Difference between Eco, normal and sport modes

[DixieTGS]

I think details in post #47 by @rtenterprises may explain the difference of opinion. The suggestion is that by not using regen you won't be slowing the car as quickly and won't have to accelerate as much later.

That much I think is true, but in doing so the speed profile and average speed have changed, so you're no longer comparing like with like!

You would get exactly the same benefits if you had regen on and followed the no regen speed profile. In addition you would get the benefits of regen when it was a necessity to slow down more quickly.

 

[siteguru]

Setting regen level to 1 means that you can have less finesse of your right foot and still achieve reasonable overall efficiency (on motorways/fast A roads). If you can finesse your right foot you can achieve the best of both worlds by using regen level 3 - you simply minimise the amount of regen when needed via your throttle position.

 

[Rolfe]

I was using adaptive regen on the motorway, and didn't switch when I came off the motorway and on to the hilly roads in the Yorkshire dales. I liked the way the car handled.

 

[crite40]

Just how serious are some of the people on here? I tried to introduce a bit of science into the proceedings about regenerative braking and all that comes back is a wash of vague opinions and some ideas that show a COMPLETE lack of understanding of the operation of an EV. If you are not prepared to do some fairly simple measurements, then no amount of "hand waving" will get the debate anywhere. For a perfect example some figures quoted here would imply that hundreds of not thousands of watts of energy are disappearing when regeneration is used. I was using mine today on a shopping trip of ~65 km. Slowing a car like a ZS down from 80 km/h to 50 involves a big energy dissipation, if its NOT going back into the battery system then where is the heat going? Nothing smells hot. BTW what is this about the brakes "regenerating energy"!!!!! They simply turn kinetic energy into heat, just like in a "gas buggy" and experience with EV's and hybrids shows that brake wear is far less than older vehicles.
Simply put those who do not believe in regenerative braking have a LOT of explaining to do. If they really can't see that they should educate themselves in a bit of VERY basic science before waving their hands about.

 

[wattmatters]

Well, I would very much like to see some measurements of the recovered energy from regenerative braking.

I have a local mountain I've been up and back down quite a number of times. It's ~10km @ 8-9% gradient.

On the way down I tend to use OPD as I never have to use the brake pedal. The energy recovery on way down the mountain is ~40% of that consumed on the way up.

Here's an example I posted some time back with some data (all my battery data is captured and stored by my Home Assistant, so I can review consumption later):

MG4 in Australia

@wattmatters, how is the data coming from the car? Perhaps a Wifi OBD2 dongle? If so, do you have any way of preventing security attacks? I'd love to do something like this, but not if some hoodlum in a hoodie can open the doors with their laptop and some Wifi malware.

www.mgevs.com

These measurements are of course not perfect but at least they give some indication. Ignore my error in that post doing a gravitational potential energy calculation, that was an error I later corrected.

Aside from the expected losses (second law of thermodynamics and all that), the fact you are still driving the same distance (and some energy is required for overcoming wind, rolling and other frictional resistances) I suspect also the regenerative braking system has a maximum power level it will put back into the battery, so in some cases energy recovery is always going to leave some on the table.

This makes some sense given the regen braking does not slow the car down anywhere near as quickly as the regular friction brakes can (anyone who's experienced the emergency braking system will testify to that).

 

[decrep]

wattmatters, here's an excerpt from that great post of yours.

"Comparing the trips with roughly the same weight (2.3/5.9 and 1.8/4.4), the energy recovery on the descent was 40% of the energy used going up."

But I'm not sure if that is the efficiency of regen, in other words, on a flat road, converting the kinetic energy of the vehicle back to electrical energy into the battery.
I think that would be much better, depending on the rate asked not being higher than battery can handle?

 

[decrep]

I think brains come into gear, (takes a while these days), your example above, includes the motor efficiency converting electrical energy to vehicle kinetic energy.
I think we're only really concerned with what happens when you brake.
So can you half the 40% to 20% assuming accelerating and braking efficiencies are similar? Possibly braking is more efficient as drag is helping the slow down instead of hindering it.
Strong head or tail winds would of course affect both.

 

[wattmatters]

The only way I can see to get the data are using an OBD reader with high frequency data logger capturing speed and power data while doing controlled decelerations. The deceleration data will tell you the total energy dissipated while the power data will record the amount of regen.

 

[wattmatters]

But I'm not sure if that is the efficiency of regen, in other words, on a flat road, converting the kinetic energy of the vehicle back to electrical energy into the battery.

No, it's not efficiency.

 

[DixieTGS]

BTW what is this about the brakes "regenerating energy"!!!!!

I really really hope no-one intended to mean that!

I think their intention was to say something like: Pressing the brake pedal causes the car to increase the regen level where possible before activating the disk brakes.

 

[decrep]

I really really hope no-one intended to mean that!

I think their intention was to say something like: Pressing the brake pedal causes the car to increase the regen level where possible before activating the disk brakes.

There seems to be a problem with imprecise language. It's causing a lot of confusion.

