REX fuel consumption per kWh

[jadnashuanh]

The REx starts to produce electricity from the moment it turns on...but, the amount it can produce is proportional to how fast it runs. The computer won't let it run at full speed (assuming it's needed) until it warms up fully - about 10-minutes. So, if you weren't stressing the car at the time, your SOC might be able to stay constant. Once warmed up, it may turn on/off, but when on should still provide up to max power.

Your break even point may vary based on the load the vehicle is carrying (people, luggage, etc.) and the accessories you have on (lights, a/c, stereo, seat heaters, rear window defogger, headlights especially high beams, etc.). Your tire's air pressure is also a factor as would be whether you're running winter tires, summer tires, all-seasons, or square or staggered setup, as the drag would change.

FWIW, 1Hp~745.7watt-hours, so at full tilt, the 34Hp REx would produce 26.1Kw. The 170Hp motor in the i3 can draw a maximum of 126.8Kw (but not for long...the batteries can't sustain that level of output for long, they'd overheat, so it has a limited duration). That's about a 5:1 ratio of what the battery can provide to the motor verses what the REx can. That's assuming that the conversion from the REx Hp to watts was perfect...figure you'll lose at least 5-6%, probably a bit more.

 

[alohart]

One question about clarity.
Can you advise , when you press the accelerating pedal and the cold gas engine comes on, how come its able to provide instant power without any degradation. ? That kind of defies everything I know about, what not to do to ICE. Normally they need some kind of preconditioning and warming for lubrication .

This seems to be common behavior for all PHEV's with electric motors that are not powerful enough to provide sufficient acceleration. When the accelerator pedal is floored, the ICE starts and immediately increases speed to provide full power. This can't be good for the ICE's longevity. I've never read that any of these engines has an engine oil circulation system that is always on or that has an engine oil heater that keeps the oil temperature warm.

 

[EVMan]

Nice to know this info, and the 1:5 ratio.
The motor also has its limits , but due to less thermal mass, can quickly cool too.
I have not heard if anyone noticing loss of power due to motor overheat in i3.

The rex ( at low RPM) does not seam to eat into the regen in a noticeable way.

Any idea, what is the bottleneck for higher regen in i3 and in EV's in general ?
Is the battery , AC-DC inverter or the motor ?
I guess its the AC-DC inverter ????

Also the DC charging is probably much more energy then regen.

I was watching the consumer, report video , in which they were compare the new leaf , Model 3 and bolt

They said the rear wheel M3 does not do well with regen , compared to the Front wheel leaf and bolt , while downhill
The vehicle stability and dynamics might also limit regen.
But i was thinking the All wheel EVs should do much better with regen , buy i dont see data to support this.

The REx starts to produce electricity from the moment it turns on...but, the amount it can produce is proportional to how fast it runs. The computer won't let it run at full speed (assuming it's needed) until it warms up fully - about 10-minutes. So, if you weren't stressing the car at the time, your SOC might be able to stay constant. Once warmed up, it may turn on/off, but when on should still provide up to max power.

Your break even point may vary based on the load the vehicle is carrying (people, luggage, etc.) and the accessories you have on (lights, a/c, stereo, seat heaters, rear window defogger, headlights especially high beams, etc.). Your tire's air pressure is also a factor as would be whether you're running winter tires, summer tires, all-seasons, or square or staggered setup, as the drag would change.

FWIW, 1Hp~745.7watt-hours, so at full tilt, the 34Hp REx would produce 26.1Kw. The 170Hp motor in the i3 can draw a maximum of 126.8Kw (but not for long...the batteries can't sustain that level of output for long, they'd overheat, so it has a limited duration). That's about a 5:1 ratio of what the battery can provide to the motor verses what the REx can. That's assuming that the conversion from the REx Hp to watts was perfect...figure you'll lose at least 5-6%, probably a bit more.

 

[EVMan]

>>> I've never read that any of these engines has an engine oil circulation system that is always on or that has an engine oil heater that keeps the oil temperature warm.

