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Regenerative energy vs. L

6K views 22 replies 16 participants last post by  Mister Dave 
#1 ·
When I am driving through the city or suburbia, when i am approaching a red light, I often coast and brake lightly in order to get as much regenerative charging as possible. Recently, I tried shifting into low to slow the car and then witch back to drive as i approach the line. Does it matter which method i use?
 
#2 ·
From purely an energy/efficiency standpoint since there are generating losses from regeneration one would think that the more you coast, as opposed to regenerating and then accelerating, the greater the efficiency. That assumes that when in D you slow down gently using your brake pedal, which regenerates just like L, and only engage the binders when coming to a full stop.

Of course many people like L because of the one pedal driving effect it offers.
 
#3 ·
If you follow the exact same acceleration/deceleration profile, it makes no difference whether you are in D or L (but that means that for some sites you'd be very lightly on the accelerator in L or lightly on the brake in D to achieve the same pace.)

However, people being what they are, there's a tendency to choose to spend more time with your feet on the floor instead of gathering the pedals, so in practice driving in L generally means stronger deceleration. If that's paired with coasting most of the way, it might be more efficient than a slow regeneration the whole distance; if you go straight from power into regen and the higher regen rate means holding power on longer, that will certainly be less efficient.
 
#4 ·
We use low all the time in both Volts... I get between 45-50 on the '13 and 4-45 on the '11 miles on charge.

My '13 was in shop a couple of weeks ago and they gave me a Gas Spark.

Had not driven a car with no regen in about a year... was very uncomfortable.. I am use to coming off ramps and going to traffic lights with regen. I rarely use full brake unless a traffic light turns quickly on me. on the '11 with 30k miles the brakes look new.

If you use D you may not go to regen as much... being in NJ where we always have lots of traffic... I believe L is the way to go.
 
#9 ·
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If you use D you may not go to regen as much... ... I believe L is the way to go.
for the same rate of deceleration the car provides exactly the same regeneration whether in D or L. there is NO EXTRA regeneration available in L than there is by using the brake pedal....

it may be more fun, or easier to use L to slow down, that's up to your, but don't imagine that you are somehow being smarter than the car's computers about recovering kinetic energy and storing it, they are doing a better job than you could ever do.
 
#5 ·
Depends upon what you mean by "coast". If you mean just let your foot of the accelerator and lightly braking then there is no difference. If you mean shifting into neutral and lightly braking then there is no regen and the mechanical brakes are used.
 
#6 ·
I prefer the L mode since there is no definitive feedback when using the brake pedal to modulate between regen and braking, you're either braking by regen or disks but you don't know the percentage of which leading to the possibility that you're using physical brakes more than you realize and "wasting" energy. By using the throttle pedal to modulate between power/regen you can use the Kw meter in the dash display to know when you are applying power, coasting, or activating regeneration.
 
#7 ·
It's simple enough to use the leaf meter on the dash to tell when braking is being applied (when the leaves disappear completely). After a week or so of driving, it's easy to get a feel for when braking kicks in. It's kind of fun actually to try to beat the meter and avoid the leaves disappearing.
 
#8 ·
Just to add, you can drive in L at 80 mph, it isn't like L on an automatic (other then extra "engine" braking to hold speed going down hills). L just tells the car to regen aggressively. Point here is there is no need to switch between D and L, unless you feel uncomfortable pressing brake pedal down steep long hill.

I don't like how fast the Volt coasts in D so I use L. However, be cognizant of cars behind you, it doesn't have any warning light that it is decelerating like the i3 or some other aggressive regen cars. It is just like downshifting an automatic to slow down. I blip my brake pedal with the left foot if there is a car coming up behind me that might not be expecting me to be slowing.

I don't notice any efficiency differences between lightly using brake and using L though, as I said, just prefer how the car drives.
 
#10 ·
After some 2.5 years of driving experience with my 2012 Volt, I’ve concluded that some of my driving routes result in range extension of almost 10% if I drive in Normal rather than L.

A common drive is 4.5 miles on a hilly rural road with speed limit of 45 mph, then a couple of miles in a small town. In Normal mode, I try to preserve momentum—not to a full hypermile extent, as I don’t drop below 30 mph on the rural road. Preserving momentum is more energy efficient than the recovery of kinetic energy through regenerative braking.

But I don’t switch to Neutral to really try to hypermile that trip, as I would be uncomfortable with the resulting decrease in control of the car.

On a different route, though, with many hairpin curves, I drive in L because one-pedal control works very well on that route. It’s one of those stretches where a speed limit sign of 15 mph really has significance. :eek:
 
#12 ·
I don't pay attention to the leaves much so didn't catch that they disappear when you are using actual brakes, not regen. Good to know there is feedback for that then. I haven't seen the braking show up on the power flow screen either, although I don't ever watch that. I'll try to keep an eye out for that also.

It's easier for me to modulate the throttle pedal and feel the braking effect than watch the leaves to see if they disappear or not, especially when slowing. It's pretty easy to modulate the throttle to get a coast (0 Kw used) for me so L is easier.
 
#13 · (Edited)
Hi Josh, its fine to drive in L, I don't but there is no broad harm in it. Just remember that there are some circumstances when the car will turn off the regenerative braking without prior warning, most notably in wet or rough surface conditions, in this case, if you are counting on the deceleration of "L", you will have to instantly understand what has happened and get your foot over to the brake pedal. If you are headed down a curving, bumpy, wet hill in decelerating traffic at 40 mph, it will feel as though the VOLT has had a JATO pack lit off on the back end.. That's why I don't drive in L except as the manual recommends: in slow stop and go traffic. If you want to know what this feels like, head down a hill when there is no traffic sometime, in L, at 50 mph with full L deceleration force, and pop the shifter into N...

The car can also turn off regenerative braking any time it detects any one of an number of circumstance affecting the inverter or the battery coolant system or the battery itself, including if a bumpy road spashed the coolant around in the fill reservoir and uncovers the low level sensor briefly.
 
#20 ·
In fact it doesn't really matter which mode you are in. In low regen you can travel (sail) a longer distance, in heavy regen you get more regen but less distance you can generate.

If you were to put that in an equation it were possibly a "=".

D/L address different driving situations.
 
#22 ·
I've been driving with the power flow meter on the main display recently and have noticed that coasting in D has very minimal regen, 1-3 kW in general. I can get far more than that in L. I also have to hit the brakes more in D and that seems to have 0 effect on the regen. I see no additional kW during braking, which is interesting considering that people talk about regenerative braking. If coming up to a light, it really seems that driving steadily and then stopping using L results in more energy being returned to the battery. And going down a hill, when using D I need to lightly use the brakes, but when using L I need to lightly use the accelerator. Again, the brakes seem to make no difference in the power display, so using L results in more kW going towards the battery.
 
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