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Discussion Starter #1
So I've had my 94Ah BEV about a month now, and I'm loving it. It's so much fun to drive, and I'm finding I'm going out in it just because I can. It's great.

I wanted to compare notes with people to see if there's anything tips or tricks I'm missing.

  • I'm getting about 4.2-4.3 miles/kWh on average on longer motorway runs. I'm tending to sit at around 65 in Eco Pro on cruise control, tweaking the speed as necessary.
  • What do people find is the best way to get good mileage? Cruise control or manual?
  • How much do the modes really make a difference? Can you get the same effect by just behaving in comfort mode?
  • I had one night trip in heavy rain which absolutely killed the range. Dropped the efficiency down to 3.5ish. I was expecting about a 10% drop, but that's getting on for 20%. Really surprised me. Haven't worked out if that was exceptional yet.
  • Sometimes I'm finding the regen isn't as strong as I expect. I've tended to either put this down to the car being a bit cold (hence battery can't charge at full whack) or a full battery. Do other people get the same thing?
  • On one trip I got to the rapid charger on about 17% and had some time so decided to let it run to 100%. (It was an IONITY charger so it was fixed price anyway.) Up to 94% took half an hour, and then the rest took another half an hour. I was expecting it to slow down, but that's pretty dramatic. Charger said it delivered 27kWh in total, which seems high as that suggests 100% is 33kWh. Do you expect some loss when charging?
Anyway that'll probably do for now. I'm loving the car, but still getting used to it's quirks. I didn't quite realise how much I'd mentally costed up journeys in the past. I'm finding I'm doing more journeys which are for pleasure, or to do fun things. Things I'd written off as not worth the fuel cost. That's having a positive effect which I hadn't anticipated.
 

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@Weebull How are you finding things now that the weather is colder. I did 2 x 127 miles today, needing heating, quite a headwind for part of the outbound leg and patches of heavy rain on the way home. Down at 3.6 m/kWh today. 120Ah i3s.
 

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So I've had my 94Ah BEV about a month now, and I'm loving it. It's so much fun to drive, and I'm finding I'm going out in it just because I can. It's great.

I wanted to compare notes with people to see if there's anything tips or tricks I'm missing.

  • I'm getting about 4.2-4.3 miles/kWh on average on longer motorway runs. I'm tending to sit at around 65 in Eco Pro on cruise control, tweaking the speed as necessary.
  • What do people find is the best way to get good mileage? Cruise control or manual?
  • How much do the modes really make a difference? Can you get the same effect by just behaving in comfort mode?
  • I had one night trip in heavy rain which absolutely killed the range. Dropped the efficiency down to 3.5ish. I was expecting about a 10% drop, but that's getting on for 20%. Really surprised me. Haven't worked out if that was exceptional yet.
  • Sometimes I'm finding the regen isn't as strong as I expect. I've tended to either put this down to the car being a bit cold (hence battery can't charge at full whack) or a full battery. Do other people get the same thing?
  • On one trip I got to the rapid charger on about 17% and had some time so decided to let it run to 100%. (It was an IONITY charger so it was fixed price anyway.) Up to 94% took half an hour, and then the rest took another half an hour. I was expecting it to slow down, but that's pretty dramatic. Charger said it delivered 27kWh in total, which seems high as that suggests 100% is 33kWh. Do you expect some loss when charging?
Anyway that'll probably do for now. I'm loving the car, but still getting used to it's quirks. I didn't quite realise how much I'd mentally costed up journeys in the past. I'm finding I'm doing more journeys which are for pleasure, or to do fun things. Things I'd written off as not worth the fuel cost. That's having a positive effect which I hadn't anticipated.
On a motorway, I use ACC with the caveat that it can disconnect in certain conditions; eg, mist; rain and low sun.

Eco Pro reduces a number of things - all of which impact on battery use.


Water on a road will reduce the efficiency of all cars but it is more noticeable on EVs - as will the use of wipers; heating; the radio and cellphone charging.

The amount of regenerative braking was reduced 3 years ago because of two concerns. One was the failure of some key engine bolts, and the second was that an unexpected ACC disconnect at speed could result in a boot gating incident with a closely following car. Regeneration does not lead to maximum range. Maximum range is achieved with modest acceleration and speed, and MAXIMUM coasting. Regeneration is variable with pedal position and vehicle speed. It only varies with battery SOC when the battery is close to a full charge. Clearly, the battery cannot charge above 100% so if, say, you live at the top of a hill and drive down it to work, then the car will conventionally brake to give you a similar retardation effect as if it were regenerating. I notice this less in my 120Ah BEV but in my old i3 60Ah the car would brake conventionally down to an SOC of c.95%.

Rapid charging does slow down progressively and markedly above 90%. This is to ensure that the cells are not overheated. There are still many EVs on the road that can only accept a single rapid charge per day for battery management reasons. The i3 has a very good BMS. The charging rate also reduces when you use a fast charger as the battery approaches 100%.

