BMW i3

[woof]

5% means you have 0.94 kWh available, which is enough to lift an i3 around 250 meters/800 ft. That means that if you are driving at 65 mph up an incline with a 10% gradient, the buffer will be exhausted after 1.5 miles.

There is still the 25 kW sourced by the ReX, not JUST the battery buffer. The buffer will be decreasing by the amount of power that exceeds that of the ReX, not the total amount of power drawn.

 

[Yggdrasill]

There is still the 25 kW sourced by the ReX, not JUST the battery buffer. The buffer will be decreasing by the amount of power that exceeds that of the ReX, not the total amount of power drawn.

Exactly. And since travelling at 65-70 mph will require the full 25 kW, all additional power must come from the battery. And the battery will be depleted after 250m/800ft of altitude gain.

 

[surfingslovak]

5% means you have 0.94 kWh available, which is enough to lift an i3 around 250 meters/800 ft.

This is correct. However, in Europe manual REx operation is permitted, and the range extender can be engaged below 80% SOC, much like the Volt. This should allow the i3 to climb mountain passes of several thousand feet at 75 mph.

That means that if you are driving at 65 mph up an incline with a 10% gradient, the buffer will be exhausted after 1.5 miles.
ft.

A sustained gradient of 10% is an extreme use case, and the obvious solution is not to hit a large hill with a depleted battery. In Norway, you will have the option of engaging the REx early. In the US, most of the travel occurrs on freeways, and the largest gradient there is typically 6%. If my calculations were correct, and I still remember them, the i3 could travel up a 6% gradient at 45 mph. That's enough to impede traffic, and it's not advisable to go cross a large mountain with a depleted battery pack. The solution would be to charge up, which is exactly what the Air Resources Board wants. Alternatively, BMW should add about 10 kW to the maximum output of the REx.

 

[Yggdrasill]

Actually, the REX won't be offered here in Norway, so it's not actually a factor for us. (Plug-in hybrids are taxed almost as heavily as regular gas cars, so the REX would add around $20k to the price here.)

I agree that it typically won't be a huge problem, but I find it odd that BMW didn't go for 10 or 20%. 5% is really low. There is for instance one stretch of road not far from here where the altitude rises from around 30 meters above sea level to around 480 meters above sea level, over a distance of 12 km. (E134 between Notodden and Kongsberg - one of the most popular routes between Oslo and Bergen.) The average speed is usually around 50-55 mph. The BMW i3 with REX would require around 12.2 kW from the gradient and around 20 kW from the speed, and would run down the battery to nil right before reaching the top. If the buffer had been 10%, neither this road nor the one between Drammen and Oslo would deplete the battery completely, so this seems like a fairly minor adjustment for significant improvement.

 

[surfingslovak]

I agree that it typically won't be a huge problem, but I find it odd that BMW didn't go for 10 or 20%. 5% is really low.

Four words: California Air Resouces Board. The i3 was designed to fit the new BEVx category, hence the small tank size. Also the battery must be depleted before the REx is engaged to qualify for this classification.

There is for instance one stretch of road not far from here where the altitude rises from around 30 meters above sea level to around 480 meters above sea level, over a distance of 12 km. The average speed is usually around 50-55 mph. The BMW i3 with REX would require around 12.2 kW from the gradient and around 20 kW from the speed, and would run down the battery to nil right before reaching the top.

I don't believe that this is correct. You don't need 20 kW to go 50-55 mph. The power from the REx can propel the car 70-75 mph on flat ground. If you go slower than that, the extra energy will be used to keep the buffer topped off. This particular scenario is a non-issue.

 mph  |  kW
 ---- | ----  
 35   |  5.6
 40   |  6.8
 45   |  8.7
 50   | 10.9 
 55   | 12.8
 60   | 15.4
 65   | 18.0
 70   | 21.2
 75   | 25.0

If the buffer had been 10%, neither this road nor the one between Drammen and Oslo would deplete the battery completely, so this seems like a fairly minor adjustment for significant improvement.

As already noted above, even if someone imported an i3 with REx to Norway, the European version will allow manual override, and you can engage the range extender at any SOC. And once again, the 5% threshold is not something an engineer would dream up, it's the result of environmental regulation.

