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Discussion Starter · #1 ·
1st question: if you are heading to a stop sign and must come to a stop, is the regen breaking more efficient if you slowly regen vs fast regent such as using the paddle?

2nd question: hard vs soft acceleration, why does a slow acceleration save energy? I am referring to not having to slam the breaks after a hard acceleration. Just quickly reaching the speed limit quickly.
 

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1st question: if you are heading to a stop sign and must come to a stop, is the regen breaking more efficient if you slowly regen vs fast regent such as using the paddle?

2nd question: hard vs soft acceleration, why does a slow acceleration save energy? I am referring to not having to slam the breaks after a hard acceleration. Just quickly reaching the speed limit quickly.
A1: Technically light regen would be more efficient than heavier regen. The better technique would be to coast to the stop sign in Neutral with no regen, timing things so the vehicle rolls to a stop right at the stop sign but this would create traffic conflicts with other drivers in most situations.

A2: A light touch on the accelerator, using ~30kW to accelerate from a stop, is more efficient than accelerating more forcefully because it uses less instantaneous power. When you depress the accelerator you are asking the vehicle's motor to perform a specific amount of work, i.e. accelerate a body at rest (the Volt) or starting from a steady speed (current velocity), to a desired speed (new velocity) in a specific period of time (i.e, 0 MPH to 60 MPH in 7.3 seconds versus reaching 60 MPH in 12 seconds.) If you floor the accelerator the Volt is capable of sending ~120kW power to the two electric motors. For the same reason, jack rabbit starts in an ICE vehicle will use more gas than accelerating at a moderate rate.
 

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Discussion Starter · #3 ·
Jcanoe, what you say sounds right but I've noticed the opposite.
When I 1st started driving the volt, I experimented a lot L and the paddle. And also used a quick acceleration slightly above the speed limit and then coast. (Pulse and glide). Once I startled using D and slow acceleration / deceleration, my score went down.
Unfortunately in the last 2 weeks it's gotten colder (and new snow tires) and my mileage went down the drain and nothing I do will bring it back.
 

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Jcanoe, what you say sounds right but I've noticed the opposite.
When I 1st started driving the volt, I experimented a lot L and the paddle. And also used a quick acceleration slightly above the speed limit and then coast. (Pulse and glide). Once I startled using D and slow acceleration / deceleration, my score went down.
Unfortunately in the last 2 weeks it's gotten colder (and new snow tires) and my mileage went down the drain and nothing I do will bring it back.
Hypermiling techniques (pulse and glide) tend to maximize efficiency. Still, I have to believe that a slower speed up followed by a prolonged glide would be more efficient than quickly accelerating, then gliding.

When you stated your score went down, was this the EV range on the GM (guess-o-meter) or the Volt's efficiency score? I don't put much stock in either of these metrics. The only measure that makes sense is the overall Wh/mile while driving. A true test would have to include a round trip of A=>B=>A to cancel out any advantage due to elevation or wind direction.

I don't have snow tires but for the next ~5 months I am going to be heavily relying on preconditioning and use of electric heat to keep warm when I drive my Volt. I may partially charge my Volt several times per day, probably drop my overall driving efficiency by close to 50% but at least I won't be cold.
 

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Jcanoe, what you say sounds right but I've noticed the opposite.
When I 1st started driving the volt, I experimented a lot L and the paddle. And also used a quick acceleration slightly above the speed limit and then coast. (Pulse and glide). Once I startled using D and slow acceleration / deceleration, my score went down.
Unfortunately in the last 2 weeks it's gotten colder (and new snow tires) and my mileage went down the drain and nothing I do will bring it back.
Resitance loses in all the conductors will go up with the square of the current draw. Electric motors also tend to create a higher back EMF with a higher driving current, but this varies with the type of motor and how it's being driven.

I highly doubt the Chevrolet team went out of their way to make 60+ kW energy usage more efficient than ~5-30 kW usage, where most people's driving and the EPA testing tends to dwell.
 

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Hypermiling techniques (pulse and glide) tend to maximize efficiency. Still, I have to believe that a slower speed up followed by a prolonged glide would be more efficient than quickly accelerating, then gliding.
This is true for an ICE, but not an electric motor. ICE will typically hit a lower brake specific fuel consumption at a moderate amount of vacuum (~3-6 in-Hg) at lower rev ranges that you would find with someone cruising. The "pulse and glide" technique just gets the engine to that more efficient BSFC island then shuts it off and repeats. I don't think anything like that is happening with the Volt in EV mode.
 

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This is true for an ICE, but not an electric motor. ICE will typically hit a lower brake specific fuel consumption at a moderate amount of vacuum (~3-6 in-Hg) at lower rev ranges that you would find with someone cruising. The "pulse and glide" technique just gets the engine to that more efficient BSFC island then shuts it off and repeats. I don't think anything like that is happening with the Volt in EV mode.
Good to know. There has to be signficiant energy cost associated with applying full power to the electric motor(s) versus the work output, with some power lost as heat in the motor windings. If you drive the Volt like a racer your EV range will suffer and not just because you are not gliding once you hit cruising speed.
 

