|The 650cc twin cylinder engine used in the i3 is borrowed from BMW's Motorrad division and modified for the REx|
From the first word that the North American version of the i3 REx would have restrictions not found on its European counterpart, i3 enthusiasts and customers in the US and Canada have wondered how well it would work under strenuous driving conditions.
In fact, it is by far the topic I now get the most correspondence over. I have probably received over 100 emails through this blog from followers that want to know how well the range extender works and how capable it is. People want to know things like what speed the car can maintain in charge sustaining mode and for how many miles can the car maintain highway speeds on a certain percentage upgrade, and so on. I even have had people ask me if I could conduct specific tests with my car to confirm it can do what they need it to. The reason being is the 34hp REx engine can only deliver about 25kWs (although some reports say BMW upped it to 28kWs) of power. That is plenty of power for nearly all normal driving needs, but not enough for continued high speed or long upgrade driving. The problem then arises if you continue to consume more energy than the REx can deliver.
The root of the problem reverts back to BMW's desire to have the i3 REx certified a BEVx vehicle by the California Air Resource Board. This allows BMW to get the most ZEV credits per vehicle, and also allows the i3 REx to qualify for other perks, like sales tax exemption in New Jersey and Washington State. It also allows the owner to get the full $2,500 California CVRP rebate, unlike all other PHEVs which only get $1,500. However this came with a cost, one that everybody with an i3 REx from every state has to endure. BMW had to restrict the REx use to comply with CARB's BEVx classification. The European i3 REx can be manually turned on any time the state of charge is lower than 75%. This is called a Hold Mode and allows the driver to hold a higher state of charge and keep a higher battery buffer which they may need for continued strenuous driving conditions later in the journey. The North American version has no Hold Mode, and the range extender only comes on when the battery is reduced to a critically low 6.5%. For normal driving that is fine, but when really pressed for continued periods, the car cannot maintain full power.
|The European i3 REx has a Hold Mode which allows the driver to manually turn on the range extender if they need to. This feature is disabled for North America and is that is the root of the problem.|
All that said, I now have over 10,000 miles on my i3 REx and not once have I ever gone into reduced power mode, and I've actually tried to make it happen! The "problem" I'm having is the highways are relatively flat here in New Jersey and the REx can basically handle anything I give it. The times I have tried to make it happen the flow of traffic wasn't fast enough for me to maintain a speed of over 75mph for a long enough period. 75 mph on relatively flat ground seems to be the upper limit the REx can handle for continued driving. There is plenty of energy to go up and down the hills I routinely drive over, and also to have short bursts of power well past 80 mph for passing if needed in REx mode, so for me the car works perfectly and I really don't need a modification. However my friends in California and other areas of the country that have long, steep inclines to negotiate disagree, and want to see some kind of modification to allow the range extender to turn on at a higher state of charge so the vehicle has a larger electric buffer. In fact, there will soon be a two-part post here by an i3 Rex owner in California that has been obsessing a bit over this very topic. (well, I call it obsessing, he calls it studying - I'll let you be the judge when you read his post next week!)
So now that we understand the problem, what is the solution. Should BMW simply give up the value of the BEVx designation and allow the driver to initiate Hold Mode as the European i3 REx owners can? That isn't happening as far as I can tell. What I do believe is going to happen? Well for starters there will be software updates that include better indicators that the car may be headed to reduced power mode if you don't take action to alleviate it. Perhaps by slowing down 5-10 mph you can completely avoid having a problem at all. I also expect there will be a better state of charge display so the driver has more accurate display of how much power they have left. I would also love if BMW could add a display that would show the actual power draw you are using, so the driver can see if they are drawing more energy than the REx is producing. That would be an awesome tool for the driver to use in these situations and I do hope the BMW engineers consider adding it.. However I'm saving the best for last. It is my belief that BMW is working on an update that will indeed allow the range extender to turn on much earlier than the 6.5% threshold if the car determines you will need the extra power. This will work with the navigation system which accounts for topography. Once a destination is entered, the car will determine how early the REx will need to be turned on so it avoids reduced power while climbing an upgrade at the end of the journey.
|The i3's range extender sits next to the electric motor above the rear axle|