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by xvector 1998 days ago
This was the dumbest thing I experienced with my Model 3. I was expecting my regen brakes to work after I pulled out and I had to brake super hard after.

Why can’t Tesla just give us an option to keep it consistent? I guess adding video games is more important.

3 comments

Tesla has been religious about never blending regen and mechanical braking. The accelerator only controls the motors, the brake pedal only controls the brakes. They’ve broken that somewhat now with one-pedal driving mode. The only way they could make regen feel consistent with a cold or full battery would be to blend in friction braking to make up the difference, which is just not something Tesla is into doing.

My BMW i3 did this really well, FWIW.

I mean, the solution is not to charge past 90%: for most practical purposes there’s no reason to go past 90% anyways.
Because that's not how batteries work.

Regen works because the batteries are being charged by the induction of the motors taking energy from the moving car. If the batteries are full they cannot take any more change and hence cannot draw power from the motion of the car.

What do you expect them to do? Dump the current on a giant resistor and hope it doesn't melt?

> Dump the current on a giant resistor and hope it doesn't melt?

That's called an induction brake and it's already widely used in trains and semi trucks. That said, you still need a friction brake at low speeds, since the induction braking force is proportional to velocity.

Simulate the same braking curve with the physical brakes as when regen is functioning?
I suppose that's one approach. Mechanical brakes work by converting the kinetic energy of the vehicle into heat via friction, it seems fitting that inductive brakes would dump energy to heat by running current over a resistor. Though under normal braking circumstances I don't know what percentage of the vehicle's energy is lost to the brakes themselves and what percentage is lost to the friction of the tire with the road.
Can anyone do the math and tell me how big that resistor would need to be? I’ve always wondered how many watts are being dissipated by my brake pads and rotors when I stop.
Assuming your Tesla is around 2000 kg and traveling at 30 meters/s, it's got about 900,000 J of kinetic energy. Stopping in 10s is some serious power that you'd need to throw off.
All of yhe 90 kW doesn't need to be radiated in real time though as it's ok for the brake elements to heat up.
> What do you expect them to do? Dump the current on a giant resistor and hope it doesn't melt?

You know...they could use it to boil water for a built in coffee/green tea maker.

Just a thought...