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| Donner Summit is the highest point along Interstate 80 in California at 7,228 feet elevation. |
Last week we heard from i3 REx owner John Higham in a post he wrote which detailed his thoughts on the i3s range extender restrictions for the North American market. John certainly didnt mince words and offered his reasoning why he believes the range extender on the i3 should have its artificial restrictions (which are in place to satisfy CARB), relaxed a bit. John also promised to do a road trip which would take him from the San Francisco Bay area up to the 7,228ft Donner Summit in Lake Tahoe and report on the range extenders performance under these strenuous conditions. Below are his findings.
SF Bay to Tahoe by the Numbers, Part 2
Nailed it. Well, nearly.
In Part 1 of this post about all things REx, I declared that a US spec BMW i3 REx could not make the popular weekend getaway of Lake Tahoe from the San Francisco Bay area without being speed limited within 15 miles of Sacramento. How speed limited depended on the slope of the road as you climbed east into th e mountains, but top speed would range from 40 to 55 MPH. The alternative was to fully charge in Sacramento before any significant climbing begins and then again in Colfax about halfway up the hill. This makes such a drive impractical.
I also declared th at a European spec’d i3 would make it no problem, so long as one kept the diminutive 1.9 gallon tank filled and the feature known as “Hold Mode†engaged. In fact, European cars have made similar drives into the Alps.
The basis of these declarations is simple physics. In Part 2 we test the physics from Part 1.Twice. First with a U.S. spec BMW i3 REx and then with a European spec i3 REx.
OK, I lied. I dont have a European spec i3. But I do have a US spec i3 that has been modified to behave like its schnitzel eating cousin.
I drive the BMW i3 from my home in Mountain View, California to Donner Memorial Park in Truckee. The state park is placed at one of the sites where the ill-fated Donner Party settled for the winter in 1846. The snow that winter was as high as the memorial behind the i3.
A Quick Summary of Part 1
The California Air Resources Board (CARB) developed a class of car called the Battery extended range Electric Vehicle (BEVx). Some say the BEVx was never intended to be a car with mass appeal that can be driven like any ICE-mobile. But I ask, why not? Actually, what I usually say is “Why the hell not!†while shouting and pounding the table with my fist. I digress.
I believe that the BEVx class of cars represents the bridge from plain ol Internal Comb ustion Engine (ICE) cars to pure electric that will finally allow the public to embrace EVs without looking back. Except.
There is one teensy exception and it is what engineers call a "corner case." In this situation the “corner case†refers to those people who require a car to maintain freeway speeds over sustained elevation gains. That’s what this post is all about -- to test how big that corner case actually is.
Californias San Francisco Bay Area lies at sea level and the drive east to Lake Tahoe follows the Sacramento river, never gaining significant altitude for about 50 to 100 miles, depending on ones starting location. Continuing east past the capital of Sacramento begins what is at first a gentle climb into Gold Country. Assuming the route is along I-80, the slope increases significantly past Gold Country until Donner Summit (elevation 7,228 feet) is reached 95 miles east of Sacramento.
The i3s APU is sized such that it can maintain freeway speeds, but not to maintain freeway speeds and simultaneously gain significant altitude. It’s simply not possible to drive from the SF Bay Area to Tahoe in a reasonable amount of time with the US spec’d i3. Of course if you have the patience to charge every 60 to 80 miles, you can drive your i3 from the Bay Area to Tahoe or anywhere else for that matter. But that is impractical, even with with so-called fast chargers.
Since this post comes in two parts, and the test drive to Tahoe also comes in two parts, potential for confusion exists when referring to them. Let’s dispatch any confusion and call the first test The Apple Pie Test and the second test The Lederhosen Test.
The purpose of these tests isn’t to prove you can drive an i3 to Tahoe by taking logical opportunities to charge. You can. It’s been done. The purpose is to prove the assertions made in Part 1. First, that the US spec’d i3 REx is hobbled as compared to its European counterpart and second (and more importantly) that an i3 REx is more than a great EV; it has potential to be the only car you need.
