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Regenerative Braking

Regenerative Braking

I would like to know how regenerative braking works in a a Tesla vehicle. Also, I would like to know the average amount of voltage produced by it.

Babaron | 22 gennaio 2017

When you let off of the accelerator, the car begins to slow, more than a conventional car. This is enhanced by setting the regenerative braking to "standard." This slowing of the car is accomplished by using a second set of calipers in the car's wheels that grab the rotor and, instead of wasting the energy of motion by generating heat like the conventional brakes on the car, use the friction to generate electricity which then is fed back to the battery to charge it.

You can see exactly how much charging is taking place by watching your cars power meter. You can set your dash to display this meter. The amount of energy recycled to the battery is relatively small, but does increase the range of the car measurably.

See the Tesla owner's manual for more info. It is available at tesla.com

Efontana | 22 gennaio 2017

Second set of calipers is in the manual? I thought they just changed the behavior of the motor.

Bighorn | 22 gennaio 2017

@Babaron
What are you talking about--second set of calipers?! Absolute rubbish.

@OP Regeneration produces power measured in kilowatts. Batteries are referenced to either 350 or 400 volts. Maxes out at approximately 65kWs.

Captain_Zap | 22 gennaio 2017

No second set of calipers. Regen feels like a gentle downshift in a car with a manual transmission.

jordanrichard | 22 gennaio 2017

Babaron where did you pull that out of .......?

OP, simply put, when you lift off the accelerator, the motor in net effect becomes a generator and recharges the battery. You get back about 70-80% of the energy used to accelerate. So picture driving up a hill that is 500 to the top and 500 back down the other side. On the decent, you will get back about 70% or so of what it took you to go up the hill.

Re-gen has absolutely nothing to do with the brakes.

chohans | 22 gennaio 2017

Babaron:

What actually happens is as soon as you let off the accelerator the wheels engage into winding up a spring. The spring gets compressed like one of those wind-up toy cars we used to have in the 70's. Once you press on the accelerator, the spring releases the compression and propels the car forward. At this time the battery is not used and appears as if it had gained some charge. No charging actually takes place. Think of it as "virtual battery charge". There are two springs. One for light regeneration and one for strong regeneration.

/s :-}. Hey, come to think of it that might actually work!!! Damn!

SUN 2 DRV | 22 gennaio 2017

It might be helpful to not think of regen braking as a separate function or system. It's fundamentally just part of the same motor control function that can control energy flow both into and out of the motor and to and from the battery.

The accelerator pedal lets the driver control power flow over a range of roughly +320 kW to -65 kW, thus giving you both an acceleration and deceleration capability in the same pedal.

joemar10 | 22 gennaio 2017

Isn't regen accomplished by both lifting off of the accelerator as well as applying the brake? As Jordanrichard said above, the motor becomes a generator when rhe accelerator is lifted. When the brakes are applied, some sort of resistance slows the car and charges the battery. (Not sure how that is accomplished. I know,that my Prius did not need a brake job until 215,000 miles, so that is another benefit of regenerative braking. I don't know how regen braking works, but I think it has something to do with creating electrical power using resistance instead of heat due to friction.

Bighorn | 22 gennaio 2017

@joe
No, brakes slow wheels--no additional regen.

dchuck | 22 gennaio 2017

Chohans

believe it or not there are delivery trucks that do just that. Though they use compressed air not springs.

Babaron | 22 gennaio 2017

Hey all, go look at your rear wheels...mine have 2 sets of calipers! Wish I could post a pic.

Twiglett | 22 gennaio 2017

having two set of calipers doesn't mean that they're used for regen though.
Seriously, do a quick search for regenerative braking.
Wikipedia has lots of information with an explanation of its use in EVs, simple and elegant, especially the way Tesla does it. Motors provide power and regen, with the brakes doing nothing but being brakes.

Bighorn | 22 gennaio 2017

There has been a second parking brake on the rear since eliminated. Nothing at all to do with regen.

petero | 22 gennaio 2017

Paraphrasing Nick J. Howe, “Owning a Model S.”

Regen braking occurs when you lift up/off the accelerator and the current generated from the motor acts like an electrical generator when slowing down or driving downhill.

“Regen (electricity generation) is the recovery of energy by converting the car’s speed (kinetic energy) to electrical current and ultimately chemical energy in the battery. All of this occurs when the car decelerates.”

FYI. There are two sets of brake calipers on the rear wheels. The smaller are the parking/emergency brakes and the larger are the normal brakes.

DTsea | 22 gennaio 2017

babaron,

the second set of calipers are the parking brake.