What you point out is relevant insofar that the US version of the i3 is ill-suited for mountainous terrain. While the minimum SOC could be raised, if the California Air Resources Board approved such change, it might be easier to increase the maximum REx output. The engine BMW uses has been significantly derated, and it can output more power. Such modification would not require regulatory approval.

A more realistic scenario than the hypothetical situation between Drammen and Oslo you mentioned, is a trip with an i3 from the San Francisco Bay Area to Lake Tahoe. This should be a nearly ideal use case for the REx, but it won't work as well as some might expect due to the limitations imposed on range extender operation. At least one recharge will be necessary along the route, even if the gas tank was refilled, which puts the value of the REx feature in question in the US.

It should be made clear to prospects on this side of the Atlantic that the i3 with REx is no match for the Volt in terms of road tripping, and extra steps and precautions must be taken due to the lack of manual REx override in US spec cars. That said, the so-called "limp home" moniker or the concerns about the performance of the REx in general are often based on misguided assumptions combined with incorrect math and physics.

The REx will be more capable than these critics expect. It will also be very significantly constrained by its design, and it will be up to the manufacturer to educate its customers. This is going to be more problematic than it would seem. If EV enthusiasts who, by and large, are highly educated and very technical struggle with this concept, how can a dealer tech or a client adviser explain this properly to a customer?

 

[Yggdrasill]

Four words: California Air Resouces Board. The i3 was designed to fit the new BEVx category, hence the small tank size. Also the battery must be depleted before the REx is engaged to qualify for this classification.


I don't believe that this is correct. You don't need 20 kW to go 50-55 mph. The power from the REx can propel the car 70-75 mph on flat ground. If you go slower than that, the extra energy will be used to keep the buffer topped off.

I calculated a bit roughly, but add some heat, winter tires, 13% higher air resistance*, 3 passangers and it will be the case. Probably even sooner than I calculated.

The fact is that BMW has chosen a battery buffer size where there will be horror stories. I doubt the bad PR will be worth any benefits of fitting the BEVx category.

* Going from +20C to -15C increases air resistance by about 13% due to increased air density.

 

[surfingslovak]

I calculated a bit roughly, but add some heat, winter tires, 13% higher air resistance*, 3 passangers and it will be the case. Probably even sooner than I calculated.

The average speed is usually around 50-55 mph. The BMW i3 with REX would require around 12.2 kW from the gradient and around 20 kW from the speed, and would run down the battery to nil right before reaching the top.

Between 11 to 13 kW are needed to propel the i3 at speeds from 50 to 55 mph on flat terrain. You stated that 20 kW were necessary. This is a significant miscalculation, almost by a factor of 100%, and you won't be able to pass it off as a rounding error by assuming higher air or rolling resistance. As already mentioned the problem with all these Hail Mary scenarios is that people don't do their homework, and are basing their estimates on incorrect numbers. Going up a road with a 4% grade at 50 to 55 mph for 7.5 miles is not going to be a problem, no matter how you slice it or spin it.

The fact is that BMW has chosen a battery buffer size where there will be horror stories. I doubt the bad PR will be worth any benefits of fitting the BEVx category.

Let's agree to disagree for reasons stated above. I have seen enough of these horror stories on paper. None of them checked out factually.

 

[Yggdrasill]

Between 11 to 13 kW are needed to propel the i3 at speeds from 50 to 55 mph on flat terrain. You stated that 20 kW were necessary. This is a significant miscalculation, almost by a factor of 100%, and you won't be able to pass it off as a rounding error by assuming higher air or rolling resistance. As already mentioned the problem with all these Hail Mary scenarios is that people don't do their homework, and are basing their estimates on incorrect numbers. Going up a road with a 4% grade at 50 to 55 mph for 7.5 miles is not going to be a problem, no matter how you slice it or spin it.

I don't see where you get your numbers. In winter the range of the i3 can be reduced down to the 100 km area at speeds in the 50-55 mph range on flat terrain. That works out to around 16 kW. And assuming a fairly full car, weighing 1600 kg, travelling at 55 mph up the aforementioned stretch of road, that would require 14.4 kW without losses, but if you also factor in a 90% efficient drivetrain, that results in 15.8 kW required. That results in the i3 running out of charge on the stretch of road. So my initial conclusion was correct - the stretch of road isn't always unproblematic, but I'll agree my initial calculations were a bit too back-of-an-envelope. I try to use figures closer to the average situation.

