[nik.taylor]

I was wondering yesterday as i was going down a steep hill, is there an optimal regen rate? I was thinking in terms of sticking to a certain rate of kwh on the display. If i go down a steep hill with 30kwh regen at 15mph is that more efficient that 15kwh at a faster speed? Does it even matter?

 

[rmay635703]

Optimal is ZERO regen on the display (coasting)

Regen efficiencies vary with load and speed. Regen is less efficient than coasting but regen max efficiency is around full load (max regen) following a curve at any speed. Less than max regen is less effective because the motor efficiency falls below 96% when partially loaded.

To accomplish coasting, you would need to crest the hill at low speed and let gravity speed you back up to the speed limit, then use regen to hold you at the speed limit.

Pulsing max regen may be more efficient than just holding speed but far more irritating and its only 5-10% off better at most.

Likely not worth it for such a small gain.

 

[nik.taylor]

Optimal is ZERO regen on the display (coasting)

Regen efficiencies vary with load and speed. Regen is less efficient than coasting but regen max efficiency is around full load (max regen) following a curve at any speed. Less than max regen is less effective because the motor efficiency falls below 96% when partially loaded.

To accomplish coasting, you would need to crest the hill at low speed and let gravity speed you back up to the speed limit, then use regen to hold you at the speed limit.

Pulsing max regen may be more efficient than just holding speed but far more irritating and its only 5-10% off better at most.

Likely not worth it for such a small gain.

That's very helpful hypermiling info. I'll give the coasting a shot but given the amount of traffic where I live, I'll be careful when I try it so I dont annoy anyone!


Does regen tail off linearly with motor load or is it a sharp decline followed by a flatter tail off?

 

[Norton]

.... I'll give the coasting a shot ...

Are you talking about shifting to N for coasting?
Are you striving to save another penny or two a day by putting all this thought and effort into driving a Volt?
Do you know it is already as inexpensive as it gets when in EV mode? You could just drive it and not think about it!

 

[mr_raider]

Optimal regen is accomplished by maxing out the area under the power curve. It depends on regen rate (-kwh) and the time for which it is held. Ideally you want a rectangular area, i.e.raise your regen rate right at the beginning and hold it constant. This would imply no acceleration. Modulate the brake pedal right at the beginning to try to hold your speed constant. The actual speed will depend on the incline.

This is a simple 1st order differential equation. Who wants to take a crack at it?

 

[nik.taylor]

Are you talking about shifting to N for coasting?
Are you striving to save another penny or two a day by putting all this thought and effort into driving a Volt?
Do you know it is already as inexpensive as it gets when in EV mode? You could just drive it and not think about it!

Not putting in N for coasting, you can modulate the accelerator so it's effectively coasting.

Probably wont be doing a lot of this tbh, just interested in the best way to descend steep hills. I go up to Big Bear Lake a few times a year and that's a massive hill on the way home where I may want to get the max regen.

I have been checking the kwh usage between aggressive and hypermiling driving for my daily route of 10 ish miles and it's on the order of a few cents so i'm not going to be trying too hard!

 

[Norton]

...a massive hill on the way home where I may want to get the max regen....

What about setting the cruise control to the speed limit, or whatever everyone is doing, and let the car do the the work. It will regen as required. What more do you need?
On my '13 the cruise would only work like this was in L. In D it would allow the car to go above the set speed.

 

[nik.taylor]

What about setting the cruise control to the speed limit, or whatever everyone is doing, and let the car do the the work. It will regen as required. What more do you need?
On my '13 the cruise would only work like this was in L. In D it would allow the car to go above the set speed.

That's a great idea. Will give that a try when i'm up there next. Thanks.

 

[srmarti]

Considering public roads have speed limits and traffic, I think the most reasonable thing to do is go the speed limit and let the regeneration hold at that speed. On secondary and hilly back roads, low works well for this. Of course you could just use the brake pedal for more or less same effect.

 

[jsmay311]

This is a simple 1st order differential equation. Who wants to take a crack at it?

It's definitely not that simple.

Nor is coasting always the most efficient option. It's almost always, but not always. If the slope is steep enough, coasting would get you going so fast that the aero drag effects would outweigh the regen energy conversion losses.

And in real life you have to consider speed limits, of course.

But, in general, rmay is pretty close. You want to accelerate on declines and decelerate on inclines, keeping regen to a minimum (except at high speeds or when unsafe/illegal), and keeping max motor power low.

