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Regen after battery is fully charged

5102 Views 22 Replies 11 Participants Last post by  canehdian
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.
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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.
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?
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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...
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