There’s a well-worn bike path near my home in San Francisco called “The Wiggle.” It’s a meandering route that zigzags from Market Street up to the Panhandle, marking the lowest incline option for westward-bound cyclists. In this city famous for both its breathtaking hills and tech-obsessed populace, I’m constantly reminded how well-suited this place is for the electric bicycle, as illustrated by the existence of everyday “life hacks” like this pathway.
The electric bicycle, or “eBike,” is a surprisingly amenable option for those who work and live in an urban environment and don’t want the hassle or costs of a car, but also want to minimize the manual effort required to pedal a bike. Here in the United States, eBikes command a hefty premium versus their all-mechanical counterparts and have mostly been relegated to a niche customer base. Though they are gaining recognition, eBikes are much more popular in Europe and Asia. In recent iterations of the annual Eurobike conference in southern Germany, almost every bike vendor showcased a small handful of new electric models. According to the Electric Bikes Worldwide Report, approximately 35-40 million units are sold in China annually and hundreds of millions of them are out on the roads every day.
One of the most critical components in a successful eBike design is the battery pack. Older and low-end models were powered by clunky, heavy lead acid (PbA) packs, which are relatively cheap and easy to use in designs. Unfortunately, these are physically large and heavy — imagine lugging one up several flights of stairs to recharge every night! That wouldn’t be your only annoyance – your battery would basically wear out after 18-24 months.
We have found the solution with Li-ion battery cells. Great strides have been made in recent years to maximize the power output and energy densities of these batteries. These are both key requirements in enabling a compact, but dynamic power plant that motor-driven eBikes demand, while cell prices continue to fall drastically each year.
Still, the design challenges of working with Li-ion are significant. Safety is paramount, given the aggressive environments where these eBikes operate, which spans everything from extreme cold in Northern Europe to sweltering heat in Southeast Asia. There are also a multitude of possible battery configurations. In China, most eBikes are built to a 48V specification whereas the majority of European models are 36V or 24V. Of course, cost and reliability are key. A customer shelling out a few thousand dollars on a premium light electric vehicle expects it to perform well from the first day to many seasons beyond.
We built the new bq76940 family with exactly this sort of flexibility, safety and performance in mind. Rather than create a single Li-ion monitor to handle the full 24-48V range, the bq76940 introduces the idea of an elegant scalable architecture. There are three devices that are intended to affordably address a specific subset of battery sizes, while still retaining a unified feature set and interface. For example, the bq76940 is intended for 48V; the bq76930, is its medium sized sibling that handles 36V and; the smallest in the family, the bq76920, targets 18V.
The bq76940 family also enables a heightened margin of safety for the eBike battery, via onboard detection circuitry that constantly and independently checks for potential electrical dangers like over-charging. When used in tandem with standard safety protocols that would be implemented on a separate micro-controller, it’s possible to ensure a level of protection that goes above and beyond most regulatory standards.
Lastly, the bq76940 does its part to help maximize an eBike’s performance, thanks to a suite of immediate and long-term functions. It has the intelligence to discern whether the eBike is being pushed to the limit (think of a cyclist riding up a particularly steep incline) or abusing the battery (shorting the pack terminals). And by cell conditioning across tens or hundreds of charge cycles, it can also help extend the lifespan of the battery pack.
The bq76940 and bq76930, both available now, are just the latest in our efforts to help designers in this exciting new light electric mobility space. Whether you’re embarking on a new eBike or eScooter project, take a look at our new monitors — you just might find they’ll give you that extra edge to help maximize your design impact. Are you designing an eBike or eScooter? I want to hear about it!
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