Babaron | 23 gennaio 2017

Oh......OK then. Learn something new every day.

reed_lewis | 23 gennaio 2017

And the correct measurement for how much energy is generated would be kilowatts which is volts times amps. Voltage by itself means very little.

DTsea | 23 gennaio 2017

reed_lewis,

not quite.

watts are v×a, kw are thousand watts

watts are power- energy per second. to get energy units multiply by time eg watt-seconds (aka joules, J) or kilowatt-hours, used to measure energy capacity of tesla battery packs.

a kWh is of course 3.6 kJ.

SUN 2 DRV | 23 gennaio 2017

Power (watts) are an instantaneous value, not per second.

djharrington | 23 gennaio 2017

DTsea said it correctly: power = energy per unit of time. Another way to say it is that power does not measure energy, but rather the rate of energy transfer. 1W = 1J/s

He went wrong at the kWh to kJ conversion. 1 kWh is 1000 joules per second, for 3600 seconds, or 3.6 MJ.

Some other fun conversions: 1 Calorie (with a capital "C") = 1000 calories = 4184 joules; so that 100 Calorie candy bar you ate this afternoon is 418,400 joules, which is the equivalent of 116 Wh, or enough to drive a Model S about 0.4 miles.

Think about how many Snickers you could fit where the battery is located...

SUN 2 DRV | 23 gennaio 2017

Power is the instantaneous value
Energy is power integrated over time

SUN 2 DRV | 23 gennaio 2017

A couple of totally layman's way to say it and remember it:

Power (kW) is "how STRONG".
Energy (kWH) is "how strong for HOW LONG".

kW is used when measuring Performance (eg a motor related to acceleration)
kWh is used when measuring Capacity (eg a battery related to range)

DTsea | 23 gennaio 2017

dj you are right. 3.6 MJ not kJ. oops.

sun2, per second is units. it is an instantaneous value, doesnt mean FOR a second. that would be integrating energy.

for example 1 W-s of energy- 1 Joule- if exerted in a microsecond would be a MegaWatt of POWER but only 1 J of ENERGY.
.

SUN 2 DRV | 23 gennaio 2017

Volts is not per second
Amps is not per second and
kW is NOT per second

djharrington | 23 gennaio 2017

Alr

djharrington | 23 gennaio 2017

Oh damn, I thought I'd live out my years without a dreaded double post or posting error. I was going to say:

Alright you two, I think you both understand it. DTsea isn't saying that power is a "per second" value on its own, but rather power is energy per second, as in a rate. You're both on the same team. The team of physics.

DTsea | 24 gennaio 2017

1 joule is 1 kg m^2/s^2

watts are J/s BY DEFINITION IN THE INTERNATIONAL SYSTEM OF UNITS. LOOK IT UP.

SHEESH.

Remnant | 24 gennaio 2017

@SUN 2 DRV (January 22, 2017)

<< It might be helpful to not think of regen braking as a separate function or system. >>

Since Teslas have only two motors, separate control of the Right and Left wheels, as needed in Torque Vectoring, can only take place through the mechanical differential or through regular (friction) brakes.

The Friction Brakes are also useful in emergency braking, because, generally, Regen is somewhat slower, but I'm not sure this applies to Tesla, as emergency braking could also be implemented as reverse torque.

reed_lewis | 24 gennaio 2017

Yes I know that V x A is Watts, but what I was trying to say is that volts means almost nothing in terms of what is produced. It is watts or Kilowatts that means something.

radami2 | 24 gennaio 2017

Here is a great video that shows that regen has a lot to do with brakes and brake wear. Also quantifies the economies of regen wrt brakes.

https://www.youtube.com/watch?v=yIv9txhcnjQ

ihappentobeaninja | 24 gennaio 2017

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ihappentobeaninja | 24 gennaio 2017

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milesbb | 29 gennaio 2017

Induction motors provide torque at the rotor when a rotating magnetic field is applied in the stator of the motor. Torque is no longer applied to the rotor when the rotor achieves the rotating speed of the magnetic field of the stator. The rotating field of the stator is set by the frequency output of the inverter and the number of poles wound into the stator. I believe Tesla motors have 4 poles. When the the speed of the stator rotating magnetic field is less then the rotor speed negative torque is applied to the rotor, energy is transferred back to through the inverter to the batteries. Basically regenerative braking works by lowering the frequency output of the inverter. Inverter voltage is also raised or lowered to adjust the motor torque.

An induction generator does not actually make voltage. It only reacts to voltage applied to it. Without voltage applied to an induction generator you have a free wheeling rotor. I believe the Tesla induction motor/generator operates from around 400 volts down to a low value of perhaps 25 volts.