Official BMW i3 thread

[surfingslovak]

Keep in mind, as long as there is SOME battery, you'll easily be able to handle peaks over the REX, then the REX will "catch up" the battery.

-Phil

Yes, there is always the battery buffer. Only sustained climbs (like when it happens when we cross over passes) could be a problem.

Evnow, how large was the hill you were crossing this morning? Any idea how many SOC percentage points your LEAF loses when crossing it?

 

[evnow]

Evnow, how large was the hill you were crossing this morning? Any idea how many SOC percentage points your LEAF loses when crossing it?

Not sure what you mean by large - but, more importantly it is a 10% grade. Apparently, 7% is the steepest grade you can have on an interstate.

 

[surfingslovak]

Evnow, how large was the hill you were crossing this morning? Any idea how many SOC percentage points your LEAF loses when crossing it?

Not sure what you mean by large - but, more importantly it is a 10% grade. Apparently, 7% is the steepest grade you can have on an interstate.

Yes, thanks for that. What I'm wondering about is how much energy is needed to get over this hill in terms of SOC percentage. If the battery had 20% left and the REx was augmented with battery power, and the SOC dropped from 20% to 18% as a result, would that work in this use case? Perhaps the hill is small enough that no visible impact on battery SOC could be observed?

 

[evnow]

Yes, thanks for that. What I'm wondering about is how much energy is needed to get over this hill in terms of SOC percentage. If the battery had 20% left and the REx was augmented with battery power, and the SOC dropped from 20% to 18% as a result, would that work in this use case? Perhaps the hill is small enough that no visible impact on battery SOC could be observed?

I've to check it out - I've forgotten how much it consumes.

But the point was, when going up a somewhat steep hill, what can we hope for in "steady state" i.e. battery reserve is over and we are driving purely on REx.

 

[SanDust]

Yes, thanks for that. What I'm wondering about is how much energy is needed to get over this hill in terms of SOC percentage. If the battery had 20% left and the REx was augmented with battery power, and the SOC dropped from 20% to 18% as a result, would that work in this use case? Perhaps the hill is small enough that no visible impact on battery SOC could be observed?

The amount of energy needed to climb the hill is simply mass X gravity X height. The percentage of the battery needed would just be that number divided by the remaining energy in the battery.

But I think you're asking how much battery you would need in practice. That depends on how much and how long you supplement the REx. How much you have to supplement depends on how fast you're going up the hill and how steep the hill is. The power needed for hill climbing would be mass X gravity x velocity X sine angle. You'd add that to the power needed for a flat going the same speed. The deficit if any would be [Power from REx - Power needed on flat - Power needed to climb]. How much energy you would need from the battery would just be this power times how long it would take to climb the hill, which would be given by the velocity and the length of the hill.

I don't think any of this is realistic. The i3 isn't designed to be a Volt which you should be able to get you over the Grapevine at 75 MPH. It's more like a upscale Leaf with a crutch, which means that the i3 doesn't have to meet the challenges of the worst hypothetical situations you can throw at it to be successful. It just needs to get you home at a reasonable speed after the battery hits empty.

 

[TonyWilliams]

The amount of energy needed to climb the hill is simply mass X gravity X height. The percentage of the battery needed would just be that number divided by the remaining energy in the battery.

I need a formula for the Range Chart to convert the 1.5kWh of energy consumed to climb 1000 feet to be shown as a change to economy. In the LEAF, we use 65mph = 4.0 miles per kWh economy on level ground.

So, perhaps the rule of thumb should be 1000 feet elevation gain is 7% decrease in economy. Therefore, 65mph at 4miles/kWh on level ground will be 3.7miles/kWh over the 1000 feet climb. Sound good?

1.5kWh extra consumed to climb 1000 feet / 21kWh battery = 7% reduction in economy over 84 miles - 7% = 78.12 miles at 65mph

Here's the rub... Let say I climb that 1000 feet in only 8 miles? My economy at 65mph will be WAY below 3.7. So, we need a formula that recognizes both the extra 1.5kWh burned, and over how many miles.

