Proper Efficiency Gauge

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johntaves said:
EVDRIVER said:
Please be specific on implementation and calculations.
Roughly speaking:

driving efficiency = S / (Kw - A)

S = Speed.
Kw = energy going to the motor.
A = energy measured from the accelerometer.

Can you be less "rough"? Your efficiency number in MKS units is S (m/s) / (Joules/sec - Joules)?
or is the denominator (kWh - A)?
If it's the latter then its units are m/s / Joules = m/s / (m x kg x m / s^2).
I'm just trying to get a clear understanding what you're measuring and how you want to report it.
Thx.
 
sparky said:
Can you be less "rough"? Your efficiency number in MKS units is S (m/s) / (Joules/sec - Joules)?
or is the denominator (kWh - A)?
If it's the latter then its units are m/s / Joules = m/s / (m x kg x m / s^2).
I'm just trying to get a clear understanding what you're measuring and how you want to report it.
Thx.

Oops, I don't mean S, I mean D = Distance. (I fixed that post).

We want to get a reading of m/j (meters/joules), which is what we are getting with the current economy gauge (miles/kWh). However, we want this gauge to NOT ignore the stored energy in the form of potential and kinetic. So, in my lame notation, the current Leaf gauge is D/Kw and therefore you are asking what I mean by A.

A = the energy stored as kinetic and potential energy.

Kinetic and potential energy are both the same units, which are the same for Joules = Kg x m^2 / s^2

(mass over two times the speed squared) and (mass times gravity times height)

Did that clarify?
 
Actually, it is not very useful to give "credit" for climbing or accelerating (potential or kenetic energy) because we typically can recover so little of it. Not zero, but nothing dependable. Every time we brake, the mechanical brakes get applied, at least a little, and often a lot (as the light turns yellow unecpectedly, as we moderate speed going downhill, or as traffic stops abruptly).

If the averaging time of the present m/kwh meter could be adjusted by the user down to a few seconds, the meter would be quite useful. The current average (perhaps 5 miles or 10 minutes) is too often misleading.
 
garygid said:
Actually, it is not very useful to give "credit" for climbing or accelerating (potential or kenetic energy) because we typically can recover so little of it. Not zero, but nothing dependable. Every time we brake, the mechanical brakes get applied, at least a little, and often a lot (as the light turns yellow unecpectedly, as we moderate speed going downhill, or as traffic stops abruptly).

If the averaging time of the present m/kwh meter could be adjusted by the user down to a few seconds, the meter would be quite useful. The current average (perhaps 5 miles or 10 minutes) is too often misleading.
You are not comprehending what this gauge would do for you. Any gauge that shows that during regen, or when coasting, you are getting infinite efficiency is a piece of junk. This change would be useful for ICE cars too.

When you push on the go pedal, energy is converted from chemical to kinetic. That kinetic energy is energy that you can use in the future just like the energy in the battery is energy you can use in the future. This meter will tell you how efficiently you use that energy too. The fact that the regen is "little" is irrelevant. Spending your kinetic energy on motion overcoming road friction is more efficient than putting it back into the battery. This gauge will show this.
 
As I've mentioned in other threads, the little "eco" meter that's part of the "tree" display on the upper left can be very helpful in ascertaining how efficiently one is braking, i.e., regenerative versus friction braking. If you're pressing the brake pedal and that gauge is all the way to the right, then close to 100% of your braking is regenerative.

I personally use the Energy Info screen quite a bit, mainly as a guide when coasting and to help moderate power usage during acceleration and climbing. It seems to be more precise than the "bubbles". That said, there is some smoothing taking place, and it doesn't seem to be completely in sync with the bubbles. At 20 kW motor power on the Energy Info screen, I usually see three power bubbles, but sometimes four.

By the way, the eco/tree meter does reward gentle acceleration. While I am not an expert, my current understanding is that the battery pack delivers power more efficiently at moderate discharge rates.
 
johntaves said:
Spending your kinetic energy on motion overcoming road friction is more efficient than putting it back into the battery.
Generally speaking, that is true. Except when you're going particularly fast and losing a great deal of energy to aerodynamic drag. In that case you're likely better off putting some of that kinetic energy back into the battery, and then coasting at a lower speed if traffic allows.

