Wow, some highway trips that I can do in the Model S, I wouldn't be successful doing in an i3! There aren't enough gas stations along the route!!!
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BMW i3
- Thread starter gregincal
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stopcrazypp
Well-Known Member
If it started at 130-150 miles of EV range, I would consider not being a Gen III waiter (although it being a "city car" is still a big issue for me; I want at the very least a true 4 doors and 5 seats). As it is now it's a no go for me.
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It's not that you can't find a station, it's the time it takes to get off the freeway, drive to it, pull in, enter payment information, then fuel, then get back into freeway again. I don't think it results in just a 5 minute delay (unless you were treating it like a race and rushing through the process and there's no wait anywhere along the way).
SwedishAdvocate
Active Member
So assuming there are enough gas stations along the route, which there seems to be in the US, but apparently not everywhere in (Oh,) Canada (
), how long would you estimate for the average i3 REx highway fill up if you aren't 'racing'?
stopcrazypp
Well-Known Member
Off the top of my head, I'm guessing about 9 minutes (assuming the station is 2 minutes away from freeway and 5 minutes at station). It may take longer if the station is farther, if there are any stoplights/stop signs, a line, or if you consider time lost preparing for the exit.So assuming there are enough gas stations along the route, which there seems to be in the US, but apparently not everywhere in (Oh,) Canada (
That's going to be almost untolerable for longer trips (like the 380 mile trip from SF to LA). It's not just the time but the annoyance of stopping every 50 miles (I'd rather stop 2x longer every 100 miles).
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So assuming there are enough gas stations along the route, which there seems to be in the US, but apparently not everywhere in (Oh,) Canada (
I was referring to upstate New York...
I'm curious what exactly they did get out of the ActiveE program. The timing seemed wrong to actually influence the i3 in any way. Having less range than the ActiveE seems to me a major step backwards. They spent a lot of effort on "adding lightness", but it doesn't seem to have paid off with a better EV.
At least the fixes to the Spline and motor problem...
Validation of the battery and other common parts.
A year and a half reprieve from producing the i3.
Those are a couple of things that jump out in my mind.
The i3 has a frunk, I think. A red plastic gas can would probably fit nicely in there.
Drive carefully!
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They haven't released official numbers as far as I know. My impression from reviews and vague BMW statements is that it will likely get around the same combined EPA estimate as the Volt which is 37 mpg.
Paul Churchley
Member
Saying it is limited to 44mph when the battery is low isn't the whole story.
If the battery is low and the needs more power than the REX is able to supply (about 25kw) then yes, the performance drops. But it drops only while the power required is more than the REX can supply... for example going up a hill or trying to go faster than the 25kw from the REX will allow. As soon as the power required is again less than that supplied by the REX it can start to top up the battery again so there is then reserve battery power available to suppliment the REX next time more than 25kw is needed. This way the overall performance of the car is kept much higher than the 25kw suggests because most of the time, particularly about town, the car will not need all of the 25kw and so the REX is then adding to the battery reserve charge.
I haven't yet driven the i3. I am in London (UK) having a test drive in 2 weeks but as that will be around the city I won't be able to test this particlarity of the REX out.
I did wonder what kind of performance I might expect when the i3 battery is flat and the REX is running so I made a short video of me in my Nissan Leaf but driving limited to 25kw. This isn't really a fair comparison of what the i3 might be like because the i3 can charge as described above but it might be something like this when the battery is flat and you are going up a long hill particularly on a highway where your speed might also be higher.
This is a blog post I did on the likely i3 REX performance. The video is lower down the page.
http://purplemud.blogspot.co.uk/search/label/BMW%20i3
This is almost, but not the full story.
We've heard the i3 REx kicks in automatically at SOC of 6%. That's 1.33kWh.
BMW said the 25 kW REx is enough to drive at 75mph. That agrees with the Roadster figure, which has 3% better CdA but higher rolling resistance (so likely cancels out and the BMW number is realistic). However, at 70mph you will only need 20kW. So if you are driving at the speed limit then you have a 5kW overhead.
