Does the way you regen make any difference to the amount of charging done?

[Falkirk]

I was thinking of how I alternate between two styles of regen when driving and wanted to know if there was any difference in how much charge is added to the battery.

One way is to just fully let off the accelerator which gives strong regen but fairly short time.

The other is to ease off slowly and this regens longer but at a lower rate.

Which adds more kWh's to the battery?

Thanks

 

[Rocky_H]

Neither, to any measurable difference. Kinetic energy is 1/2 mass times velocity squared. The mass of the car doesn't change, so you have a fixed amount of energy you can recover based on your velocity change. From the higher current of a faster regen, there is a little bit more resistance in the wiring and maybe a little more heat in the battery cells from the faster recharge cycle, so maybe barely less efficient from faster regen, but it's such a short time, it will be insignificantly different.

 

[Falkirk]

Thanks @Rocky_H for your answer. Makes sense, I didn't expect either would be very different but I was curious if they really were the same or not and what you say is true and also pretty much not measurable!

Do what you want, it's all good!

 

[ewoodrick]

I disagree with Rocky_Hs response.
The motor created far more usable regen when at higher speeds than it does at lower speeds. The reason why Rocky_Hs answer is theoretically correct from one perspective, but flawed is that the voltage that is produced is much higher at faster speeds and that's one of the factors that is needed for the most regen.

With V9, you should be able to see the regen curves for both methods and calculate the area under the curve, that's the total amount generated.

if you are letting your foot off of the accelerator slowly, you are very possibly creating no regen, just allowing the cars to coast.

 

[Rocky_H]

I disagree with Rocky_Hs response.

It's physics.

The motor created far more usable regen when at higher speeds than it does at lower speeds. The reason why Rocky_Hs answer is theoretically correct from one perspective, but flawed is that the voltage that is produced is much higher at faster speeds and that's one of the factors that is needed for the most regen.

You are talking about creating a very high spike of instantaneous power for a very short time, and saying, "Look! That is a high number!" But a high spike for a short time, versus a lower instantaneous value for a longer time still will result in about the same total amount of energy collected.

if you are letting your foot off of the accelerator slowly, you are very possibly creating no regen, just allowing the cars to coast.

Well, sure, that would be even better than fast or slow regen. Letting the car play out its momentum into gradually slowing forward motion (basically coasting) doesn't have the losses of motor conversions and battery charge and discharge of slowing down with regen and then having to apply power again.

 

[Snow Drift]

I literally had the same question. I usually ease off and just get enough braking force to slow as necessary. This generates a small green line for a long time.

But, in more aggressive or defensive situations I need heavy braking and it’s a longer line with obvious more pronounced forward inertia shift.

 

[wwu123]

I disagree with Rocky_Hs response.
The motor created far more usable regen when at higher speeds than it does at lower speeds. The reason why Rocky_Hs answer is theoretically correct from one perspective, but flawed is that the voltage that is produced is much higher at faster speeds and that's one of the factors that is needed for the most regen.

With V9, you should be able to see the regen curves for both methods and calculate the area under the curve, that's the total amount generated.

if you are letting your foot off of the accelerator slowly, you are very possibly creating no regen, just allowing the cars to coast.

And by the way, that latter approach is the way hypermilers get the most overall efficiency. You don't want to regen, if you can avoid it, better for efficiency to let that coasting take you farther. Of course regen is better than friction braking, but coasting is even better.

 

[David99]

You should regen slowly to get better efficiency overall. Regenerating gently over a longer period of time will always end up using less energy for the same miles driven. Not because it is more efficient, but because your average speed is lower. If you start decelerating earlier and use light regen all the way to the stop, your average speed is slower than when you maintain speed to the last moment and then use max regen. Higher speeds = higher aero drag = higher overall energy loss = more energy used to drive the same distance.

I think it's also very annoying for car behind you if you drive in a way where you keep speed until the last moment and then decelerate hard. It is also uncomfortable for your passengers.

 

[electrictorque]

This.. there will always be losses when charging batteries. So you better off coasting.

 

[Jedi2155]

From the motor perspective, and my experience with the Chevy Volt's PM motor regen characteristics, its much more efficient regening at a higher power (shorter stops with higher regen, vs gradual regen over a longer distance).

For reference, the Volt was regen efficiency was between 50 to 75% efficient in capturing regen energy. Standard/Normal regen on the Model 3 is limited to 0.2g's of regen so at low rates of decel you're probably looking at well under 50% efficiency.

Not sure how accurate this chart is and if there is an updated one based on Tesla's drive trains but it should give you an idea that regenerative braking isn't as great as simply coasting.

