Which Regen Mode is Most Efficient?

[Riv E In]

Is it obvious when the truck is using the brakes instead of just regen?

The brake pedal should move

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[JerseyGreens]

I've been trying to keep an eye on this and don't have scientific feedback...

On highway cruising I've gotten better efficiency with Low Regen.

 

[slomotion16]

High regen is more efficient for most people because it leads to more one-pedal driving. The only scenario in which high regen might be less efficient is if the battery is unable to accept the charge. This WAS common in older Teslas, I think pre-2018, in cold weather, where the battery has not warmed up.

 

[Chewy734]

The brake pedal should move

Sure, but how would I know it’s moving? All I’m doing is modulating the accelerator pedal to come to a complete stop in high regen.

 

[Riv E In]

Sure, but how would I know it’s moving? All I’m doing is modulating the accelerator pedal to come to a complete stop in high regen.

You can see it. Or float your left foot on it.

 

[Chewy734]

You can see it. Or float your left foot on it.

Well, I wouldn’t be looking down there while braking. Floating my left foot on the brake pedal would be annoying and uncomfortable.

I suppose in software, they could easily distinguish between the two cases and show it graphically in the green regen curved line. Maybe that would be useful?

 

[NeedSumCoffee]

In the city, high regen is most efficient.
On highways, no regen is most efficient.

 

[racekarl]

On highway cruising I've gotten better efficiency with Low Regen.

High regen is more efficient for most people because it leads to more one-pedal driving.

In the city, high regen is most efficient.
On highways, no regen is most efficient.

All of these boil down to driving behavior. There is most likely no intrinsic or technical efficiency advantage to high or low regen, assuming as noted that both operate within the maximum limits of the electrical system.

 

[HyperionMark]

This probably goes without saying, but some probably need to hear it. It's not like you get 100% of your energy back with regen. Most systems are probably in the 60-70% range. So in other words, the most efficient form of regen is none.
Obviously you need to use braking sometimes but some people drive gunning it or slamming on the brakes. Regen can't save stupid driving.

 

[NeedSumCoffee]

All of these boil down to driving behavior. There is most likely no intrinsic or technical efficiency advantage to high or low regen, assuming as noted that both operate within the maximum limits of the electrical system.

It’s really boils down to basic electrical concepts. There are zero motors that are 100% efficient. Any regen at all will have losses converting potential energy to electricity. Coasting will always be more efficient than any form of regenerative braking.

 

[Ottoman]

I once Ascended sequoia, it was around 7,000ft.. It took 40% or so to get up the mountain.. and I only Regenned like 6% on the way down.. I was so disappointed I felt robbed..

I turned off regenerative assistance ever since.

 

[electruck]

It’s really boils down to basic electrical concepts. There are zero motors that are 100% efficient. Any regen at all will have losses converting potential energy to electricity. Coasting will always be more efficient than any form of regenerative braking.

These statements make absolutely no sense. Coasting is absolutely not more efficient than regenerative braking.

First, with regen, you are converting the kinetic energy of a moving vehicle into chemical potential energy stored by the battery.

Second, regen is not 100% efficient but remember, with regen, we're talking about inefficient power generation which should not be confused with inefficient power utilization.

Look at it this way, if you coast to a stop, you waste 100% of the vehicle's kinetic energy (lost to the environment). If you leverage regenerative braking to come to a stop, you are able to recapture part of that energy and send it back into the battery. So with regen, you only waste roughly 20% of the vehicles kinetic energy instead of 100%. Hence regen is less inefficient than coasting and it is fundamentally wrong to state that coasting is more efficient than regenerative braking.

https://www.tesla.com/blog/magic-tesla-roadster-regenerative-braking

 

[usofrob]

These statements make absolutely no sense. Coasting is absolutely not more efficient than regenerative braking.

First, with regen, you are converting the kinetic energy of a moving vehicle into chemical potential energy stored by the battery.

Second, regen is not 100% efficient but remember, with regen, we're talking about inefficient power generation which should not be confused with inefficient power utilization.

Look at it this way, if you coast to a stop, you waste 100% of the vehicle's kinetic energy (lost to the environment). If you leverage regenerative braking to come to a stop, you are able to recapture part of that energy and send it back into the battery. So with regen, you only waste roughly 20% of the vehicles kinetic energy instead of 100%. Hence regen is less inefficient than coasting and it is fundamentally wrong to state that coasting is more efficient than regenerative braking.

https://www.tesla.com/blog/magic-tesla-roadster-regenerative-braking

The point is that you're always using the energy to overcome coasting resistance. That's baked in to any movement forward. The vehicle is always overcoming resistance (air drag, rolling, etc.). To coast to a stop without regen would take a very long distance. So, during that time, you're not spending any energy to move that distance.

