Does your i3 inspire you to drive it like a hot hatch?

[Gonville]

.....Or maybe UK roads really are that bad.

They are. With run flats you have to be looking for every single pothole and if you hit one you need to visit the dentist.

 

[FrancisJeffries]

The fact the i3 is fun to drive is perhaps it's achilles heel because the range goes down at an alarming rate if you use its available torque at the lights.

I don't see why it's thought that heavy acceleration (using the available torque) greatly reduces the available range ("at an alarming rate").

My feeling is that it’s not the acceleration that uses up the battery – it’s staying at the high speed you achieve after doing it. Here’s why I think so:

Acceleration from 0 to 60mph is said to take 7.9seconds on the Rex version. Let’s say that the full 170bhp is being used for all those 7.9 seconds (which it assuredly won’t be). 170bhp is around 127kW. So the total drain from the battery during acceleration is (127 * 7.9/3600)kWh, or just under 0.3kWh. That’s only 1.5% of the 18.8kWh battery capacity. That’s the same amount you’ll use in the next mile of motoring at 60mph! So that's why I think it's speed, not acceleration, which affects the range.

So why not enjoy the full performance on offer?

EDIT: :idea: After writing this, I realised that the acceleration you use HAS NO EFFECT on range WHATSOEVER! Range (i.e. residual battery charge) depends ONLY on the speed you reach.

It's because acceleration requires work (which comes from the battery) to be done to increase the kinetic energy of the vehicle. That's the energy which can be recovered during regeneration. The kinetic energy varies as the square of the speed (as does wind resistance), so accelerating to higher speeds requires more kWh from the battery. But as I showed above, the kWh to accelerate is a tiny fraction of the total battery capacity. The charge taken from the battery to get to any desired speed is always the same whether you take it quickly or slowly.

So we can use all the torque on offer happy to know that it comes at no extra range cost. :lol:

 

[sasman]

I hope this is true...it sounds too good to be true..i think i have read on this forum that you can accelerate with no extra power consumption ..but then someone said that its not true..you accelerate hard you use more power?...
I wont be able to verify until october thats when i get my hands one 1




Rob

 

[FrancisJeffries]

I hope this is true...it sounds too good to be true..i think i have read on this forum that you can accelerate with no extra power consumption ..

Fear not! It's DEFINITELY true. A-level physics. Yippee!
(And I speak as a Chartered Engineer.)

 

[Stevei3]

Hi Francis,

alas, an easygoin' driving style has proven to be more economical, in practice... At least for our i3. Maybe because you drive faster for longer when accellerating quickly (?). But you're right about the fact that a high end speed is the real kWh-eater.

Regards, Steven

 

[surfingslovak]

So we can use all the torque on offer happy to know that it comes at no extra range cost. :lol:

I hope that I'm not spoiling the fun, but since this has come up before, I think it's necessary to point out internal losses in the battery. The battery pack has an internal resistance of about 100 to 200 Milliohm. If you assume an average power-output of about 100 kW during acceleration and a nominal battery voltage of 360 Volt, this results in an electrical current of about 280 Amps.

If you consider the internal resistance at play here, the battery acts as an 8 to 10 kW heater in this scenario. While a few hard accelerations will go unnoticed, if you accelerate full-throttle every single time, there will be a noticeable impact. Assuming that you do it about 40 to 50 times a day for a few seconds, then that's like running a 10 kW heater for 5 or 6 minutes every day. This shaves off about 1 to 1.5 kWh from your charge, which is approximately 5 to 7% of your usable battery capacity.

Full-throttle acceleration is fun, but it will have a range impact if practiced on a continuous basis. Thankfully, electricity can be produced sustainably, and energy storage, including batteries, will improve over time. For now, it's what it is.

 

[ultraturtle]

I hope this is true...it sounds too good to be true..i think i have read on this forum that you can accelerate with no extra power consumption ..

Fear not! It's DEFINITELY true. A-level physics. Yippee!
(And I speak as a Chartered Engineer.)

FrancisJeffries is correct, of course. "Definitely true." It is the best kept secret of early adopters. We can accelerate an EV balls-out, guilt free, and free of worry about impacting range. There are a couple cases to be made, but with a caveat.

