[NM_Nick]

I recently fully charged my Volt at a relatively high elevation. After it was charged I proceeded to drive downhill, which resulted in the Volt attempting to regen some power back into the batteries. But since the batteries were already fully charged it appeared to switch to gas mode and started logging gas miles. Except that the ICE was not running and the Volt still appeared to be in 100% electric mode. What was the Volt doing? Is this how it handles a situation where the batteries cannot accept further charging? If so, where was the regen power going? Were the brake pads possibly being used instead of regen without my knowledge?

I have a 2015 Gen 1 Volt.

 

[wordptom]

Philosophically speaking, if you start driving down a long hill with a full battery charge, at some point the downhill regen will fill the small buffer at the top. At that point you are moving downhill, not drawing any grid power from the battery or regenerating any power back into the battery, so you no longer meet the criteria for "Electric Mode" driving. Until you once again start drawing battery power, distances driven will register as Gas Miles.

 

[NM_Nick]

So if it's not regening any power into the batteries then where is the power going? After it switches into this pseudo "gas" mode it appears to still be harvesting electrical power.

 

[canehdian]

It's a common bug.
The system sees extra power that it doesn't know where it came from because not from the battery, so assumes gas.
Probably somewhere in a thousand nested if statements there's an 'else count as gas miles' clause.

 

[2VoltFamily]

So if it's not regening any power into the batteries then where is the power going? After it switches into this pseudo "gas" mode it appears to still be harvesting electrical power.

It goes no where. It just provides resistance to provide braking.

 

[TSquare]

I recently fully charged my Volt at a relatively high elevation. After it was charged I proceeded to drive downhill, which resulted in the Volt attempting to regen some power back into the batteries. But since the batteries were already fully charged it appeared to switch to gas mode and started logging gas miles. Except that the ICE was not running and the Volt still appeared to be in 100% electric mode. What was the Volt doing? Is this how it handles a situation where the batteries cannot accept further charging? If so, where was the regen power going? Were the brake pads possibly being used instead of regen without my knowledge?

I have a 2015 Gen 1 Volt.

It is running the two electric motors against each other to simulate regen. In the Gen 1 models, there is a bug in the software that causes it to record it as gas miles even though the ICE is not running and no gas is used. I would see this all the time in my 2013, however now in my 2017 I have not seen this happen yet. They must have squashed that bug for Gen 2.

 

[wordptom]

Not long ago in a different thread discussing Mountain Mode, scottf200, one of this forum’s moderators, posted a response from GM that originally appeared in 2012 that might help answer your question. I’m not good at posting links, so I’ll just quote the citation. Of course, this is speaking of the Gen 1 Volt:

" 02-01-2012 #18 Chevrolet Customer Svc
Senior Member
Join Date Aug 2010
Location Detroit, MI

@ pauldon,

You have come across a feature of the vehicle which protects the battery from overcharging. Under certain circumstances, the electric motors will resist one another to provide braking in addition to the friction brakes on the vehicle. In order to meet emission requirements, the Volt does not spin the engine, but uses clutch 2 in the drive unit to link both motors. When the vehicle is at low speeds, clutch 2 requires that the resultant planetary gearset speeds increase to compensate. You will hear the electric motors at higher speeds, which is certainly a change from their normally silent operation.

The Volt was validated using the steepest, longest descent in the nation, Pike's Peak. With a full battery, the volt can descend Pike's Peak without issue with a combination of friction brakes and the electric motors. This is part of the Voltec propulsion system which has many more delighting features waiting for you to discover.
Volt Advisor Trevor
Chevrolet Volt Advisor Team
(877) 486-5846
[email protected] "


...note that by counting it as Gas Miles, you artfully increase your MPGcs (gas mileage when using gas) by increasing your total Gas Miles without increasing Total Gas Used... so... bug/schmug... would you prefer that it artificially inflate your AER and ev mileage by counting it as Electric Miles?

 

[PrivatePilot]

So ideally, if you know you're at a high elevation and will be descending a long grade and can/will benefit from regen, one would be best to not fully charge the batteries?

 

[2VoltFamily]

So ideally, if you know you're at a high elevation and will be descending a long grade and can/will benefit from regen, one would be best to not fully charge the batteries?

One would think so.

