Can Electric Bikes Charge When You Pedal?
Coming out of electric cars and hybrid vehicles, you might wonder: what about electric bikes? Can electric bikes charge when you pedal?
The short answer: yes, a rare assortment of electric bikes happen to be able to recharge the battery while braking (not pedaling), and this feature is called regenerative braking. Although the concept looks good on paper, the technology is still in its early stages, where the overall efficiency is around 5-10%.
Depending on the circumstances, this might help you extend the range on your bicycle, but it’s highly unlikely and not a sustainable solution for most consumers. That said, if you are interested in the technology and want to invest in an Electric bike with regenerative braking, bear with me as I explore several related topics, such as:
- How Electric Bikes Recharge the Battery using Regenerative Braking
- Pros and Cons of a Regenerative Braking System on an Electric Bike
- Common Questions Regarding Electric Bikes with this Technology
So let’s convert that chemical energy into mechanical energy and roll in.
How Electric Bikes Charge The Battery Using Regenerative Braking
Understanding the fundamentals of how the regenerative braking system operates is pretty simple: it transfers the momentum of your wheels to the electric motor, which, when rotating in the reverse mode, generates electricity instead of consuming it. This electrical energy is redirected to charge the battery.
In an electric bike (or other electric vehicles) with a regenerative braking system, there are two methods for reducing the speed: friction brakes (using the conventional brake pads or disc brakes) and the electric motor’s regenerative brakes.
Whenever the rider eases into the brakes when climbing down hilly terrain or coming to a gradual stop at a traffic light, the controller on the electric bike commands the motor to stop forward motion and use that built-up momentum to keep the motor running backward.
When the motor is running backward, it generates electricity (instead of consuming), and now this electrical power can be used to charge the battery. When the rider releases the brakes, the motor disables this “reverse mode” and propels the bike forward. (Standard bike/E-bike operation.)
When the bike is braking using regenerative power, it cannot slow down immediately; hence, when the rider needs to make an emergency stop (by instantly pulling on the brake handles with greater force), the controller enables the friction brakes instead. (Check out this video to learn more.)
Therefore, a regenerative system requires complex electrical and mechanical components, from the brake handles to the electric motor. It is why regenerative braking systems are expensive and not commonplace in most electric bikes.
How Efficient is a Typical Regenerative Braking System?
For our favorite brand of electric cars: Teslas, the efficiency of its regenerative capabilities are around 10-20% depending on the terrain; hence, you would be able to get 20% more range on your Tesla under the right conditions.
Unfortunately, for E-bikes, the numbers are not that favorable; we are looking at 5-10% efficiency even under the best of conditions. So if you ride for 10 miles or so, you might only be able to gain an extra mile thanks to the regenerative braking system. (Provided you encounter more hilly terrain with lots of opportunities to use your regenerative brakes.)
So in the case of E-bikes, the kinetic energy produced by the drive wheel and used to generate electricity may not be worth the hefty price tag found in most “regen” E-bikes.
Benefits of Regenerative Braking
When considering the advantages of regenerative technology, there are two significant advantages: increased range and less wear on the brake pads.
Improved Range
A regenerative electric bike is not just a marketing tool or gimmick for various brands and manufacturers to flaunt around. Despite its meager returns, an E-bike with a regenerative braking system will deliver a better range than a traditional electric bicycle.
So depending on the distance, terrain which wouldn’t require more braking (with higher torque), and your riding style, you might be able to make more use of the regenerative system than the average E-cyclist.
Less Brake Wear
Since a regenerative braking system would transfer the braking torque to the motor, (using “engine braking”), your E-bike will seldom use the friction brakes (conventional disc or V types) to slow down. It minimizes the wear and tear on your traditional braking system and increases the lifespan compared to regular E-bikes and pedal-powered bicycles.
However, your riding style will mostly dictate how this happens. If you make slow and gradual decelerations, where the braking torque is just enough for the regen system to kick in without skipping over to the friction brakes, you will rarely wear down the friction brakes in your E-bike. (Especially useful for cargo E-bikes which would carry a heavy load and require constant deceleration.)
