Estimated Range Prediction / Energy Used Calculation

[Zzzoom3]

I'm finding it difficult to judge how many miles I truly have remaining during a drive. I find the range estimate to fluctuate too much. The predicted range doesn't seem accurate.

Yesterday I returned from a 99 mile drive with the range indicating 8 miles remaining. Looking at the energy used during the overnight charge, 14.017 kWh was used to reach full charge. If I have 18.8 kWh available, that tells me I had approximately 4.8 kWh remaining.

So why only 8 miles? The trip computer indicates my average consumption as 4.1 mi/kWh. Why wasn't I being shown a range estimate in the order of 18-19 mi available?? Is there any display that shows how much energy has actually been used during driving? If so, where is it? This would be very helpful to know in order to determine how many miles you really have left.

 

[jadnashuanh]

The i3 app will show you the energy used (in miles/KwHr), the amount you regenerated, and the miles driven.

 

[Zzzoom3]

The i3 app will show you the energy used (in miles/KwHr), the amount you regenerated, and the miles driven.

The app only shows the average electrical consumption and recuperation in miles per kWh. I can't calculate how many miles I should have left if I don't know how much energy has been used from the high voltage battery or how much remains. It also doesn't explain why I was being told I had 8 miles of range when I had more than 4 kWh left in the battery. This implies the range calculation was based on 2 mi/kWh when the reported average is double that? What gives?

Bottom line: Owners need an accurate battery capacity readout. Surely the system is already monitoring this. So let me see it somewhere, preferably, in the eDrive display or the Trip display. The system should not reset the value until the next full charge occurs.

 

[Chrisn]

The app will give you a SOC. Remember that EV miles end when you are at 6.5% SOC. So a rough estimate might look something like:

[(SOC-6.5%)*18.8] * 4 = Approx miles left. If the dash shows a different number then it is presumably related to recent draw higher or lower than 4M / kWh consumption...

 

[Zzzoom3]

The app will give you a SOC. Remember that EV miles end when you are at 6.5% SOC. So a rough estimate might look something like:

[(SOC-6.5%)*18.8] * 4 = Approx miles left. If the dash shows a different number then it is presumably related to recent draw higher or lower than 4M / kWh consumption...

Not sure where you are getting that? Are you talking about a REX? I've got a BEV which allows 90% of the absolute SOC to be utilized. The 10% you can't use is where the 18.8 kWh usable comes from that everyone likes to talk about. In the BEV, when you get to 14.2% absolute (4.9% relative), you'll be in the so-called "restricted drive power range". Performance of the drive train is reduced due to the low state of charge of the high-voltage battery. The heating and air-conditioning system is switched off. On the driver display, the little battery icon turns yellow and the battery bars turn yellow.

In any case, this is a simple calculation if you know how much battery you've used since the last full charge minus any regen recovery. A plain readout indicating how much energy you've used in kWh since the last full-charge would be ideal. It counts up from zero and counts down during regen, therefore, telling you exactly how much you've got left in the tank .. easy really. Not sure why BMW seems to hide this and why I can't get an accurate range remaining estimate?

Has anyone else seen this happen to them? Is this the case of an intentional glass half full scenario so the silly consumer doesn't strand themselves?

 

[jakell64]

There is a bar that indicates the state of charge. Four bars, really. My commute is 32 miles. It uses a bar and a half. From that I can extrapolate that I have a bit over 20 miles per bar.

Or, you can look at your average KwH usage across all of your trips (you can get that by going to the eDrive screen). Mine is 4.7. 4.7 * 18.8 = 88 miles. So 22 miles per bar.

You can also track your current KwH consumption by going to the Trip Info screen. So if you feel like driving a little crazier you can do the same calculation.

I agree it would be nicer if they would just show a percentage right there on the screen rather than the graphical representation. There are many hints from folks "in the know" that a change is coming that will make us happier.

 

[Zzzoom3]

There are many hints from folks "in the know" that a change is coming that will make us happier.

I sure hope so because right now it is a guessing game when it need not be.

 

[KurtEndress]

I’d like a SOC percentage too, but it’s fine if it’s buried in some information screen. I’d use it mainly for logging statistics on a trip or charge which I currently do by resetting the trip information with each charge and then noting the miles and mi/kWh figures.

While I’m driving I’m going to be doing mental approximations to calculate range if I don’t trust the guess-o-meter. So I’ll glance at the battery bar and pick a simple fraction of the battery remaining like 2/3 and figure that against my total range. Knowing the SOC is at exactly 63% isn’t that helpful as I’m not going to be doing exact math behind the wheel.

