than 1/2.

Thus, in terms of rotor heat loss more motors are more efficient but obviously that's not the whole story.
 

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I've argued before that 4 motors is more efficient and it is in terms of I^2R losses especially in town where you are accelerating and decelerating a lot. If you have 2 motors each must supply half the torque and thus draw half the current. The I^2R losses are thus 1/4 unit per motor and there are two motors so the total is 1/2. With 4 motors each produces 1/4 the torque, draws 1/4 the current and develops 1/16 unit of loss. But there are 4 motors so the total loss is 4/16 = 1/4 which is less than 1/2.

Thus, in terms of rotor heat loss more motors are more efficient but obviously that's not the whole story.
It would be interesting to know if R1 cuts off two motors in conserve mode only on highway/hi speed or they are cut off in all conditions while in conserve mode.
 

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In the previous post I mentioned heat derived from the inverters. This could well be what the quote means by "active battery heating through power electronics". The fascinating thing about this quote in the implication that perhaps they are intentionally fiddling with the transistor gating waveform in order to make the inverter less efficient and thus have it produce more heat than it otherwise would. Ordinarily the want the transistors to switch as fast as possible so they are either in the full on or full off state for as much of the switching cycle as possible. In those states they dissipate little power (still enough that cooling is required, however). It is when the devices are in the intermediate state, i.e. during the transition from on to off or conversely that they produce heat. By prolonging that interval the inverter can, while still inverting, serve as a heater as well obviating the need for a separate electrical heater. I, of course, have no proof that they are doing anything of the sort but it would be devilish clever of them.
Your description of "active battery heating through power electronics" is along the lines of what I thought as well. It stills seams like it would be better to just have an inexpensive resistive heat element to actively heat rather than have our expensive inverters which prefer being at a low temperature doing it. Obviously the waste heat could still be utilized.
 

 
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