First would be the physics case. Since (unlike an internal combustion engine) an electric motor's efficiency curve is essentially flat across its power range, there is no comparatively greater loss in efficiency at greater acceleration rates. Also (unlike lead acid batteries), lithium ion batteries do not lose capacity at greater discharge rates, there is essentially no loss in capacity by accelerating at higher rates. Internal resistance is a thing, but it is significant to note that the energy lost to it as a result of discharging a lithium ion battery for a given time at a given rate is equal to the energy lost discharging for half that time at twice that rate, i.e. no measurable loss of range accelerating at high rates.

This is not the case for lead acid batteries, so many folks have a difficult time adjusting their thinking. Many folks interested in EVs come from a solar energy background where internal resistance of a lead-acid battery is a very big deal, and a significant factor in sizing a lead acid battery bank. The higher the discharge rate, the higher the internal resistance, the greater the heat generated, and the lower the total energy storage capability of the battery. The capacity of a lead acid battery discharged quickly, say in 2 hours, is roughly 58% of the capacity of that same battery discharged slowly, over the course of 100 hours. For this reason, lead acid battery spec sheets do not state a single ah capacity, but rather a broad range of them based on discharge rate, with most manufacturers standardizing somewhat on the 20 hour rate for comparison purposes. So, how does a wise EV engineer deal with potential capacity losses due to high discharge rates?

• 1. She chooses the right battery technology for the job. Ever wonder why Lithium Ion battery capacity is never stated at a "20 hour" rate but rather as a single number? It is because all of the factors (to include internal resistance) that might otherwise contribute to reduced capacity at high discharge rates are inherently so small that they do not significantly affect a Lithium Ion battery's capacity. Consider this comparison of AGM (a lead acid technology) to lithium ion:
  
  
  
  
  
  2. She chooses the best battery chemistry for the job. The NMC (Nickel-Manganese-Cobalt Oxide) chemistry BMW chose for the i3 has the lowest self heating rate of any Lithium Ion battery chemistry currently available for use. It is lower than the LOM chemistry used in the Nissan Leaf and Chevy Volt, and (rumored) NCA chemistry of the Tesla Model S. (http://batteryuniversity.com/learn/article/types_of_lithium_ion)
  
  3. She sizes a massive battery bank so that even at high total discharge rates, each individual cell is discharged relatively slowly. Ever wonder why a 60 kWh Tesla Model S accelerates more slowly than an 85 kWh model? Them Tesla engineers are some smart folks, and intentionally limit the maximum discharge rate of individual cells, making the power draw on each cell similar for the two cars even though they are capable of accelerating at different rates.
  
  4. She designs an effective thermal management system. No manufacturer to date has attempted to rival the refrigerant based coolant system of the BMW i3.
  
  5. She limits the maximum power draw. Ever wonder why power is limited to 170 hp and top speed is limited to 93 mph / 150 km/h? It ain't because it is significantly more expensive to make a more powerful motor. It is more likely to limit power draw on the battery bank.

That's the science case, fairly cut and dried. The human nature case, unfortunately, is where things fall apart. Anecdotally, folks generally find that the faster they accelerate, the lower their range. There is good reason for this, and it is simply that when they accelerate more quickly, they spend more time at higher speeds where aerodynamic drag is a major factor. It is not the acceleration itself that cuts into range, it is the extra time spent at higher speeds (typically due to getting there more quickly).

Consider the case of two automobiles, both accelerating and decelerating between stoplights about 2100 feet apart, covering the same distance in the same time, but accelerating at different rates (decelerating at the same rate, in order to maximize regeneration).

The red line represents the more "conservative" acceleration rate, from zero to sixty in 16 seconds, whereas the blue line represents a vehicle accelerating at twice that rate, (almost the maximum i3 acceleration rate) of zero to sixty in 8 seconds. The faster accelerating vehicle need only accelerate to ~ 43 mph and hold that speed for about 17 seconds before joining its slower accelerating partner in the same sub-50 kW deceleration that will provide regenerative braking energy recuperation. What is most fascinating about this graphic is that the faster accelerating i3 is theoretically using less energy to cover the same distance in the same time, because the aerodynamic drag caused by the time spent at higher speeds than the red line vehicle prior to the red/blue crossover is massively eclipsed by the aerodynamic drag above that point, as aerodynamic drag is a function of velocity squared.

All theoretical however. The problem is getting folks to understand that you can honk on the accelerator and beat everyone off the line up to a reasonable speed without penalty, but it is nearly impossible to get folks to limit their top speed after doing so. This car is just too damned fun.

 

[fdl1409]

Full power acceleration is not quite without penalty. At the same max. speed, your average speed is higher. Only if you drive a given distance in the same time you will use higher max speed when acceleration is lower.

Worst of all, voltage goes down due to internal resistance when discharge rate is higher:

Any drop in voltage is a loss, transformed into heat. This diagram is for normal temperatures, things get worse as temperature drops.
Curves look very similar if you compare different temperatures. Higher discharge rate deteriorates efficiency just the same as lower temperature, and both factors multiply.

I believe that very short bursts of acceleration ( 1-2 seconds ) are less harmful, as it takes some time for the voltage curve to drop to the lower level of persistent high discharge rate, as I have seen for example in the data of Mitsubishi i-MiEVs battery. Because of that, I frequently accelerate like that, push the pedal down for a short moment, enough to shoot up speed by 10-20 mph.

There is no doubt that higher discharge rate always reduces efficiency. This effect could be very low if batteries have small internal resistance - or are bigger. For example lithium titanate has a very large advantage here, hardly any losses when discharge rate is high AND even at very low temperature. So we can hope that things will get better.

Battery losses are however only one of several factors. Others are efficiencies of electric motor/generator and power electronics. I believe that between 10 and 100% of rated power motor efficiency is well above 90%. There could still be an advantage or disadvantage at higher power rates. We just don´t know that. Power electronics is even more uncertain. I would expect lower efficiency at higher loads due to growing resistance.

Frank

 

[ultraturtle]

Full power acceleration is not quite without penalty.

Agreed. But that penalty is quite low.

A quick glance at the graphic might lead one to believe that accelerating at 6C (roughly the 8 second zero to sixty acceleration of the previous graphic) would extrapolate to as much as a 16% reduction in range - pretty severe, but luckily not the case. Let's put aside the fact that BMW i3's NMC chemistry has a lower self-heating rate than the Lithium Iron Phosphate chemistry of this graph, as well as the other 4 points above that mitigate the loss effect of heat, and pretend these are the discharge characteristics of the BMW i3 battery for illustration purposes.

First let's compare two vehicles accelerating to the same speed - the first discharging the battery pack at a 3C rate for 16 seconds, and the second discharging the battery at twice that rate - 6C for 8 seconds. From the chart, the 3C capacity would be approximately 94%, with the 3C capacity approximately 84%. C = 21.6 kW, so the first vehicle would consume (3 x 21.6 kW x 16 sec)/3600 x 1/0.94 = 306 Wh. The second would consume (6 x 21.6kW x 8 sec)/3600 x 1/0.84 = 343 Wh, or a 12% increase in consumption, but only for that 8 seconds of acceleration. The key number is the 37 Wh difference between the two acceleration rates. Even if you were to do a zero to sixty acceleration every four minutes of an 80 minute drive to depletion of the useable capacity (18.8 kWh), you would be expending less than an additional 4% of battery capacity (or range) by accelerating twice as quickly each time. Muddying the comparison are the related facts that (assuming you achieve the same top speed) you will get where you are going more quickly, and that you will spend more time at high speeds, and therefore greater drag by accelerating more quickly.

A more reasonable comparison covers the same distance in the same time, making the previous graphic more relevant. It narrows the consumption gap, possibly reversing it. Given the choice of covering the same distance in the same time, one can choose to accelerate slowly to a higher speed or more quickly to a lower speed, but now the quicker acceleration (and greater loss) is necessary for less than 6 seconds. The savings in aerodynamic drag at 43 mph over the slower accelerating vehicle's increase to 60 mph and higher speed deceleration mitigates, if not eclipses the small difference in efficiency.

And again, BMW has gone to great lengths to invest in the lowest self-heating battery technology, the most effective possible cooling system, sized a massive battery bank, and has limited power draw all in an effort to reduce range reduction associated with battery self heating. I'm confident the i3's efficiency under strong acceleration is significantly better than these speculative numbers.

 

[surfingslovak]

Agreed. But that penalty is quite low.

That depends on your point of view. Compared to lead-acid battery performance, it's low. Compared to a more ideal case, it's not. The total heat losses are about 10% of the power output generated by the motor. This is supported by empirical observation at electric car races as well. While the internal resistance of lithium-ion batteries is relatively low, it's not zero.

And before you say again that BMW went to great lengths to produce a better battery than anyone else, which may or may not be true, I would challenge you to come up with a realistic estimate about what the internal resistance of the pack might be. We measured it on several LEAFs, and it clocked in anywhere between 120 and 300 Milliohm, depending on the SOC, temperature and age of the pack.

While it's correct to point out that lithium-ion batteries don't suffer from a pronounced Peukert effect, their operation is not free of losses. You might enjoy looking at the photo below. It depicts Tesla Roadsters cooling their batteries between hot laps at Laguna Seca on July 1, 2012. This was a fantastic event, and I highly recommend anyone who can make it there this year to attend. They welcome both competitors and spectators. You can register via the link below.

REFUEL 2014 Registration

 

[FrancisJeffries]

Ultraturtle said:

if you were to do a zero to sixty acceleration every four minutes of an 80 minute drive to depletion of the useable capacity (18.8 kWh), you would be expending less than an additional 4% of battery capacity (or range) by accelerating twice as quickly each time.

The rate of acceleration does not affect the amount of battery charge used, as I showed in my first post on this topic. What counts is the total velocity increment.

However, this thread started life as a discussion about whether we're inspired to drive the i3 like a hot hatch? My answer will definitely be "yes" - when I get it. But I realised that hot hatches aren't driven at constant speed - quite the opposite! And so accelerations and slowings-down under regeneration will definitely eat the battery because I doubt whether as much as half the discharged energy gets back to the battery during regeneration. So lots of speed changes (however intense they are) will take its toll on the battery, and hence range, after all.

But who cares? I've ordered the Rex, and am ready to keep stopping for top-ups on long journeys. On short journeys, the UK government even (unwittingly! ) encourages me to drive as hard as I like by paying me 17.4p/kWh for my PV electricity. I plan to charge the car - when I can - only when the sun is shining :lol:

 

[Firebird23]

Hi Cab,

in addition to what has been said already:

1. oversteering comes very very late (caused low center of gravity) but very agressive (thin tires). If you switch DSC to minimun you can have fun, but its hard to be controlled.
2. Due to light weight (BEV) and instant torque of 160HP you will be the fastest car on each traffic light. (Of course others will catch up and overtake close to the next traffic light - and they will be a lot noisier). I have tested that on some 911er and Maserati

3. For higher cornering speed and a more precise steering experience you need to go for an I8. Even if it is slower for the first 20m

Have fun,
Dirk

 

[mkaresh]

After reading this thread, I really need to find the time to drive one. Some great posts, thanks, guys.

 

[CompuMagic]

I have over 1650 miles in my i3 REx (fully loaded Giga), having bought it off the showroom floor on May 28th in the Hudson Valley, NY, USA.

I have floored it a few times. When in comfort mode it is the most responsive. With 3 other people in the car with me, demonstrating its power in comfort mode, for just a small stretch, 0 to 50, basically blew their minds. It is simply amazing. I compare it to a mag-lev ride at an amusement park like Six Flags. You really feel it kick you in the back! Zoooooooooommmm!!!!!!

I have several times put the pedal to the metal in order to get out of a bad traffic situation and it is quite practical in that respect. I have also shown off a few times, just to demonstrate to very curious onlookers or people who actually started asking me about the vehicle in parking lots and sometimes on the road at stop signs or lights. I was not able to look back to see their jaws drop but I am sure they did.

If you are in ECO PRO+ mode and floor it, it is not as snappy but it is still very quick and at 55MPH is starts to warn you and still lets you exceed 55 but gives you feedback in the way of a slight hesitation (as noted by Tom in one of his early posts). I always drive the car in ECO PRO + mode unless I am demonstrating or absolutely have to have the air conditioner going (ECO PRO mode is good enough for that). I often have my windows cracked an inch or so instead of using the air conditioner or even the fans. The iPhone app is very useful in showing your driving stats too. My stats are pretty good compared to the "community" which it shows on various graphs.

It is currently in the shop getting the software update to fix the check engine light. Apparently it is quite a process, having headquarters remotely connected to the vehicle to perform the update. They warned me it could take up to 3 days. I believe it will only be 2.

The car is a pure joy to drive. And I drive it very conservatively, at or under the speed limits and milking that regenerative braking and glide mode for all it's worth. I love when the miles remaining actually go UP as I drive (depending on terrain, speed, etc). The most I have gone is 91 miles, with 11 remaining (and another person in the car with me), and the gas generator has never come on for me yet. Perhaps I need to in order to prevent stale gas.

My range anxiety is much less than it was when I first started driving the i3.

 

[roperld]

Has anyone driven the i3 in all 3 modes over the same distance at the same speed to compare the amount of kWh used for the 3 modes?

 

[Zzzoom3]

)The most I have gone is 91 miles, with 11 remaining (and another person in the car with me), and the gas generator has never come on for me yet. Perhaps I need to in order to prevent stale gas.

My range anxiety is much less than it was when I first started driving the i3.

There is a maintenance mode in the REx. It will operate the engine at certain intervals automatically.

 

[CompuMagic]

)The most I have gone is 91 miles, with 11 remaining (and another person in the car with me), and the gas generator has never come on for me yet. Perhaps I need to in order to prevent stale gas.

My range anxiety is much less than it was when I first started driving the i3.

There is a maintenance mode in the REx. It will operate the engine at certain intervals automatically.

Yeah I found that out, after 1600+ miles... http://www.mybmwi3.com/forum/viewtopic.php?f=10&t=1231

 

[user 1096]

Yeah, but..watch those gauges.

I still have my 04 545iS 6-spd and am loathe to sell it, even though this i3 seems to live up to its "fastest 0-40 mph
BMW made" legend.

 

[user 1096]

)The most I have gone is 91 miles, with 11 remaining (and another person in the car with me), and the gas generator has never come on for me yet. Perhaps I need to in order to prevent stale gas.

My range anxiety is much less than it was when I first started driving the i3.

There is a maintenance mode in the REx. It will operate the engine at certain intervals automatically.

Mine came on the afternoon I drove mine home......depends on time and use to date. It only lasted a few minutes in city traffic.

 

[user 1096]

I have over 1650 miles in my i3 REx (fully loaded Giga), having bought it off the showroom floor on May 28th in the Hudson Valley, NY, USA.

I have floored it a few times. When in comfort mode it is the most responsive. With 3 other people in the car with me, demonstrating its power in comfort mode, for just a small stretch, 0 to 50, basically blew their minds. It is simply amazing. I compare it to a mag-lev ride at an amusement park like Six Flags. You really feel it kick you in the back! Zoooooooooommmm!!!!!!

I have several times put the pedal to the metal in order to get out of a bad traffic situation and it is quite practical in that respect. I have also shown off a few times, just to demonstrate to very curious onlookers or people who actually started asking me about the vehicle in parking lots and sometimes on the road at stop signs or lights. I was not able to look back to see their jaws drop but I am sure they did.

If you are in ECO PRO+ mode and floor it, it is not as snappy but it is still very quick and at 55MPH is starts to warn you and still lets you exceed 55 but gives you feedback in the way of a slight hesitation (as noted by Tom in one of his early posts). I always drive the car in ECO PRO + mode unless I am demonstrating or absolutely have to have the air conditioner going (ECO PRO mode is good enough for that). I often have my windows cracked an inch or so instead of using the air conditioner or even the fans. The iPhone app is very useful in showing your driving stats too. My stats are pretty good compared to the "community" which it shows on various graphs.

It is currently in the shop getting the software update to fix the check engine light. Apparently it is quite a process, having headquarters remotely connected to the vehicle to perform the update. They warned me it could take up to 3 days. I believe it will only be 2.

The car is a pure joy to drive. And I drive it very conservatively, at or under the speed limits and milking that regenerative braking and glide mode for all it's worth. I love when the miles remaining actually go UP as I drive (depending on terrain, speed, etc). The most I have gone is 91 miles, with 11 remaining (and another person in the car with me), and the gas generator has never come on for me yet. Perhaps I need to in order to prevent stale gas.

My range anxiety is much less than it was when I first started driving the i3.

I'm in Albany and am thwarted from getting BMW iPhone data App.....it says it is no longer USA available. Can you please tell me where to find the app (not UK site)....

Thx,
Ray