Regenerative Braking

[calwoo]

I’ve been wondering how regenerative braking extends the available range compared with simply coasting whenever possible. My last car, a Merc 250e (hybrid) had coasting as one of the regen options selectable by paddles behind the steering wheel, and when you had to use the brakes while coasting they did charge the battery. I’ve missed this on the MG4 so have started putting it into Neutral whenever possible. However using the brakes from Neutral does not regenerate, but switching back into Drive does. Another thought - does ACC or TJA regenerate on slowdown?

 

[jpk]

I prefer to coast as much as possible and brake whenever needed as it can't be as efficient trying to recoup the energy expended going from 0-70 than what you'd harvest slowing from 70-0. Also level 1/weak regen is akin to coasting on our cars and shows up -5 on the power reading when coasting, increasing up to -25 when breaking

 

[siteguru]

Try using Adaptive regen ... it'll use level 1 regen most of the time, but if you touch the brakes it'll increase the regen level (then apply the physical brakes if needed). You can also feather the throttle to give the same effect as coasting (i.e. regen = 0%).

 

[Vingnut]

@calvoo AAC and TJA is regenerating on slowdown.

 

[calwoo]

@calvoo AAC and TJA is regenerating on slowdown.

Thanks. I’d chosen adaptive regen following siteguru’s recommendation but it seems to switch back to 3 on restart.

 

[siteguru]

It will - that's the default setting per MG.

(After the time/money they'd spent on Adaptive regen, it's a wonder that they didn't set that as the default. After all, what matters is that the car is in a standard condition on each start-up, not that the standard condition has to be highest regen).

 

[Rolfe]

I asked my dealer this. He said he supposed they wanted to squeeze the last ounce out of the regen. I thought, why did they bother with the adaptive in the first place then.

 

[calwoo]

I set Adaptive Regen as a Custom option, but after a new start it’s back at 3.

 

[siteguru]

See my previous reply.

 

[Brettus]

The lack of saving settings has caught me out as I almost exclusively use OPD and it’s down at the bottom so I’ve missed setting it a couple of times and almost sailed out into traffic from the car park heh. Obvs I’m learning but the idea that it always gives a predictable drive isn’t so for the actual driver. It might be reliable for any odd bod hopping in my car but hey ho. Already been done to death I know. Just I can gripe about it with a little authority/sympathy now I have one

 

[ukslim]

The setting is all about how the pedal feels; how the position of the pedal maps to target speed, and nothing else.

There is no such thing as coasting. There is only the car's perception of whether you want to go faster, slower, or the same, and it's action to get you there.

Eco/Normal/Sport will affect how quickly it accelerates when you ask it to go faster.

The regen setting will affect how quickly it slows down when you ask it to go slower.

But other than that, just put your foot at the position matching the speed you want to go, and let the car do the rest. If gravity is pulling it faster than the target speed, regen will apply and you'll see the power meter go into negative figures.

A weaker regen setting just means you need to raise your foot further before it feels as if it's braking. And in some cases that means it doesn't slow as quickly as you'd like, so you have to apply the brake pedal.

(One thing I'm not certain about is whether touching the brake pedal always means the "real" brakes are applied. You can imagine a design where the brake pedal causes regen braking at first, and only applies friction when really needed).

When cruising, use cruise control. It'll always use regen on steep enough downward slopes.

 

[siteguru]

On my MG4, touching the brake pedal increases the regen % first (up to 25% - normally the regen goes to about 20% max) and only thereafter are the physical brakes applied (if necessary, or if coming to a complete stop).

 

[ukslim]

I thought about this a bit more, while I was away from my desk for a bit... . There might be a minor case for coasting, but probably not enough to let it bother you unless you're really pushing for hypermiling marginal gains.

Say you're driving into a biggish dip on a big road. There's a classic on the A14 east of the M6... So it's a big downhill, that curves into a climb, back to around the level you started.

In an ICE, you'd ease off the accelerator as gravity starts to speed you up, and you'd end up with your foot off the gas, congratulating yourself on using only enough fuel to idle the engine. Maybe gravity gets you going so fast that you're forced to brake, and you're annoyed because you've wasted some free energy, and worn your brake pad a bit. Perhaps you allow yourself to exceed the speed limit, just to make the most of this free energy, and save your brake pads.

Then as you go into the climb, you've still got momentum, which carries you some way up the hill, so you have to press the accelerator in gradually, later than if you'd started motionless at the bottom.

