Loss of Power in Real Life after 30 seconds

[EVMan]

Since the max power of the car is only available for i think 30 seconds or so ( don't remember numbers from the book) , after which i think the motor overheats etc

i Was thinking, if any one experienced it in real life , say while driving up a steep grade at high speed etc, after some time , the pickup is reduced.


Since gas powers don't experience this loss of power , it may be , you overtake some one , and then they overtake you ...

 

[JohnKelly]

There is no loss of power unless your battery is very low. You can go up any hill an ICE can go up at normal speeds... you can accelerate with no loss of power. Not sure where you got this idea.

 

[alohart]

There is no loss of power unless your battery is very low.

Not necessarily true.

You can go up any hill an ICE can go up at normal speeds... you can accelerate with no loss of power.

True if "normal speeds" don't include the top speed.

Not sure where you got this idea.

Maybe from these entries in the i3 motor performance table on p.17 of BMW's 06 I01 High-voltage Components Technical Training Manual:

Maximum peak output: 125 kW/170 bhp for a maximum duration of 30 s
Maximum continuous output: about 75 kW continuous

i3 drivers have reported a loss of power when driving at top speed for an extended period of time.

 

[JohnKelly]

I have never noticed this. Interesting, thanks. It would be a pretty extreme situation to have this come into play I'm thinking. Floored for 30 seconds.

 

[EVMan]

Climbing up a steep grade like 6-8% at a speed of 80 ( normal traffic speed) , does need a lot of flooring......

 

[JohnWasser]

I don't think it can be done on a level road. Looks like it takes about 17 seconds to reach the 150 kph limiter. After that, the power backs off to about 40 kW (26.6 kWh/100km @ 150 kph).

https://youtu.be/8eh2hnlKpR8?t=357

How steep of a slope does one need to drive up to use 125 kW for more than 30 seconds?

It looks like it might not be possible on the US Interstate Highways System. For military planning purposes, US interstate highways are limited to a 7% grade (7 rise in 100 run). At that slope, to go 1000 meters vertically you have to travel about 14.3km horizontally. One hill-climb video leads me to believe that it takes about 8 kWh to lift an i3 by 1000 meters. If you do that in 1 hour (14.3 kph) your burn rate is 8 kW higher than traveling on the flat. If you do it in 1/10th hour (143 kph) your burn rate should be about 80 kW higher than on the flat. It's going to be a tough call whether you hit the speed limiter (150 kph) or the maximum power (125 kW) first.

 

[bornelectric2018]

I have some anecdotal evidence: I live in Los Angeles, and there are some great canyon roads nearby. I have a 2019 i3s REx (120aH), and I've taken it out on some canyon carving expeditions. On my first such outing, I was trying to keep pace with an ICE sports car (within the safe limits of tire adhesion, of course!), on a winding uphill road, and within a few minutes of really pushing the car, I noticed a pronounced decrease in accelerator response. I could mash the accelerator pedal all the way down, but the i3s just wouldn't accelerate any faster. I'm pretty sure this was due to effects of thermal management/limiting.

 

[EVMan]

Hmm,
So first lesson, Dont be overconfident, when you start to race ICE cars.... (within the safe limits of tire adhesion, of course!),
The shorter, the better for you at lower starting speeds , The Longer it lasts, or at higher speeds, ICE start to fight back..

2nd, technically , you motioned 2019 model.
The motor was really designed for the 22KWH battery max type of draw with the lighter weight of 22KWH.

So unlike other EV'S, you have a situation where you have, over the years , a lot more capable and heavier battery , but the motor is the bottleneck

 

[alohart]

2nd, technically , you motioned 2019 model.
The motor was really designed for the 22KWH battery max type of draw with the lighter weight of 22KWH.

So unlike other EV'S, you have a situation where you have, over the years , a lot more capable and heavier battery , but the motor is the bottleneck

Regardless of the battery pack capacity, an i3 motor consumes the same maximum power, and the battery pack outputs the same maximum power, so the motor, its control electronics, and the battery pack should not overheat at any different rate on a 120 Ah i3 than on a 60 Ah i3. An i3S motor does produce a slightly higher maximum power, so it, its electronics, or its battery pack might overheat slightly sooner than on an i3.

The 120 Ah battery pack is only 40 kg (88 lb) heavier than the 60 Ah battery pack, only a 17% increase. That's not a significant difference.

If a more powerful motor were installed, the capacity of its cooling and that of its electronics and battery pack would need to be increased to avoid more rapid overheating. Increasing the cooling capacity would be a significant change possibly including a higher capacity A/C compressor and condenser and a larger coolant radiator. With the i3 never intended to be a high-volume car, such changes were probably never going to happen.

 

[JohnWasser]

within a few minutes of really pushing the car, I noticed a pronounced decrease in accelerator response.