For short bursts of acceleration you have all the power from the battery on tap. For hill climbing, you get 25kW from the REx and whatever else is needed comes from the battery.
Once you are over the hill, the REx or (if you are descending) regen will top up the buffer again.
Let's try to work this out.
Highest point on the UK motorway network is on the M62 at 372 metres above sea level. I'm not sure what the lowest point on that motorway is but let's take the climb as 350 metres.
Maximum motorway grade is 4% or 1 in 25. So to climb 350 metres the horizontal distance is 8750 metres. That means the distance traveled is 8757 metres and at 112 km/h (70mph) that takes 281 seconds.
I'll take the weight of the car as 1.5 tonnes.
Plugging all this into the formula for power to climb a hill we get:
(1500 x 9.81 x 350) / 281 = 18.33 kW
Now we already had 5 kW available from the REx when travelling at 70 mph so we need a supply of 13.33 kW for the hill climb, over and above the power being used to overcome aerodynamic drag and rolling resistance.
We have 1.33 kWh in the buffer. If the buffer is being asked to supply 13.33 kW then it can do so for ~0.1 of an hour or 6 minutes or 359 seconds.
As we saw above, we need this power for 281 seconds, so there are 78 seconds spare for the highest motorway hill in Britain if you keep to 70 mph or 112 km/h. And the assumed figures above are conservative.
If you drive at 75 mph then you will not give the car the opportunity to refill its buffer after periods of higher demand. If you drive over 75 mph then you are using more than 25 kW and this must be coming from the battery buffer. This is just the velocity cubed power law coming in to play. So yes, if you regularly drive above the UK speed limit then you will find you have an empty buffer when you reach a hill.
The exception is driving into a constant headwind. This will require higher power and hence you may need to slow down or turn the REx on early. I presume the i3 has a power gauge, in which case the driver should be aware of what he or she is using and keep speeds at an appropriate level, but even this will not force a slow down to 45 mph if you maintain the buffer. This is the same with any EV - if you drive into a headwind you will see higher energy consumption. But what chance a >10mph non-stop headwind hitting you dead on?
I'd like BMW to put a buffer SOC meter on there as well, it will be a very useful display to have when running in REx mode.
We've heard the i3 REx kicks in automatically at SOC of 6%. That's 1.33kWh.
BMW said the 25 kW REx is enough to drive at 75mph. That agrees with the Roadster figure, which has 3% better CdA but higher rolling resistance (so likely cancels out and the BMW number is realistic). However, at 70mph you will only need 20kW. So if you are driving at the speed limit then you have a 5kW overhead.
For short bursts of acceleration you have all the power from the battery on tap. For hill climbing, you get 25kW from the REx and whatever else is needed comes from the battery.
Once you are over the hill, the REx or (if you are descending) regen will top up the buffer again.
Let's try to work this out.
Highest point on the UK motorway network is on the M62 at 372 metres above sea level. I'm not sure what the lowest point on that motorway is but let's take the climb as 350 metres.
Maximum motorway grade is 4% or 1 in 25. So to climb 350 metres the horizontal distance is 8750 metres. That means the distance traveled is 8757 metres and at 112 km/h (70mph) that takes 281 seconds.
I'll take the weight of the car as 1.5 tonnes.
Plugging all this into the formula for power to climb a hill we get:
(1500 x 9.81 x 350) / 281 = 18.33 kW
Now we already had 5 kW available from the REx when travelling at 70 mph so we need a supply of 13.33 kW for the hill climb, over and above the power being used to overcome aerodynamic drag and rolling resistance.
We have 1.33 kWh in the buffer. If the buffer is being asked to supply 13.33 kW then it can do so for ~0.1 of an hour or 6 minutes or 359 seconds.
As we saw above, we need this power for 281 seconds, so there are 78 seconds spare for the highest motorway hill in Britain if you keep to 70 mph or 112 km/h. And the assumed figures above are conservative.
If you drive at 75 mph then you will not give the car the opportunity to refill its buffer after periods of higher demand. If you drive over 75 mph then you are using more than 25 kW and this must be coming from the battery buffer. This is just the velocity cubed power law coming in to play. So yes, if you regularly drive above the UK speed limit then you will find you have an empty buffer when you reach a hill.