EV battery charging losses depend on the internal resistance of the cells. Say you're charging a 10V battery at a rate of 100 watts (stored energy per time). For a perfect battery that would require you apply 10V at 10 Amps. But if the battery has a 1 ohm resistance you'd actually need to apply 11V meaning you'll need to supply 110watts of power to get 100watts to the battery. The remaining 10 watts goes as waste heat which is why it is often the case when the car is rapid charged after a long drive, you will hear the battery cooling fan running as a result of BMS invention (this also adds to charging inefficiency).

Finally, to get back to where we started. It is worth remembering that if wind and wet road drag is 'X' at 30 mph, then at 60 mph the electric engine will have to overcome '4X' to maintain a steady speed.
 

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Discussion Starter #5
@Weebull How are you finding things now that the weather is colder. I did 2 x 127 miles today, needing heating, quite a headwind for part of the outbound leg and patches of heavy rain on the way home. Down at 3.6 m/kWh today. 120Ah i3s.
I've not noticed the temperature drop, but that's mainly because I didn't get a lot of time with the car before it dropped. Right now it tends to come down to dry/wet and wind just depending on the day.
 

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On a motorway, I use ACC with the caveat that it can disconnect in certain conditions; eg, mist; rain and low sun.
I don't have ACC. so just normal CC for me. My question was more "do people find using CC more efficient?"

Eco Pro reduces a number of things - all of which impact on battery use.
Indeed, but I find the soft 65 limit (which I know is adjustable, but it seems a good compromise) a little disconcerting. If I could get the gains by setting HVAC down, and adjusting my driving style, I think I'd rather do that. Also means I don't have to remember to select it all the time. So, I was wondering if it's doing anything you can't do yourself?

The amount of regenerative braking was reduced 3 years ago because of two concerns. One was the failure of some key engine bolts, and the second was that an unexpected ACC disconnect at speed could result in a boot gating incident with a closely following car.
Interesting. I've been aware of the slow feathering-in of the regen when disengaging CC, partly because I thought it was good that the car didn't decelerate hard.

I was more commenting on what I perceive as day to day changes, but I'm not sure if they are real or just me trying to justify my misjudging of things and having to resort to the physical brakes. What you say later about high SoC explains some of it. I'm wondering if there's a temperature aspect too... i.e. a recharge limit when the battery is cold.

Maximum range is achieved with modest acceleration and speed, and MAXIMUM coasting.
Indeed, which was why I was wondering about CC being good for range. It seems to do very little coasting.

...if, say, you live at the top of a hill and drive down it to work, then the car will conventionally brake to give you a similar retardation effect as if it were regenerating. I notice this less in my 120Ah BEV but in my old i3 60Ah the car would brake conventionally down to an SOC of c.95%.
Are you saying that it will activate the physical brakes, whilst not on CC, just because you lifted off the accelerator? I've not noticed this one.

It is worth remembering that if wind and wet road drag is 'X' at 30 mph, then at 60 mph the electric engine will have to overcome '4X' to maintain a steady speed.
Yes, the force due to air resistance goes up in a square law, but the power needed, and so the drain on the battery, goes up in a cube law (i.e. 8X). Power is Force x Velocity, so it adds an extra 'v' term.

That extra 5mph from 65 to 70 costs you ~25% extra power. Fortunately going faster also gets you there quicker, so the energy used is only ~16% higher (i.e. for overall energy used you're back down to V^2)
 

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This excellent post explains why friction brakes are used at high SOC rather than regen. The use of braking was very noticeable on the 60Ah i3 - particularly, if the brake discs were slightly rusty. The i3 attempts to maintain one pedal driving at all SOCs. I rarely touch the brake pedal. BMW has thought about this as well as there is a process that applies the brakes from time to time.

To understand the reason for that you'd need to know a bit about how Lithium Ion cells charge.

Charging the cells causes a temporary increase in cell voltage which is greater the higher the charge (regeneration) rate.

At the same time a Lithium Ion cell can't be allowed to exceed the maximum charge voltage (typically 4.1 to 4.2 volts per cell) even for a moment as the cell can be damaged by excess voltage. Battery management systems are really strict about not exceeding the maximum cell voltage on Lithium Ion cells.

This is the reason why the charge rate tapers down on a rapid charge - by the time you get much past 80% the battery cant take the full charge rate without the voltage going too high, so charge rate (current) is reduced to keep the voltage in range. The closer you get to 100% the lower the charge rate to stay within the safe voltage range.

By the time you get to say 99% charge the maximum charge rate possible might typically be less than 1kW.

So if you set off on a full battery and drive a mile down the road causing the charge rate to drop to 99% there is theoretically enough "room" in the battery for the regenerative energy from stopping from 30mph, however at a maximum charge rate of under 1kW the deceleration would be so low as to be barely noticable.

Moderate regeneration on a car like my Ion is in the order of 15-25kW, on a car with strong regeneration like an i3 I'd say it's probably in the order of 50kW - no way can a battery at 99% state of charge take a regenerative charge rate of 50kW or even 15kW and hence at that high state of charge you have little or no regenerative braking as the battery simply is not in a position to accept that high charge rate.