I think I understand what you're after here. You want some indication as to how the driver's current behavior is going to affect the overall range/efficiency of the car. For example, while regenerative braking is generally good, having to brake at all is usually a negative. At most driving speeds (except particularly low or high speeds), coasting would yield the highest possible instantaneous score. Maintaining a steady, moderate speed at low power would yield a relatively high score; maintaining the most optimal speed (which might only be 12.5 mph without climate control) would be rewarded. Both acceleration and braking would yield lower scores, depending on the magnitude and whether there is regenerative braking.

The eco/tree meter does some of this, but only up to a certain point. For example, doing lots of slow, stop and go driving can earn many trees, but in the end is not necessarily more efficient than taking the freeway instead and maintaining a steady 55 mph.
 
abasile said:
johntaves said:
Spending your kinetic energy on motion overcoming road friction is more efficient than putting it back into the battery.
Generally speaking, that is true. Except when you're going particularly fast and losing a great deal of energy to aerodynamic drag. In that case you're likely better off putting some of that kinetic energy back into the battery, and then coasting at a lower speed if traffic allows.

No, in that case you are still better off coasting freely, letting air resistance slow you down. Every kWh not put into overcoming resistance is a kWh wasted, and putting it back into the battery wastes something like 20% of it.

Ideally you should not have been going that fast in the first place :lol:


Edit: I've bodged a simulation for coasting vs. regen braking from 70MPH to 55MPH. What's a good value to plug in for regen power (kW) and regen efficiency?
=Smidge=
 
Smidge204 said:
Edit: I've bodged a simulation for coasting vs. regen braking from 70MPH to 55MPH. What's a good value to plug in for regen power (kW) and regen efficiency?
=Smidge=

There is no one value. What temperature is your battery (and how much is regen limited from a cold battery)?

Age of the battery will increase its internal resistance, and presumably how much regen is possible (we don't, obviously, have much data on this with the LEAF).

Are you coasting up or downhill? Eco mode or D ? N, of course, will coast but provide no regen.
 
my Prius has a DTE gauge as well. on my last fill up it was at 530 miles. problem is in winter, i only get around 450 miles (SO does not even know the meaning of efficiency) and lucky to average 45 mpg despite an opportunity to average at least 50 mpg with minimal effort.

so all the complaints against the GOM is based on our erroneous impression that "some other" vehicle in our past did a better job.

BUT, there are more than 10 million incidences annually (could be much more this is 2007 stats...) of people running out of gas in a 400 mile range vehicle that has several dozen "quick charge" options. also, many reports that calls to roadside asst has jumped because people are now trying to make it to cheaper gas stations.

http://abclocal.go.com/wtvd/story?section=news/local&id=6185576" onclick="window.open(this.href);return false;

so what forum do i go to petition for better gas gauges?
 
You guys are trying to reinvent something other people have invested great detailed time doing, people with more EV experience. If you go to the Aptera forum there was an expensive thread on range and efficiency tools. The LEAF forum is not a tech forum, people have been discussing these issues in detail for years on other forums. EVDL, EV tech list? Etc. Like so many topics here, there are better sources for information and learnings for those serious about doing something with this information.
 
Smidge204 said:
abasile said:
johntaves said:
Spending your kinetic energy on motion overcoming road friction is more efficient than putting it back into the battery.
Generally speaking, that is true. Except when you're going particularly fast and losing a great deal of energy to aerodynamic drag. In that case you're likely better off putting some of that kinetic energy back into the battery, and then coasting at a lower speed if traffic allows.
No, in that case you are still better off coasting freely, letting air resistance slow you down. Every kWh not put into overcoming resistance is a kWh wasted, and putting it back into the battery wastes something like 20% of it.
Air resistance increases exponentially with velocity, whereas moderate regenerative braking can be performed at reasonable efficiency irrespective of velocity. By using regen to slow from, say, 90 mph (to pick an extreme example), you can put some energy into the pack and at the same time greatly reduce the air resistance going forward.

