Range fluctuations

[user 4830]

Hello there,
I am a new i3 owner, sorry if this is a naïve question. I have search the forums, but could not find anything to this extent.

Can anyone explain how the car calculates the remaining range and why does it changes quite a bit when the car is stationary? Let me use today as an example:
- I started in the morning with car showing 103 miles of remaining range. Drove 9 miles to work, mostly downhill At the end car showed 105 miles of remaining range. So far so good.
- Came back to the car at the end of work day. Still the same range. Drove back same distance to home. At the end car shows about 98 miles remaining. Did not plug it in.
- Had to run some errands in the evening. Started the car, but mileage now shows 82 miles remaining. This is after the car stayed in garage for about 2 hours.
- Drove to a nearby sports field. Turned of the car and waited in it for 15 minutes. Heating on.
- Turned it back on, this time the mileage remaining is back up to 105 miles. Drove back home, it dropped a bit.

It all seems quite puzzling.

Regards,
Maciek

 

[jadnashuanh]

The estimated range is a sliding average based on the last 18-miles or so. It assumes that your next miles will match the previous. If you change from city stop and go to high-speed highway, it assumes that you're still doing city driving, or vice versa the other way. Then, the ambient temperature makes a difference. For example, my i3 was in a moderately warm garage. I moved it outside to put my ICE in after a trip and the next morning, because it was near zero F outside, the range to empty had dropped about 25-miles and all I'd done was move it maybe a 100' from the night before.

I've had many instances where I've arrived at my destination where the estimated range had not gone down because the driving was less stressful on the batteries.

To maximize your range, while plugged in, if you think of it in advance, set a departure time, or if not, precondition. Using the grid for that verses drawing from the batteries helps. Also, if you set a destination in the nav system, because the car will then know the characteristics of the roads (elevation changes and speed limits), your range estimate will be better. Otherwise, it has no idea if your next miles will match the previous ones, but makes a guess. That guess isn't always right. The same thing exists on an ICE that has a range to empty...change from city driving to highway, and that estimate will be off for awhile. The thing isn't omniscient...it can make guesses, but they are not always right.

Those differences are more critical on an EV than an ICE, since you can refill the gas tank a lot quicker than the batteries, and, typically, will have lots more range in between needing to do so.

 

[user 4830]

Thank you for the detailed response. I understand it is an estimate, and I expected the changes due to temperature changes. What I think threw me off a bit is the change in the range estimate while the care was stationary. But I guess some of that estimation process explains it. Agree that it's the same in ICE car, but I guess I never paid so much attention to it

I started doing hte preconditioning in the morning, while still plugged in. It helps and sure it is nice to get into a warm car.

Thanks a lot!
Maciek

 

[jadnashuanh]

When it's cold out, there can be a big difference between the BEV and the REx when it comes to the impact of heating. On the BEV, it has a heat pump, so unless it is really cold out, it's MUCH more efficient at heating than the REx, which ALWAYS uses resistance heaters (think toaster) to make heat. The heat pump can get more than 3W of heat out of 1W of input, while the REx it's 1:1.

The miles/Kw readout can give you a good idea of what you're using, and you can relate that to remaining distance.

 

[Tacfoto]

That is an interesting think to know about the REx. I have the Rex and was always impressed at how much heat it created. Even when running on the REx.

 

[alohart]

I have the Rex and was always impressed at how much heat it created. Even when running on the REx.

It's not how much heat an electrical resistance element can produce (answer: plenty), but how much power is required to produce that heat. Whether the REx is running makes no difference because the heat it wastes is not used to heat the cabin. The BEV's heat pump doesn't produce any heat but merely transfers heat from the outside air into the cabin, a much more efficient process.