To reach full regeneration the battery state of charge has to be low enough that the battery can charge at the full regenerative charging rate, which depending on car, battery size and design, how much regeneration the car can do etc could be anywhere between about 80 and 95%.

One minor complicating factor in this is that if you have a resistive cabin heater turned on - which is typically up to about 5kW on maximum, you may be able to achieve about 5kW of regenerative braking even with a battery that is full or nearly full - as the energy is going into the heater instead of the battery.

I notice this effect on my Ion where with the heater on full at 100% charge I still get a relatively small amount of regeneration, however with the heater off at 100% charge I get none at all.

This was brought home to me yesterday when I drove the car for the first time in months with the heater turned off and wondered why I had no regeneration for the first couple of miles, before remembering that's how it behaved last summer!
 

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This morning was cool, started up from cold, turned off the heater and drove sedately for 8.1 miles to the office via town to drop my youngest off. I took the boring route as well - straighter roads, so lots of coasting and not so much speeding up / slowing down for corners. No heat plus low speed gave me 5.3 miles/kWh, so it didn't mind much starting with cold batteries.
 

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I recall
This morning was cool, started up from cold, turned off the heater and drove sedately for 8.1 miles to the office via town to drop my youngest off. I took the boring route as well - straighter roads, so lots of coasting and not so much speeding up / slowing down for corners. No heat plus low speed gave me 5.3 miles/kWh, so it didn't mind much starting with cold batteries.
EU testing suggests........ WLTP range is based on a temperature of 23C.

Quote: Comparing energy consumption results over WLTP at -7°C and at 23°C, both without cabin climate control, a 27% increase was found due uniquely to the cold temperature effect over mechanical parts (drag and friction increase in moving components) and battery performance. A further 38% energy use increase was then observed for the WLTP test at -7°C with the climate control activated, due to AC Compressor operation. Unquote

Clearly, testing can only replicate real World conditions in a limited - but consistent - way.
 

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A further 38% energy use increase was then observed for the WLTP test at -7°C with the climate control activated, due to AC Compressor operation.
More if your i3 doesn't have the optional heat pump. At -7, the car is probably using a blend of heat pump and resistance heat anyway.
 

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More if your i3 doesn't have the optional heat pump. At -7, the car is probably using a blend of heat pump and resistance heat anyway.
I am not sure that you are right. I should have made the point that the quote was taken from a chamber test report on a 2014 i3Rex which, as you know, does not have a heat pump option.


The key conclusion was:

Quote: Results demonstrated that ambient temperature strongly affects vehicle energy use over the considered test cycles and a similar variation trend is observed across tested temperatures: over all driving cycles, maximum energy consumption is reached at -30 °C, while minimum is touched at 23°C. As a consequence, the attained driving range was significantly reduced at cold temperatures (between 40% and 70% of the compared standard testing conditions). The energy consumption increase due to the use of cabin heating, together with battery performance deterioration at negative temperatures were found to be the main causes for driving range reduction. It is worth stressing that information about EVs performance degradation at cold temperature is not available to customers. Unquote
 

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Of all the things mentioned above I find the single overwhelming factor that reduces range is motorway driving. We have a long section of the M4 with a speed limit of 50mph and if you travel for, say, 20 miles at that speed you will notice a big improvement in range. Drive at 70 mph and the range just melts away, that’s why Eco Pro Plus has a soft stop at 56 mph. When I pop up to the golf club (2.5 miles) I tend to select Eco Pro Plus as it switches off the a/c which is easier than manually doing it. No point trying to heat or cool the car for such a short distance. Actually we find the i3 stays quite warm and I often switch to Pro Plus anyway.

Cruise control is handy for managing speed cameras but is not the most economical way of driving and that’s the same for ICE vehicles. There are occasions when it is better not to force the car to speed up to its set point. I doubt that it makes a big difference though.

Cruise control can be slightly dangerous with EVs. For example, if you have it set to say 30 mph then increase your speed to 50 mph because the speed limit changes you need to remember that 30 mph is still the default speed. When you come to slow down and take your foot off of the accelerator the regen braking kicks in BUT when you reach 30 mph the regen suddenly stops and your speed reverts to 30 mph. This doesn’t happen with ICEs because your foot is usually on the brake which disables cruise.
 

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Discussion Starter #16 (Edited)
We have a long section of the M4 with a speed limit of 50mph and if you travel for, say, 20 miles at that speed you will notice a big improvement in range. Drive at 70 mph and the range just melts away, that’s why Eco Pro Plus has a soft stop at 56 mph.
I've found https://www.ecalc.ch/evcalc.php quite good for getting a feel for this. It's not the most intuitive tool, but when you put a route in it gives you consumption for a range of speeds. A route I just put in gave 4.6miles/kWh at 55mph and 3.4miles/kWh at 70mph. That's 35% more energy for the same trip.

This doesn’t happen with ICEs because your foot is usually on the brake which disables cruise.
It's a subtle difference, but one to be aware of. I wonder if in time they'll have a rule like "If the brake lights are on when the car slows to the set speed, CC must be disabled".
 
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