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Ok, im willing to agree that hard acceleration and then gliding does not save energy, but why does hard regen with the paddle and L waste energy?
Regen is not as efficient as we would like to believe, probably no more than 60% overall. Coasting (gliding) in neutral (not in D) is more efficient at covering distance as the only losses are due to tire/road resistance and air resistance than converting forward momentum into electrical energy. Regenerative braking requires converting momentum into electricity (with associated losses), then storing this in a battery or capacitor (more losses), retrieving the energy from the battery or capacitor to power a motor (still more losses) at a later time. A mechanical flywheel would be a much more efficient way to store the vehicle's momentum for later use. A vehicle the size of a city bus could easily contain a flywheel in addition to batteries and electric motor(s).
 

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Discussion Starter · #10 ·
Hypermiling techniques (pulse and glide) tend to maximize efficiency. Still, I have to believe that a slower speed up followed by a prolonged glide would be more efficient than quickly accelerating, then gliding.

When you stated your score went down, was this the EV range on the GM (guess-o-meter) or the Volt's efficiency score? I don't put much stock in either of these metrics. The only measure that makes sense is the overall Wh/mile while driving. A true test would have to include a round trip of A=>B=>A to cancel out any advantage due to elevation or wind direction.

I don't have snow tires but for the next ~5 months I am going to be heavily relying on preconditioning and use of electric heat to keep warm when I drive my Volt. I may partially charge my Volt several times per day, probably drop my overall driving efficiency by close to 50% but at least I won't be cold.
What metrics do you not trust? MPGE and range left on battery? I've wondered if the MPGE was a little flacky. I don't know yet if I trust them two.
 

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Discussion Starter · #11 ·
Regen is not as efficient as we would like to believe, probably no more than 60% overall. Coasting (gliding) in neutral (not in D) is more efficient at covering distance as the only losses are due to tire/road resistance and air resistance than converting forward momentum into electrical energy. Regenerative braking requires converting momentum into electricity (with associated losses), then storing this in a battery or capacitor (more losses), retrieving the energy from the battery or capacitor to power a motor (still more losses) at a later time. A mechanical flywheel would be a much more efficient way to store the vehicle's momentum for later use.
Say you are 1000 ft from a stop sign. Your going 40 MPH. If you gradually, evenly, come to a stop over that 1000 ft vs wait till the last 100 ft and use the paddle to a stop. In that scenario, what regenerated more power?
 

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The EV range displayed on the driver information center screen is influenced by many factors. As long as the route you drive today is the same as last week and the road and traffic conditions are the same and the temperature has not appreciably changed the EV range will be accurate. If any of the parameters change then the actual EV range can be higher or lower than indicated.

I especially do not care for the efficient score on the energy screen. I've pretty much stopped looking at it since it includes factors that you cannot control such as the air temperature and the terrain (there may not be a better route to your destination than one that includes some hills.) I think the climate control score should be removed from the efficiency score since this energy usage already is considered when calculating range. It does not help me change my driving behavior to lower my score by -3.5 - -5.0 when I use the electric heat. I understand the electric heat uses energy, I use the electric heat and AC to either defrost/defog the Volt's windshield for visibility or to keep warm.
 

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Discussion Starter · #13 ·
The EV range displayed on the driver information center screen is influenced by many factors. As long as the route you drive today is the same as last week and the road and traffic conditions are the same and the temperature has not appreciably changed the EV range will be accurate. If any of the parameters change then the actual EV range can be higher or lower than indicated.

I especially do not care for the efficient score on the energy screen. I've pretty much stopped looking at it since it includes factors that you cannot control such as the air temperature and the terrain (there may not be a better route to your destination than one that includes some hills.) I think the climate control score should be removed from the efficiency score since this energy usage already is considered when calculating range. It does not help me change my driving behavior to lower my score by -3.5 - -5.0 when I use the electric heat. I understand the electric heat uses energy, I use the electric heat and AC to either defrost/defog the Volt's windshield for visibility or to keep warm.
Do you trust the MPGE? I don't know if I do or not. Seems kinda wacky. The only one I trust it the miles and KW used.
 

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Say you are 1000 ft from a stop sign. Your going 40 MPH. If you gradually, evenly, come to a stop over that 1000 ft vs wait till the last 100 ft and use the paddle to a stop. In that scenario, what regenerated more power?
It would be very close.
 

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Do you trust the MPGE? I don't know if I do or not. Seems kinda wacky. The only one I trust it the miles and KW used.
I trust the MPGe but think the lifetime MPGe figure is a better overall metric. The MPGe can change so rapidly that you cannot use the information to adjust your driving. There should be a trip/waypoint specific MPGe that you can reset that does not require you to fully recharge the battery before the MPGe is reset.
 

