How CARB’s Rules May Restrict the Operation of the BMW i3 Range Extender


View From Behind

View From Behind i3 Sans Body

According to the UK price list for the i3 the range extender will automatically come on when the state of charge falls to 18%. I’ve been guessing that will happen at about 20% so I was pretty close. It will then attempt to maintain the battery SOC at 18%, while allowing the car to continue to drive along relatively uninhibited. The only time there will be a problem is if your driving is demanding a high level of energy output for a prolonged period of time.

Tom Moloughney at Live i3 Reveal: Photo Credit - Hugo Becker

Tom Moloughney at Live i3 Reveal: Photo Credit – Hugo Becker

For instance, driving along at 60 mph on a flat surface you may only need 10 or 11 kW’s to sustain the charge because that’s about all you’ll be consuming. That’s no problem for the REx because it can provide up to 25kW’s of constant supply. However if you need to drive up a steep grade at highway speeds for 10 continuous miles or so you may have a problem because the car will likely draw more than 25kW’s under these strenuous conditions. The 18% buffer combined with the REx pumping out it’s maximum output will allow the drive to continue for quite some time, but after a while of using more energy then it is capable of replacing, it will eventually need to reduce power output.

What happens then is unclear but I would imagine the car would slow down to a speed it can maintain power for. Again, this should not happen on flat land, as the energy consumption should be able to be replace by the REx. It will also have plenty of power for most hills and bursts of speed when needed. I’m talking about long, extended drives up steep inclines that happen at the end of your journey after you’ve already depleted the battery and the range extender has come on.

Personally, I have a situation where this could come into play myself. My in laws live in Vermont and the last 10 to 15 miles to their house is mostly uphill. I’d already have the range extender on by the time I get to this final leg of the journey so I’m curious if I’ll have a problem making it. I could stop along the way and charge for a while if necessary but I’d prefer just driving nonstop. After all, that’s why I’d get the range extender; so I don’t have to stop to charge along the way of a trip.

Chevy Volt Tackling a Mountain

Chevy Volt Tackling a Mountain

So what can be done to alleviate this? The Chevy Volt has a “Hold Mode” that the driver can initiate at any time. This manually turns on the range extender without waiting for it to automatically turn on when the battery is depleted and holds the battery state of charge at the level it was when you turned it on. Sounds like a great idea, so is BMW going to do the same thing?

Yes, and maybe no. If you look at page 8 of the UK price list that I provided the link to above, you’ll see it says: “Manually activated when the vehicle is below 80%”. Brilliant! So, if you buy an i3 in the UK, you can turn on the range extender once the state of charge drops below 80%. Therefore, if you know you’ll be driving up a long, steep hill or mountain at the end of your journey, you can turn on the range extender and “hold” the charge, so when you arrive at the mountain you’ll have plenty of charge to complete the journey. Perfect, so US customers will get this feature also, right? Unfortunately, maybe not.

See Chevy Volt's "Hold" Mode?

See Chevy Volt’s “Hold” Mode?

California is the #1 market for electric vehicles in the US and one of the reasons they sell so well there is zero emission vehicles are allowed carpool lane access regardless of the amount of passengers. This is a highly sought after perk in California and cars that qualify for it usually sell very well. The all electric i3 will definitely qualify, but the under the new more strict rules for PHEV’s, an EV with a range extender will only qualify for the valuable HOV access sticker if it operates this way: “engine operation cannot occur until the battery charge has been depleted to the charge-sustaining lower limit”. So that means the range extender cannot be manually turned on at 80% and still qualify for HOV access in California.

A Closer Look At BMW's 34 hp Extended Range Generator's Location Behind The Rear Seats

A Closer Look At BMW’s 34 hp Extended Range Generator’s Location Behind The Rear Seats

It’s clear to me BMW will make the i3 conform with CARB’s rules so it will have HOV access is California, but will they do this to all the US cars, or just for the ones shipped to California? I don’t have the answer. I tried to get clarity on this at the i3 Premier but nobody wanted to confirm it one way or the other.

Hopefully, that means a decision hasn’t been made on this yet and there is hope for the rest of us. If so, and the powers to be at BMW find their way to read this post, please consider offering the same ability to manually turn on the REx for US customers outside of California. The vast majority of customers in the US don’t need carpool access, why should they have their range extender neutered so people in California can have it? This is a simple software change. It’s available in the UK and probably for the rest of Europe so it’s not like it will cost BMW anything to develop.

Let’s hope BMW does the right thing and makes this feature available to US customers outside of California. It really makes the range extender a more useful asset, this shouldn’t be a hard decision to make.

Editor’s Note: This post first appeared on Tom’s BMW i3 blog.  Check it out by clicking here.

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36 Comments on "How CARB’s Rules May Restrict the Operation of the BMW i3 Range Extender"

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“Again, this should not happen on flat land, as the energy consumption should be able to be replace by the REx.”

