Maybe a dump question, but it's physics

[ColumbiaR]

I'm interested in the efficiency of the Tesla M3 regeneration system. So, I wonder if anyone has done a test, say, like Pike's Peak or Mt Washington.

I envision recording the battery charge at the bottom, then driving to the top and noting how much was consumed in the climb. Then, going down and noting the charge at the bottom.

How much of the cost of ascending would be regained?

Anyone tried this?

 

[mmanner]

I'm interested in the efficiency of the Tesla M3 regeneration system. So, I wonder if anyone has done a test, say, like Pike's Peak or Mt Washington.

I envision recording the battery charge at the bottom, then driving to the top and noting how much was consumed in the climb. Then, going down and noting the charge at the bottom.

How much of the cost of ascending would be regained?

Anyone tried this?

You would have to try to go when there wasn't much traffic so you could go fairly steadily and evenly up and maybe more importantly, down (without having to use the brakes at all). I think there has been some testing of this, but can't recall where I saw it. Google it and I bet you'll find some.

 

[SalisburySam]

I love your thread title. I’m old enough to remember when a laxative was called a “physic” and therefore definitely a “dump question.”

Thanks so much for both the memory and the chuckle.

Now what was all this about regen?

 

[BQst]

I'll bite.

I've read the full regen process (motion to electrons and back to motion) loses about 30%. So about 70% of the energy used to climb will be restored during the descent.

But you're still driving a 24 mile route (Pike's peak). So your total energy use = energy required to go 24 miles at your chosen speed + 30% of the energy required to climb that elevation.

But I also think the descent down Pike's peak is much steeper than regen can absorb, so you'll have to use some mechanical braking to make the turns, so you'll get back less than 70% of the energy it took to climb it.

Hmmm... Maybe someone with more physics chops can take it from there.

Ben

 

[Lasttoy]

I tested it at Jaskson Hole. From top of mountain to town I added 10 miles. I was actually going to fast a couple times and had to tap the brakes. It really works. Around town it's a joke.

 

[Matsayz]

So I've driven from Buena Vista to Aspen while on a road trip. Coming down Independence pass I believe into Aspen I GAINED over 20miles of range. That was the first time I put faith in the car nav and my car saying it would make it to the destination and it did. Regen is an amazing thing

 

[camalaio]

I've done exactly what you've said, controlling how I drive and keeping basically the same 55km/h up and down. No climate control or anything.

Going up I used 2.7kWh.

Going down I gained 1.0kWh (net was slightly lower due to 0.5kW constant usage for the car being on, this is just the gained amount).

This 37% is both a lot lower than what other people say and a lot less than the Nav expects to recover. In fact, when it comes to long descents, the Nav routinely estimates significantly more Regen than I actually get. Could be something wrong with my car.

 

[MXLRplus]

The regen electrical losses are about 25%. This is a combination of battery internal resistance both ways, inverter losses both ways, and designed efficiency when using a motor as a generator.

Then you have lose aero losses both ways.

Then rolling resistance losses both ways.

Finally the mechanical losses of the reduction gears and CV joints.

The recovered amount is never going to hit 50%. At freeway speeds, you'll recover 30-40%. At slower speeds, you can come close to 50%.

 

[AtomicNucleus]

It’s physics time!
Potential Energy = mass x gravity x height
This is the energy you gain and have due to gravity when you drive up a mountain. Your car converts electricity to motion or Kinetic Energy.

By the law of conservation of energy, the amount of energy you gain when you go up a mountain and the amount of energy you spend getting up there is the same.

HOWEVER, there is drag and rolling resistance and motor inefficiency and whatnot. So the energy you gain going up the hill is less than the energy you spent getting up there in the first place.

To make it worse, when you regenerate on the way down, you are again losing energy to drag, rolling resistance and motor inefficiency.

In an ideal world without any inefficiencies, you should gain all the energy you spent climbing a mountain back when you regenerate.

In the end, you still lose some energy. It can be easily calculated as long as you know the % inefficiencies and the weight of the car and height of the mountain.


For example if you lose 5% to the motor when you go up the hill, the energy you spent will be (1.05 x KE)

Overall you still lose quite a bit of energy even with regeneration but it’s an excellent deal compared to ICE cars with no regen and idling.