Amount of Regen from Volt using DashDaq

[techtom]

Borrowed a friends DashDaq with Volt OBD PIDs. Took a route home that gives me a diverse set of driving conditions so I could see the regen performance.

Average Results... 20% Energy recovered from regenerative braking
Which adds about 6 to 8 electric miles to a commute, saving about 2 gallons of gas each week, if you charge both ways. If I did my calculations right???

Snapshot of data below....
DashDaq data on the left. Calculated data on the right.

dashdaq_data_and_calcs.jpg

[Henry_FL]

Nice chart!

[Flemingljr]

very cool, were you driving in Low mode.

[slyastro]

Yes very nice work !!

I'm surprised ... I thought that regen could be much more ??

Maybe there is more Regen in L mode? Hope you were NOT in L mode ...

Sly

[techtom]

I was in L mode some of the time, but not all the time. I like L mode for congested driving, but not on open highway/interstate driving.

Remember the 20% regen number I'm showing is just the average number for an average driving run. The max at any given point in time can be much more.

For example... I posted this (see pic below) sometime back, but may be worth a repost.



This is data from a test I did going from an all out sprint (pedal to the medal), and releasing at 30 mph.
One test I let "L" regen apply the braking (with a little help to stop with the brakes at the end)
Another test was in "D" using the brakes to mimic the same stopping decel as I did in "L", stopping at the same point.
Then I repeated "L" and "D" with aggressive braking.

Take aways?....
1) If you're an aggressive braker, you'll get better performance from "L" than "D". If not, they don't make much difference.
2) The maximum amount of power recovered was 65%, no time for terrain, friction or many other factors to apply. However, ramping up to a higher speeds or different accel rates may yield different results.

[saghost]

Yes very nice work !!

I'm surprised ... I thought that regen could be much more ??

Maybe there is more Regen in L mode? Hope you were NOT in L mode ...

Sly

If I'm understanding what I'm seeing correctly, what the OP is describing isn't the percentage of energy dissipated in braking recovered, which should be higher.

I think what the OP is saying is that 20% of the energy used to drive the car during their test was energy recovered from regenerative braking - that if only friction brakes had been used the car's battery would have been dead in 83% of the distance it got. This result will be heavily dependent on driving profile - a theoretical trip where you accelerate to one speed and stay at it for the entire trip has no energy to recover that way except at the very end, while a trip involving a stop sign every half mile will have a lot of opportunities.

I don't have hard numbers on energy recovered from braking and returned to the drivetrain at the moment; from the component efficiencies I'd expect it to be in the 50-80% range.

[RobertSullivan]

Just a theoretical question based on physics. If you drive for 10 miles via a route that offers a lot of regen opportunities versus a route that is a steady speed with no braking and the average speed for both routes is the same, which route will take the battery level down farther?

[tboult]

Just a theoretical question based on physics. If you drive for 10 miles via a route that offers a lot of regen opportunities versus a route that is a steady speed with no braking and the average speed for both routes is the same, which route will take the battery level down farther?

Did not say what the elevation change was (part of how one can get regen.. ). Presuming it is flat.

Then the steady speed will be better. To get the same average speed on a flat route, the regen route will have to accelerate to higher speeds and then can slow via regen. The acceleration to higher speeds costs energy, higher speeds = more drag = lower efficiency then the regen is not 100% efficient so does not recapture it.

[RobertSullivan]

Yup, I was just trying to make a point that regen is great but it does not create more energy it just captures some of what would have been lost as heat in the brakes. So if there is a choice of routes the steadier state route is the better choice rather than a lot of stop and go and up and down hills. But a choice of expressway at high speed versus city stop and go would favor the stop and go due to the lower speeds.

[DCFusor]

Wow, for once you've left me speechless - except to agree. This is the correct stuff, and even a physicist/engineer has to say, well, yup.

Makes me glad GM left some room at the top. After a mile of flat-to-up, I go 4 miles down when going anywhere (that is, miles of going downhill, not that much elevation change) then another 6 along the river - gentle down on average. At the end of that ten mile total, it's the norm for me to show only one electric range mile used! (and sometimes none if I drive real carefully) So regen works pretty darned well. Coming back of course, it's another story.

Today, from full charge, round trip to nearest general store:
(car preheated in driveway, fan only thereafter)
At departure, 35 miles electric range showing at full charge (usually conservative)
27.7 miles driven round trip
at return - 14 miles range still showing, gas used = 0.

I was hypermiling at about 35 - but now I know I can hot-rod this most common trip for me and always make it. Cool!

I used D (and normal with cruise control) when the hills were gentle going down and I wouldn't gain too much speed and lose energy to wind resistance, but L (and sport) for the steep downhills - only intervening in the cruise control when my brain could obviously do a much better job. All CC's, even this really good one, just can't know not to floor it just as you're cresting a hill and will be coasting down real soon anyway and gaining speed - but my brain can handle that one just fine. Ahh, some software guy ought to incorporate GPS so the CC could know that sort of thing someday. CC is tighter in sport mode FWIW, or seems like it.

So if the hills are gentle, it seems you do a little bit better in normal mode, and avoid regenning into the battery just to need power to climb the next small rise - at low speeds, coasting does do a little better since you're not wasting so much heating up the wind resistance and there's no round trip loss in the batteries. For steep situations, sport and L make cruise control a lot tighter and you don't gain too much speed going down, where you'd waste more to the wind. And yup, we have some real steep hills - the kind that will take you zero to 80+ going down in neutral. For those, it's better to regen.

This is about 1000 feet net elevation going out, climbing all that back up on return. But of course it's a lot of up and down even if the average is up, or down. Lots of minor lumps and bumps.

As I live halfway up the mountain, I can also arrange to return in MM by going over the top, then regenning all the way back to my place - that gives me a few miles more charge left at my house than MM alone will - but I don't usually do that as it's a couple more miles for most trips to go that way. Nice to know though.