I pull 25kW going 75mph on flat land in my Volt, so speed will also affect how long you can go before turtle mode, (also if a heater is being used which can pull up to 6kW)

We have to assume that the i3 will require less power, as its considerably lighter than the Volt…Weight is an enemy…and the i3 has an optional heating system that is claimed to take a lot less juice…It should be standard though…not optional

At 75mph steady-state, weight is not a concern (maybe slight more tire resistance), but wind force is huge. What is the Cd and Cda of the BMW i3? It looks less “slick” than the Volt, but I don’t know the #’s

The i3 has aerodynamics identical with the 2011/2012 LEAF, which had a Cd of 0.29. The width and height are very close, although the i3 could have more more aero wheels with lower rolling resistance. The LEAF owner community amassed an impressive collection of real-world data, and I’ve listed a few representative mph/kW value pairs below. They were derived from Tony Williams’
range chart:

mph | kW
—– | —-
35 | 5.6
40 | 6.8
45 | 8.7
50 | 10.9
55 | 12.8
60 | 15.4
65 | 18.0
70 | 21.2
75 | 25.0

This data would indicate that the i3 should be capable of traveling up to 75 mph on flat terrain, even if the battery has been depleted.

Cars with only enough power for 75 mph top speed are frankly not acceptable to most US buyers. There will be exceptions, and this will be fine for city driving on surface streets, but that is not enough for 2013. It has been many decades since this level of performance was accepted, most examples are pre-WWII.

I also find the 2 gallon gas tank annoyingly limiting as well. The Chevrolet Volt is vastly superior to the i3 in both gas power and range, although the i3 does have more EV range.


That said, I think it’s worth noting that the top speed of the vehicle is 93 mph. The speed will likely not be limited to 75 mph. I quoted this figure to give an idea of how much energy the REx can supply by itself. As long as the battery has some energy left, it will be able to provide supplementary power and this type of limitation should not apply.

BMW documentation offers an idea of the remaining charge in the battery: it’s 18% or about 3.5 kWh. This should be enough to lift the car 3,000 feet. It would also be enough to allow it to drive at the speed limit for about 15 minutes. That’s substantial, especially in urban environments, where the car is supposedly going to be used.

Remember, that in REx mode, the combustion engine will recharge the battery in all but the most strenuous circumstances. This reserve can then help provide the extra power needed when you need to accelerate on the freeway, for example. I would take all this information with a grain of salt and defer judgement until more information is known and real-world test drives have taken place.

Do we know how much of the battery BMW is using?

“engine operation cannot occur until the battery charge has been depleted to the charge-sustaining lower limit”

What is this rule supposed to do? What is the logic behind it? If they were attempting to make sure people were plugging in their PHEV or EREV instead of burning gasoline, I doubt this rule would have any effect. In fact it might have the opposite effect.

CARB sure does have some wacky rules.

It’s to differentiate between a small range extender designed for very limited use and the engine in a PHEV which is specifically designed to be used on long trips.

What this article doesn’t make clear (maybe deliberately for journalistic effect) is the issue is only whether it gets the _white_ HOV sticker instead of the _green_ HOV sticker for PHEVs. The white sticker would likely last longer than the green one.

There are additional conditions on a “BEVx”, like 80+ mile AER and extender range no more than the AER (which this article also doesn’t mention). A BEV with a small, clean, range-anxiety reliever

Fortunately or not CARB rules do not apply to most of the US. So unlike GM, BWM can probably sell the i3 without a Hold mode in CA and with one in the rest of the US.

The scenario that Tom talks about though is resolved in the Volt not with the Hold mode, but rather with the Mountain mode, which starts the generator to keep the SoC at 40%

It’s funny how BMW is rediscovering the wheel and presenting it as if they figured it out first.

Yes, this is what the world needed, an expensive Volt.

The Volt did start something. The ELR, i3 ReX, i8, etc show that the Volt was a good idea.

Rules likely apply to Part 177 ZEV states in addition to California (New York, Oregon, & ~7 others) through 2017 model year.

Anyway, probably doesn’t matter after January 1st, 2015, unless Californa extends the HOV incentive.

At some point too many rules become a disincentive to further ZEV adoption. Own, drive PEV, (ZEV) because its an all around great V.

There is a difference between manually turning on the RE below 80% and hold mode. Hold mode can be selected at any SOC. So sounds like for sure we will not have Hold mode in the i3. The 80% turn on point for the ICE is more like the Volts Mountain Mode. Approximately the same kwh’s will be held in reserve.

Hard to say what Carb will do.

but anyway. Good article Tom M.

Sounds like you have decided on the RE so I lose my bet.

Thanks for writing this, Tom. I am now a little less confused how CARB and the i3 play together. Here’s to hoping that the rest of the US won’t get a “neutered” range extender for California’s sake.

I suspect that the limitation regarding when the ReX can be turned on will be configurable by a service technician. This is similar to BMW’s stance on Stop-Start. From the factory, it defaults to ON each time you start the car. However, you can ask the dealer to turn it off so your choice is persistent. They could do the same, but have guidelines as to which vehicles are eligible for the change. For example, they may decline the change if the vehicle has White HOV stickers.