But of course, I only looked at two stretches of road that are near my home and I drive regularly. If I wanted to find a more problematic stretch of road, I could look at any of the mountain passes between Oslo and Bergen. Most of the roads require passing over the Hardanger Plateau, over 1100 meters above sea level. RV7 for instance has one section of road where the road climbs 1230 meters over a distance of 26 km. With fairly full car weighing 1600 kg, the climb would require 5.9 kWh including drivetrain losses. Driven at 50-55 mph, this would require 18-20 kW, plus the 10-16 kW from the speed, so 28-36 kW. Even in the best case scenario, the i3 would run out of juice before reaching the top.

In all likelihood, there are hundreds, if not thousands, of stretches of road in Norway that would be problematic for the i3 REX. The US has probably 10-100 times as many problematic stretches of road.

 

[surfingslovak]

I don't see where you get your numbers.

I'm confident in my numbers. Let me ask you in return, where did you get yours? Most of these alarming posts are based on incorrect assumptions.

In winter the range of the i3 can be reduced down to the 100 km area at speeds in the 50-55 mph range on flat terrain.

Yes, but in your original post, you did not assume wintry driving conditions. You stated that 20 kW of power output are needed to propel the i3 50 to 55 mph on flat terrain. This not only incorrect, it's grossly incorrect.

]
That works out to around 16 kW. And assuming a fairly full car, weighing 1600 kg, travelling at 55 mph up the aforementioned stretch of road, that would require 14.4 kW without losses, but if you also factor in a 90% efficient drivetrain, that results in 15.8 kW required. That results in the i3 running out of charge on the stretch of road. So my initial conclusion was correct - the stretch of road isn't always unproblematic, but I'll agree my initial calculations were a bit too back-of-an-envelope. I try to use figures closer to the average situation.

The weight and drivetrain losses are nearly immaterial at those speeds. What is far more significant is the frontal cross-section and the aerodynamic drag. The weight is needed to calculate instantaneous power, and the total energy expended to traverse the altitude difference in question. I believe that this part of your calculation was correct, but did not double-check it.

But of course, I only looked at two stretches of road that are near my home and I drive regularly. If I wanted to find a more problematic stretch of road, I could look at any of the mountain passes between Oslo and Bergen.In all likelihood, there are hundreds, if not thousands, of stretches of road in Norway that would be problematic for the i3 REX. The US has probably 10-100 times as many problematic stretches of road.

As already noted above, I agree that the i3 is ill-suited for mountainous terrain. That said, the i3 will allow manual override in Europe, and by your own admission, the REx trim will not be sold in Norway. Therefore, the horror scenario you are painting bears little relevance.

The situation will be different in the US, which I readily admitted, and you failed to acknowledge. This changes nothing about the frequent and fundamental misunderstanding about the physics at play here. I listed the instantaneous consumption figures above for your reference, they are very close to actual, and I would suggest that you verified your calculations. Obviously, they assume 20°C and no A/C or heater use. They reflect actual consumption, including all losses.

I appreciate your point of view, and I wish that I had all day to post on TMC, and argue about things, but I don't.

Have a good evening.

 

[Yggdrasill]

I'm confident in my numbers. Let me ask you in return, where did you get yours? Most of these alarming posts are based on incorrect assumptions.

The 100 km in winter figure is a guesstimate based on various real world experiences. I'll admit it isn't perfect, but neither are your figures, from what I can determine. Are the figures for a "comparable" EV, or are they actually from the i3? And are the figures for the i3 with REX or without?

Yes, but in your original post, you did not assume wintry driving conditions. You stated that 20 kW of power output are needed to propel the i3 50 to 55 mph on flat terrain. This not only incorrect, it's grossly incorrect.

I didn't mention weather with a single word. You assumed I meant summer conditions. But I agree I overestimated. I didn't want to get too bogged down in the details, when even you don't object to there being stretches of road that are problematic. We've already agreed that there are issues with the i3 on some stretches of road, and we are only discussing the degree to which this is the case.

The weight and drivetrain losses are nearly immaterial at those speeds. What is far more significant is the frontal cross-section and the aerodynamic drag. The weight is needed to calculate instantaneous power, and the total energy expended to traverse the altitude difference in question. I believe that this part of your calculation was correct, but did not double-check it.

