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Discussion Starter #1
Can someone explain the engineering reason to avoid hard braking?
I see that the energy ball discourages hard braking, but I can't figure out why.
At a constant deceleration rate starting from 45 MPH, initially the energy ball is happy and lots of power is regenerated back to the battery.
Then as the car slows the energy ball drops into the "bad" zone. I have to lift off the brake pedal, reducing regen, and decreasing my deceleration (extending my stopping distance) to pull the ball back up into the happy place.
I would have thought that a constant deceleration rate, and greater regen, would be a good thing, or at least not a bad thing.
Based on the amount of regen power, it doesn't seem likely that the friction brakes are being employed, but that might be the issue, without my realizing it.
If there is an appropriate previous thread, please let me know.
 

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Because it wastes energy and causes wear and tear. But if needed, stomp on them. However, many people race from stoplight to stoplight wasting fuel to start, wasting pads to stop. A somewhat slower start and gliding/regen stop get's you to the next stoplight just as fast as the guy doing jackrabbit start/stops, but you use less fuel and your bakes last longer.

Try switching between D and L to slow down if you don't want to feather the brake pedal. The green ball helps your game.
 

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When the green ball starts to go outside the circle and starts turning yellow, you are using friction brakes, if it stays within the cirdle, you are using regen braking only.
 

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Discussion Starter #4
I'm not confident that this is true. I would accept that answer if it weren't that the regen value is much higher the harder I brake. Why would the system invoke friction brakes when regen is making a significant contribution? Yes, I know all about rabbit starts and stops, as it applies to ICE cars. Fast starts waste as much energy in an EV. But the regen value tells a different story on fast braking.

Are there any systems engineers on the forum who have specific engineering knowledge of the regen braking system? Not that I don't appreciate the input from knowledgeable contributors, I am simply in need of a detailed analytical response.
 

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Drive around in low for a day or 2, you will get educated on what max regeneration feels like. Afterwards driving in "D" you will have a feel for the threshold after which friction braking kick in.
 

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I'm not confident that this is true. I would accept that answer if it weren't that the regen value is much higher the harder I brake. Why would the system invoke friction brakes when regen is making a significant contribution? Yes, I know all about rabbit starts and stops, as it applies to ICE cars. Fast starts waste as much energy in an EV. But the regen value tells a different story on fast braking.

Are there any systems engineers on the forum who have specific engineering knowledge of the regen braking system? Not that I don't appreciate the input from knowledgeable contributors, I am simply in need of a detailed analytical response.
- Higher regen rates are less efficient.
- The harder you've had to brake, the earlier you could have {braked|lifted off} had you {been paying attention|left sufficient space|learned the light sequence|not been in such a great hurry}
 

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I'm not confident that this is true. I would accept that answer if it weren't that the regen value is much higher the harder I brake. Why would the system invoke friction brakes when regen is making a significant contribution? Yes, I know all about rabbit starts and stops, as it applies to ICE cars. Fast starts waste as much energy in an EV. But the regen value tells a different story on fast braking.

Are there any systems engineers on the forum who have specific engineering knowledge of the regen braking system? Not that I don't appreciate the input from knowledgeable contributors, I am simply in need of a detailed analytical response.
First the Volts brakes are 100% regen until a certain point then it starts to blend in the rear friction brakes for dynamic stability. Then maximum regeneration happens then it starts to blend in the front friction brakes for maximum stopping power.

While you are correct in that harder stops show a higher instantaneous power flow back into the battery they are not more efficient.
example 1 a 50KW regen for 5 seconds = 70Wh of energy However example 2 10KW regen for 30 seconds = 83Wh of energy.

Add to the fact that not 100% of that energy does not make it back to the battery. The regen energy is still subject to charging losses and charging losses grow exponentially with power.

So in example 1 above you might get 70Wh but might experience 50% charging losses at that 50KW rate so you only recover 35Wh into the battery. But in example 2 you might have only 20% charging losses so 66Wh gets recovered into the battery.

As a note charging losses are related to the electrical current squared times the resistance of all electronic components and the internal battery cell resistance (which increases with higher states of charge).
 

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I have learned to use the brake pedal gingerly and prolong the regen period as long as possible, so if I see a stop ahead of me I will lift off the throttle EARLY and the modulate the brake pedal to try and maintain between 7 and 10 kw of regen for as long as possible.
 

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First the Volts brakes are 100% regen until a certain point then it starts to blend in the rear friction brakes for dynamic stability. Then maximum regeneration happens then it starts to blend in the front friction brakes for maximum stopping power.

While you are correct in that harder stops show a higher instantaneous power flow back into the battery they are not more efficient.
example 1 a 50KW regen for 5 seconds = 70Wh of energy However example 2 10KW regen for 30 seconds = 83Wh of energy.

Add to the fact that not 100% of that energy does not make it back to the battery. The regen energy is still subject to charging losses and charging losses grow exponentially with power.

So in example 1 above you might get 70Wh but might experience 50% charging losses at that 50KW rate so you only recover 35Wh into the battery. But in example 2 you might have only 20% charging losses so 66Wh gets recovered into the battery.

As a note charging losses are related to the electrical current squared times the resistance of all electronic components and the internal battery cell resistance (which increases with higher states of charge).
This is the kind of answer that I understand the OP wanting. Thanks Neromanceres 8^)
 

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Drive around in low for a day or 2, you will get educated on what max regeneration feels like. Afterwards driving in "D" you will have a feel for the threshold after which friction braking kick in.
But Low isn't max regen, as anyone with a 2013 or later Volt can easily determine from the power meter in the DIC. From other discussions, we know regen can dump 55-60kW into the system. (I'd love to see the negative numbers no-slope and pedal-free, for D, L, and paddle regen from a couple of people with Volts newer than mine, just so we can get that all in one place...)
 

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Discussion Starter #11
Thanks very much for the clear and informative answer. The description coincides with the energy ball's indications. With this knowledge I will be more inclined to drive as the energy ball would like me to.
 
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