US i3 Rex dangerous when climbing hills

[Chrisn]

Hello.

I picked up my BMW i3 REX yesterday. I live in the SF Bay Area (North-east corner). I frequently travel to the beach near Santa Cruz, CA via Highway 17 (for those who may be familiar with the area). I feared that this could be a challenge for the i3 as the base of the hill over to the beach is about 60 miles away from home (meaning battery could run out before climbing the hill).

Let me start by saying I knew that REX mode has some power limitations, and I don't expect to use the REX in daily commuting. But this is a trip I make every couple of weeks. I saw no definitive info from BMW on the nature of the REX limitations, but had read online that you could cruise at 75MPH on flat ground and that it would maintain 45-50MPH on grades. The speed limit on Highway 17 is 50 MPH, so I felt like even the worst case would be tolerable. I was wrong.

After the ICE kicked on, the car maintained speed for maybe 5 minutes, then began to feel very weak. On the next uphill section, my speed fell quickly from 50MPH down to 25MPH and was falling (this while at WOT). Cars backed up behind me and I needed to put on the hazard blinkers and crawl to the next turn out.

I waited on side of road while the engine continued to run (but seemingly not at full load). I did not know how long to wait. After 3-5 minutes, I attempted to merge back into traffic (I was still on an uphill section). The car initially had good power, accelerated to ~40MPH, then crapped out and fell back to 25MPH. I crawled to next turnout and waited 10 mins. That was enough to get me over the next hill and get me on my way.

This wasn't just annoying. It was dangerous.

Is there any way for US owners to force on the REX early to preserve charge? The Chevy Volt has this even though the ICE by itself can still maintain speed.

Any advice (beyond finding a charging station at the base of the hill and wasting a couple of hours)? Perhaps when the DC fast charge network is built, a 15-20 minute coffee break wouldn't be too bad. But for now I am at a loss.

 

[jadnashuanh]

There is no currently available way to force the REx on earlier in the NA market (at least in the USA and Canada...not even sure if they are selling it elsewhere in NA yet).

The car will go into battery preservation mode at (if I remember correctly) 1.9% on the REx, and the REx won't come on until it's around 6.5%, so if you are stressing things (i.e., using more power than the REx can provide), you will continue to draw down the battery reserve and eventually hit that brick wall.

The only way around this is to either find a charging station to top off, forego some of the creature comforts - switch to Eco Pro or Eco Pro+ mode earlier on in the trip, and maybe take advantage of all of the prompts to help you go more economically, or, take a different vehicle or route.

I'm been saying this on this forum for awhile...it really depends on where and how you drive whether the car, BEV or REx will work out for you. It is designed as a city, commuter car, and at that, it does well.

 

[Zzzoom3]

There has been much debate about such a scenario on this forum in recent weeks. Much of it centered about just how much power the REx really delivers and how it affects performance when you get into this very low SOC battery scenario. Yours is the 1st post from someone, as far as I know, that has actually encountered it.

BMW has limited when the REx will operate in the U.S. so it meets the guidelines which qualifies it to CAFE standards and obtains the most credit even though it has a range extender. I think the category is BEVx or something similar.

Next time you know you'll need to arrive at the hill with a higher SOC prior to ascending. It will be interesting to find out just how much SOC you need to have available in order to make it at "normal" speed.

• - I'm curious if you had the vehicle in Comfort Mode while you were traveling to and up the hill?
  - What was your SOC was when you got to the beginning of the climb?
  - Did you expect to arrive with little or no charge and that the REx would get you up the hill or were you sort of experimenting?
  - What was the SOC at the start of the climb?

 

[jadnashuanh]

FWIW, even if you could turn the REx on earlier, if you drive far enough under those circumstances, you could run into the same problem. With your total distance being fairly reasonable, if you could have turned it on early like they can outside of NA, you may not have run into this situation, but it's always there if you're stressing the thing once the SOC gets low enough. THe car has a strong will to survive! It will not let you dangerously discharge the batteries beyond a certain point, and that's true with both the BEV and the REx - you'll hit the same brick wall, it's just that the levels are different, and if you then can drop your load, the REx can recover on its own, the BEV cannot without a stop to recharge somewhere. This can be critical, but the results are not a secret.