Smidge204 said:
Ideally you should not have been going that fast in the first place :lol:
True enough. On many long downhill sections of freeway here in California, it is easy to exceed 80+ mph simply by coasting. When traffic allows, I like to use regen to hold my speed down to 55-60 mph until close to the bottom of the hill, at which point I'll let it creep up to 65-70 mph. The alternative would be to simply coast at terminal velocity on the entire descent, thus throwing more energy to the wind.
 
Yep- and cars with more regen then the LEAF get quite a bit recovered. For those that don't believe in regen or think the LEAF regen needs work Ask Tom Gauge of ACP how much he gets back in his xbox when driven in SF and the bay area. If desired, that car will only touch the brake pads in the las 1-2 MPH to hold the car in place. I've driven this car and it is a great EV experience.
 
EVDRIVER said:
You guys are trying to reinvent something other people have invested great detailed time doing, people with more EV experience. If you go to the Aptera forum there was an expensive thread on range and efficiency tools. The LEAF forum is not a tech forum, people have been discussing these issues in detail for years on other forums. EVDL, EV tech list? Etc. Like so many topics here, there are better sources for information and learnings for those serious about doing something with this information.
If you'd care to provide links to those forums, that would be appreciated. Sure, we can Google around, but still.

I'm not sure what you mean in stating that the LEAF forum is not a tech forum. I agree that the level of technical depth might not be as great as some other forums. However, significant portions of this particular discussion are LEAF-specific, including my comments on the eco/tree meter.

It seems to me that it might be possible, without a huge amount of effort, to include some additional "efficiency" functions in a future version of Gary's SOC meter.
 
there are "techy" subforums here but this is really not one of them. sure the request is valid, but has been requested SEVERAL times already in slightly varying ways.

i think Nissan has gotten the message
 
TonyWilliams said:
There is no one value.
Granted, yes. But I'm talking about a simulation strictly for comparison between regen brake to slow down vs. coasting down. I want to demonstrate, one way or the other, if recovering X% of the vehicle's kinetic energy through regen is worth it compared to losing that energy to air resistance at higher average speeds. Until now I've basically been asserting that it's better to coast, but I'd like to try some math and find out if I'm right or not.

So right now I'm guessing 80% overall regen efficiency and 5kW regen rate, for light braking to slow down a little at highway speeds. I've no idea what a reasonable regen rate would be for these conditions.
=Smidge=
 
Smidge204 said:
right now I'm guessing 80% overall regen efficiency and 5kW regen rate, for light braking to slow down a little at highway speeds.
Seems like a reasonable place to start. If you're trying to slow more quickly, then the regen rate could be 20 kW, but that would likely reduce the regen efficiency.
 
abasile said:
johntaves said:
Spending your kinetic energy on motion overcoming road friction is more efficient than putting it back into the battery.
Generally speaking, that is true.
The point is not to debate this. The point is to make the gauge give us this info. The change I am suggesting will provide this info, so we don't have to have to debate it.
abasile said:
The eco/tree meter does some of this, but only up to a certain point. For example, doing lots of slow, stop and go driving can earn many trees, but in the end is not necessarily more efficient than taking the freeway instead and maintaining a steady 55 mph.
The circle/trees are an unbelievably stupid gauge; one where pretty much no owner comprehends what it tells you.

The change I am talking about for the economy gauge, is fundamentally sound. Imagine if we were discussing accounting. Employees of the company buy computers to do their job. Sometimes they return the computer for a refund. If the accounting practice was to put the return of that computer as revenue, it would simply be wrong. It doesn't matter that that revenue is small compared to the real revenue.

Putting the energy that went to potential and kinetic in the waste category, is just plain wrong. It causes the current gauge to rise too high when you accelerate and go negative when you decelerate, which is logically incorrect.

If they did it my way, then updated the software to do it the current way, everyone would be pissed off.
If they updated today's software to do it my way, you might at first be wary, but after a few miles, you'd be disgusted that they gave you the other crap at first.
 
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