I read, in case of non plug in hybrids, circulation keeps happening always.
The engines initially is warmed up, if cool. and engine can stay off at the most for a few mins only.
But then , the engine has to be ON in every trip, un-like in PHEVs, where it may not be needed for most trips ( and always on circulation may be a wasting energy )

One question about clarity.
Can you advise , when you press the accelerating pedal and the cold gas engine comes on, how come its able to provide instant power without any degradation. ? That kind of defies everything I know about, what not to do to ICE. Normally they need some kind of preconditioning and warming for lubrication .

This seems to be common behavior for all PHEV's with electric motors that are not powerful enough to provide sufficient acceleration. When the accelerator pedal is floored, the ICE starts and immediately increases speed to provide full power. This can't be good for the ICE's longevity. I've never read that any of these engines has an engine oil circulation system that is always on or that has an engine oil heater that keeps the oil temperature warm.

 

[jadnashuanh]

The regeneration is not adjustable via coding as far as I can tell...but, it is definitely adjustable as BMW did change it in one of their firmware updates (IOW, I think that it's hard coded, not an adjustable parameter like like many other things in the car).

The generator, I'm pretty sure produces ACV, and if so, the maximum regen would be limited by the ac-dc converter, or 7.4Kw - the same as when charging with an EVSE. I'm not positive on that.

 

[alohart]

I have not heard if anyone noticing loss of power due to motor overheat in i3.

From the BMW i Training Manual High-Voltage Components chapter:

"The maximum power of 125 kW can only be made available for a maximum duration of 30 s. Otherwise, the components of the drive train would be damaged through overheating – this affects not only the electrical machine, but also the high-voltage battery and the electrical machine electronics."

The maximum continuous motor output that would avoid overheating is about 75 kW.

Any idea, what is the bottleneck for higher regen in i3 and in EV's in general ?
Is the battery , AC-DC inverter or the motor ?
I guess its the AC-DC inverter ????

Regen power cannot exceed propulsive power, so that's the upper limit imposed by the motor, motor electronics, and cooling capacity.

From the BMW i Training Manual High-Voltage Components chapter:

"in theory [maximum motor power] could also be used in the alternator operation during brake energy regeneration. However, in practice only a fractional part of this maximum value is used in alternator operation. As a result, the braking torque at the rear axle is restricted so as not to affect the driving stability by the brake energy regeneration."

Also the DC charging is probably much more energy then regen.

I haven't found a maximum regen power after a quick search of this manual. I recall reading that it might be as high as 50 kW, or about the same as the maximum DC charging power, but I don't know how accurate that might be.

But i was thinking the All wheel EVs should do much better with regen , buy i dont see data to support this.

That makes sense because the regen power is split between 4 rather than 2 wheels, so the effect of strong regen on vehicle stability would be reduced.

 

[EVMan]

This data is interesting - 'The maximum continuous motor output that would avoid overheating is about 75 kW'.
This is probably less for a similar range ICE, as with ICE , i guess, power can be more continuous at peak for some minutes

I wonder , what will become bottleneck first, for a i3 going uphill at 80 Miles per hour at a 6 % or higher grade up

Will it be the drive motor , which can heat and cool quickly , or the battery with larger thermal mass. but limited C rate

Of course with new battery upgrades in i3 , the battery capacity just keep increasing
So in 64h , it may be the battery , but in 94h , it may be the motor as bottleneck.

 

[EVMan]

I read - I-Pace’s ability to deliver 300 kilowatts (400 horsepower) for sustained periods of about 10 seconds only,
The car is good but at the bottom of the list, when it comes to efficiency , with current software

 

[jadnashuanh]

Very high current rates create some significant heating. This is one reason why some of the newest designs are going with 800v battery packs...for the same current, you can transfer that linear, proportionally larger amount of current to get the work done. This allows them to deliver more power out of their battery at high currents for longer before things would start to overheat. Larger conductors and higher capacity connections start to get quite expensive and bulky, so there's a practical limit when weight is an issue in an EV as to how much current you need and for how much time. Cooling also takes power, so there are some tradeoffs. It's also why cars quickly evolved from 6vdc to 12, and soon, 48v systems will be much more common.