 

[Zzzoom3]

and if you then can drop your load, the REx can recover on its own

What do you mean "drop your load". Keep it clean man! :lol:

Seriously though, what electrical load would you be dropping? The car has already dropped whatever load it can. There ain't anymore to shed? It's not Apollo 13 with Mission Control coming up with some workaround for you behind the scenes! And by "recover on its own" I presume you mean running the motor in order to recover some SOC but that only works until you run out of gas!

Best course of action is to make sure you've got enough juice in that high voltage battery pack before you get going up the climb me thinks

 

[jadnashuanh]

Load, as in draw on the battery, as in shut off things that aren't keeping the vehicle moving such as the a/c, fans, radio, etc. - anything you can that will reduce the load/draw on the batteries, that will keep you going further.

 

[RJBarry]

Same exact thing happened to me. I was do a fairly long round trip and ran out of electric just about the midway point. On the way back I had 3 long grades. Admittedly, I wasn't really paying attention and, though the car was in ECO mode, I was probably going a little over 70 maybe and had the AC on.

On the first grade I noticed that the high-end blue and grey bars started to disappear from the "performance display" in my console. Once they caught up with the white indicator of my current performance, the car started to drastically loose power. When all of the bars on the right hand side had disappeared, the car had exactly NO power. I had it floored and it just kept loosing speed. Just as the original poster, I had my flashers on, but felt that I had to pull over once my speed got too low.

I noticed on the blue charge bar there is a little triangle that indicates just a little bit of charge. The bar was showing no charge at all when I pulled over. However the REX continued to chug and once the charge in the blue bar built back to the little triangle, then the bars on the performance bar started to come back. Once all the performance bars were back, I managed to pull back into traffic and get up and over the hill.

On the next two hills, as I approached them I proactively put it in ECO pro+ mode, turned off the AC altogether and started the grade at 55 (to the annoyance of other drivers since the speed limit is 65) and while some of the performance display bars started to disappear, they never caught up to my white indicator, so I never lost any power/speed. I just got a little warm since there was no AC.

That first hill was pretty scary though.

 

[Zzzoom3]

Load, as in draw on the battery, as in shut off things that aren't keeping the vehicle moving such as the a/c, fans, radio, etc. - anything you can that will reduce the load/draw on the batteries, that will keep you going further.

The car does this whether you want it to or not below 1.9% relative SOC ...

 

[MarkN]

...
Is there any way for US owners to force on the REX early to preserve charge? The Chevy Volt has this even though the ICE by itself can still maintain speed.

Any advice (beyond finding a charging station at the base of the hill and wasting a couple of hours)? Perhaps when the DC fast charge network is built, a 15-20 minute coffee break wouldn't be too bad. But for now I am at a loss.

At http://www.mybmwi3.com/forum/viewtopic.php?f=12&t=966&start=40 I posted instructions on how to turn on "Exhaust-gas test mode" that will force the REx to run for up to 20 minutes with the important limitations that the rear hatch has to be open and the car must be stopped. You could try this and see if it lets you charge the battery enough to complete the hill.

 

[Zzzoom3]

I noticed on the blue charge bar there is a little triangle that indicates just a little bit of charge. The bar was showing no charge at all when I pulled over. However the REX continued to chug and once the charge in the blue bar built back to the little triangle, then the bars on the performance bar started to come back. Once all the performance bars were back, I managed to pull back into traffic and get up and over the hill.

I'm wondering if you ever got any range warnings?

 

[jadnashuanh]

I'd be surprised if the car didn't issue an alert, but then, you have to recognize and respond to it!

There's a learning curve experience with driving an i3, regardless of whether it is a BEV or has the REx as to what it can do, and how best to maximize your experience. But, you need to go into the purchase and use with some understanding of its limits - it is not an ICE where it keeps going until it just stops when you run out of fuel...the i3 will run in a degraded mode for awhile before stopping...you just need to deal with it. If that is too much, sorry, you bought the wrong car. So far, I love mine - it meets my needs and hasn't let me down yet. But, then, I'm a retired engineer that went into this with a pretty good understanding of what it was and what it could do. Call me anal if you must, but it's not a car for everyone.

