Recuperation

[Boatguy]

I understand the concept, but not the app's metric. Recuperation is expressed as mi/kWh.

So what does 15.5 mi / kWh mean?

 

[mindmachine]

I understand the concept, but not the app's metric. Recuperation is expressed as mi/kWh.

So what does 15.5 mi / kWh mean?

I noticed that, it doesn't make sense. Maybe it should say .155 mi/kwh

 

[KurtEndress]

Just as power used is measured in mi/kWh so is the power regenerated. When it tells you that you used 4.1 mi/kWh that means you drove 4.1 miles for each kWh used. Similarly when it says you recuperated 15.5 mi/kWh that means that one kWh was recuperated for every 15.5 miles driven. Smaller numbers mean higher recuperation. Take the inverse if it makes more sense to you. 1/15.5 = 0.065 kWh recuperated for each mile driven.

 

[Chrisn]

It still seems like a ridiculous and meaningless number. In cruise control on a flat empty road, you would recuperate nothing and yet this is the most efficient driving possible (at any speed).

A better metric is the percentage of optimal regenerative braking that was actually achieved, which I assume is maximized by gentle off-throttle, single-pedal (never touching brake pedal) operation.

 

[nowtta60]

It still seems like a ridiculous and meaningless number. In cruise control on a flat empty road, you would recuperate nothing and yet this is the most efficient driving possible (at any speed).

A better metric is the percentage of optimal regenerative braking that was actually achieved, which I assume is maximized by gentle off-throttle, single-pedal (never touching brake pedal) operation.

???
Of course you won'trecuperate anything while maintaining steady speed. But That's like saying mpg is a ridiculous metric if you are sitting in the car with the engine off.

Its recording how much energy you have recovered, the opposite of what you used.

Asking what you"could" have recovered isn't really feasible, just like along for what you could have used I'd you drove better isn't.

 

[jadnashuanh]

A road is rarely perfectly level, and you'd be surprised how often the car ends up coasting or regenerating while on cruise.

 

[Chrisn]

Asking what you"could" have recovered isn't really feasible, just like along for what you could have used I'd you drove better isn't.

I disagree. The ONLY important metric is the portion of what COULD have been recovered versus what WAS recovered. The raw "recovered" number tells you nothing of interest.

The maximum potential recovery is knowable from existing sensors in the car (notably speed, acceleration, throttle input and brake input).

The percent of optimum is valuable information, not the raw regen number. In a non-plug-in hybrid, the number is interesting because it tells you how much energy (that started as gasoline) is stored in the battery instead of vented as friction heat from brakes--- real upside. That is interesting data. What useful information is in the "raw" regen number in a BEV? It's useless trivia as it just measures the round-tripping of energy that STARTED in the battery (which, given heat loss is a BAD thing that you should want to minimize). If you disagree, please explain.

 

[Chrisn]

A road is rarely perfectly level, and you'd be surprised how often the car ends up coasting or regenerating while on cruise.

I agree, but an optimal cruise control feature would seek to minimize this by allowing speed to drift +/- say 3MPH to smooth/minimize acceleration and regen since the round-tripping of electricity is not 100% efficient. Regen is only your friend if the alternative is friction braking-- coasting will always be better.

 

[jadnashuanh]

How much have you used your cruise control? I have to ask as I find it programmed to avoid any rapid changes in speed. Going down a hill, it regenerates just enough to maintain the speed, but starting back up the other side, it takes it a bit to recover to your set speed if it dropped a little on the change over. Even the Adaptive cruise control is somewhat slow to take off after a stop (somewhat dependent on the following distance you have setup). As opposed to most CC on an ICE, the time to set speed is a little lazy. I don't think it is perfect by any means, but it does a very creditable job.

 

[Boatguy]

Just as power used is measured in mi/kWh so is the power regenerated. When it tells you that you used 4.1 mi/kWh that means you drove 4.1 miles for each kWh used. Similarly when it says you recuperated 15.5 mi/kWh that means that one kWh was recuperated for every 15.5 miles driven. Smaller numbers mean higher recuperation. Take the inverse if it makes more sense to you. 1/15.5 = 0.065 kWh recuperated for each mile driven.

That is what I thought it meant, but I was confused by the statistics which generally are graphed with "better" values to the right. In this case, I guess a better value is to the left, with a lower number, i.e., recuperating a kWh in fewer miles.

Since we also have net consumption in mi/kWh, we can get to gross consumption (i.e., the lead foot index). Using the inverse values makes that easier for me to understand. Consider an outing which reports 5mi/kWh of consumption and 10mi/kWh of recuperation. This works out to 200Wh/mi of consumption, 100Wh/mi of recuperation, and 300Wh/mi of gross consumption. Net consumption can be manipulated by changing gross consumption or recuperation. In this example the driver has a bit of a lead foot, but is very adapt at anticipating changes and exploiting coasting.

I'm not sure how useful any of this information is, but I guess if you drove the same route regularly you could try to improve your power consumption by studying the recuperation rate.

 

[nowtta60]

Asking what you"could" have recovered isn't really feasible, just like along for what you could have used I'd you drove better isn't.

I disagree. The ONLY important metric is the portion of what COULD have been recovered versus what WAS recovered. The raw "recovered" number tells you nothing of interest.

The maximum potential recovery is knowable from existing sensors in the car (notably speed, acceleration, throttle input and brake input).