Furthermore, the lower the speed, the less air resistance and more efficiency. So, the less time you spend at the max speed, the more efficient you can be. And, the more coasting you do, maybe you won't even have to come to a stop, which is even more efficiency gained.

In order to use regen, you'll come to a stop quicker. So, to go the same total distance, you need to spend more time pushing yourself forward to overcome the normal resistance at the 'max' speed. Then, you'll use regen to get only some of that energy back.

When driving my Tesla, I regularly try to use the minimum regen and coast up to light. I suspect this is why in general people using low regen can get the best efficiency. But, I don't believe there is any difference between partially letting off the throttle on high regen, and fully letting off on low regen for the same amount of regenerative force. So, if you can manage your right foot, then leaving it on high will give you the benefit of being able to stop quicker when you need to, but still use lower regen when available.

However, it's also the case that electric motors aren't equally efficient under all conditions. I certainly know that when flooring my Model 3 Performance, it nets using a lot more energy when going to the same cruising speed than moving up to the speed more slowly. I've seen graphs that show the most efficient is relative low power at a moderate rpm. So, I suspect that the Rivian (and Tesla) are less electrically efficient at the motor when using high regen than low regen. I'm not sure if the difference would be enough to notice. Where as the difference between using regen and not using regen would be different.

 

[NeedSumCoffee]

These statements make absolutely no sense. Coasting is absolutely not more efficient than regenerative braking.

First, with regen, you are converting the kinetic energy of a moving vehicle into chemical potential energy stored by the battery.

Second, regen is not 100% efficient but remember, with regen, we're talking about inefficient power generation which should not be confused with inefficient power utilization.

Look at it this way, if you coast to a stop, you waste 100% of the vehicle's kinetic energy (lost to the environment). If you leverage regenerative braking to come to a stop, you are able to recapture part of that energy and send it back into the battery. So with regen, you only waste roughly 20% of the vehicles kinetic energy instead of 100%. Hence regen is less inefficient than coasting and it is fundamentally wrong to state that coasting is more efficient than regenerative braking.

https://www.tesla.com/blog/magic-tesla-roadster-regenerative-braking

You lack basic understanding of reality

 

[electruck]

The point is that you're always using the energy to overcome coasting resistance. That's baked in to any movement forward. The vehicle is always overcoming resistance (air drag, rolling, etc.). To coast to a stop without regen would take a very long distance. So, during that time, you're not spending any energy to move that distance.

Furthermore, the lower the speed, the less air resistance and more efficiency. So, the less time you spend at the max speed, the more efficient you can be. And, the more coasting you do, maybe you won't even have to come to a stop, which is even more efficiency gained.

In order to use regen, you'll come to a stop quicker. So, to go the same total distance, you need to spend more time pushing yourself forward to overcome the normal resistance at the 'max' speed. Then, you'll use regen to get only some of that energy back.

When driving my Tesla, I regularly try to use the minimum regen and coast up to light. I suspect this is why in general people using low regen can get the best efficiency. But, I don't believe there is any difference between partially letting off the throttle on high regen, and fully letting off on low regen for the same amount of regenerative force. So, if you can manage your right foot, then leaving it on high will give you the benefit of being able to stop quicker when you need to, but still use lower regen when available.

However, it's also the case that electric motors aren't equally efficient under all conditions. I certainly know that when flooring my Model 3 Performance, it nets using a lot more energy when going to the same cruising speed than moving up to the speed more slowly. I've seen graphs that show the most efficient is relative low power at a moderate rpm. So, I suspect that the Rivian (and Tesla) are less electrically efficient at the motor when using high regen than low regen. I'm not sure if the difference would be enough to notice. Where as the difference between using regen and not using regen would be different.

If you're decelerating, you're not "spending any energy" - as in not consuming from the battery. However, you are consuming the kinetic energy of the vehicle to overcome those friction forces and that is wasting a portion of the vehicle's total available energy. You're also not consuming any energy from the battery if you use regen to decelerate. The difference is, when coasting, you are wasting 100% of the vehicle's kinetic energy. With regen, you are wasting less than 100% of the vehicles kinetic energy.

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