That's how I see it, but what actually slows the car? Because the car is slowed more than the friction of an ICE car that coasts longer but eventually will stop on level ground. If its not the brake pads, some power must be applied to reduce the speed of the car to that degree.
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Why isn't regen integrated with the brake pedal?
- Thread starter dennis
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- Driving Dynamics Model S
Being in motion means the car has kinetic energy. Brake pads use friction to "convert" the kinetic energy to waste heat. By comparison, an electric motor uses this kinetic energy to generate electricity which charges the battery pack.
In both situations the kinetic energy is being used (which results in the car slowing down), but with an ICE it essentially becomes wasted energy in the form of heat. With an EV that energy is used to charge the batteries, which means it is used in a much more efficient manner.
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See, that's the part I understand, but what if not friction of brake pads is actually slowing the car down?
swaltner
Active Member
Physics, particularly conservation of energy, which states that energy can neither be created nor destroyed.
As mentioned earlier, the car has a certain amount of kinetic energy (E = Mass * Velocity * Velocity). You are generating electricity (energy) inside the motor, which is being driven by the wheels. This electricity (energy) has to come from somewhere, which happens to be the kinetic energy of the car. Since you are reducing the kinetic energy of the car and the mass of the car can't change, the energy comes by slowing the car down.
The same thing would happen by a windmill generating electricity, just on a much larger scale than what is happening on the car. The air moving across the windmill face generating 1 MW of electricity would cause the air to slow down. The very same principle is being applied in the car to slow it down.
The responses ot your comment are all correct.
But to be more specific, it's magnetism. When the system is in regen mode, there's a strong magnetic field induced in the motor/generator. The rotor (which is being turned by the drivetrain when decelerating) is being forced thru this magnetic field, which resists it. As the rotor is forced through the magnetic field, in generates the electricity which is funneled back to the battery pack.
It's the same principle as what causes the motor to turn when electricity is applied to it in "forward" mode. If consuming 60 KWh of power will supply "N" amount of acceleration force, then reversing the system to build a magnetic field that uses the kinetic energy generate 60KWh of energy will also supply the same "N" amount of deceleration force.
That makes more sense to me. Thanks for taking the time to refresh my memory of physics classes from a time ago.
Sure thing.
I love the net effect... "one pedal driving" is very cool... and it's even more fun to watch your WHPM counters start dropping
Its even more fun when your average since last charge goes negative! I have one regular trip where that's the case, having managed numbers as low as -24Wh/mi.
strider
Active Member
Just think about using your arm to turn a crank generator radio, flashlight, etc. You are taking energy from your muscles and spinning a motor (motor and generator are the same thing, just depends on the direction of energy flow) to generate electricity. In the model S, instead of your arm spinning they're using the spinning wheels.
I like that. Those crank generators sow down fast when you stop cranking. And that's where they release energy in the form of electricity. Though I still don't understand technically what brakes the car....
strider
Active Member
The (magnetic) resistance of the generator to being spun is what slows down the car. When you're hand-cranking a generator you are having to constantly put in energy to keep it spinning. In the Model S the energy being put in is the speed of the moving car. As energy is used to spin the generator the car slows down.
Wait, I have another tack. Take the above crank generator and connect it via a clutch to a flywheel. Disconnect the clutch and spin the flywheel. Once the flywheel is spinning engage the clutch so the generator will spin. The flywheel will slow down. Now imagine the flywheel is sitting on the ground and the whole contraption could roll like your car.
Mr. Eastwood, I have hands-on experiment for you
Buy a neodymium magnet (you know, the super powerful kind that you can barely loosen without pliers). Find a piece of aluminium sheet, or even better, copper. No, wait, get one of each. Place the sheet of metal on a table, put the magnet on top. It will not stick, as aluminium (and copper) is not magnetic. Place a coin next to the magnet.
Now quickly lift one end of the metal sheet up, so that the sheet is at a 45 degree angle to the table. The coin will immediately slide onto the table, while the magnet will slide down much more slowly.
