Cruising to a stop down hill.

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ashdeacon

Member
Joined
Sep 20, 2018
Messages
12
Hi all,

I have an energy regeneration question for you. I looked around and some similar items have been discussed but not quite the same.

This is a real life example, since I live at the bottom of a long descent....

Say I am driving down a long hill and I need to stop at the bottom of the hill.

I basically have 3 options which all involved energy recapture.

I can gradually regenerate over the whole descent in D mode.

Or I could brake more later in the slope in B mode

Or I could brake really late with the e-pedal.

I guess my question is does gentler more gradually regeneration capture more energy vs more intense energy regen??

I guess the real answer is to do a real life experiment, though I am not sure I have sensitive enough readouts of battery charge to make this meaningful...

Ash.
 
I would think the regen rate won't affect efficiency, unless you exceed 30 kW (the max regen rate).

What's more likely to impact overall efficiency is air drag at higher speeds. So, I would likely use ECO level regen down the entire hill as that should keep your speed in check best and thereby lower losses due to air drag.
 
ashdeacon said:
Hi all,

I have an energy regeneration question for you. I looked around and some similar items have been discussed but not quite the same.

This is a real life example, since I live at the bottom of a long descent....

Say I am driving down a long hill and I need to stop at the bottom of the hill.

I basically have 3 options which all involved energy recapture.

I can gradually regenerate over the whole descent in D mode.

Or I could brake more later in the slope in B mode

Or I could brake really late with the e-pedal.

I guess my question is does gentler more gradually regeneration capture more energy vs more intense energy regen??

I guess the real answer is to do a real life experiment, though I am not sure I have sensitive enough readouts of battery charge to make this meaningful...

Ash.

The slower descent will give you more charge. Otherwise the vehicle speeds up and encounters more air resistance. Drag increases with the square of the airspeed so doubling speed gives 4 times more drag and the energy will go towards fighting drag instead of charging the battery.
 
Good point on the speed drag.... I will aim for constant smooth speed and gradually braking as I near my end point.

Ash.
 
Yes, so both these factors would argue against going Neutral (accelerating down the hill by gravity) and then braking a lot in B or e-pedal and suggest more gradually D all the way down may be more beneficial.

Ash.
 
The correct answer is - it depends...

On less steep grades, you can often coast in neutral the whole time. On steeper grades, I usually use ECO regen and put it into B mode only if I'm still picking up too much speed.

So, there aren't really any golden rules to lean on for all circumstances, it's a bit of an art and there's definitely a learning curve but it's worth the effort on longer trips.
 
Understood.

I never even looked into Eco Mode to be honest. Mainly because I did not like the unresponsive throttle. So I assume Eco regen braking is somewhere between D and B mode?

I will give it a try on my next descent....

Thx
Ash
 
ashdeacon said:
Understood.

I never even looked into Eco Mode to be honest. Mainly because I did not like the unresponsive throttle. So I assume Eco regen braking is somewhere between D and B mode?

I will give it a try on my next descent....

Thx
Ash

Eco mode only re-maps the throttle curve, it does not remove any level of performance. I.e., you still have have command of the full 0-100% of power. I find it extremely helpful for smooth driving at lower speeds as it takes away the twitchiness, and if I want high power it's still there.
 
powersurge said:
Please stop worrying about regen.... It does not really matter.... It probably accounts for 3-5% of your battery range..

Depends on where you drive. I've seen more like 30% on a mountain drive. Flat and no stops might reach zero added range.
 
Can't speak for others, but I use a combination of N/D/ECO/B mostly cause it's a fun challenge. I don't drive like a Granny, so it's not really about getting the absolute max efficiency and range for me.

Having that skillset comes in handy too, when it can make the difference between having to stop for an extra charge rather than knowing you can make it with hyper-miling.
 
powersurge said:
Please stop worrying about regen.... It does not really matter.... It probably accounts for 3-5% of your battery range..

Back when I used to bother with CarWings stats, regen accounted for a fairly steady 10% of the car's motor energy. My typical pattern was about 2/3 highway 1/3 city. I'm sure it's less for hypermilers.
 
alozzy said:
Can't speak for others, but I use a combination of N/D/ECO/B mostly cause it's a fun challenge. I don't drive like a Granny, so it's not really about getting the absolute max efficiency and range for me.

Having that skillset comes in handy too, when it can make the difference between having to stop for an extra charge rather than knowing you can make it with hyper-miling.

Amazing!

Man, I would jump out the window or the car if I were a passenger and had to watch you do all that switching to get a few more watts of electricity..

Remember that a full charge costs about a buck or two ... So to do all that to save 10 cents seems like a lot of work... I think there comes a point when being able to survive on saving your resources becomes more than it's worth. Sure, I could live on 80% off clearance bread and water, but does it really matter.

Just an opinion. I am also guilty of trying to outsmart the Leaf "electron" fairies. When I first got my Leaf, I could charge at a free charger at a college 1/2 mile from my job... I would charge, and ride my bike back and forth to work. Then I moved to a different location, 1 1/2 miles from the charger. I stopped the bother because riding a bike that far to save $.50 of electricity each was not worth it....
 
@powersurge LOL, I hear ya - it's not for everyone. Like I said, I just find it fun and I don't always bother. It's not about the $$$ either, I know electricity is cheap. It's about forming habits too, the LEAF's limited range will eventually become an issue for me but, by learning these techniques now and making them habitual, I'll be able to stretch out the LEAFs useful life a bit...

I'm also fully on the EV bandwagon now and minimizing my energy use just seems like the right thing to do. We've also changed every CFL and incandescent bulb in our house to LEDs, we set our thermostat lower (69F daytime, cooler at night) and put on sweaters, we use our LEAF for 90% of our trips, etc - it all adds up...
 
@powersurge

Where do you get those 3-5% stats for regen??

During my first month of Leaf ownership I did 1600 miles (66 hours of driving) and used 460kWh electric of which 120kWh was generated, so my net use was 340kWh, so about 4.7 miles/kWh and just over 25% of energy used was regenerated.
 
"a lot of work??"

E pedal always. Its instantaneous regen to whatever degree is needed. Has anyone noticed the huge power draw when driving in neutral? Its a huge difference from the previous LEAFs...
 
powersurge said:
Please stop worrying about regen.... It does not really matter.... It probably accounts for 3-5% of your battery range..

I don't know where you came up with those numbers, but my experience with two different LEAFs is that regeneration offers significant benefit in stop/go city driving and some benefit in slow/go highway driving.

I noticed a severe drop in useable range during typical stop/go city driving, but only a slight impact to freeway range when the original battery in my 2011 deteriorated enough to reduce regeneration (and limit DC quick charging rate) in cool weather. It was particularly noticeable when there was a sudden drop in temperature during November 2012 and the original battery was down to 10 capacity bars.

The 2015 has more useable range in stop/go city driving than in highway driving because it recovers energy when slowing/stopping. I typically use "B" mode to minimize the need to use the brake pedal. There has not been a significant loss of regeneration with the 2015 even after 66,000 miles in Phoenix on the original battery.
 
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