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In CS mode (aka battery depleted or hold mode) accelerating from a stop will first use an electric motor, then power up the ICE to take over and charge the depleted battery as acceleration tapers off. Under hard acceleration (e.g., passing on a highway), the Volt will continue to use both an electric motor and the ICE to provide necessary power. How long will it continue to draw on the depleted battery to do this? Does the answer change whether you have a depleted battery or are in hold mode?

All theoretical, of course. Just curious if anyone has done this.
 

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In principle, it will draw on the battery until the load declines, then use the ICE to rebuild the battery charge. The car keeps about a kilowatt hour of extra power for this purpose.

If you aren't in Mountain or Hold mode and you have a sustained high demand (climbing a mountain at freeway speeds,) the car will eventually reduce power to keep from overdischarging the battery - you'll get a DIC message "propulsion power reduced" and the car will slow until the engine is producing enough power to sustain the load.
 

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I believe it will draw on the battery as long as the power necessary exceeds what the generator is capable of producing which is somewhere around 60KW. I know there is an additional buffer programmed into the battery that will allow you to tap into that buffer in the event that the battery has been depleted as well as gas which allows somewhere around 2-3 miles additional "emergency" range. I believe this is tapped into until power demand no longer exceeds generator output at which point the generator rebuilds the buffer to the minimum SoC for the battery again. I imagine hold just shifts to whatever the battery SoC is at that time as the new "minimum" and functions the same. If the power under a fully depleted battery is too low, you'll likely get a reduced propulsion power warning, but that shouldn't be given if in hold.
 

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I've run all the Appalachian mountain freeways first thinking mountain mode would be required, it's not. Eventually on a trip through the mountains east of Phoenix Arizona on state highways the climb was steep enough to really tax the system. I did not get reduced propulsion message, but wow that little 4 banger was screaming.
 

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This is anecdotal, but, hold seems to dip into the (larger) buffer more than CS. This results in the engine running less RPMs to keep up. Both '13 Volt and '14 ELR did it. I don't have any long mountain climbs here on the plains though.

In theory, hold just sets the lower SOC to whatever it is when hold is engaged. It seems to be a little more complex than that in practice.
 

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It will draw as much as it needs to until the battery is completely exhausted, then propulsion power is reduced to the max the engine/generator is capable of producing (55kW)
 

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This is anecdotal, but, hold seems to dip into the (larger) buffer more than CS. This results in the engine running less RPMs to keep up.
I noticed that using Hold in the Colorado mountains as well. It seemed (to me anyway) that the behavior of battery/ICE/RPMs is based on what percentage of the remaining battery window you have used.
So with a larger amount of remaining battery (like using Hold), it takes longer to get to the bottom of the window where the system removes engine RPM/noise & vibration limits and starts running at max power.

Mountain Mode, on the other hand, seems to be extremely aggressive about doing everything possible to maintain the SOC at the top of the MM window. Which makes sense, it doesn't know if the next hill is longer and steeper than the current one.
 

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In CS mode (aka battery depleted or hold mode) accelerating from a stop will first use an electric motor, then power up the ICE to take over and charge the depleted battery as acceleration tapers off. Under hard acceleration (e.g., passing on a highway), the Volt will continue to use both an electric motor and the ICE to provide necessary power. How long will it continue to draw on the depleted battery to do this? Does the answer change whether you have a depleted battery or are in hold mode?

All theoretical, of course. Just curious if anyone has done this.
Keep in mind that when the Gen 1 Volt is driving in Extended Range (CS) mode under one-motor operation, the gas engine isn’t providing any propulsion torque at all. It’s clutched to the second motor, transforming it into a generator that supplies the primary motor with electricity and, when needed, recharges the battery (according to Wikipedia’s Chevrolet Volt article, the electrical power from the generator is sent primarily to the electric motor, with the excess going to the batteries, depending on the state of charge of the battery pack). Switching the primary motor’s fuel source from battery to generator output (and utilizing the battery as a buffer) would be more efficient than just draining and recharging the battery.

Under certain speed and torque demand conditions, two-motor operation is more efficient, and for the Gen 1, that means the ICE, which is turning the generator (the second motor), is now also helping to turn the wheels. My understanding is that under hard acceleration such as passing on the highway, the Gen 1 Volt switches from two-motor operation back to one-motor operation, in which case the ICE again is not providing any propulsion torque at all.

The Gen 2 Extended Range operation is far more complex.
 

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Mountain mode can definely be required, coming from the bear tooth pass going up in hold mode with 5 miles left I hit reduced propulsion mode going up, could not re enter hold and top speed was 20-30 mph.

On the summit going down the motor was still racing with max regen to boot, took some time before it shut off.
 

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I suppose I should have specified that I was asking about the Gen 2. Thanks for replies, all!
Same deal, but gen2 can go much further before PPR is activated.
The engine is able to contribute more energy to the system, so the battery doesn't need to top up as often. Still can happen on long sustained uphill climbs if your power level remains above that which the engine is able to provide.
 
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