So, on level road at 65mph at 4.0, the car will consume 2kWh, plus 1.5kWh to climb the 1000 feet, which means 8miles / 3.5kWh = 2.28 miles/kWh.

So, we need a formula for miles traveled and elevation change = economy * battery capacity = range.

 

[SanDust]

So, we need a formula for miles traveled and elevation change = economy * battery capacity = range.

Your range charts are based on energy. The issue with the i3 is more about power. If it takes 7.84M joules to get a 1600 kg Leaf up 500 meters, you can do that by using 7,840,000 watts for one second or 2,180 watts for one hour or 90.74 watts for one day. From an energy standpoint, a small amount of power over a long time is the same as a large amount of power over a short time. However, a small amount of power, in this case 90.74 watts, would not be sufficient to drive the Leaf up the hill.

This means that it doesn't matter from a energy standpoint whether you're going up the hill at 50 MPH or 65 MPH (though speed will change the power requirement and impact the range through aerodynamic and powertrain losses). You'd need more power but not more energy, making your idea of reducing the range by a percentage equal to the amount of energy lost when climbing divided by the energy available from the battery a good one. Hill climbing effectively reduces the amount of energy by a fixed amount. However, when you reduce the energy available, keep in mind that the Leaf should be able to recover 80% of the energy needed to climb through regen when coming down. Since the Leaf recovers 80% of what it lost lost going up the hill when it comes down, the loss is 20%. Going with the example above, if the Leaf battery holds 75.6M joules (21 kWh), then the climb would reduce the range by (7,840,000 X .2)/75,600,000 or 2%.

 

[TonyWilliams]

... Since the Leaf recovers 80% of what it lost lost going up the hill when it comes down, the loss is 20%. Going with the example above, if the Leaf battery holds 75.6M joules (21 kWh), then the climb would reduce the range by (7,840,000 X .2)/75,600,000 or 2%.

The LEAF doesn't recover ANY of the energy if you don't go down a hill, or you start at the top of the hill at 100% charge, or the battery is exceptionally cold, etc.

So, no, your concept is not what I'm looking for.

 

[SanDust]

So, no, your concept is not what I'm looking for.

I'm unsure what you're looking for so that's not surprising!

I can tell you that every 250 meter climb will take 1.09 kWh. I can tell you that it will take an extra 25.82 kW to climb a hill with a 6% slope at 60 MPH. (Note this is 1.67X the 15 kW the Leaf is using on a flat). But even if you know the speed, unless you also know the slope and the length of the hill you can't easily come up with a percentage that fits neatly into your chart.

Still think the best idea would be to say something like subtract 4 miles for every 250 you climb and add 3 miles for every 250 meters you descend. That's approximate but close enough. Trying to use percentages won't work because your charts are based on kWh/mile whereas hill climbing calculations give you kW or kWh. There is no obvious way to convert kW or even kWh to kWh/miles, and unless your units are the same you can't calculate percentages.

 

[Vlad92]

How much will the lease on i3 be ? Without knowing the price, residual etc. we can't obviously calculate. But we can speculate ... I've used the Leaf SL residuals. I took $46k as the MSRP and $850 destination. This brings the post tax credit price just below $40k, which I think is something BMW might aim for.

15k miles, 2k down, 36 months, 0.002 MF, 49% residual : $560/month.
15k miles, 2k down, 36 months, 0.001 MF, 49% residual : $500/month.
15k miles, 2k down, 24 months, 0.002 MF, 61% residual : $560/month.
15k miles, 2k down, 24 months, 0.001 MF, 61% residual : $490/month.

Do these numbers include the $7500 tax credit passes along in the lease? They seem high to me. My Volt was $42k and my lease is only $300 / month with 0 down for 36 months. I personally am very excited about the i3 and see it as a viable Volt replacement when my lease is up in 2015.