As already noted above, I agree that the i3 is ill-suited for mountainous terrain. That said, the i3 will allow manual override in Europe, and by your own admission, the REx trim will not be sold in Norway. Therefore, the horror scenario you are painting bears little relevance.

The issue has never been Norway, as such, it's just that the roads I'm familiar with happen to be in Norway. The roads in some US states aren't very different, perhaps except for being designed for higher speeds, so any issues that would occur here would also occur in the US. That is where we will see the horror stories, and they will only increase in frequency and magnitude as more and more i3 are sold.

The situation will be different in the US, which I readily admitted, and you failed to acknowledge. This changes nothing about the frequent and fundamental misunderstanding about the physics at play here. I listed the instantaneous consumption figures above for your reference, they are very close to actual, and I would suggest that you verified your calculations. Obviously, they assume 20°C and no A/C or heater use. They reflect actual consumption, including all losses.

One thing your figures may disregard is that roads aren't always straight. As physics describe - to change direction is to accelerate. And acceleration requires energy. Another thing I mentioned was I couldn't tell if your figures were for the i3 with REX or without. The i3 with REX has approximately 10% higher consumption.

Real world conditions are rarely exactly as they are in the laboratory, and it is easy to get bogged down in the details. But as I said before: We've already agreed that there are issues with the i3 on some stretches of road, and we are only discussing the degree to which this is the case.

I appreciate your point of view, and I wish that I had all day to post on TMC, and argue about things, but I don't.

Have a good evening.

Good morning.

 

[rabar10]

Briefly mentioned on the ELR thread -- BMW aired a 30-second commercial for the i3 during the Olympics:
Gas 2 | Video: BMW i3 Commercial Gets It Right

I think this ad works on several levels -- electric cars are quiet, they are fun to drive, and they are interconnected (dad gets a text when son plugs car in after sneaking out with it for the evening).

 

[Rifleman]

I think this ad works on several levels -- electric cars are quiet, they are fun to drive, and they are interconnected (dad gets a text when son plugs car in after sneaking out with it for the evening).

I completely agree, this was a great EV commercial.

 

[tom66]

That is actually a lot better for an ad than I expected. It really emphasises the advantages of EVs.

 

[jomo25]

Yup, no reason Chevy couldn't do something similar for the Volt. But all of the Volt commercials sucked.

 

[JST]

Briefly mentioned on the ELR thread -- BMW aired a 30-second commercial for the i3 during the Olympics:
Gas 2 | Video: BMW i3 Commercial Gets It Right

I think this ad works on several levels -- electric cars are quiet, they are fun to drive, and they are interconnected (dad gets a text when son plugs car in after sneaking out with it for the evening).

Also, they are just like regular cars, in the sense that they are a great place to make out with your girlfriend.

 

[tess1988]

could someone please tell me if the i3 with range-extender is like the chevy volt as far as if you run out of electrity the ICE starts and then if you need to refill again you can stop at another gas station because i watched a review that made it sound like after the petrol/gas ran out the i3 would just stop

 

[tom66]

The i3 is a pure series plug in hybrid, with the ICE acting to generate electricity only. The ICE is active infrequently: only when battery SOC% drops below about 5% in the US model. So yes, if the ICE is running and you run out of fuel, you would stop (as soon as that 5% is gone, which would go very quickly - probably 3 or 4 miles.)

 

[woof]

Welcome, Tess!

could someone please tell me if the i3 with range-extender is like the chevy volt as far as if you run out of electrity the ICE starts and then if you need to refill again you can stop at another gas station because i watched a review that made it sound like after the petrol/gas ran out the i3 would just stop

Just keep filling it with fuel, it'll keep going. It's not a one time use thing. The ReX is a normal everyday gasoline powered electric generator...it just happens to be in a car. If the fuel gets low, fill it up! But yes, if the ReX is out of fuel, and the battery is flat, the car will stop. No source of energy means it will no longer move.

 

[Grendal]

Yup, no reason Chevy couldn't do something similar for the Volt. But all of the Volt commercials sucked.

Most of them did suck, however, the testimonial commercials were fabulous. Those focused on the strengths of the car and how much their owners loved them. They only ran them for a short while though. GM's Superbowl ad for the Volt was the worst: even aliens can't figure out how the car works.

 

[tommolog]

Autocar recently posted this video review of the i3: