how many batterys could the BEV have
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alohart
Well-known member
Adding more battery cells to the REx engine and exhaust space probably wouldn't be too difficult, but adding them to the frunk area where the gas tank is would mean extending the refrigerant cooling system far enough that doing so would probably be expensive. Doubling the battery pack capacity would add at least 500 pounds to the weight of a BEV making it more than 200 pounds heavier than a REx. So the suspension and probably tires would need to be beefed up adding even more weight.
Charging an empty battery pack to full would take almost all night unless the charger's power was increased. Edit: To be clear as Jim explained below, when I wrote "charger", I was referring to the on-board charger, not an EVSE. As Jim suggested, increasing the on-board charger's power would not be trivial.
This weight penalty would mean that the range wouldn't be doubled. This is probably one of the reasons why battery pack capacities have generally remained less than 30 kWh. Battery cell charge densities, both weight and volume, need to increase considerably before large battery packs would be reasonable for smaller cars.
Charging an empty battery pack to full would take almost all night unless the charger's power was increased. Edit: To be clear as Jim explained below, when I wrote "charger", I was referring to the on-board charger, not an EVSE. As Jim suggested, increasing the on-board charger's power would not be trivial.
This weight penalty would mean that the range wouldn't be doubled. This is probably one of the reasons why battery pack capacities have generally remained less than 30 kWh. Battery cell charge densities, both weight and volume, need to increase considerably before large battery packs would be reasonable for smaller cars.
jadnashuanh
Well-known member
Since the charging devices are IN the i3, increasing the capacity of the EVSE above one that can provide 7.4Kw would have NO effect on the time it would take to recharge the i3, regardless of the battery pack installed. TO get more, the KLE and another module I don't remember the name of, would have to be upgraded, increasing the heat load, increasing the weight, decreasing the gain in range. It's all a big tradeoff between weight and range. The big advance will come with higher density power storage in the batteries which would maintain the capacity, but reduce weight and therefore range, or make a bigger increase in range by maintaining the weight, but use more for higher capacity (possible because they would be lighter).
Jeffj
Well-known member
A Tesla has roughly 4 times the battery capacity of an i3 (85 kWh vs. 22 kWh), but its range is only roughly 3 times (265 miles vs. 81 miles). This is partially reflected in the efficiency of the i3 (~4 mi/kWh) vs. the Tesla (~3 mi/kWh). That difference in efficiency explains a lot about the range difference. Note that the Tesla is also much more aerodynamic than the i3 (don't know the exact CD's) which negates some of the lowered efficiency at highway speeds.
jadnashuanh
Well-known member
The bigger Tesla has about an 80Kwhr battery, or over 4x the usable capacity of the i3, but it does NOT get 4x the range of the i3...weight has its penalties. Throw in the fact that the Tesla is huge in comparison, meaning some of the mobility of the i3 in its intended use (city) where length, width, turning circle are more important than freakish zero-sixty times and maybe it starts to make sense.
Longer range will come to the i3 as the lighter, higher energy density batteries get proven and the manufacturability gets worked out. From a longevity viewpoint, just from the number of cells in a Tesla battery, there are LOTS more opportunities for failure in their battery architecture than in the way things are done in the i3. The i3's battery pack should last a long time. I'm not as confident Tesla's will. Time will tell. The i3's arrangement is modular, from what I know, Tesla's isn't, so it's replace rather than repair.
Longer range will come to the i3 as the lighter, higher energy density batteries get proven and the manufacturability gets worked out. From a longevity viewpoint, just from the number of cells in a Tesla battery, there are LOTS more opportunities for failure in their battery architecture than in the way things are done in the i3. The i3's battery pack should last a long time. I'm not as confident Tesla's will. Time will tell. The i3's arrangement is modular, from what I know, Tesla's isn't, so it's replace rather than repair.
jadnashuanh said:
but dont you all think instead of just leaving empty space where the rex goes a 10kw battery pack would have been a better idea and would actually give it a true 120mile ish range.
BMW have a lot of wasted space on the i3 just look under the dash for one, two people could fit in there and the frunk could be doubled in size if it was arranged better.
my personal thoughts are it should have motors in the wheel hubs (even more space saving).
Putting motors in the wheels is not straightforward but is already happening for buses (BYD are already doing it) but then it's a different car from an i3.
One interesting battery development is the solid state DryLyte battery that Bosch have just acquired. This gives about 300Wh/kg, about twice that of the BMW i3s LMO/NMC (120Wh/kg). The BMW i3's 22kWhr battery pack weighs 204kg from an i3 kerb weight of 1200kg (108Wh/kg).
The Tesla uses type 18650 NCA cells. The 85kWh battery pack has 7,616 cells and weighs 540kg from a kerb weight of 2,100kg. (157Wk/kg).
The i3 Rex has resistive heating because fitting the ReX means that there isn't room for the heat pump.
One interesting battery development is the solid state DryLyte battery that Bosch have just acquired. This gives about 300Wh/kg, about twice that of the BMW i3s LMO/NMC (120Wh/kg). The BMW i3's 22kWhr battery pack weighs 204kg from an i3 kerb weight of 1200kg (108Wh/kg).
The Tesla uses type 18650 NCA cells. The 85kWh battery pack has 7,616 cells and weighs 540kg from a kerb weight of 2,100kg. (157Wk/kg).
The i3 Rex has resistive heating because fitting the ReX means that there isn't room for the heat pump.
alohart
Well-known member
That would have been an interesting option but would have made the BEV more expensive and probably heavier than the REx. For those of us who don't need or want more range or weight, I would have hoped that the current battery pack size would have remained an option.busaman said:
I like the concept of hub motors, but adding substantial unsprung weight would likely have resulted in a car that BMW could not claim to be the "ultimate driving machine." If a car is light enough not to require too much power, and all 4 wheels have hub motors so that each hub motor is not too heavy, hub motors might be acceptable in a car. Right now, battery pack weight is such that more powerful hub motors and friction brakes would be necessary which makes hub motors less attractive. But the time might come in the future when hub motors will work well.busaman said:
PluviaPlumbum
Well-known member
I do wonder if the limitations posed by CFRP production would allow for an i3 Stretch. Based upon a further 2-4 cells in the battery tray? which would give approximately another 25- 30% range potential for say 100- 150 miles. OK I know its not a linear relationship as the weight factors don't work like that in the real world. But I would imagine BMW has allowed sufficient manufacturing flexibility in the Leipzig plant to allow for something along those lines. That would allow for four conventional doors and an estate vehicle format rather than a city hatch - oops sorry I think I have just described the i5 
Jeffj
Well-known member
If BMW makes an i5 with only 100-150 miles of range, they deserve to get all the derision that will be humped on them. I don't think you can sell a mid-size SUV or sedan that doesn't get at least 200 miles on a charge - there is simply too much announced (not yet delivered!) competition coming. And I don't think BMW is that dense.
Jeffj said:
What if they did something along the lines of i8? This is pure speculation mind you, but if they could make a mix mode drivetrain with an all electric range of 100-150 miles with gasoline range of the same that would be compelling, no? Even an i3 type of Rex solution would be interesting.
Yes, I know it is not a pure BEV, but a BEV with 200-300 miles of range does have a lot of weight drawbacks.
alohart said:
well i have to disagree on two points, 1 i fail to see how a small 10kw battery pack could possibly cost more (but may be marginally heavier than) an ICE,GENERATOR,EXHAUST AND FUEL SYSTEM,DME AND ASSOCIATED PARTS.
and secondly lets face it the i3 is nice but definatley NOT or even close to the ultimate driving machine if you push it a bit it lurches all over the place.
i honestly think hub motors are the way forward.
PluviaPlumbum
Well-known member
Jeffj said:
Not if they put a more refined genset into the mix, The i3's development costs were probably reigned in with Rex option coming from their scooter stable. but a detuned 3 cyl Mini motor may fit the bill. I really hope they keep with a series hybrid rather than ape what others are doing.
alohart
Well-known member
I have read cost estimates of $11,000 for the 22 kWh i3 battery pack with its associated electronics and cooling system which would all be needed in a 10 kWh (not kW which is power, not energy). If true, 10 kWh would cost an additional $5,000. But that doesn't include the cost of a higher capacity cooling system that would likely be needed to cool a 45% larger battery pack and the beefed up suspension that would be required to carry the additional weight. Compared with the $3,800 cost of the REx, a 10 kWh battery pack addition would almost certainly be more expensive at today's battery cell costs. Of course, this will change in the future as battery cell costs decrease.busaman said:
Add the substantial weight of a hub motor to each wheel and the i3 would be even farther from the ultimate driving machine because it would be more difficult to control wheel bounce over rough pavement and maintain its current ride characteristics.busaman said:
There are several companies that have been promoting hub motors for several years, but no car manufacturer has chosen to use them. Mitsubishi has conducted research with hub motors and has shown them on an EV prototype, but none of Mitsubishi's EV's uses them. Nevertheless, reductions in weight and cost of the hub motors should eventually make them an attractive alternative.busaman said:
im not convinced does anyone actually know how much all the ICE / generator and all its components actually weighs i wouldn't mind betting it will be pretty close to the weight of an extra 10kwh battery pack.
and still on the ultimate driving vehicle honestly the i3 is rubbish (i drive in my working day at least 5 different cars) and if you lean on it it will bite you i have tried and almost ended up in a field (but that said its not a race car nor intended to be one)
but all that said i like it and happy with mine.
and still on the ultimate driving vehicle honestly the i3 is rubbish (i drive in my working day at least 5 different cars) and if you lean on it it will bite you i have tried and almost ended up in a field (but that said its not a race car nor intended to be one)
but all that said i like it and happy with mine.
busaman
The i3 ReX weighs 1316kg and the i3 weighs 1195kg. Difference is 121kg so that's what the range extender weighs when it's installed.
The i3 battery is 108Wh/kg so for 10kWhrs it would weigh 93kg.
The range would then go up by about 50% less the range lost through having a heavier vehicle. A good but realistic range is 4.5miles per kWhr so i3 (with 18.8kWhrs) is 85miles and i3 with extra battery (28.8kWhrs) is 121 miles. ReX is 160 miles and refuellable.
I know which I would choose.
Hope that helps.
The i3 ReX weighs 1316kg and the i3 weighs 1195kg. Difference is 121kg so that's what the range extender weighs when it's installed.
The i3 battery is 108Wh/kg so for 10kWhrs it would weigh 93kg.
The range would then go up by about 50% less the range lost through having a heavier vehicle. A good but realistic range is 4.5miles per kWhr so i3 (with 18.8kWhrs) is 85miles and i3 with extra battery (28.8kWhrs) is 121 miles. ReX is 160 miles and refuellable.
I know which I would choose.
Hope that helps.
jadnashuanh
Well-known member
I expect an i5 vehicle to have essentially unlimited range, which means some larger, on-board power from either an ICE, or maybe a FC (less likely, at least initially). Whether they make it only a generator, or integrate it into the powertrain a la the i8 for extra oomph, is still a major decision. I expect that the battery pack will be sufficient for most people to use EV mode only for most of their driving. I don't think BMW knows where they are going with that vehicle, and they've said, no new I-series models until 2020 or so. That isn't to say that there won't be tweaks to the existing pair