 

[siteguru]

FWIW if you look at the power meter on the driver display, it'll show up to 100% power output when driving but only up to 25% power input when "braking". (I've no idea what these percentages relate to, but it's evident that less power is recovered via regen than is utilised via driving - as @wattmatters has shown. So ensuring that you don't slow down the vehicle more than necessary (using appropriate regen) for the conditions leads to more efficient driving, not simply the level of regen set).

 

[wattmatters]

The MG4 user manual....

 

[crite40]

Ah!! That's better. Now we are using a bit of basic science and common? sense. Of course you will never get all the energy back or you would have an EV with unlimited range AND a perpetual motion machine. The highest level I have ever heard of (under laboratory conditions) is about 85% so if you get 50 or 60% on the road that is fine. You are right about the emergency brakes too, the other day a cyclist got close enough to trigger mine when he swerved over a bit far and it was a good thing my seat belt was set up properly. They are really powerful on my 2022 ZS!!! The car is charging from solar as I write and it is late winter here in NZ Yesterday I got 43km worth of solar power with passing clouds in 4 hours and hope to get it back to full charge today.

 

[decrep]

Comparing what you use getting up to speed to what you get back when you stop, is interesting and gives the overall efficiency of accelerating and slowing down.
But I thought we were interested in the efficiency of regen.
If that's the case, the energy used getting up to speed is irrelevant.

 

[crite40]

But the energy used in getting up to speed largely becomes the Kinetic energy of the EV and its total mass. THAT is what is supplying the energy that the regenerative braking recovers. A bit of basic physics is all you need. Electrical energy is converted to kinetic energy and kinetic energy (you know. the old ½mv² thing) is converted partially into electrical energy by using the motor as a generator.
So the energy getting up to speed is hardly irrelevant, that is the first factor in determining the energy budget of the whole system. Remember energy is not created or destroyed but converted into other forms. The whole debate is about how much of the kinetic energy is converted into useful electrical energy in the battery. Versus how much is wasted as heat in one form or another after all a "gas buggy" wastes it ALL.

 

[decrep]

Depends what you want to know. If you're only interested in the recovery efficiency then you have to subtract the acceleration inefficiency, but we don't know the efficiency of the motor getting up to speed or how much energy is used after the acceleration.
The motor doesn't just have to accelerate the mass of the car, it also has to overcome drag, so the watts going into the motor aren't the same as the car's kinetic energy.
That should be easy enough to calculate, from its mass and its velocity.
I'm sure Mr Google will give me the formula.
So it's a very rough guide, the kinetic energy of the car will be less than the power going into the motor, but do we know how much less?

The interesting thing to compare is the overall efficiency of a BEV compared to a conventional ICE vehicle.

 

[MG4JP]

While regenerative braking offers undeniable benefits, it's crucial to understand that, from an efficiency standpoint, it should only be used to replace the brake pads (when there is no other alternative and you really need to slow down or stop).

In theory, optimal fuel efficiency is obtained when the vehicle is driven with minimal resistance. And ideally, modulating vehicle speed to the desired level (or even bringing the vehicle to a complete stop) should be achievable without relying on any kind of braking.

Also, high levels of regenerative braking will often create bad driving habits - it's easy for the driver to lift-off the accelerator pedal more than needed and then right after compensate for that with some extra power. Not only that, but driving with regenerative braking deactivated (or as close to that as possible) will teach you to predict and anticipate your next move help lifting-off earlier (and thus drive in a more fuel efficient way).


In short: braking always means losing energy. Of course, if you really must brake/stop, then it's best to do it so only using regenerative braking. But then again, the best thing is to not brake at all and turning regenerative braking to low/off will help you with that and provide an overall more efficient ride.


Also, if anyone cares, personally, I adjust my regenerative braking settings based on the driving conditions I'm facing and this is my typical use of it:

• Open roads or urban environments with minimal traffic: minimal regenerative braking.
• Congested urban areas (characterized by unpredictable traffic patterns, frequent stops and starts), hilly terrain, or spirited driving: higher levels of regenerative braking.

 

[decrep]

And ideally, modulating vehicle speed to the desired level (or even bringing the vehicle to a complete stop) should be achievable without relying on any kind of braking.

That's the way I try to drive my ICE vehicle, but annoys the hell out of the cars behind me if I push it too far. A car doing 70kmh takes ages to roll to a stop, and friction brakes have to be used, if you don't want to suffer heaps of abuse from other drivers. Using Regen on the other had still annoys those behind you but nowhere near as much and nowhere near as much energy is lost.

We really must get a handle on just how efficient regen is. My thought is about 80%. So you don't loose an awful lot slowing down, it's the speeding back up that takes the most.

Any way, I'm staying on OPD or level 3.
I'm getting pretty good now after a few months, judging just when to start easing off, so no brakes are needed
Rolling to a halt just isn't practical.

 

[Seajays]

Don't forget also that the regenerative aspect is not just a factor of the mechanics of the motor/generator, other things come into play too, such as the current temperature of the battery and the current state of charge of the battery, both of which will affect how much of the recovered energy can be effectively stored again.