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Discussion Starter #1
Hi guys, I take delivery of my car on Saturday, I’m trying to understand how it works. I’m interested in exactly how regen works when the battery is depleted. I know the generator doesn’t attempt to charge the battery once it’s empty, but what happens if you decent a huge hill for 5 miles, would regenerate add a couple of miles to your (previously empty) range which you can then use ? And would this then show as 2 miles remaining on the battery gauge ?

Thanks for reading :)

Paul
 

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Regenerative braking is an alternative to friction braking in a Volt, and it works both when you are driving in Electric Mode using battery power and when you are driving in Extended Range Mode using gas.

Once regen puts power into the battery, however, the distance you drive on that regen battery power will be classified under the driving mode you were in when you created it.

Not all battery powered miles are recorded as Electric Miles. The energy usage screen tracks miles driven in Electric Mode (using grid battery power) vs miles driven in Extended Range Mode (when using the range extender), not miles driven on battery power vs miles driven when the engine is running.

If you drive down a long hill in Hold Mode or with a fully depleted battery, regenerative braking will put some charge back into the battery. At the bottom of the hill, the car will then use that regen battery power to drive some battery powered miles that will be counted as Gas Miles because you obtained the regen while driving in Extended Range Mode. If you drive down the same hill in Electric Mode, the regen-battery-powered miles will be recorded as Electric Miles.
 

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One of the recommendations that I picked up on this list is to never drain the battery completely. When you get to one or two bars switch to "Hold" mode. On my 2015 and traveling the hills of the Hudson Valley, I would then "see" the regen charge the battery coming down a long hill when I switched to normal at the top of the hill. It probably didn't make any difference in gas mileage but I like to see what was left in the battery. Also check the forum for discussions on how having a few bars when driving in "Hold" gives slightly better performance. Enjoy the Volt - it's an amazing car!

2017 Premier, DC1 DC2 Nav ACC
 

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No reason to keep a charge in the battery in a Gen 2. In the Gen 1 Mountain Mode is your friend if you're going to be driving in serious hills and mountains.
 

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If you press the leaf button it will show via diagram when it's on engine, battery or engine and battery dynamically. Basically it will drive by engine using a motor as generator to produce the electricity for the other electric motor. When going up hill or acceleration it will use the engine and some from battery (a buffer). When coasting to a light or going down hill it will switch off the engine and the regen created will fill up the buffer for next use. If the engine is still being used and the buffer needs to be refilled it will speed up the engine and produce the extra electricity to fill the buffer. It is all automatic and does what is most efficient you don't have to worry about it and no input on your part is needed.


If you are going up a mountain (more up than down) you can drive in mountain mode to charge up to 40% so you have plenty of battery for battery assist.


If you are going down a mountain (mostly down grades) you can switch to normal to run on battery using the long downgrades to regen the battery up and using that to run on the short flats or short upgrades.


It is always a good idea if you are on a longer jaunt and are coming into city driving to keep some battery (half?) by driving in hold mode and switching to normal when you hit the repeated traffic lights (or traffic jams).


If you screw up or don't want to worry about it or "play the game" just drive it in normal mode and let the car take care of itself (like the 6 million dollar man, it has the technology).
 

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Discussion Starter #6
thats really useful advice, it's a surprisingly difficult thing to understand.... if you're trying to, I have a little more knowledge now, so I understand basically that regen is used even with the battery empty, but in reality, anything you regen on downgrades is likely used up once you're on the flat ? and that (probably) the engine won't turn off, but you'll be using up that regen electric power.... but probably not notice it ?

the test drive was rather smooth, I was most impressed, should have the car this weekend, I hope there are no major issues with it :)
 

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so I understand basically that regen is used even with the battery empty, but in reality, anything you regen on downgrades is likely used up once you're on the flat ? and that (probably) the engine won't turn off, but you'll be using up that regen electric power.... but probably not notice it ?
When the battery is depleted and the gas powered generator starts to produce electricity, you will see it on your dashboard, it will show two different indicators, one for the electricity coming from the battery and one for the electricity coming from the engine. It will also show if the electricity is being used (yellow) or put back into the battery (green).