The graph was pulled off somewhere here, but can't remember where:
Leap Cad Systems - A Knowledge Science approach to energy innovation

 

[jerry33]

In general, the longer it takes to go from X to zero, the more efficient you are. Regeneration is better than throwing the energy away using only the friction brakes, but that’s it. There are many energy conversion losses:

Kinetic to mechanical
Mechanical to electrical
Electrical to chemical

 

[Jedi2155]

In general, the longer it takes to go from X to zero, the more efficient you are. Regeneration is better than throwing the energy away using only the friction brakes, but that’s it. There are many energy conversion losses:

Kinetic to mechanical
Mechanical to electrical
Electrical to chemical

I still don't entirely agree the generalized statement of the longer it takes, the more efficient it is. The issue is much more piece wise. Take for example your losses you mentioned:

Kinetic to mechanical - Maximizing this time will net best efficiency. This is driven by air resistance/rolling resistance.
Mechanical to electrical - Minimizing this time will net best efficiency due to motor design.
Electrical to chemical - Negligible. Lithium-ion cells typically have 99% faradiac efficiency. For other chemistries such as lead acid you would be right (low charging rates are better), but lithium is a non-issue.

 

[jerry33]

I still don't entirely agree the generalized statement of the longer it takes, the more efficient it is. The issue is much more piece wise.

I can offer an anecdote:

 

[Jedi2155]

I can offer an anecdote:
View attachment 347329

Now I'm interested in what your average speed is....

 

[Emmexx1]

One of my favorite parts of the regen is the light to light dash in vegas against other cars. High power burst, then letting the regen capture the energy back while the ice doesn't get the gas back and has to use up their brake pads

 

[David99]

The discea out regen not comes up again and again. Coasting vs Regen is Apple and oranges. In most normal driving situations on freeways or cities you don't have the space between other cars to coast to a stop. I have recorded how much throttle and regen I use just driving normal and it's actually much more than I thought and I'm a rather conservative driver. I always look way ahead and try to drive consistent and smooth. My daughter says I drive like a grandma LOL
Coasting is only good when you need to slow down very gradually. It happens very rarely in normal traffic. Maybe I'm a little biased because I live in Los Angeles and there are always lots of cars on all roads. I constantly have to adjust my speed to traffic which means I use regen a lot.

If anyone thinks coasting is practical in city traffic, please take an ICE car and try to drive through a busy city without touching the brake pedal. Just accelerate and coast

Regen is as efficient as acceleration. The argument that we should avoid regen because it's not 100% efficient makes no sense. Only if you have a more efficient alternative. Coasting isn't. Coasting does not slow the car down enough in 95% of the cases in normal traffic. It's also not more efficient. It's just letting the aero drag and friction (mostly from the tires) slow the car down over a long distance. Those losses are always present. All the time. So there is nothing special about coasting.

Just think about it this way. You on a gentle downhill road. You let the car roll down freely and the car will go down at 80 mph. At the end of the downhill section you have not used any energy. The energy from going downhill has been lost mostly in aero drag.
Now go the same road, and Regen a little the entire time staying at 40 mph. At the end of the downhill section you will have regenerated some energy. Going half the speed has reduced the aero drag to 1/4 and that energy was now available to regen. In the first case you have use no energy. In the second case you gained some energy back.

 

[jerry33]

The discea out regen not comes up again and again. Coasting vs Regen is Apple and oranges. In most normal driving situations on freeways or cities you don't have the space between other cars to coast to a stop. I have recorded how much throttle and regen I use just driving normal and it's actually much more than I thought and I'm a rather conservative driver. I always look way ahead and try to drive consistent and smooth. My daughter says I drive like a grandma LOL
Coasting is only good when you need to slow down very gradually. It happens very rarely in normal traffic. Maybe I'm a little biased because I live in Los Angeles and there are always lots of cars on all roads. I constantly have to adjust my speed to traffic which means I use regen a lot.

Right. Most of the time you have to use some, or even a lot, of regen. I have a non-standard commute so, at least in the morning, I miss 90% of the traffic. But regen is not an all or nothing scenario, so you can us as much or little as the situation calls for. As far as I can tell, there's not a significant difference between coasting and a small amount of regen in the amount of energy you save. Also if you are going down hill at a high speed, there is a point where you are just pushing air and gaining nothing from coasting, in that case some regeneration and descending a bit slower is much better than just coasting.

If you have one of the newer cars that doesn't have a decent power metre, you can't really drive using the instrumentation anyway.

 

[jerry33]

Now I'm interested in what your average speed is....

The average on a trip is about 55 mph but that includes going through town, unhurried dining stops, and recharging stops. In town it's lower because of all the traffic lights and stop signs. It doesn't take too many stops to lower the average speed significantly. About half the miles on my car are trip miles.

 

[Jedi2155]

I don't necessary recommend the most efficient driving method because its not the safest so I try to optimize between safety and max efficiency on my braking.

In regards to the coasting vs.regen, To optimize for efficiency, I basically try to regen as late as possible without having to hit the brakes. Basically the greater the regen power/speed, the more efficient the motor is.

 

[David99]

I did some measurements with my Model S if anyone is interested
most efficient regen speed measured