The exception is driving into a constant headwind. This will require higher power and hence you may need to slow down or turn the REx on early. I presume the i3 has a power gauge, in which case the driver should be aware of what he or she is using and keep speeds at an appropriate level, but even this will not force a slow down to 45 mph if you maintain the buffer. This is the same with any EV - if you drive into a headwind you will see higher energy consumption. But what chance a >10mph non-stop headwind hitting you dead on?
I'd like BMW to put a buffer SOC meter on there as well, it will be a very useful display to have when running in REx mode.
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Paul Churchley
Member
Thanks for that David
Well, I wouldn't argue with you on anything mathematical so thanks for doing that. So it seems from that then that in theory there should be very few times when the performance is limited due to low buffer.
Again, I am not arguing here but I can't help feeling that the theory might not match up with real-world use. Not because your maths is wrong or that BMW has anything wrong but because people won't drive it the way that is needed to maintain the buffer. Early adopters will grasp the necessity to maintain the buffer through sensible driving but will the average BMW buyer that decides to go electric? I hope BMW can do a reasonable job at educating the buyers accordingly and that is good enough for me. If they then run out of buffer they will have been warned
Paul
Well, I wouldn't argue with you on anything mathematical so thanks for doing that. So it seems from that then that in theory there should be very few times when the performance is limited due to low buffer.
Again, I am not arguing here but I can't help feeling that the theory might not match up with real-world use. Not because your maths is wrong or that BMW has anything wrong but because people won't drive it the way that is needed to maintain the buffer. Early adopters will grasp the necessity to maintain the buffer through sensible driving but will the average BMW buyer that decides to go electric? I hope BMW can do a reasonable job at educating the buyers accordingly and that is good enough for me. If they then run out of buffer they will have been warned
Paul
This is the difference with the Volt/Ampera and i3 REx.
Volt can sustain 100 mph all day long on the ICE because the 55kW generator can supply enough to go that speed (see below). However, it nominally keeps a small battery buffer for short bursts of 111kW acceleration which is fine for that purpose, but no good for long high speed mountain climbs if power requirement goes over 55kW. This is why GM made mountain mode. Having said that, there is nowhere in the UK that is high enough or fast enough to need mountain mode although I have managed to empty the buffer from repeated acceleration (5 speed bumps in a row can do it).
On the other hand, the i3 is the inverse of this. As we have seen, it can sustain 70 mph but realistically not 75 mph on REx mode. Yet it has a larger buffer and more peak power on hand. So even running on REx you will get the rapid acceleration and you can do that more times before the buffer is empty, compared to the Volt. Likewise, the larger buffer will mean that you can climb most hills with that tiny engine without thinking about it. There may be circumstances where you will have to turn the REx on early for a climb, much like the Volt's mountain mode, but they are not going to be affecting us in the UK.
So BMW's engineers have taken the Volt range extender concept to its logical extreme: The smallest engine they could get away with to sustain motorway speed, while using a larger battery to compensate for transient high power situations. As long as you stay within (UK) law then you will be ok and you will not find yourself out of power to accelerate if you haven't been naughty. For the target market I think this is absolutely fine. If, on the other hand, you regularly sit at a ton in your M5 and you want to trade that in to have the i3 as your sole car, you should probably think again.
Volt can sustain 100 mph all day long on the ICE because the 55kW generator can supply enough to go that speed (see below). However, it nominally keeps a small battery buffer for short bursts of 111kW acceleration which is fine for that purpose, but no good for long high speed mountain climbs if power requirement goes over 55kW. This is why GM made mountain mode. Having said that, there is nowhere in the UK that is high enough or fast enough to need mountain mode although I have managed to empty the buffer from repeated acceleration (5 speed bumps in a row can do it).
On the other hand, the i3 is the inverse of this. As we have seen, it can sustain 70 mph but realistically not 75 mph on REx mode. Yet it has a larger buffer and more peak power on hand. So even running on REx you will get the rapid acceleration and you can do that more times before the buffer is empty, compared to the Volt. Likewise, the larger buffer will mean that you can climb most hills with that tiny engine without thinking about it. There may be circumstances where you will have to turn the REx on early for a climb, much like the Volt's mountain mode, but they are not going to be affecting us in the UK.