 

[Chrisn]

OP here.

I got a range warning when I put the destination in the Nav (90 miles each way). As an aside, if the car "knows" that it will need the ICE at some point (90 mile trip each way), it would seem that California bureaucrats would allow some intelligent management of finite battery charge. E.g., the GPS "knows" that I need to climb a grade at the 65 mile point. Why not maintain a minimum 20% buffer until over the hill? The car "knows" that I will STILL fully deplete battery on far side of hill therefore no net increase in gas burned.

To be clear: I got NO warnings as I began climbing the hill, and no warnings as the SOC dropped to minimum. No warnings ever. If the cars sees my SOC dropping from 5% to 2.5% very quickly and "knows" via GPS that I am gaining altitude, it might be nice to get a "Reduce speed or risk loosing power" (or whatever).

I knew the limits in the abstract-- but I got the car YESTERDAY and I still learning. I certainly could have (and might in future) drive more conservatively before approaching hill to start with more SOC. In this case, it was in the default comfort mode with A/C on (although it cut out when power started to drop).

Another thought: to qualify for the CA credits, the main hurdle is: more EV range than ICE range plus no ability to prematurely switch to ICE. It seems to me, however, that AFTER YOU ARE IN CHARGE SUSTAIN mode, you ought to be able to select a mode that rebuilds the SOC from 5% to (say) 10%. You'd have to be VERY unlucky (like me) to flip into the ICE in the middle of a giant hill and run SOC from 5% to 0% before the ICE has a chance to warm up and build SOC as you drive up and down hills. The more typical case is that you flip over to ICE and you know you have hills coming. How could Calif complain about that?

 

[Surge]

I posted the same thing a few weeks ago. There is no alert issued by the car.
You see the bars disappear in the display, as was mentioned in this thread, and that's it.

I tested my demo REx at varying speeds, and it definitely cannot maintain 75 mph for very long. Even on FLAT roads, 75 depletes the battery after several minutes, and then the car loses power.

68.75 mph was about the best it could maintain on flat highway. Note that this is Actual speed, as measured through an iPhone app. Indicated speed was 70.63 mph. We all know that BMWs in particular overstate the speed, so we have to be careful we are talking about actual or indicated speeds.

Anyway, at an actual speed of 68.75 mph, it seemed to cruise fine on flat, but then a VERY SLIGHT UPHILL GRADE, caused it to lose a bit of power. It went down to about 60 mph, and then once we were back on flat ground, it went back to 68.75.

This was with just me in the car (~180 lbs), no AC, Comfort mode. I don't think ECO PRO makes any difference in this case (i.e., it won't let you cruise faster).

So that said, it's worrying and actually DANGEROUS to drive long distances using the backup REx… Unless you drive below 68.75 mph. How much below, I'm not sure. I guess you would want to actually build charge in the battery while cruising, to be sure that you had passing and climbing power when you need to.

If word of this gets out, BMW is going to have a real issue on its hands. I don't know about where you live, but driving below 70 mph is considered below average. Cars will aggressively pass you. Most people cruise at 75-80 mph… to know that you cannot do that for more than a few minutes, is not good.

Another 'x' for the REx, in my view.
At least with the BEV, you can go as fast as you want. And you are likely to drive it more cautiously, thereby extending your range.

 

[KurtEndress]

This is disappointing news. It sounds like you need more than a 6.5% buffer to deal with some hills. I am unhappy CARB and BMW denied NA customers the ability to switch the REX on early.

In the BMW University W20 Engine document there is a graph on page 56 illustrating engine RPM as a function of speed. For noise reasons the engine only operates at high RPM at higher speed. It reduces the REX engine RPM at lower speeds even for a depleted battery. According to the graph at 0.7% battery the REX maximum speed of 4300 RPM is reduced below 70 km/h down to an idle of 2400 RPM at about 18 km/h.

It seems to me that this could lead to a negative feedback situation. If the hill was steep enough the the REX at 4400 RPM couldn't sustain a speed of 70 km/h (43.5 mph) it would have to slow down at some point. Once the i3 started slowing below 70 km/h the REX would reduce in RPM to avoid excessive noise at low speeds. Less RPM means less power generated which means even less speed so the RPM is reduced even further.