What happened was that the very powerful magnetic field through the magnet penetrated the electrically very conductive metal sheet, and when the magnet moves, its magnetic field will also move. When a magnetic field moves in the presence of an electrical conductor, electric current will be created in that conductor. This effect is called electromagnetic induction. This electric current will create a magnetic field of its own, which opposes the field that created the current in the first place, and thereby slow the fall of the magnet.
Essentially the same thing is going on inside a regenerating motor. But the motor is more refined, and is able to capture the electric current so it can be used to charge the battery, instead of going to waste as heat.
Next you can test different metals - the more conductive the metal, the slower the magnet will fall. Copper will slow the magnet more than aluminium, aluminium will slow it more than lead, and a sheet of plastic or wood will not slow it whatsoever. If the metal sheet was a superconductor, the magnet would not have moved at all.
Buy a neodymium magnet (you know, the super powerful kind that you can barely loosen without pliers). Find a piece of aluminium sheet, or even better, copper. No, wait, get one of each. Place the sheet of metal on a table, put the magnet on top. It will not stick, as aluminium (and copper) is not magnetic. Place a coin next to the magnet.
Now quickly lift one end of the metal sheet up, so that the sheet is at a 45 degree angle to the table. The coin will immediately slide onto the table, while the magnet will slide down much more slowly.
What happened was that the very powerful magnetic field through the magnet penetrated the electrically very conductive metal sheet, and when the magnet moves, its magnetic field will also move. When a magnetic field moves in the presence of an electrical conductor, electric current will be created in that conductor. This effect is called electromagnetic induction. This electric current will create a magnetic field of its own, which opposes the field that created the current in the first place, and thereby slow the fall of the magnet.
Essentially the same thing is going on inside a regenerating motor. But the motor is more refined, and is able to capture the electric current so it can be used to charge the battery, instead of going to waste as heat.
Next you can test different metals - the more conductive the metal, the slower the magnet will fall. Copper will slow the magnet more than aluminium, aluminium will slow it more than lead, and a sheet of plastic or wood will not slow it whatsoever. If the metal sheet was a superconductor, the magnet would not have moved at all.
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20 years ago in college physics this may have made sense to me. Unfortunately I just read blah blah blah blah blah. Just kidding. But it amazes me the level of knowledge I no longer possess that at one time I did.Mr. Eastwood, I have hands-on experiment for you
Buy a neodymium magnet (you know, the super powerful kind that you can barely loosen without pliers). Find a piece of aluminium sheet, or even better, copper. No, wait, get one of each. Place the sheet of metal on a table, put the magnet on top. It will not stick, as aluminium (and copper) is not magnetic. Place a coin next to the magnet.
Now quickly lift one end of the metal sheet up, so that the sheet is at a 45 degree angle to the table. The coin will immediately slide onto the table, while the magnet will slide down much more slowly.
What happened was that the very powerful magnetic field through the magnet penetrated the electrically very conductive metal sheet, and when the magnet moves, its magnetic field will also move. When a magnetic field moves in the presence of an electrical conductor, electric current will be created in that conductor. This effect is called electromagnetic induction. This electric current will create a magnetic field of its own, which opposes the field that created the current in the first place, and thereby slow the fall of the magnet.
Essentially the same thing is going on inside a regenerating motor. But the motor is more refined, and is able to capture the electric current so it can be used to charge the battery, instead of going to waste as heat.
Next you can test different metals - the more conductive the metal, the slower the magnet will fall. Copper will slow the magnet more than aluminium, aluminium will slow it more than lead, and a sheet of plastic or wood will not slow it whatsoever. If the metal sheet was a superconductor, the magnet would not have moved at all.
mknox
Well-Known Member
Well, I learned something! I though the brakes were pure hydraulic and that all the re-gen was controlled from the accelerator.
When you press the brake pedal you're getting friction braking as well as maximum regen. At least that's my understanding and user experience.
Correct. Try coasting down a steep hill. Check your regen level (most likely less than 60kw). Now press on the brake. Regen does not increase.
That observation is why I started this thread.
It is possible that the amount of regen is limited by the car's speed. ie. at lower speeds, it is possible that the actual regen mechanism cannot grab a full 60 kW of power from the wheels. I'm just speculating here, but it is possible there is a technical hardware limitation, rather than just a software limitation.
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