What currently puzzles me is that the gas tank on the REx is suppose to give about the same range as the battery, but the figures it gives me aren’t very close to each other. The gas range reads distinctly lower; maybe 20 miles less. Does it remember the one time I used the REx at highway speeds and now it judges the gas range by that trip while the electric range is judged my slower and more efficient low speed travel?

 

[ultraturtle]

What currently puzzles me is that the gas tank on the REx is suppose to give about the same range as the battery, but the figures it gives me aren’t very close to each other. The gas range reads distinctly lower; maybe 20 miles less. Does it remember the one time I used the REx at highway speeds and now it judges the gas range by that trip while the electric range is judged my slower and more efficient low speed travel?

I have the same issue, and yes, when I used the REx it was mostly at highway speeds. Anybody else?

 

[Zzzoom3]

In a general sense, I'm not sure what everyone means when the refer to "SOC". Is it a real value, representing how much energy is usable in the battery?

In any case, everyone seems to be in agreement that we need a better way to gauge actual range remaining. All I am looking for is a usage meter that counts up after the battery is fully charged. It should display in kWh to a tenth of a kWh. It should count up as I drive and count back during regeneration. For example, if it read "10.8 kWh Used", I now know there is 8 kWh remaining available for driving. My average overall consumption seems to be about 4.0 kWh. This tells me I have 32 miles before I'm empty. Even better, show this range to me and show me the range remaining before I am in the "restricted driving" state.

Currently, I can't tell how the range display calculation works and it doesn't appear accurate which is the worst part. We need to be confident that the range we are being shown is reliable.

 

[BrianStanier]

What currently puzzles me is that the gas tank on the REx is suppose to give about the same range as the battery, but the figures it gives me aren’t very close to each other. The gas range reads distinctly lower; maybe 20 miles less. Does it remember the one time I used the REx at highway speeds and now it judges the gas range by that trip while the electric range is judged my slower and more efficient low speed travel?

I don't see this. Uusally the two are faily close. And when driving more efficiently on electric I see the electric range and the petrol range increasing together (and vice-versa).

 

[Boatguy]

I'm not sure what everyone means when the refer to "SOC".

It stands for State of Charge, the percentage remaining or 1-percentage consumed. Sort of a gas gauge for batteries.

 

[jadnashuanh]

While out driving, probably more of an issue in the winter, especially if the car is parked in a heated garage, I would expect the SOC to drop just from the fact it moved into a much colder environment, even without actually moving very far. Those in Europe have had an opportunity to run their vehicles through a winter, cold weather trial. How much different has your SOC been between winter and this summer? Might give us new owners a heads up for the coming, colder months.

 

[Boatguy]

The interesting thing about this thread is that everyone wants to have more data so they can second guess the guess-o-meter. Did BMW get the algorithms for the guess-o-meter so wrong that any of us could do a better job in our heads? It's possible that they did, but not all that likely.

It's important to understand that batteries are not digital devices, they are chemical devices. They are definitely non-linear in both charge and discharge rates. Lithium Ion in particular has a wicked discharge curve wherein their voltage falls quite steeply at lower states of charge, compared to lead acid variants (liquid, gel, AGM, etc.) that have a more linear voltage / SOC curve. The batteries won't deliver a constant voltage as they discharge and at some point the voltage is too low to be used by the drive motor, even though there is in theory remaining capacity.

I lived on a boat for 4 1/2 years with all systems (refrigerators, freezers, lighting, communications, etc.) fed by a large 24v battery bank (2,000 lbs). Rule of thumb for many was to discharge to 50% SOC before charging. I took mine down to 40% routinely, but at 20% the voltage would be insufficient to power some of the devices. Even a momentary very high discharge rate (>200a) could drag the voltage down low enough to cause the inverter to shut down. Granted they were not lithium ion which does behave a little differently, but the principals are the same.

My suggestion is to give BMW a little credit on the guess-o-meter and question whether we each know enough about the i3 systems, and these particular batteries, to do a better job of predicting available range. It's not a linear extrapolation of SOC.

 

[kevinb61]

My suggestion is to give BMW a little credit on the guess-o-meter and question whether we each know enough about the i3 systems, and these particular batteries, to do a better job of predicting available range. It's not a linear extrapolation of SOC.

For me personally, the mileage "meter" does exactly what I want it to do. Gives me a good estimation of how many miles I can drive (and in 2000 miles, so far it's been very good at estimating). Knowing for instance 36% SOC for me is useless. What I want to know is how many miles I can go (along with the "gas" meter that we already have), because I know how much farther I need to go.

As long as it's an "additional" option for the display...great.

 

[Zzzoom3]

Did BMW get the algorithms for the guess-o-meter so bad that any of us could do a better job in our heads? It's possible that they did, but not all that likely.