Then according to the chart when you are stopped the REX will at best idle at 2400 RPM and I think it shuts down when the SOC reaches 3.5%.

When the REX first comes on it idles at 2200 - 2400 RPM to warm up for about six minutes depending on temperature. So you are probably most at risk of performance problems for those first six minutes or so. When I tested my REX for the first time on Sunday I noticed that the battery bar initially seemed to be slipping below the triangle that I assume marks 6.5% where it switches on. Latter it recovered back to the triangle mark and seemed to have no problems holding there at highway speeds through rolling terrain.

 

[Zzzoom3]

This is disappointing news. It sounds like you need more than a 6.5% buffer to deal with some hills. I am unhappy CARB and BMW denied NA customers the ability to switch the REX on early.

All REX owners, whether they think this affects them or not, IMO should make a call or send a message to BMW NA and let them know that you do not appreciate being handicapped this way. BMW listens to owner's feedback. It may not make a difference in the short-term but could make a difference going forward.

 

[DHP]

Someone over on the BMW i3 facebook group did the math and posted this table around max speed vs hill grade. Real life is probably a couple mph lower

MPH % grade
81 0
74.25 1
67.5 2
60.75 3
54.9 4
49.5 5
44.55 6
40.05 7
36.45 8
33.075 9
30.375 10

 

[mindmachine]

To me as a retired engineer, this scenario of the crippled ICE is ridiculous. It is not California's fault as much as BMW's greed. BMW could have said no we will not cripple the ICE in North America and thus they would have lost some of their precious CARB credits. It's all about greed/money to BMW so if we owners inthe other 40 non CARB states raise enough stink I think BMW will do something to fix it. It is only a software issue in the non CARB states. It can easily be fixed if BMW will only cooperate with non CARB state owners of the car.

Lets raise a stink so sour that they (BMW) have to deal with it/fix it (at least for non CARB states!

 

[Surge]

It's not just a software issue. Remember that the gas tank itself has been physically stunted, it's smaller by 2L, I think.

Stupid. Just really dumb.

 

[Surge]

Someone over on the BMW i3 facebook group did the math and posted this table around max speed vs hill grade. Real life is probably a couple mph lower

MPH % grade
81 0
74.25 1
67.5 2
60.75 3
54.9 4
49.5 5
44.55 6
40.05 7
36.45 8
33.075 9
30.375 10

Agree that real life is lower. I could not maintain 81 mph with 0% grade. There's no way.
One person in the car, no baggage.
Best I could do for sustained driving (no traffic), is an actual speed of 110 kph, 0% grade.

 

[cwerdna]

(FWIW, I live in the SF Bay Area but don't go up/down 17 much. I have taken my Leaf from the South Bay to Capitola over 17 and back and I know someone who traverses that hill in their Leaf regularly...)

This is disappointing news. It sounds like you need more than a 6.5% buffer to deal with some hills. I am unhappy CARB and BMW denied NA customers the ability to switch the REX on early.

All REX owners, whether they think this affects them or not, IMO should make a call or send a message to BMW NA and let them know that you do not appreciate being handicapped this way. BMW listens to owner's feedback. It may not make a difference in the short-term but could make a difference going forward.

IMHO, at minimum, the OP and anyone who has personally experienced extreme slowness vs. prevailing traffic speeds doing a hiill climb on the REx should contact BMW corporate and have them formally note the issue/complaint. I doubt they'll have any sort of resolution immediately or in the short term, judging by the speed at which they've been resolving/attempting to resolve currently/recently known i3 issues.

Since the OP has used the words dangerous and indicated the lack of warning, I'd also suggest filing a safety complaint w/NHTSA at http://www.safercar.gov/ after contacting BMW.

IMHO, yes, 25 mph up highway 17 is dangerous vs. the speed of other traffic. Either BMW needs to provide a mountain mode (like the Volt) or provide more warnings and explicit dealer training/messaging. Sure, the OP knew there'd be limitations, but I suspect there will be buyers/lessee who have no clue.

(My wimpy 110 hp Prius and 107 hp '13 Leaf make it over the same grade w/o issue.)