Oh yeah. No math in this post. I promise.
The Apple Pie Test
The Apple Pie Test is simple: try to “REx it†to Tahoe and see how far you get. (Oh, I’ve made REx a verb, but the Oxford dictionary hasnt caught up yet.) Since this is my test, I get to make up the rules. The rule is simply to take a BMW i3 as CARB intended it to be delivered to the public and drive it along I-80 until the car becomes speed limited, then compare the observed results with the predicted results from Part 1.
To do this test I left the Benicia, California, CCS fast-charger with 90% SOC and a predicted range of 60 miles. The drive toward the Tahoe region is essentially flat for about 63 miles along I-80, then the road climbs into the Sierra Nevada mountains. I planned this section of the drive to be all electric until such time I hit the foothills. The goal was to set the cruise control to the posted speed limit (65 MPH) and simply keep driving powered by the REx until the car became speed limited.
In Part 1 I calculated that the car would become speed limited at about 725 feet elevation gain and by using the elevation profile in Go ogle Earth, I estimated that would occur about 12 miles east of Sacramento.
The actual drive didn’t work out exactly like that, but close enough for the rough assumptions that were made. At first the speed limitation was subtle. I started to suspect the car was speed limited at around 800 feet elevation (750 gained), “flooring it" to coerce an increase from 65 MPH with the cruise control set, I achieved about 67 or 68 but no more. But by 950 feet elevation gain the effect was no longer subtle. Not only could I no longer keep pace with traffic, but was feeling very vulnerable and was searching for an exit in earnest. On some of the steeper portions of that section I was un der 55 MPH indicated with traffic whizzing past at 70 MPH and above.
The BMW i3 was clearly speed limited on this section of road after leaving Sacramento powered solely on the REx
This photo was snapped moments after the previous photo
Anyone who has owned a BMW for very long can tell you that the speedometers are optimistic by at least 5%, if not 7%. So, that 58 MPH in the photo is closer to an actual speed of 55 MPH. In Part 1 of this post I made a table of predicted top speed as a function of the grade of the road. Using the GPS coordinates of the road and Google Earth, I found the grade of the road at the precise point is 3%; the table from Part 1 predicts a top speed of 60 MPH on a 3% grade; close, but some refinement of that table is in order.
In summary, the Apple Pie Test demonstrated that all that analysis, the calculations, graphs and so forth from Part 1 were within the margin of error that could be expected for the rough assumptions that were made.
More importantly, It proves that you can’t just REx it to Lake Tahoe in an i3. Luckily, there is a CCS charger in Sacramento, so moments after the above photos were taken I turned around a nd headed straight for it. With the miracle of regeneration the i3 got its SOC back up to a respectable level and I REx’d it all the way back to that CCS charger with no issues.
Hold Mode and Coding
The Lederhosen Test requires the use of a feature known as “Hold Modeâ€, which is on all Euro-spec i3 equipped with the REx; perhaps even all such cars destined for anywhere in the world outside of North America. What Hold Mode does is engage the REx (or more specifically in CARB-speak the APU) to maintain the battery State of Charge (SOC). Sounds a bit boring and perhaps it is.
The fact of the matter is, US spec’d cars have Hold Mode; the car’s onboard intelligence switches it on automatically when the battery SOC reaches 6.5%. The European version of the car also will switch on Hold Mode automatically when the battery SOC reaches 6.5%, but the European version also allows the driver to manually engage Hold Mode whenever the battery SOC is 75% or less.
The difference in the US spec’d car and its European counterpart is perhaps subtle, but as we shall see, the difference means everything if you require a car to maintain freeways speeds and gain significant elevation simultaneously.
What is important here is to understand that the US-spec cars do in fact have the European-spec Hold Mode programmed into the car. The menu option that allows the driver to engage Hold Mode manually is simply hidden from the i3’s iDrive menu. For someone skilled in the seedy underbelly of the BMW tuner world known as “coding,†enabling this hidden feature in the iDrive menu is trivial. To be clear, this practice is most likely frowned upon by both BMW NA and CARB.