What you will notice is that even in that mode, the engine will not be running all the time. That is in part because of the electricity generated by regen and in part because there will be a buffer of charge created from the electricity generated by the gas powered generator, to allow the car not to run the engine a low speed or from a dead start.

So even if the driving feels no different whether the electricity comes from the battery or from the gas powered generator, you will be able to see on your dash when the engine is running and when its not, as well as if the electricity generated by the engine is being used, or put back into the battery.
 

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You didn’t mention the model year of the Volt you are purchasing. The 2011/2012 Volts had no Hold Mode. The 2011 Volt had no "kWh Used" on the energy usage screen in the center console. The 2011/2012 Volts defaulted to 12 amps for 120-volt charging, later models to 8 amps.

To assure battery longevity, GM restricts the amount of usable power in the battery of the Gen 1 Volts to ~65% of full capacity. "Full charge" is less than 100% state of charge, and "fully depleted" is more than 0% soc. The "switch to gas" soc is, in fact, about 5% above the "hard floor" soc, below which the power is inaccessible in order to preserve the battery.

When running with a fully depleted battery, the Gen 1 Volt uses gas-generated electricity as fuel to power the large traction motor, but the car still utilizes that small amount of accessible battery charge as a buffer. If you request more power than generator output can produce (e.g., stomp on the accelerator to pass a car), some power from the buffer is "borrowed," and when demand lessens, generator output recharges it. If you coast in D or L to a stop when the light turns red (or descend a long hill), regen will increase the soc above the "switch to gas" soc, and when you then step on the accelerator (the light turns green, or you reach level terrain) and the soc is above the "switch to gas" soc, the engine will not run while that excess power is used by the motor.

Same thing happens when the Volt is using Hold Mode, just substitute the "Hold Mode soc" (where it was when you switched to Hold) for the "switch to gas" soc.

The amount of regen created doesn’t depend on the driving mode, and the car itself doesn’t care if the distance you drive using regen-battery-powered miles you get from the regen is credited to Electric miles or to Gas miles. Driving up the hill in Hold Mode, then driving down it in Normal Mode doesn’t change the number of battery-powered miles you drive, only the ratio of electric/gas miles.

The Gen 1 Volt’s range extender is, in effect, a portable generator, creating fuel for the motor. The fuel consumption rate of a generator whose output load is a motor propelling the car at 60 mph is greater than if the output load were a motor propelling the car at 20 mph, but it is not three times as much. If the Volt’s engine was running continuously, you would get better "gas mileage" at 60 mph than at 20 mph. To minimize gas consumption, the engine is cycled off and on as you drive to supply power as needed.
 

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and keep in mind that

" generator doesn’t attempt to charge the battery once it’s empty"

is not true

Would be better to say will not charge the battery above a set point and things like MM mode move the set point
 

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It is always a good idea if you are on a longer jaunt and are coming into city driving to keep some battery (half?) by driving in hold mode and switching to normal when you hit the repeated traffic lights (or traffic jams).
I drive our 2017 in this manner all the time - So far, I've never ran the battery down to the point where it switches to the gas mode by itself

In the Hold mode, the car gets incredible gas mileage at steady speeds, with no stop signs or lights. On secondary roads at 50 mph or less, I frequently see upwards of 55 mpg. Freeways at 70 it's in the very high 40's. No matter where I'm going, I try to always be in EV mode for ALL stop and go city driving and ALL lower speed driving . . . . anything 40 mph or less. I do try to get back home with the battery as close to depleted as possible, but since the last 5 or 6 miles is all low speed, with some stop and go, I never want to do that in the gas mode

So - I'm switching between Normal and Hold quite often as I drive. As soon as I get up to speed on the freeway on ramps, I'll use Hold and just before exiting, I'll switch back to Normal. If my trip is short enough to make the round trip in the EV mode, I use that exclusively and never switch to Hold

High speeds have lots of wind resistance and that eats up battery power, so I don't waste that on the freeway, whereas low speed, stop and go driving is ideally suited to the EV mode, regenning power as you slow to stop, plus it's a real waste of gasoline using Hold mode. Drive in the mode best suited to the trip you're on and you'll have the lowest costs all around

Don
 

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Hi guys, I take delivery of my car on Saturday, I’m trying to understand how it works. I’m interested in exactly how regen works when the battery is depleted. I know the generator doesn’t attempt to charge the battery once it’s empty, but what happens if you decent a huge hill for 5 miles, would regenerate add a couple of miles to your (previously empty) range which you can then use ? And would this then show as 2 miles remaining on the battery gauge ?