That sounds like the motor or battery eventually approached its maximum operating temperature. I wonder which one. If the motor overheats first (I think the battery has active cooling) someone should produce an active cooling system for the electric motor as a performance add-on.

 

[EVMan]

"The 120 Ah battery pack is only 40 kg (88 lb) heavier than the 60 Ah battery pack, only a 17% increase. That's not a significant difference."


This is very interesting. Given the big drop of the Rex fuel economy from 39 Mpeg ( 2014) to 31 Mpeg (2019), it looks like the 40Kg is making a huge difference.

 

[alohart]

Given the big drop of the Rex fuel economy from 39 Mpeg ( 2014) to 31 Mpeg (2019), it looks like the 40Kg is making a huge difference.

I believe the maximum RPM of the REx engine was increased between 2014 and 2019 to increase its output power and thus the REx generator output. Running at a higher RPM decreases its fuel efficiency.

Several features that added to the total U.S. vehicle weight were standard in 2019 and optional in 2014 (e.g., DC fast charging, seat and battery pack heating), so the 2019 REx is more than 40 kg heavier than the 2014 REx. Nevertheless, this weight increase seems too low to explain the total increase in the REx fuel consumption rate.

 

[eNate]

The EPA has stats saying a 100 pound decrease can result in a 2% fuel efficiency increase in smaller cars. When they say "smaller" I'm sure they really mean either lighter-than-average weight or lower powered-than average. I'm not sure the i3 checks either of those boxes. Yet still, I wouldn't call 88 pounds insignificant. At the other extreme -- 1/2 HP & 250 lb vehicle + driver -- when I put an 80 pound kid on the back of my cargo bike I can definitely notice the difference!

 

[JasonPro]

I have some data related to this topic. I autocross my two i3's and have seen this power loss occur a few times within 60 seconds from cool start.

2017 i3 ReX (chipped to i3s) - never saw the power loss (also include an event in Lincoln, NE) despite using the motor like the i3S would and with more weight.

2018 i3S BEV - power loss has occurred multiple times at 2 events. Both events were in Lincoln, NE in warm/hot temps with a cool, rested car. These courses tend to be a bit faster, grippier, and modestly long (though longer courses elsewhere did not have the problem, but likely less full throttle). At about 60 seconds power bars go away and very noticeable power loss (similar to very cold conditions). This happened near the end (about 5 seconds left) each run. Power returned just seconds later a bit after crossing the finish line. After each run I was removing the back panel and blowing a fan over the motor and circulating A/C to help move fluids. (Same problem happened on the first run with cold motor and later runs with these cooling attempts in place - seems unrelated). One time I was successful at softening my throttle and maintaining my speed better and I avoided the power cut - but wasn't as fast.

I have read elsewhere this could be software triggered rather than any temp sensor. The software anticipates the impending overheat due to throttle inputs and limits power output. My thought is maybe the i3S has a different threshold coded into the software since it is capable of higher output. Perhaps, the i3 chipped to i3S did not have this different threshold. Of course, it could all just be chance or coincidence. I don't know anything myself about the software.

If anyone has any knowledge on this topic, I would appreciate any insight you might have. The last time I had this error I was competing in the SCCA National Championship and the power loss cost me a trophy.

 

[m6rk]

Since the max power of the car is only available for i think 30 seconds or so ( don't remember numbers from the book) , after which i think the motor overheats etc

i Was thinking, if any one experienced it in real life , say while driving up a steep grade at high speed etc, after some time , the pickup is reduced.


Since gas powers don't experience this loss of power , it may be , you overtake some one , and then they overtake you ...

Are you talking about this, by chance? This is form a 2018 i3s BEV.

 

[JasonPro]

Are you talking about this, by chance? This is form a 2018 i3s BEV.

Yep. Exactly that. Is that being discussed somewhere? Have a link?
I have similar (blurry) images with my camera pointed at my dash (warm 80+ degrees F, though).

 

[robthebold]

Are you talking about this, by chance? This is form a 2018 i3s BEV.

That happened to me last summer in my '17 i3 REX. I got the reduced performance warning and I felt the lack of throttle response. And it got worse. Eventually I noticed the bars on the ePower arm were decreasing -- I didn't know they did that. It was operable at 5 bars on level streets, but at 2 it couldn't get out of its own way . . . or even accelerate away from a red light. Eventually it shut down dramatically. After a rest, it got better -- a little better -- but the problem came back. I plotted the least hilly path to the dealership, turned off cabin climate and drove super slow. Still had to take a couple breaks but made it without a tow.

The problem? The drivetrain was overheating due to coolant pump failure. Total pump failure: squirrels had chewed the wiring harness!! Repairs cost almost $500 of troubleshooting and disassembly/reassembly labor + $10 of wire.