So BMW's engineers have taken the Volt range extender concept to its logical extreme: The smallest engine they could get away with to sustain motorway speed, while using a larger battery to compensate for transient high power situations. As long as you stay within (UK) law then you will be ok and you will not find yourself out of power to accelerate if you haven't been naughty. For the target market I think this is absolutely fine. If, on the other hand, you regularly sit at a ton in your M5 and you want to trade that in to have the i3 as your sole car, you should probably think again.
surfingslovak
Member
Excellent analysis, David, I agree 100%. I was a bit surprised by the reaction many EV enthusiasts had, when they heard that BMW will be using a motorcycle engine as their range extender. Typically, the assumption was that it cannot possibly work. How disappointing; what was BMW thinking?
When you run the numbers, however, you might realize that if the battery can supplement the REx, 25 kW average power output is adequate for the vast majority of use cases. Having at least 20% battery capacity as a buffer, which approximately matches Volt's charge sustaining mode, would allow for normal acceleration, and hill climbs of up to 4,000 feet at an average speed of 75 mph. Granted, this might be less of a concern in the UK or in Hungary, but it's going to affect drivers in the US and elsewhere. Particularly, if the REx cannot be engaged manually.
I perused several CARB documents this morning to get a better understanding of the regulatory requirements, and I'm concerned about the market reception of this solution. The Volt has been criticized on occasion for the perceived overkill in terms of providing an effective range extender. Although GM might have some room for optimization, at least their approach provides nearly identical performance in EV and REx mode, and allows for long-distance travel.
I'm concerned that the i3 REx spec with less than 25 kW effective net power output, 6.5% remaining SOC, and a 2.3 gallon tank might be simply too compromised to be of real value. I don't think that this is the outcome CARB or BMW had in mind.
While I'm eagerly awaiting more test drive reports, I would point out what others have mentioned earlier: BMW should at least consider boosting the maximum gross power output of the REx to about 30 or 35 kW. The engine is rated for up to 65 hp (48.5 kW), and there is plenty of room to do this. Noise or vibration concerns will be the least of worries for someone trying to climb a hill with a critically low battery. The REx is reportedly already very quiet and barely noticeable when running.
An increase of the maximum REx power output would not impact compliance with regulatory requirements. Moreover, CARB stated that they were interested in gathering feedback from BEVx vehicles on the market, and will consider adjusting the the ZEV mandate to improve BEVx market acceptance, and help increase the total number of EV miles driven.
2012 AMENDMENTS TO THE ZERO EMISSION VEHICLE REGULATIONS
When you run the numbers, however, you might realize that if the battery can supplement the REx, 25 kW average power output is adequate for the vast majority of use cases. Having at least 20% battery capacity as a buffer, which approximately matches Volt's charge sustaining mode, would allow for normal acceleration, and hill climbs of up to 4,000 feet at an average speed of 75 mph. Granted, this might be less of a concern in the UK or in Hungary, but it's going to affect drivers in the US and elsewhere. Particularly, if the REx cannot be engaged manually.
I perused several CARB documents this morning to get a better understanding of the regulatory requirements, and I'm concerned about the market reception of this solution. The Volt has been criticized on occasion for the perceived overkill in terms of providing an effective range extender. Although GM might have some room for optimization, at least their approach provides nearly identical performance in EV and REx mode, and allows for long-distance travel.
I'm concerned that the i3 REx spec with less than 25 kW effective net power output, 6.5% remaining SOC, and a 2.3 gallon tank might be simply too compromised to be of real value. I don't think that this is the outcome CARB or BMW had in mind.
While I'm eagerly awaiting more test drive reports, I would point out what others have mentioned earlier: BMW should at least consider boosting the maximum gross power output of the REx to about 30 or 35 kW. The engine is rated for up to 65 hp (48.5 kW), and there is plenty of room to do this. Noise or vibration concerns will be the least of worries for someone trying to climb a hill with a critically low battery. The REx is reportedly already very quiet and barely noticeable when running.