 

[Paulacton84]

drive safely and make good use of the communally shared resource (the road). you are trying to optimize the total losses of 3 loss curves that you don't have good enough equations for to understand: 1- linear loss with rolling speed, 2- exponential drag losses varying with speed- recovery efficiency under varying conditions of slope and speed and charge state. In general regeneration is pretty inefficient (50-65% kinetic energy back out from what you put in) so I'd go with a higher speed, but that is to qualitative to be meaningful...

 

[canehdian]

Set cruise control at your max safe/legal speed you want to go, set it in L, let the car regen as required. Don't overthink it.

 

[rmay635703]

Considering public roads have speed limits and traffic, I think the most reasonable thing to do is go the speed limit and let the regeneration hold at that speed. On secondary and hilly back roads, low works well for this. Of course you could just use the brake pedal for more or less same effect.

Speed limit is a limit, it is not the lower limit of the road, nor does it mean he will stay "slow" for very long if its a steep hill.
I know because many 70mph highways here have amish buggies and farm tractors driving 5mph on them.

Anyway I get 6.x + Miles per KWHR all summer and yes coasting does account for a huge percentage of that, when I drive "normalish" but at similar speeds with regen I drop into the 5.x area.

As for the upper limit on coasting efficiency it is over 65mph and probably not really apart of this discussion unless he has a mountain, then he would just use "L" or regen to hold speed under his local limit

 

[srmarti]

Speed limit is a limit, it is not the lower limit of the road, nor does it mean he will stay "slow" for very long if its a steep hill.
I know because many 70mph highways here have amish buggies and farm tractors driving 5mph on them.

Anyway I get 6.x + Miles per KWHR all summer and yes coasting does account for a huge percentage of that, when I drive "normalish" but at similar speeds with regen I drop into the 5.x area.

As for the upper limit on coasting efficiency it is over 65mph and probably not really apart of this discussion unless he has a mountain, then he would just use "L" or regen to hold speed under his local limit

I did say speed limit AND traffic.

 

[wordptom]

Ah, but the question is, if there’s a massive hill on the way home from Big Bear Lake and you don’t want to just take your foot off the accelerator and let gravity take over, do you get more regen back into the battery by the time you hit the bottom of the hill if you descend in L with the cruise control set to 20 mph (or other slower speed) than you would if the cruise control was set to 60 mph (or whatever the speed limit is on that road), or is there a better method of maximizing the regen obtained from any single given descent than by using the brake pedal or L with cruise control to maintain a steady speed?

 

[srmarti]

It's moot if the speed limit is 60 and you get a ticket or get run off the road for doing 20 and blocking traffic, etc.

I would generally be in cruise and low if conditions permit. Don't know if this is optimum, but it provides regen and maintains speed well.

 

[Norton]

IF there is an efficiency curve of goes in current vs. goes out current for this Li-Ion battery pack, it could be established in the lab.
How would this effect an actual Volt owner that would be able to drive according to this curve, (if there is one)?
Would the savings amount to a penny's worth of electrons driving this way, even if you were not obstructing traffic?

 

[theo1000]

.. or the difference between getting home or calling the tow truck. With the EV recharge infrastructure as spotty as it is, there is every chance that even bolt drivers will occasionally have to know how to squeeze out those electrons. For that day when Plans A , B, C & D have failed

 

[Sean Nelson]

.. or the difference between getting home or calling the tow truck. With the EV recharge infrastructure as spotty as it is, there is every chance that even bolt drivers will occasionally have to know how to squeeze out those electrons. For that day when Plans A , B, C & D have failed

That depends on whether you expect to get 238 miles or whether you expect to get 150, say, miles. You can drive it worry-free with the latter attitude, whereas that's not possible with any of the other relatively cheap EVs.

 

[Norton]

.... For that day when Plans A , B, C & D have failed

As a BEV driver I know that Plan A: Go slower, always works.

I watch the distance to destination on my nuvi and the GOM range.
If they start to get close to the same amount, I SLOW DOWN, turn the heater down/off and then watch as that range number starts climbing above the distance number.

No amount of going downhill at 30 MPH vs. going with traffic is going to have a noticeable impact on that number.
(if there even is a measurable difference)

IF I was coming down the Rockies do you really think it matters if I get X amount of regen vs. X.01 of regen?

IF you are ready to step it up to a BEV,, don't be a dummy.
The Flat Bed of Shame will cure you of that after only one ride!