Energy efficiency in ACC?

[Ian 2455]

Can anyone shed any light on whether it is more or less officient to use ACC, especially for a longish (over 100 miles) journey?

 

[Alb]

I've never done a comparison but intuitively I'd say ACC was less efficient.

 

[Ian 2455]

I've never done a comparison but intuitively I'd say ACC was less efficient.

I drive down to Wales from London fairly regularly (174 miles door to door). Did it today in 7° weather, arriving with 18% SOC and 36 miles of range left.
At the outset I had 100% SOC and was showing 277 miles on the GOM.
This was the first time I had used the ACC for an appreciable distance and I have to say that I might be a convert...
On my return journey I will stick to my trusty right foot and see if there is any major difference.
Could it be that the lack of regen whilst using ACC is going to be a factor??

 

[fred12345]

ACC is not regenerative in ZS, it uses brakes - although I'm not sure about the latest 2025 model ... I found ACC to be a bit iffy, sometimes going 1-2 mph over, sometimes under and somehow not quite smooth keeping the set speed as my old diesel ...
The most effective drive is to get stuck behind a truck and drive 55 mph ... if you want to be a bit more adventurous, follow a National Express bus, they go anything between 60-70 mph ...
p.s. ACC will also use up your brake pads, not much but it adds up ...

 

[EvTek23]

I'm with @Alb on this one. It may well be more efficient if your journey is level most of the time. I've stopped using it now because I remember seeing the power up to 40 to 45 % or more when going up gradients, whereas if you drive the car you tend to "drive to the road", slowing slightly going up hills while watching the power, the car in ACC however will keep the speed constant and just keep on increasing the power to achieve this. I also didn't like the way it switched from power to regen in the way it could be felt as a slight jerk. Driving the car you can be more subtle while changing from power to regen.
There is the theory too that low or no regen should be used on a long journey as the power used to regain speed if you overly slow by taking your foot off the accelerator would be more than what had been recovered during the slowing. With no regen the car obviously slows much less so takes less power to regain speed.

 

[Bam Bam]

Can anyone shed any light on whether it is more or less officient to use ACC, especially for a longish (over 100 miles) journey?

Depends how you drive, but @Alb and @EvTek23 have explained it pretty well.

Speed up downhill to get momentum (rather than regen), slow down uphill. Essentially keep the power percentage level as close to zero as you can downhill while keeping up with the speed of the road (i.e. below about 20-25% power unless it is a really steep hill).

A possible exception would be if you can recognise and then follow a hyper-miler and then let the ACC stick the relevant distance behind them.

 

[Jamesrr]

I've never done a comparison but intuitively I'd say ACC was less efficient.

Why? I'd say the opposite*.



*However I have an MG4 and regen absolutely is performed when using ACC and going downhill or slowing.

 

[Coulomb]

Why? I'd say the opposite

I think Alb feels that the ACC is too jerky to beat a human driver aiming for low energy consumption, even on the models (hopefully all recent models) that use regen to correct over-speed when ACC is active.

With the right software/firmware, I think that ACC would indeed be able to beat most humans, but I suspect that MG/SAIC/Bosch aren't there yet.

 

[fred12345]

Why? I'd say the opposite*.

*However I have an MG4 and regen absolutely is performed when using ACC and going downhill or slowing.

I think this particular question was from a ZS EV driver so the answers relate to that car...
without regen on cruise, ZS uses brakes to control the speed; on newer MG models ACC could be more effective but not much compared to a careful driver and it really depends on the type of the road, length of journey and traffic conditions.

Personally, I don't think it's worth worrying about it ... Best to drive and enjoy the drive, and if one or the other option really uses that much more energy, just stop and charge a few minutes earlier than with extra "savings" (and sufferings) ...

 

[decrep]

There is the theory too that low or no regen should be used on a long journey as the power used to regain speed if you overly slow by taking your foot off the accelerator would be more than what had been recovered during the slowing. With no regen the car obviously slows much less so takes less power to regain speed.

For energy to be "recovered" you'd need to see the power meter go -ve.
How often does thus happen? For me only when I intentionally slow.
However with max regen there is likely to be a less stable speed than with no regen.
But I'll be sticking with OPD unless I really really need to hypermile

 

[Alb]

Why? I'd say the opposite*.

I think Alb feels that the ACC is too jerky to beat a human driver aiming for low energy consumption

My experience of ACC (on the S5) is that it has an annoying tendency to modulate the throttle under load change and this gives bursts of power rather than smooth delivery. It's as if the derivative term in the speed controller is a bit too aggressive.

 

[Bam Bam]

For energy to be "recovered" you'd need to see the power meter go -ve.
How often does thus happen? For me only when I intentionally slow.

If you go down a steep hill on ACC it will go negative.

However with max regen there is likely to be a less stable speed than with no regen.
But I'll be sticking with OPD unless I really really need to hypermile

If you can be accurate enough with the throttle the mode shouldn't make a massive difference.

 

[Coulomb]

If you go down a steep hill on ACC it will

The early ZS EVs (pre hybrid and pre face lift) don't regen with ACC. The power meter just stops dead at zero, and doesn't go negative, until you cancel ACC, then regular regen allows for negative acceleration. Speed is controlled by friction braking only, when ACC is active.

I still own one (the blue half of my avatar).

 

[poldark]

I'll have to double check but I was sure my Gen2 ZS also doesn't regen on ACC

 

[Bam Bam]

The early ZS EVs (pre hybrid and pre face lift) don't regen with ACC. The power meter just stops dead at zero, and doesn't go negative, until you cancel ACC, then regular regen allows for negative acceleration. Speed is controlled by friction braking only, when ACC is active.

I still own one (the blue half of my avatar).

Apologies, I was thinking of our MG4.

 

[fred12345]

I'll have to double check but I was sure my Gen2 ZS also doesn't regen on ACC

Definitely not having regen in ACC, mine was also second generation ZS