 

[SanDust]

Do these numbers include the $7500 tax credit passes along in the lease? They seem high to me. My Volt was $42k and my lease is only $300 / month with 0 down for 36 months. I personally am very excited about the i3 and see it as a viable Volt replacement when my lease is up in 2015.

Yes, he used the $7500 as cap reduction. If a car costs $10,000 more then the monthly will go up by $150. Your Volt may have carried an MSRP of $42K but you probably didn't pay that for it and there may have been some lease cash in there as well.

My lease payment for the Leaf is around $350/month. That was with $1000 off MSRP and the standard lease terms at the time.

 

[MrIanB]

Is the I3 about the size of a Honda fit? If so, I am taking it off my list. I can not go to smaller vehicle than my 2011 Chili Leaf. That's just my opinion.

Ian B

 

[surfingslovak]

Ian, I referenced the dimensions in an earlier post. If the quoted figures are correct, the outside dimensions should be very comparable. The i3 will be apparently about foot and half shorter than the LEAF, and will have less trunk space. The pure EV version is said to have a small front trunk (frunk) as well.

i3 Coupé:
--------
156" long
69" wide
61" tall

LEAF
--------
175" long
70" wide 
61" tall

 

[MrIanB]

Ian, I referenced the dimensions in an earlier post. If the quoted figures are correct, the outside dimensions should be very comparable. The i3 will be apparently about foot and half shorter than the LEAF, and will have less trunk space. The pure EV version is said to have a small front trunk (frunk) as well.

i3 Coupé:
--------
156" long
69" wide
61" tall

LEAF
--------
175" long
70" wide 
61" tall

Thanks for the info. Off the list it goes. Can not go smaller than Leaf.

Ian B

 

[evnow]

Thanks for the info. Off the list it goes. Can not go smaller than Leaf.

BMW claims the internal dimensions are more like the 3 series car. We will have to wait and see. Leaf isn't the most optimal use of space, anyway.

BTW, Inifiniti LE will be coming out at the same time - with about the same range for a few thousand dollars less.

 

[shikataganai]

BTW, Inifiniti LE will be coming out at the same time - with about the same range for a few thousand dollars less.

How can you claim this? Pricing and final specifications for the LE and the i3 alike haven't been released. Plus, all of the LE concept cars to this point have merely claimed that they're outfitted with the LEAF's 24 kWh pack. I think it'd be an idiotic decision, but Infiniti may end up releasing an EV with less range than the LEAF courtesy of the same pack + higher curb weight.

 

[evnow]

How can you claim this?

"rumors" + some statements by Nissan execs.

If you want to go by released statements, you can say we know nothing about i3 or LE production vehicles. What we have seen are just the concepts. The dimensions quoted above are for the concept, not production.

 

[TonyWilliams]

I think it'd be an idiotic decision, but Infiniti may end up releasing an EV with less range than the LEAF courtesy of the same pack + higher curb weight.

What I call the "slow train wreck" scenario. In speaking briefly about this with the mucky mucks at Nissan, they realize (now) that a 24kWh advertised capacity battery probably won't do it.

 

[evnow]

In speaking briefly about this with the mucky mucks at Nissan, they realize (now) that a 24kWh advertised capacity battery probably won't do it.

They "realized" this long time back - Infiniti LE was designed with more space allocated to the battery.

 

[KJD]

I think it'd be an idiotic decision, but Infiniti may end up releasing an EV with less range than the LEAF courtesy of the same pack + higher curb weight.

What I call the "slow train wreck" scenario. In speaking briefly about this with the mucky mucks at Nissan, they realize (now) that a 24kWh advertised capacity battery probably won't do it.

An Infiniti with a 24kwh battery pack would be a huge huge mistake. I can not believe they would be this stupid, but then again.....