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Window sticker ratings indicate the Gen 2 Volt’s electric fuel tank holds (53/106 =) 0.5 Ge, or 16.85 kWh of "from the wall" power. After charging losses are deducted, you have ~14.1 kWh of usable power in one full charge.

The energy usage screen calculations for Trip and Combined MPGe (and, I suspect, Lifetime) ignore any regen created and used during the trip (that’s also true for the quantity of power used to drive the electric miles - "kWh Used" is a net calculation of grid power used less regen put back into the battery). If you don’t do any partial recharging, the amount of "electric fuel used" during any trip that shows "14.1 kWh Used" for however many electric miles are achieved will be 0.5 Ge, and the trip MPGe will be double the electric miles driven (just like 106 miles is double the rated 53 miles in a single charge).

The relationship of electric miles to kWh Used is the same as the relationship of electric miles to Ge used when regen is ignored. If you can drive 60 ev miles on a full charge, "120 MPGe" sounds much more impressive than "4.26 miles/kWh," and the vehicle does the calculation for you and displays it on the screen.

MPGe is based on "from the wall" power, so I don’t know how the display would deal with partial recharges. Perhaps the Ge quantity consumed for any amount of total electric miles driven, including driving less than a single charge or more than a single charge because of partial recharging, would simply be the fuel in one full charge (0.5 Ge) multiplied by the fraction indicating the amount actually used relative to the usable kWh in a full charge.

For example, if partial recharging enabled you to drive 80 electric miles and the display showed "20 kWh Used" perhaps the trip MPGe would be calculated using 0.5 Ge x 20/14.1 = 0.71 Ge, so that the trip MPGe = 113. Or if you drove only 27 miles using 7.05 kWh, the fuel used = 0.5 x 7.05/14.1 = 0.25Ge, and the trip MPGe = 108.
 

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jcanoe: I understand your logic of coasting in neutral. I'd like to point out that this is illegal in most states (impossible to enforce, of course!). As you pointed out, it's also not practical in most situations involving traffic.
...just sayin'...
 

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Discussion Starter · #19 ·
Window sticker ratings indicate the Gen 2 Volt’s electric fuel tank holds (53/106 =) 0.5 Ge, or 16.85 kWh of "from the wall" power. After charging losses are deducted, you have ~14.1 kWh of usable power in one full charge.

The energy usage screen calculations for Trip and Combined MPGe (and, I suspect, Lifetime) ignore any regen created and used during the trip (that’s also true for the quantity of power used to drive the electric miles - "kWh Used" is a net calculation of grid power used less regen put back into the battery). If you don’t do any partial recharging, the amount of "electric fuel used" during any trip that shows "14.1 kWh Used" for however many electric miles are achieved will be 0.5 Ge, and the trip MPGe will be double the electric miles driven (just like 106 miles is double the rated 53 miles in a single charge).

The relationship of electric miles to kWh Used is the same as the relationship of electric miles to Ge used when regen is ignored. If you can drive 60 ev miles on a full charge, "120 MPGe" sounds much more impressive than "4.26 miles/kWh," and the vehicle does the calculation for you and displays it on the screen.

MPGe is based on "from the wall" power, so I don’t know how the display would deal with partial recharges. Perhaps the Ge quantity consumed for any amount of total electric miles driven, including driving less than a single charge or more than a single charge because of partial recharging, would simply be the fuel in one full charge (0.5 Ge) multiplied by the fraction indicating the amount actually used relative to the usable kWh in a full charge.

For example, if partial recharging enabled you to drive 80 electric miles and the display showed "20 kWh Used" perhaps the trip MPGe would be calculated using 0.5 Ge x 20/14.1 = 0.71 Ge, so that the trip MPGe = 113. Or if you drove only 27 miles using 7.05 kWh, the fuel used = 0.5 x 7.05/14.1 = 0.25Ge, and the trip MPGe = 108.
I am trying to follow you on this Wordptom, very interesting reading but what is GE?
 

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I always thought that when you accelerate hard, it's using more energy but for less time (you get to speed much faster), so it should balance out, right? Seems like decent logic but it just isn't correct. The fact is, the harder you accelerate, the more losses you incur and it's just less efficient. You are heating the tires against the road, heating the motor(s), wiring, it's more efficient to drain batteries slower, and so on.

Having said that, you do gain back some of the losses by getting up to speed faster and getting off the accelerator faster, but it just can't counter the fact that you'll always lose a little more energy by stressing parts more and causing more heat losses. I don't know what the numbers are but it's not like you double the amount of energy used if you accelerate at 60kW vs 30kW. It's probably more like 10% or 20% less efficient.

Mike
 
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