An increase of the maximum REx power output would not impact compliance with regulatory requirements. Moreover, CARB stated that they were interested in gathering feedback from BEVx vehicles on the market, and will consider adjusting the the ZEV mandate to improve BEVx market acceptance, and help increase the total number of EV miles driven.
2012 AMENDMENTS TO THE ZERO EMISSION VEHICLE REGULATIONS
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stopcrazypp
Well-Known Member
All of the changes suggested there seem to be to allow the Volt to qualify as a BEVx. If they only remove one provision (the APU range limit) that's already enough to make the car much more useful while keeping the "spirit" of law. But with all three, it's easy to see why CARB doesn't want to allow those changes.
Paul Churchley
Member
I get the feeling from the PR stuff going on here in the UK that BMW didn't really design the REX to be used as the main power source for the car on long trips and that they expect the i3 to be considered, and used as, a 100% BEV, with the REX as a backup for when there is no charging and to help with range anxiety. Contrast that with the Volt which was designed up front with the generator as a viable alternative to the battery on long trips.
As a backup, being used mainly when there is no charging, I think the REX is a great solution. It isn't the overkill that the Volt would be for someone using the car mainly on battery most of the time but it does have the "get you out of trouble" capability that the Leaf doesn't have. I totally agree with SurfingSlovak tho, slightly more power from the REX, slightly bigger gas tank, slightly more in the buffer (for the USA) and it would be a serious contender against the Volt for those wanting more thant he Volts's 40 miles battery range.
I have a Leaf and a Ampera (UK Volt). I use the Leaf daily and the Ampera on trips I cannot do in the Leaf. If I were in the market now for a car like the Volt I would seriously be considering the BMW i3 as a possible.
As a backup, being used mainly when there is no charging, I think the REX is a great solution. It isn't the overkill that the Volt would be for someone using the car mainly on battery most of the time but it does have the "get you out of trouble" capability that the Leaf doesn't have. I totally agree with SurfingSlovak tho, slightly more power from the REX, slightly bigger gas tank, slightly more in the buffer (for the USA) and it would be a serious contender against the Volt for those wanting more thant he Volts's 40 miles battery range.
I have a Leaf and a Ampera (UK Volt). I use the Leaf daily and the Ampera on trips I cannot do in the Leaf. If I were in the market now for a car like the Volt I would seriously be considering the BMW i3 as a possible.
While this same engine produces much more horsepower in the bike application, there is also the issue of thermal dissipation to consider. It's in a small space with a small radiator and that is likely the reason BMW limited it to 34bhp.
I'm confident that a multinational car company that has spent billions on this launch knows more about what they are doing than a few armchair critics and bloggers. They've said it will sustain 70 mph in REx mode and the numbers give me no reason to doubt it.
For TEG's Lake Tahoe test then yes, you will have to turn the REx on early a la mountain mode on the Volt.
The scenario I described before is pretty much worst case for this country. And of course, that hill is not likely to be 4% grade all the way but by not knowing for sure, that is what I have to assume. In the Telegraph review that started this discussion off again, the guy is driving through the undulating hills of Kent and not a high pass over the Pennines. That is why I called Broder - nothing to do with wanting to be an i3 fanboy (because it has its other flaws) but just getting facts straight. I am not saying this was deliberate (although given the Telegraph's position on any green technologies and their traditional readership, I wouldn't bet against it) but it could be a journalist that got found out by speeding and is now covering his ass.
I'm confident that a multinational car company that has spent billions on this launch knows more about what they are doing than a few armchair critics and bloggers. They've said it will sustain 70 mph in REx mode and the numbers give me no reason to doubt it.
For TEG's Lake Tahoe test then yes, you will have to turn the REx on early a la mountain mode on the Volt.
The scenario I described before is pretty much worst case for this country. And of course, that hill is not likely to be 4% grade all the way but by not knowing for sure, that is what I have to assume. In the Telegraph review that started this discussion off again, the guy is driving through the undulating hills of Kent and not a high pass over the Pennines. That is why I called Broder - nothing to do with wanting to be an i3 fanboy (because it has its other flaws) but just getting facts straight. I am not saying this was deliberate (although given the Telegraph's position on any green technologies and their traditional readership, I wouldn't bet against it) but it could be a journalist that got found out by speeding and is now covering his ass.