So in response to the common question: will regenerative braking damage my brakes? No.
Drawbacks of Regenerative Braking
Unfortunately, there are major drawbacks when considering a regenerative braking system, and this mostly amounts to the complexity of the mechanism, cost, the lower efficiency (which we already talked about), and the effect on the other components such as the brakes, tires and electrical system.
Negative Torque Distribution
When the regenerative brakes are applied, it is applied on the drive wheel (in most electric bikes, it’s the rear wheel). While the regen brakes are working on the rear wheel and the front wheel is spinning freely, it can create a situation called negative torque distribution wherein the tires can skid.
Thankfully, this only occurs when the E-bike uses a front hub motor instead of a rear hub; hence many E-bikes with regenerative braking only come in rear hub drives.
Complexity and Cost
As I mentioned, the regen braking mechanism is very complicated. Therefore, integrating such a system into a compact vehicle such as an electric bicycle is no small feat. The extra materials and manufacturing processes will drive up the cost, transferring these to the user, who now has to pay double or triple the price of a regular E-bike.
Weight
The regenerative mechanism will become a burden when you have to pedal on your own after the battery capacity of your E-bike’s battery pack has depleted. In most electric bikes, the motor will always be connected to the drivetrain: trying to generate electricity. So instead of becoming a means of recouping wasted power, it becomes a glorified dynamo that’s making you pedal twice as hard.
High Temperatures
The direct drive rear hub motors used for regen braking tend to generate a lot of heat, especially around the electrical system (which comprises the motor, controller, and the E-bike battery). Unless the system is designed to accommodate this extra heat, it will compromise the entire system, especially the E-bike batteries, which need specific temperature ranges to charge/discharge efficiently.
The Type of Electric Bike Motor that Works Best
Regenerative electric bicycles will not come with a mid-drive motor because you can’t rotate a mid-drive motor in reverse (or transfer the wheel’s momentum) to generate electricity. The only solution is to go with hub drives, specifically direct drive motors on the rear wheel.
Why Not Geared Hub Drives?
In the case of geared hub drives, there are a lot of moving parts, such as the planetary gear system and the high RPM motor. So when trying to reverse the motor (as a means of generating electricity), a geared hub drive will not even come close to the efficiencies of direct drive hub motors.
Since a geared hub drive operates at a much higher RPM (hence the need for gears), the regen torque provided by the braking momentum will not be enough to generate a significant amount of electricity. Also, you would have to reverse the motion of the planetary gear system, which is a nightmare of its own.
Why Not Front Hub Motors?
Apart from a direct drive motor, you also need it to be a rear hub motor instead of a front hub to avoid the negative torque distribution issue I mentioned above. Even in a regular electric bicycle, a front hub drive can become unstable when steering at higher speeds, and when you factor in the torque issue, there’s a greater chance of skidding.
Common Questions Regarding Regenerative Braking in E-bikes
Can you Top Up an Electric Bike Battery When You Pedal?
Unfortunately, with the current efficiency levels of regenerative braking systems, you would need to pedal (and brake) the entire day to top up your E-bike battery. It won’t be fun since you will have to pedal twice as hard to reach your destination and make sure the motor keeps generating enough current.
Can an Electric Bike Recharge the Battery During Throttle Mode?
No, electric bikes with a throttle mode do not have any other mechanisms to recoup the momentum from the bicycle wheels. The only solution is regenerative braking, and as you’ve probably figured out by now: it’s not the most ideal.
What are Some Actual Electric Bikes With Regenerative Braking
Here’s a list of several manufacturers who currently have Regenerative E-bikes out on the market, do note, however, that these are expensive bikes.
Final Thoughts
Electric Bikes cannot generate power by your pedal force, but they can harvest the momentum from your brakes to generate extra energy using regenerative braking. Only 5-10% of energy can be typically captured via this mechanism; hence, it is not very efficient for the average E-cyclist.
Also, regen E-bikes are twice as expensive and have several other drawbacks, making them less ideal for various situations.
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