Now, in an EV that's all different. You can keep your foot in the same position all the way (though they might have coded it differently, to feel more familiar, and it'll depend on settings). As you go down the slope, the software will noticed that it's speeding up, and automatically deliver less power to the motors. Then if gravity makes you exceed the target speed, it'll apply regen, and suck some that energy back into the battery.

When you ascend again, momentum will still carry you some way up the slope, the software will deliver power as that momentum runs out, and keep you going the same speed -- and a lot of that energy will be the energy it harvested from regen on the way down.

BUT. Regen is only about 65% efficient. Maybe if you watch the power meter and try and keep it on zero - that is, genuinely coasting - then use that momentum for the upward slope ahead, that's more efficient. It probably involves breaking the speed limit, same as in an ICE.

For me, it's interesting from an academic point of view, but I don't think it'll make enough difference to make it worth the effort on my own journeys.

Of course going slower up hills always saves fuel. The question is, does regen mean going slower down hills saves fuel? Or is it more efficient to turn that energy into momentum than into electrons?

 

[the briggie]

It does have blended braking. Regen first with a light touch, you should be able to see that, then pressing harder physical brakes. Hence the reason it is always recommended to try to use the physical brakes occasionally to keep the discs clean imo.

 

[Tigger]

The question is, does regen mean going slower down hills saves fuel? Or is it more efficient to turn that energy into momentum than into electrons?

Given that converting gravity into momentum is (almost) 100% efficient, then doing this is more 'efficient' than regen. However, efficiency isn't everything - going too fast requires extra attention, concentration and skill. Regen is easier! And if there is a car in front of you going 70 which you can't overtake, regen is your only option . . .

 

[mg4mc]

Note that I would ever do this - ahem- On long downhills that aren't too steep you can always coast by knocking it into neutral it's very efficient (so I've been told).

Keep your hand on the selector so you can select drive again quickly if required.

 

[YaR]

Where I live there are lots of small hills leading to corners or, when coming into town or some villages, 50mph downhill roads that turn into 30mph at the bottom so in an ICE you have to do a lot braking, even if you have a habit of coasting where possible. Obviously in this case having and using regenerative braking saves energy even if it is considerably less than 100% efficient.
As an experiment I've been doing my commute using the adaptive setting and regen 3 (I'd use OPD, but it's too aggressive for the higher speed sections). Too early to tell for sure but my current feeling is that regen 3 gives a few extra fractions of kw/h efficiency.

 

[SteveM]

Given that converting gravity into momentum is (almost) 100% efficient, then doing this is more 'efficient' than regen. However, efficiency isn't everything - going too fast requires extra attention, concentration and skill. Regen is easier! And if there is a car in front of you going 70 which you can't overtake, regen is your only option . . .

Ah, but no one has yet considered wind resistance. I too have wondered which is most efficient. As you descend, the speed picks up and you lose energy to air resistance at a rate proportional to the cube of the speed. Surely at some point it is better to put the potential energy into the battery, even allowing for the 65% hit - probably safer too.

 

[Mick b]

I’ve been wondering how regenerative braking extends the available range compared with simply coasting whenever possible. My last car, a Merc 250e (hybrid) had coasting as one of the regen options selectable by paddles behind the steering wheel, and when you had to use the brakes while coasting they did charge the battery. I’ve missed this on the MG4 so have started putting it into Neutral whenever possible. However using the brakes from Neutral does not regenerate, but switching back into Drive does. Another thought - does ACC or TJA regenerate on slowdown?

I

I’ve been wondering how regenerative braking extends the available range compared with simply coasting whenever possible. My last car, a Merc 250e (hybrid) had coasting as one of the regen options selectable by paddles behind the steering wheel, and when you had to use the brakes while coasting they did charge the battery. I’ve missed this on the MG4 so have started putting it into Neutral whenever possible. However using the brakes from Neutral does not regenerate, but switching back into Drive does. Another thought - does ACC or TJA regenerate on slowdown?

you have three settings, if you set 1 it should free wheel, but l think 3 maybe is defaut settig

 

[Tigger]

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you have three settings, if you set 1 it should free wheel, but l think 3 maybe is defaut settig

Hi Mick, I see you had problems with the Quote function repeating itself. I have struggled with Quote myself, and tend to prefer Reply, but if you wish to respond to two different posts, you have to use Quote.

Does anybody know if there is a tutorial to help users with these functions?