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PostPosted: Thu Dec 29, 2011 9:22 am 
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Smidge204 wrote:
abasile wrote:
johntaves wrote:
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 wrote:
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.

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PostPosted: Thu Dec 29, 2011 9:28 am 
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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.


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PostPosted: Thu Dec 29, 2011 9:38 am 
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EVDRIVER wrote:
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.

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PostPosted: Thu Dec 29, 2011 10:05 am 
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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

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PostPosted: Thu Dec 29, 2011 11:49 am 
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TonyWilliams wrote:
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=


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PostPosted: Thu Dec 29, 2011 11:58 am 
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I'm sorry, but I have to strongly disagree!

EVDRIVER wrote:
The LEAF forum is not a tech forum...

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PostPosted: Thu Dec 29, 2011 12:08 pm 
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Smidge204 wrote:
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.

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PostPosted: Thu Dec 29, 2011 3:14 pm 
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Smidge204 wrote:
TonyWilliams wrote:
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.


TickTock did some of those test with actual data. I'd search his reports on this forum.

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PostPosted: Thu Dec 29, 2011 4:43 pm 
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abasile wrote:
johntaves wrote:
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 wrote:
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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PostPosted: Thu Dec 29, 2011 5:23 pm 
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DaveinOlyWA wrote:
sure the request is valid, but has been requested SEVERAL times already in slightly varying ways.

Please provide an example.


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