Thanks for reading :)

Paul
Mountain mode will recharge the propulsion battery to around half charge even after the car has switched to gas.
 

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Mountain mode will recharge the propulsion battery to around half charge even after the car has switched to gas.
But those will be the most expensive miles you'll drive - You don't get near the mileage you would in Hold mode and the electricity you stuff in the battery is many times the cost of charging at home

Don
 

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But those will be the most expensive miles you'll drive - You don't get near the mileage you would in Hold mode and the electricity you stuff in the battery is many times the cost of charging at home

Don
Definitely, but the OP said that it will not charge itself.
 

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You shouldn’t use Mountain Mode to recharge the battery unless you plan to use up that recharged power before you finish your trip. If you use MM to build up a charge before heading up the mountain, then switch back to Normal after cresting the final pass and use up the charge.

While it is true the cost of recharging your battery via Mountain Mode is a little more expensive than recharging it from the wall plug (perhaps twice the cost?), that’s not the choice you are making. Your choice during a trip is to use MM to recharge the battery, then drive battery-powered "Gas" miles, or use the same amount of gas to drive normal Extended Range Mode Gas miles without using MM. If the number of "Gas" miles driven are the same, neither method is more expensive.

Here’s how I view it. For the Gen 1 Volt, the Self-Charging Chevy Volt video shows a 2012 Volt using MM to recharge a fully depleted battery while parked. It takes ~15 minutes to do so, using 0.36 gallons of gas.

Wikipedia says the MM-maintained buffer is at the 45% state of charge for the 2011/2012 Volt. If the usable soc window is 20-85% soc, then MM provides 25/65 of a full charge using 0.36 gallons of gas, and a full charge would use ~0.94 gallons (and would take ~ 40 minutes).

You could then drive 35-38 battery powered miles (depending on model year) in a Gen 1 using a battery that was fully recharged via MM by using ~1 gallon of gas in the generator, or about the same distance you could drive in Extended Range Mode using 1 gallon of gas in a car rated at 37 mpg.

IOW, if you use MM to recharge the battery, and then use that MM-recharged battery power to drive "Gas" miles, your total Gas Miles is where it should be for the quantity of gas used, and so is your MPGcs "gas mileage."

Keep in mind the Gen 1 engine is more fuel efficient when running at full speed to recharge the battery than when being cycled off and on while driving normally in Extended Range Mode.

I don’t know if anyone has ever performed a similar test using a Gen 2 Volt (i.e., to see how much gas is used to charge the car to the MM-maintained ~2 bar level and how long it takes to do it), but it seems reasonable to think the Gen 2 would self-charge at similar fuel consumption rates, so it might be possible that MM could fully recharge a fully depleted Gen 2 battery using ~1.25 gallons of gas.

If so, you could then drive 53 battery powered miles in a Gen 2 using a battery that was fully recharged via MM by using 1.25 gallons of gas in the generator, or about the same distance you could drive in Extended Range Mode using 1.25 gallons of gas in a car rated at 42 mpg.

If you arrive home with a fully depleted battery, then using Mountain Mode to recharge the battery during the trip and using up that MM-recharged battery power to drive "Gas" miles shouldn’t add any extra expense to the cost of the trip or affect your gas mileage.

It may be more expensive to charge the battery using gas and MM instead of pulling electricity from the wall socket, but the difference in cost for one full charge is approximately the cost of 1 or 1.25 gallons of gas (Gen 1/Gen 2, @ $3/gallon = $3/$3.75) vs the cost of electricity for a full charge (~12.5 kWh / 16.85 kWh from the wall, @ $0.12/kWh = $1.50 / $2.02). These miles become more expensive only if you use MM to create more electricity than you need to reach the next recharging station. And since MM will not let you charge the battery beyond the 4 bar/2 bar level, arriving home with that fraction of a full charge or less remaining in the battery isn’t really costing you very much.
 
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