To satisfy scientific curiosity, I “coded†my i3 to enable Hold Mode, Euro-style. On to the Lederhosen Test! (click through this link to read about how to code your i3: Code your i3)
The Lederhosen Test
As noted in the last paragraph of the Apple Pie Test, as soon as I became speed-limited near Auburn, I turned around and returned to Sacramento and specifically to the CCS fast charger there. After plugging in and after i3’s SOC had reached 90%, I once again set out along the same route toward my final destination in Truckee, California, near Lake Tahoe. Hold Mode is only available if the SOC is 75% or less, so after leaving the CCS charger I drove the first 12 or 13 miles all electric.
The CCS fast-charger in Sacramento in Sacramento is at an elevation of 50 feet.
The only difference in the two drives was the SOC at the bottom of the hill and manually engaging Hold Mode. This simply means the REx was used in the Apple Pie Test to “hold†a 6.5% SOC but on the Lederhosen Test, it was used to “hold†a 75% SOC.
Engaging Hold Mode at 75%. Note there are 88 miles to my destination, with 39 miles of all-electric range available.
In Part 1 of this post I calculated that by engaging Hold Mode at 75% SOC the i3 should be able to climb essentially any mount ain pass in North America, so long as one keeps the gas tank filled. What isn’t visible in the photo above is that Donner Pass, a 7,228 foot climb, is between me and my destination; it is time to put my hypothesis from Part 1 to the test.
With Hold Mode engaged, as one drives the i3 the REx keeps the battery SOC constant at the level set. If driving conditions are such that the REx (due to its limited power output) cannot keep the battery SOC maintained, then energy from the battery makes up the difference and the battery SOC falls commensurately.
Soon after leaving the CCS charger in Sacramento and engaging Hold Mode at 75% SOC I found myself once again in Auburn near where I had turned around just 90 minutes earlier during the Apple Pie Test. It was time for a lunch stop.
As expected the battery SOC falls as elevation is gained
The photo above was taken at my lunch stop in Auburn. Note that the SOC has fallen 4% to 71% at 1210 feet elevation (1160 feet of gain). If I had stopped the car and let the REx run sufficiently long, the SOC would have returned to 75%. But that would have both taken time I didn’t want to spend and defeated the purpose of the Lederhosen Test. So, after a quick bite to eat I got back in the car and re-engaged Hold Mode at 71% SOC.
Leaving Auburn, I resumed toward my destination of Donner Memorial State Park 65 miles away in Truckee, California. The only thing between me and my destination was Donner Pass at 7228 feet, one more stop for gasoline, and the potential to run out of battery. But I had done my homework and was confident that I had plenty of energy left in the battery to complete my drive.
It was the perfect day for such a drive; the sky was a beautiful blue, the temperature was in the mid 70’s, the traffic light and SiriusXM’s Classic Vinyl accompanied me. During the drive I took pictures of the i3’s displays every 1,000 feet of elevation gain, but suffice it to say that the battery SOC slowly dropped in an expected and predictable fashion as I glided up the mountains slope. After 45 minutes or so I once again stopped to top off the fuel tank.
The i3’s other “fast charge†port. I don’t like to use this method of adding energy, but sometimes a guy’s gotta do what a guy’s gotta do.
The battery SOC has fallen from 75% to 54% after climbing 5300 feet.
After refueling, Donner Summit was less than 30 minutes away. I found myself so absorbed in monitoring the progress of the battery SOC prediction that I nearly blew past the sign marking the summit!
The i3, with Hold Mode engaged, used a mere 31% (75% at the bottom of the hill less 44% at the summit) of its SOC to gain nearly 7,200 feet of elevation. In simple terms, one can think of it as if the REx’s power output is used to propel the car forward, the battery’s power output is used to climb the hill.