The percent of optimum is valuable information, not the raw regen number. In a non-plug-in hybrid, the number is interesting because it tells you how much energy (that started as gasoline) is stored in the battery instead of vented as friction heat from brakes--- real upside. That is interesting data. What useful information is in the "raw" regen number in a BEV? It's useless trivia as it just measures the round-tripping of energy that STARTED in the battery (which, given heat loss is a BAD thing that you should want to minimize). If you disagree, please explain.

chris.. I'm not arguing it wouldn't be useful, just that it not a simple figure to work out what could have been done. forget EVs for a minute... what you are asking is the same as asking a ICE car to tell you what MPG you could have got had you driven differently.

Back in EV land.. what figure could it come up with? The car can't know you had to slow down to allow granny to cross the road, or that

Isn't the best figure a regen of 0 anyway? Shows you have planned ahead and can "roll" the car to a stop without using wasteful regen. So we are back to the regen telling what you did recover, vs 0?

 

[Chrisn]

How much have you used your cruise control? I have to ask as I find it programmed to avoid any rapid changes in speed. Going down a hill, it regenerates just enough to maintain the speed, but starting back up the other side, it takes it a bit to recover to your set speed if it dropped a little on the change over. Even the Adaptive cruise control is somewhat slow to take off after a stop (somewhat dependent on the following distance you have setup). As opposed to most CC on an ICE, the time to set speed is a little lazy. I don't think it is perfect by any means, but it does a very creditable job.

I use it all the time and agree that it is good, but the fact that it leads to some regen is not a good unto itself. It is a lesser evil, which friction braking being the worst case and constant power and/or coasting being the ideal.

 

[Chrisn]

I'm not arguing it wouldn't be useful, just that it not a simple figure to work out what could have been done. forget EVs for a minute... what you are asking is the same as asking a ICE car to tell you what MPG you could have got had you driven differently.

Back in EV land.. what figure could it come up with? The car can't know you had to slow down to allow granny to cross the road....

Isn't the best figure a regen of 0 anyway? Shows you have planned ahead and can "roll" the car to a stop without using wasteful regen. So we are back to the regen telling what you did recover, vs 0?

First, just to be clear, the i3 and most other BEVs you the throttle to modulate positive and negative acceleration, so "coasting" is a bit of a fuzzy concept-- unless you shift to "N." But I hear you.

It can't know about granny, but it can know a lot-- enough to consider granny an anomaly. It provides SOME directionally useful info, whereas raw regen provides very little in terms of driving style. Agree that zero regen is optimal in theory, but not achievable in practice (very hard to truly "coast" to full stop (versus implicitly causing regen braking by lifting off throttle)). A very simple proxy would be to measure the net kWh used (or, hopefully, gained) between the beginning of a deceleration event and a full stop or a resumption of constant speed. Knowing its approx mass, it can simply observe the SOC and velocity at the beginning and end of such events and can come up with a best case and an actual. Whatever the methodology, you get the idea.

As an aside, the Ford Energi system reports this info.

 

[Boatguy]

I'm not arguing it wouldn't be useful, just that it not a simple figure to work out what could have been done. forget EVs for a minute... what you are asking is the same as asking a ICE car to tell you what MPG you could have got had you driven differently.

Back in EV land.. what figure could it come up with? The car can't know you had to slow down to allow granny to cross the road....

Isn't the best figure a regen of 0 anyway? Shows you have planned ahead and can "roll" the car to a stop without using wasteful regen. So we are back to the regen telling what you did recover, vs 0?

First, just to be clear, the i3 and most other BEVs you the throttle to modulate positive and negative acceleration, so "coasting" is a bit of a fuzzy concept-- unless you shift to "N." But I hear you.

It can't know about granny, but it can know a lot-- enough to consider granny an anomaly. It provides SOME directionally useful info, whereas raw regen provides very little in terms of driving style. Agree that zero regen is optimal in theory, but not achievable in practice (very hard to truly "coast" to full stop (versus implicitly causing regen braking by lifting off throttle)). A very simple proxy would be to measure the net kWh used (or, hopefully, gained) between the beginning of a deceleration event and a full stop or a resumption of constant speed. Knowing its approx mass, it can simply observe the SOC and velocity at the beginning and end of such events and can come up with a best case and an actual. Whatever the methodology, you get the idea.

As an aside, the Ford Energi system reports this info.

I agree that the total recoverable energy can be known for a given deceleration cycle. Physics tells us the amount of energy in a mass traveling at certain speed and BMW knows how much of that energy will be lost due to drag, rolling resistance, energy conversion etc. before it can be stuffed back in the battery. So it doesn't matter if I'm driving on a freeway or around town, each deceleration cycle, even if it doesn't terminate with a stop, has a knowable amount of recoverable energy. Telling me how much I am recovering versus the optimal amount would be much more useful than the raw mi/kWh data.

It may well be that I'm unable to reach 100% of potential recovery because granny steps out in front of me, but that's for me to know and use to understand my less than 100% score.

 

[ultraturtle]

A better metric is the percentage of optimal regenerative braking that was actually achieved, which I assume is maximized by gentle off-throttle, single-pedal (never touching brake pedal) operation.

The i3 has a brake pedal? Handy to know. Is it that thing to the left of the accelerator?

 

[Soapboxjonny]

can't remember the last time i used my brake pedal !!

 

[jadnashuanh]

It's a good idea to use the brakes once in awhile since otherwise, they'll get a nasty coating of rust on them. A little is normal, but extended non-use can become an issue.