Saturday, March 26, 2011

BMW i3: Light Weight Means Less Energy Storage Needed

The Power Electronics & Battery System of the i3's Drive System

The previous post here showed a video about CFRP, the material that will be used in the "Life Cell" of the 2013 BMW i3. The picture above is part of the other component of the cars unique LifeDrive architecture, the drive system. This is the energy storage and power electronics the car will employ. Suprisingly, it may only use a 16 kWh battery pack, exactly half the size of the pack in the upcoming BMW ActiveE, yet give the vehicle roughly the same range of the larger, heavier and less efficient ActiveE. However it is possible that the 16 kWh is the "usable" amount of energy which would mean the pack would be around 20 kWh. BMW hasn't announced the actual size, so this is really speculation at this point.

To put that accomplishment in even better perspective, the battery is only about 45% of the size of the battery pack currently in the MINI-E's yet the car is bigger, has two more seats, much more storage space and is expected to offer the same driving range.

The batteries used will be the same that are in the BMW ActiveE, which will launch as a trial lease program this fall. They are newly developed Lithium-ion cells which will be using a nickel-manganese-cobalt chemistry made by SB-Limotive. SB-Limotive is a joint venture of Korean conglomerate Samsung and German parts giant Bosch. The ActiveE will use 192 cells in 25 modules in three separate battery blocks as opposed the the picture above where the i3's batteries are all located in one enclosure, a result of the car being a purpose-built EV and not a retrofitted ICE platform like the ActiveE. It's been rumored the i3 may use only 96 cells, in 48 smaller modules(only 2 cells per module) packed in rows under the Life Cell driving compartment and be thermally conditioned.

The end result means two main things. The battery is usually the most expensive part of an EV, and since the battery pack will be half the size of the ActiveE, it will cost significantly less to manufacturer, helping to keep the selling price of the i3 to a reasonable point. Secondly, less batteries means less weight and helps to further increase efficiency.

Complete Battery & Drive System of the 2013 BMW i3
Of course, none of this information has been "officially" released by BMW so it is speculation on my part. However, since it has been "reported" and "rumored" by many different media outlets I think it's safe to assume it is mostly accurate. The only question I have is whether the 16 kWh is the total pack or the usable amount which is usually about 80% of the packs total energy storage capacity.


  1. e-mobility has great opportunity and promise. BMW is taking a great step in advancement. The extensive use of carbon will begin to be common in the future. I think the i3 will be very good if price can be controlled perhaps even sold at loss off the start to gain traction. High efficiency must also offer enjoyable driving experience too

  2. Yes the battery cost has been reduced, but the CFRP body will drive the price up significantly. This car has to sell under $45,000 before any rebates or incentives if it has a chance to sell in any significant numbers.

  3. I have heard rumors of a ~1500 lb weight (maybe that was without the batteries) for the i3. Exciting, if true. As a teenager during the first gas crisis, I turned in my 5,000lb Ford wagon on a 1,100lb Honda car. Best thing that ever happened to me. Mileage went from 11 to 45 mpg, tires went from $90 to $25. Saved on insurance and maintenance, with a healthy increase in the fun factor to boot. Only by experiencing the contrast do you realize what is possible, and what is unnecessary. Weight is the enemy of efficiency, of agility. Lightness, the feel of performance. If it weren’t for physics, people would mistake light weight for magic. Waiting to see BMW invoke the magic.

  4. Anon: Great story! As for total weight, I don't really think it's possible to get as low as 1,500lbs with the battery pack (probably weighs about 350lbs by itself and also the safety regulations. Back in the 70's it was a lot easier to make light weight cars, the OEM's just didn't want to. Then came the stricter safety regs in the late 80's and it became a lot more difficult. I owned a 1986 CRX si that weighed 1,800lbs by 1990, the exact same car weighed 2,184lbs, just about entirely because of the new requirements.
    As for the i3, I have heard 2,100lbs to 2,300lbs tossed around, with slightly lighter for the European version that has less safety regulation. It will definitely be one of the lightest cars on the road.

  5. Nice pictures. Have you seen this in person?

  6. The battery is the component that determines the high cost of electric vehicles. Use in the new electric models of BMWi3 batteries smaller entail costs more affordable and a lower weight will achieve greater efficiency from the vehicle. All this information are really useful. Congratulations for the blog!