 

[NM_Nick]

Very interesting, but not surprising. The car's kinetic energy has to go somewhere. And if it's not into the battery via regenerative braking it sounds like they use a combination of clutches, motor resistance, and friction braking to expel that energy.

What I didn't mention is that I actually live at the top of said hill. I'll have to change my normal commute to a path that doesn't start off downhill, but hits the downhill portion only after I've used some kWh's and have room in the battery for normal regen.

 

[canehdian]

Or if that's not doable, set your charge schedule to delayed mode to complete x minutes after you usually leave such that the battery is only y% charged.
Values which you'll find with experimentation

 

[wordptom]

Very interesting, but not surprising. The car's kinetic energy has to go somewhere. And if it's not into the battery via regenerative braking it sounds like they use a combination of clutches, motor resistance, and friction braking to expel that energy.

What I didn't mention is that I actually live at the top of said hill. I'll have to change my normal commute to a path that doesn't start off downhill, but hits the downhill portion only after I've used some kWh's and have room in the battery for normal regen.

Depending on the season, you could turn the heat or the air conditioning on High to create some power demand as you start down the hill. Perhaps it might be enough to prevent regen from filling the buffer... or perhaps unplug and then pre-condition before starting out in the morning to take a little off the top before leaving???

Or... after you’ve traded in your Volt for a new Bolt, you’ll discover the Bolt’s Energy Settings menu allows you to select Hill Top Reserve when charging, with options of Off, On, On - Home Only, or On - Away Only. Turning it completes the charging earlier (I’m not quite sure where the cutoff point is), leaving a larger cushion at the top for those who encounter regen opportunities upon leaving the charging station...

 

[llninja]

It goes no where. It just provides resistance to provide braking.

It can't go nowhere. The momentum has to be converted to something somewhere. Could it be possible when the battery is maxed out that the car actually puts the ICE into the drivetrain to dissipate the momentum as heat? Only WOT can confirm if this is what the car is really doing.

 

[canehdian]

It's the unicorn mode that earlier quote said exists but WOT says does not.

Until someone actually records data of it happening, we have to assume it doesn't exist and it just stops regen.

If it does exist, the only way I can think of it working is that MGB is set to full regen (more than would normally be extracted from downhill coasting in L) and MGA is set to add that energy back to the system so that the electricity is passed from one to the other (@90%x90% efficiency) = 19% energy removed from the system as heat and out the coolant/radiator. At max regen of 60kW that's 11.4kW of deceleration possible.
That is what is rumoured to happen, but if that is physically possible, I don't know. But the numbers seem like a reasonable level of deceleration can be maintained from this.

 

[homesteadelectric]

I was at the wind power visitor center near Ellensburg (very interesting, BTW), they had an L2 charger so I charged to full. Then left on an 18 mile steep descent to the Columbia River, the range kept increasing from regen. Once it reached 63 miles I switched to gas because I was nervous about the battery. Seemed to be real range that I could use later tho.

 

[llninja]

I was at the wind power visitor center near Ellensburg (very interesting, BTW), they had an L2 charger so I charged to full. Then left on an 18 mile steep descent to the Columbia River, the range kept increasing from regen. Once it reached 63 miles I switched to gas because I was nervous about the battery. Seemed to be real range that I could use later tho.

I wouldn't worry about possibly overcharging the battery. The engineering behind this car is solid. It's not that you're overcharging the battery, but the guessometer was adjusting your expected range based on driving conditions. There wa son need to switched to ICE.

 

[jupitermoon]

In my Spark EV, regen would completely turn off if the battery was full or say the battery was hot due to sitting in a garage in summer.

The brakes would act as though they were normal brakes with no regen at all.

 

[canehdian]

I wouldn't worry about possibly overcharging the battery. The engineering behind this car is solid. It's not that you're overcharging the battery, but the guessometer was adjusting your expected range based on driving conditions. There wa son need to switched to ICE.

And in this case, switching to gas really just changes the picture on the dash. The engine wouldn't start with continuous negative (generation) or net zero energy flow.

 

[homesteadelectric]

So where does that energy go? Does the Volt have a way to load dump? At some point the battery cannot accept any more charge.

Also what is the highest range anyone has seen in this scenario?

 

[CLine]

I, too, start my commute at the top of a long descent. Is there anyway to program the car to stop charging at set charge level, say 80%?