regen efficiency

[George S. Bower]

Has anyone with dashdaq gotten a handle on the regen efficiency of the Volt? I'm sure it must be a function of the rate of decelleration...ie it can only absorb so much power...but let's keep it simple.

Here's the problem:

delta elevation=2500'
distance=27 miles
Volt wt=3850#

I calculate that the theoretical energy that can be recovered in this situation is 3.63 kwh.

What percentage of 3.63 kwh can the Volt capture in this situation under ideal (no extreme braking) situation??

[Neromanceres]

George,

Here is a link to another thread which the op uses DashDaq to get some data on regen.

http://gm-volt.com/forum/showthread....-using-DashDaq

[ajwilliams7]

I posted once before on this issue. I only have the indicators in my Volt but I have made numerous measurements and have deduced that the max regen efficiency is somewhere around 80%. This, of course, is when only the regen is being used to slow down the car on level roads or keep it steady on a downward incline. When heavy braking is applied more energy will be wasted.

[tboult]

Has anyone with dashdaq gotten a handle on the regen efficiency of the Volt? I'm sure it must be a function of the rate of decelleration...ie it can only absorb so much power...but let's keep it simple.

Here's the problem:

delta elevation=2500'
distance=27 miles
Volt wt=3850#

I calculate that the theoretical energy that can be recovered in this situation is 3.63 kwh.

What percentage of 3.63 kwh can the Volt capture in this situation under ideal (no extreme braking) situation??

With 27miles and 2500', that is about 100' elevation drop per mile, so it is mostly driving that would be measured, not regen.

And that then depends very much on the speed of driving. When I did 75miles on a charge I had a net elevation gain (from start to end of charge) or about 1500m. But in from the peak of loveland pass to where I ended was about 2500m. See this thread
http://gm-volt.com/forum/showthread....e-charge/page2

I don't have a dashdaq but I can measure battery SOC via OBDII. I can see what I can measure in a region steep enough that i don't have to drive, just put it in L and regen. Later in teh summer I'll do loveland again and get much more detailed measurements.

I could very easily get OBDII measurements on a section with 300ft gain over about 1mile in a subdivision where I can do 35-45 which should allow just driving in L and would have low wind impact. Would that be useful ?

[George S. Bower]

With 27miles and 2500', that is about 100' elevation drop per mile, so it is mostly driving that would be measured, not regen.

And that then depends very much on the speed of driving. When I did 75miles on a charge I had a net elevation gain (from start to end of charge) or about 1500m. But in from the peak of loveland pass to where I ended was about 2500m. See this thread
http://gm-volt.com/forum/showthread....e-charge/page2

I don't have a dashdaq but I can measure battery SOC via OBDII. I can see what I can measure in a region steep enough that i don't have to drive, just put it in L and regen. Later in teh summer I'll do loveland again and get much more detailed measurements.

I could very easily get OBDII measurements on a section with 300ft gain over about 1mile in a subdivision where I can do 35-45 which should allow just driving in L and would have low wind impact. Would that be useful ?

seems like if we had a known elevation drop and we drove at a constant speed where we know the road load (I have a little equation that's good from around 55-75) and we watched how many kwh we picked up from the top of the hill to the bottom we could figure it out.

[tboult]

seems like if we had a known elevation drop and we drove at a constant speed where we know the road load (I have a little equation that's good from around 55-75) and we watched how many kwh we picked up from the top of the hill to the bottom we could figure it out.

My point was that there is very little regen going on at highway speeds. I go down 800' over then up 200' just about every day, and logged it multiple times and watched my powerflow almost every day. (I don't always take the highway, the backroads are slower speeds and more regen, but also more stop signs/lights).

There are only a few sections of the 800' drop where I can see regen happen. On the highway @65mph its only on sections with more than 4% grade or higher that I see regen. The rest of the time the gravity helps make it easier on the engine but its not measuring regen.

Here is a plot of my normal drive profile


I only see a little regen around mile 4, 7 and a lot at 13-14 (when I exit the highway).
I could provide batter SOC along that route if you like, but as I said, its very little regen.


My suggestion was the following profile


which is about a mile of 4-6% grades in a neighborhood so I can probably set CC at say 30mph and get a lot of regen.

[George S. Bower]

Yes tboult you got me looking at my calcs and the amount of kwh/mi I save going down the slight grade is less than the kwh/mi it takes to hold the car at 65 so there is no regen. It just takes less power to drive the car forward on that grade.

I'll look at the profiles you posted and get back...thx

[DonC]

Well you're looking at 750 meters and 1800 kg so at 9.8 m/s/s we have 13,.23M joules. Convert to kWh and you have 3.675 kWh. If you're traveling 27 miles using 1 kWh to go three miles, perfect regen will get you an additional 11 miles. Maximum regen is probably about 80%. (I think Scott has posted a map someplace). The Volt can handle 60 kW so I doubt you'd be pushing the maximum limitst. Here BTW is a post from Trevor about how to maximize your regen:

VoltSoundz, I've done a little research on the topic with our Volt team and the Volt's maximum sustained regeneration is 60 kW. The amount of regen varies widely on vehicle speed, incline (load), and stability controls. 60 kW is achievable if the Volt is braking from freeway speeds or going down a hill while braking. To maximize regen, move the green ball down until the point when the green leaves are very faint and just barely disappear. That is the point when the friction brakes are blended in to the braking torque. When shifted to Low, there is a more aggressive coast regen curve. The amount of regen in Low again varies on many factors, but continue to use the green ball to modify your driving style for best results. Drive safely and have fun with your Volt!

[George S. Bower]

The Volt can handle 60 kW so I doubt you'd be pushing the maximum limitst. Here BTW is a post from Trevor about how to maximize your regen:

are you sure about that?? that's a 4C rate on the batery. I wouldn't expect more than 1 or 2 C would be allowed by GM.

[George S. Bower]

tboult,

for your suggested profile of 300' in 1 mile at 30 mph.
theoretical energy recovered at 100%=.435 kwh
at 80% regen efficiency=.348 kwh

energy reqd to drive vehicle forward at 30 MPH on flat and level road =150wh/mile using 85% conversion efficiency in EV mode for motor and inverter that equates to .176 kwh out of the pack.

so you should see .172 kwh of increase in the battery SOC= around 1 mile of EV range
It would be a crude science experiment because the numbers are small,,

but interesting none the less