Boatguy, I have to say that they have gotten it wrong. They've gotten many things right and I love the car but the range estimate algorithm is honked up. Just observe what it does and you'll see what I mean.

Today, I left my house with a full, preconditioned charge. I put the car in ECO PRO. The bars were full, the range read 88 miles. I started driving. In less than 1 minute, I watched the range readout change from 88 to 71 right in front of my eyes. The blue bars remained full. How do you explain that? I can't

 

[kevinb61]

Did BMW get the algorithms for the guess-o-meter so bad that any of us could do a better job in our heads? It's possible that they did, but not all that likely.

Boatguy, I have to say that they have gotten it wrong. They've gotten many things right and I love the car but the range estimate algorithm is honked up. Just observe what it does and you'll see what I mean.

Today, I left my house with a full, preconditioned charge. I put the car in ECO PRO. The bars were full, the range read 88 miles. I started driving. In less than 1 minute, I watched the range readout change from 88 to 71 right in front of my eyes. The blue bars remained full. How do you explain that? I can't

I've seen that today myself. I was tooling along at 65 mph in ECO PRO and it was telling me "x" amount of miles (I think it was around 60 left). Then I got pissed at somebody who cut me off, and started doing 78+ to pass him, and kept doing that speed to pass an upcoming logging truck. By the time I was done, and back down to my original speed, my distance remaining was like 30 miles. After a minute (or two, or three, can't remember). it went back to the original estimates (albeit with a mile or two missing now!). Obviously it's algorithm has to take into account current power/speed/accessories/etc., and updates every so many "x" minutes.

Personally, I have seen it estimate between 91 and 75 before I leave the driveway. It always settles down for me within the first mile.

 

[jadnashuanh]

It seems that the indication takes your current use and extrapolates with some hysteresis built in. Then, not knowing how you'll drive, how much regen you'll be able to achieve and how heavy your foot is, just like when driving an ICE, the estimates are just that, an estimate. My GT has a miles to empty, but that only works well at steady speeds. It might say 500-miles after completing a long highway trip, but now that I'm home doing stop and go, it might really only get 300-miles on the same tank. At a steady state run on flat ground, it's probably perfect. Some people can't drive at a steady rate and even with nobody around, they may waffle 10-15mph as they drive. Some haul ass uphill, and some crawl, then switch on the way back down. A simple stop could easily affect the overall range available, especially if you used the brakes verses regen to slow down. I haven't driven the car long enough to get a good feel for how often it updates the distance calculation, but I have seen it only drop a couple of miles after going 7-10 once I was able to get onto an open road without having to stop and go.

Basically, keep the charge/discharge from getting way to the right, and don't' use the brakes, and you'll go much further than if you peg that meter to the right all of the time. The car isn't omniscient...it can only go on history, and if yours isn't consistent, your results will vary. The EPA rating is likely pretty close.

 

[Boatguy]

Did BMW get the algorithms for the guess-o-meter so bad that any of us could do a better job in our heads? It's possible that they did, but not all that likely.

Boatguy, I have to say that they have gotten it wrong. They've gotten many things right and I love the car but the range estimate algorithm is honked up. Just observe what it does and you'll see what I mean.

Today, I left my house with a full, preconditioned charge. I put the car in ECO PRO. The bars were full, the range read 88 miles. I started driving. In less than 1 minute, I watched the range readout change from 88 to 71 right in front of my eyes. The blue bars remained full. How do you explain that? I can't

I'm just suggesting it's a much more difficult problem than predicting range in an ICE vehicle.

The more relevant question is what raw data would you, or others, like to see, and how will you process it to produce a more accurate range forecast? If it can be done I certainly want to support it and take advantage of the improvement.

 

[Zzzoom3]

The more relevant question is what raw data would you, or others, like to see, and how will you process it to produce a more accurate range forecast? If it can be done I certainly want to support it and take advantage of the improvement.

I started this thread with exactly what you are asking. An energy used readout on the trip computer, onboard info, or eDrive display. Counts up from zero, accounts for regen, shows me exactly how much of my 18.8 kWh I have used since my last full charge.

Bottom line is I mostly ignore the range remaining indication next to the blue bars. I wish I could turn it off. However, I'm finding the Blue Bars are actually pretty reliable indicators. In my case, each bar gives me at least 20 miles. So I use that then look at my distance to go. I made a long trip today of almost 200 mi in my BEV and this method worked very well for me to know that I was able to reach each destination on my trip.

Once again, the Navigation color warnings (Red and Yellow) are mostly inaccurate because they use the calculated range value to key off. On my 1st leg, when the range went to 71 miles after 1 minute of driving, the NAV came up and told me I won't get there (74 miles away). I made it with 1 Bar remaining (20 miles by my estimate). Interestingly, the range readout said 15 mi.