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Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 11:54 am
by JPWhite
davewill wrote:You post this a lot, and I have tried this several times but it never works. The car soon slows down 1 mph and starts using power at much the same rate as before.
I agree any benefit from utilizing coast on the CC is temporary. It's gonna take the same amount of energy to move you forward at say 55mph regardless how you got there.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 5:26 pm
by DaveinOlyWA
i think we are all overestimating the benefit of regen here.

the amount of power to slow to zero is much less than the power it took to get it there.

accelerating means wind friction and gravity are overcome. both of which ADDS to the effort to slow down which is power not available for regen

after we calculate that, then we can start with the losses associated with regen. one posted 66% efficiency, ok. i can buy that. now remove the energy from gravity and wind resistance and what is left?

30-40% maybe? either way, i think that is still pretty good although i doubt its that high.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 6:45 pm
by EVDRIVER
DaveinOlyWA wrote:i think we are all overestimating the benefit of regen here.

the amount of power to slow to zero is much less than the power it took to get it there.

accelerating means wind friction and gravity are overcome. both of which ADDS to the effort to slow down which is power not available for regen

after we calculate that, then we can start with the losses associated with regen. one posted 66% efficiency, ok. i can buy that. now remove the energy from gravity and wind resistance and what is left?

30-40% maybe? either way, i think that is still pretty good although i doubt its that high.
The wind is there on both ends as a fixed constant, like a brake dragging. Regen losses are easily calculated in the system components. Everyone seems to miss the large losses due to the software limited LOW power of the LEAF regen under many circumstances which goes to brakes.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 10:28 pm
by planet4ever
DaveinOlyWA wrote:the amount of power to slow to zero is much less than the power it took to get it there.

accelerating means wind friction and gravity are overcome. both of which ADDS to the effort to slow down which is power not available for regen
Sorry, Dave, but I think you are wrong on this one. Yes, it is true that if we run a hypothetical test on a frictionless system in a vacuum we should in theory be able to recover all energy when slowing that was expended while speeding up; and that is certainly not true with air in the system. But the losses due to air resistance are part of the cost of getting from A to B in less than infinite time. They are related to your instantaneous speed, and their instantaneous values have nothing to do with whether you are accelerating or decelerating. You are still making forward progress while slowing, and the air drag is a penalty against that progress, not against the deceleration.

Ray

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 11:29 pm
by SanDust
DaveinOlyWA wrote:30-40% maybe? either way, i think that is still pretty good although i doubt its that high.
Yes, rolling resistance and drag and drive train losses (don't forget them, the Leaf's motor isn't very efficient at higher speeds) are dead weight losses. No way to recover those. The energy you can recover through regen is deceleration, either from slowing down or from coming down hills. As an overall number I'd think 30% would be on the high side but attainable.

Regen itself though might be 70% efficient in the best case (one way return, 55% round trip).

This is what I meant by saying that people use different numbers for regen efficiency so you have to understand what number they're talking about.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 11:45 pm
by Herm
Regen is very effective if used at moderate speeds in heavy stop and go traffic, since it cant be 100% efficient then its always better to drive as if you had no brakes.. but it does take longer to get anywhere.

A modern motor/inverter should be as efficient accelerating or decelerating, and lithium ion batteries are already very efficient at moderate SOC usages so I would not be surprised if 85% or higher regen efficiencies (for a one way electrical roundtrip) are achieved... at least during some portions of the braking cycle.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 11:49 pm
by SanDust
planet4ever wrote:Sorry, Dave, but I think you are wrong on this one. Yes, it is true that if we run a hypothetical test on a frictionless system in a vacuum we should in theory be able to recover all energy when slowing that was expended while speeding up; and that is certainly not true with air in the system. But the losses due to air resistance are part of the cost of getting from A to B in less than infinite time.
I think he's agreeing with this though I may have misunderstood what he was trying to say. I find it easier to think in terms of what regen can do. Regen can turn kinetic energy into chemical energy. That's it. It can't turn heat into chemical energy. Hence anything that creates heat, such as drag which heats the air, or rolling resistance which heats the tires and road, can't be recovered by regen.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Tue Sep 06, 2011 11:56 pm
by SanDust
Herm wrote:A modern motor/inverter should be as efficient accelerating or decelerating, and lithium ion batteries are already very efficient at moderate SOC usages so I would not be surprised if 85% or higher regen efficiencies (for a one way electrical roundtrip) are achieved... at least during some portions of the braking cycle.
I can't see how 85% would be possible. Since the drive train is something like 80% efficient and you need 10% overvoltage for charging, something around 70% would seem to be the max best case for a one way trip from wheels to battery. Round trip, battery to battery, you're looking at something more like 55% (.8 X .8 X .9).

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Wed Sep 07, 2011 11:06 am
by LEAFfan
davewill wrote:
LEAFfan wrote:7. To stay in the neutral bubble and to keep your speed constant once up to speed, you can use the CC by going one mph over what you want, then push down quickly on the button and it will put you in the neutral bubble.
You post this a lot, and I have tried this several times but it never works. The car soon slows down 1 mph and starts using power at much the same rate as before.
So you are saying that you use the same power from the energy screen with one bubble as I do with the neutral bubble? Interesting, but not with my LEAF. I can see a slight difference between the two, no matter what speed I'm going in the neutral bubble. In fact, at low speeds, I have seen ZERO for more than 30 secs (no needle) on the energy screen while it's in the neutral bubble. How do you think I can get 6.5m/kW h (dash) on a 22 mile city trip (no impeding traffic) and 9.1m/kW h on the 15mph loop otherwise? I always use the neutral bubble with CC.

Re: Stoaty's Guide to Energy Efficient Driving of the Leaf

Posted: Wed Sep 07, 2011 12:11 pm
by davewill
LEAFfan wrote:So you are saying that you use the same power from the energy screen with one bubble as I do with the neutral bubble? Interesting, but not with my LEAF. I can see a slight difference between the two, no matter what speed I'm going in the neutral bubble.
No. I'm saying that the CC always goes back to using the same number of bubbles shortly after I try your "trick" of clicking the CC down 1 mph.