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Discussion Starter #1
The Mt. San Jacinto aerial tramway is great. The parking lot is about 2500' above sea level and basically a straight grade up from the valley floor (which is Palm Springs, and in the summer the whole area is freaking HOT).

In my older Generation 1 volt, I've used cruise control set to 35mph on the downhill drive, and it's great: it keeps the speed and charges the battery as you descend. But in that case, the battery was perhaps 50% charged.

I had the chance to try this in my Gen 2 volt. Other than it being a completely new car, the other difference was that this time the battery was at 100%, because I recently discovered that there is a level 2 charger in the parking lot.

The experience was not what I expected. Basically, the Volt would oscillate between two states: keeping the downhill speed, and absolutely giving up and just flying down the hill. It would shift between these two modes back and forth every few seconds, and there was a lot of noise coming from the engine. There were no warning messages and I think that the cruise control remained engaged (though I could be wrong, as I was having to hit the brakes pretty often to keep my speed down.)

I realize this is an extreme edge case in terms of temperature, grade, and charge level, so I'm not really faulting the Volt engineers here, but it was not the best driving experience.

Didn't I read somewhere that the Gen2 would handle this situation by dissipating energy in some other way, opposing the two motors or something? Or maybe I was hitting some other thermal limit?
 

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There were no warning messages and I think that the cruise control remained engaged (though I could be wrong, as I was having to hit the brakes pretty often to keep my speed down.)
Was this behavior under (D) or (L)? The regen should appear more aggressive under (L)
 

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Perhaps since it was fully charged to start- there was no way to use regen to slow down?
 

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Right, being fully charged, it couldn't do normal regen. I don't remember, does g2 actually do conventional engine braking in this case? Bolt has a nice "feature" called hilltop reserve. It won't charge fully in that mode, but saves a reserve, so that regen can work going downhill.
 

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Did you test the paddle to see if there was ANY regen at all?

I think the Gen 2 charges "full" to a higher SOC than the Gen 1, and provides much less opportunity for regen above that when fully charged. I have a minor downhill slope a block from my house that I occasionally take on my morning commute, when fully charged, and I usually get no regen down that hill.

Obviously, the best way to test is to try a partial charge and see what happens. Agree that it should be more predictable no matter what.
 

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The Gen 2 Volt, when fully charged, has very little battery space at the top into which regen can flow. That’s why the Bolt offers a Hilltop Mode charging option that stops the charge before it reaches Full. When headed downhill with a full charge, regenerative braking soon becomes inaccessible without a place to put the regen, and it’s friction brakes all the way unless, as you say, the car is programmed to deal with "can’t regen" conditions by opposing two motors or ??? Perhaps you should have switched on some maximum comfort mode air conditioning to gobble up power underway, which might have created some battery space to refill via regen.
 

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What you describe still shouldn't happen. Regardless of battery SOC, if the ACC is set to a certain speed, the car should maintain that speed using regen or friction brakes. I'm not aware that ACC is somehow disconnected from the friction brakes. That would make no sense.
 

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With our 2016 Volt we use hold mode quite often. We always use at least 2-3 KWH of battery and then switch to hold mode. This allows the battery to fully capture the regen when going downhill. If we don't when going downhill with a fully charged battery the engine / electric motor sounds and feels different than with a partially discharged battery...
 

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Yes, your battery was too full. Next time, don't charge at the top.

If you do need to charge at the top of a mountain, you can use a delayed charging mode and set your departure time to a time that is later than your actual departure to avoid a full charge.
 

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What you describe still shouldn't happen. Regardless of battery SOC, if the ACC is set to a certain speed, the car should maintain that speed using regen or friction brakes. I'm not aware that ACC is somehow disconnected from the friction brakes. That would make no sense.
As I was reading all the theories about *what should happen* I was wondering how ACC would play into this, since it does have access to friction braking - I'm guessing his car *isn't* ACC equipped

Don
 

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As I was reading all the theories about *what should happen* I was wondering how ACC would play into this, since it does have access to friction braking - I'm guessing his car *isn't* ACC equipped

Don
Agreed. If just regular cruise control, then D, L or SOC makes no difference. The car will simply roll faster and faster downhill. In L that rolling might start out a little slower. And if SOC is full then rolling in L will be just like in D.
 

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As many point out here-if battery full,regen unable store any electricity.I found this using Volt gen2 descending into Hilo (HI) off Inouye Highway /200/Saddle Road from top of about 6600 feet down to near sea level.Having just used regen off Mauna Kea down to Saddle Road and now full electrically,noticed no regen occurring going downhill and car wanting to accelerate on cruise control.Of course friction brakes needed ,which deactivates cruise control,and tried max air conditioning to use up some battery capacity.Just something to be aware of when battery full.
Don-2017 Volt LT
 

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It wouldn't matter (D / L) if the battery is fully charged at the top of the mountain... In this case, regen braking becomes unavailable (no place for the energy to go besides HVAC), and all you have is friction braking (and possibly engine braking).

A couple years ago, I spent part of my summer vacation at the Kaibab lodge near Kaibab Peak (Grand Canyon, north rim). Left Phoenix, in the morning, reached the Lodge not long before nightfall. Kaibab Peak is perhaps the highest peak in Arizona. My Gen 1 Volt made the climb from Phoenix to Kaibab like a champ in mountain mode.

I had neglected to top off my gas at Jacob Lake, so I had slightly under half tank gas, and battery about 40% when I arrived at the lodge.

A couple days and 35 miles later (round trip to the north rim lodge), the battery is still at 40% and even less gas remains. I nervously start down the mountain hoping I had enough gas, still in mountain mode at the top of the mountain. Regen braking and cruise control are working together well to maintain my speed.

Half way down the hill, my engine stops.

It took me a minute to realize that the battery was now at 70%, and the engine had shut down normally. I didn't need to burn any more gas before I got to Jacob Lake....

I'm glad I HADN'T charged the car at the lodge as I was considering.
 

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If I was headed DOWN the tallest mountain peak in Arizona with 40% battery and a FULL tank of gas, I wouldn't have started the engine at all . . . .

Don
 

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Yeah... I wasn't thinking about coming down the mountain. Instead, I was thinking about how far that gas station was (and why didn't I top off the gas when I had the chance?!??!)

Even after 5 years of EV driving, I still suffer from thinking like an ICE driver. :confused:
 

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I hear you!

Coming from 6 years driving a pair of pure EV's, I'm still thinking of our Volt as a pure EV . . . . which is able to still keep going beyond it's EV range

I do tend to run the engine on the freeways and use EV mode for everything else when we're making longer trips though. We can go several hundred miles and return home with some EV miles still left, so we're not operating as efficiently as we could be. Live and learn!

Don
 

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With our 2016 Volt its always nice to have 10 miles or so of electric range when on a trip. You never know when you will be in a traffic jam with stop and go for miles, and you never have to worry about the gas engine firing up. Then when heading home and a few miles away you can go to normal mode and use up those extra electric miles stored...
 

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With our 2016 Volt its always nice to have 10 miles or so of electric range when on a trip. You never know when you will be in a traffic jam with stop and go for miles, and you never have to worry about the gas engine firing up. Then when heading home and a few miles away you can go to normal mode and use up those extra electric miles stored...
Don't forget that just re-warming the engine after it's been off for a while can burn up 4-8oz of fuel before the engine gets back up to operating temperature. It may burn less just running intermittently in the heavy traffic.
 

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Discussion Starter #20
Thanks for all the great comments. To clarify, my car does have ACC and there was zero evidence of it using friction braking to maintain the downhill speed.
 
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