Paul Churchley
Member
I think you are just trying to make the facts fit your argument. Much more likely is that he just drove in his normal dumb driving style (i.e. not very eco) and drained the buffer.
You say you want facts... well, as far as I can see, there no real-world, owner-driver, facts yet that the i3 will or will not perform as you say it will inspite of your convincing argument and figures. Also, there is no evidence yet that in real-world, normal and legal driving that you won't still drain the buffer.
I would prefer to see us all keep an open mind in amongst our speculations until people have owned one and reported what they find. Any media reviews or even test drive reviews, are likely not to properly represent an owner experience. It will be interesting to see if your total faith in the numbers actually holds up in the real-world driving experience.
As for the argument that BMW have spent a lot and therefore should know what they are talking about... I own two EVs, a Leaf and a Ampera (Volt), and I can assure you that many aspects of the pre-launch PR or reviews didn't transfer over to the real-world. The main one being range, and so I am naturally skeptical over the BMW claims over the i3. Sorry.
You say you want facts... well, as far as I can see, there no real-world, owner-driver, facts yet that the i3 will or will not perform as you say it will inspite of your convincing argument and figures. Also, there is no evidence yet that in real-world, normal and legal driving that you won't still drain the buffer.
I would prefer to see us all keep an open mind in amongst our speculations until people have owned one and reported what they find. Any media reviews or even test drive reviews, are likely not to properly represent an owner experience. It will be interesting to see if your total faith in the numbers actually holds up in the real-world driving experience.
As for the argument that BMW have spent a lot and therefore should know what they are talking about... I own two EVs, a Leaf and a Ampera (Volt), and I can assure you that many aspects of the pre-launch PR or reviews didn't transfer over to the real-world. The main one being range, and so I am naturally skeptical over the BMW claims over the i3. Sorry.
That is essentially what I have said. But normal dumb driving style being going with the significant number of drivers who treat the speed limit as a threshold.
Thanks for acknowledging they are convincing. My point is that this argument can be dealt with by schoolboy physics that it should have been possible for anyone to research, follow and criticise. Instead we had hand-wavey arguments going on for days and weeks. You don't need to 'take it on faith' that this will work or not. Sure, we can use more sophisticated models to refine the answer but I'm trying to use conservative numbers and simple maths to get a lower bound on what it can do.
Besides, that's not what Robert Llewellyn told me on Thursday. He says that after 50 miles of 65-70mph motorway driving on REx in heavy traffic, the EV range was exactly the same.
I do not have 'total faith in the numbers'. Faith is something you might have at church. That's not how engineering works. I've invited people to check. However, if I'm wrong I'd like to know numerically why I'm wrong. Just saying 'we have to wait and see' is not an answer. This is stuff that can be calculated to enough precision pretty easily.
As you know, the range claims your were told are based on the EU NEDC test, which frankly is a crock of doo doo. Everyone knows this - it produces over inflated MPG figures and over inflated EV range claims, yet it suits the ICE manufacturers as their product looks better and it gets more cars into lower tax bands. It doesn't take long to find academic papers that rubbish NEDC and champion something better.
Now look at the US EPA range ratings - for the Volt/Ampera they are bang on for motorway driving in average weather and my Leaf friends say it is the same for them. BMW will have to publish that too.
The NEDC situation is so laughable that Renault had to publish the 133 mile range for the Zoe and then undermine it by saying you will get 60-90 miles in the real world.
However, this is not the same as BMW designing a car that can sustain motorway speed and getting it so wrong that you will find yourself limping in the slow lane. That would be egg all over Bavarian faces. Can you seen Munich's finest making that mistake? They've had test mules for over 2 years. They are actively telling people not to try to drive 75-80 mph on REx precisely because of this.
You want real world experiences. They are out there. It took me a couple of minutes to find this.
BMW i3 Forum View topic - BMW I3 REx driven everywhere
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