The Evelo Blog

Why Don’t More Bikes Use Regenerative Braking?

/ 5 Comments

In today’s installment of our 3 Minute Electric Bike Video Series, where we demystify electric bikes we are talking about why more electric bikes don’t offer regenerative braking on their bikes.

It is often referred to as “regen braking” for short and so upfront I want you to know that although it is definitely possible, it’s really not an efficient or practical and there’s a number reasons why.

Regenerative brakes require a Direct Drive Motor, which are a different type of motor than you see in typical electric bikes. These motors are very heavy in comparison to the other types of motors out there. Since electric bikes tend to be heavier than their traditional counterparts, this makes a difference in the distance you will be able to go on our charge.

In addition, Direct Drive Motors don’t offer a freewheeling mechanism that will insulate the rider from the motor. That’s fine as long as your battery has charge. Once your battery runs out of charge it means that as you pedal, not only do need to move yourself and the bike, but you also need to push against the resistance of the motor. It really makes for some hard going!

Over the course of a single charge, you are only realistically going to get back about 5% of the of the overall charge of the battery. So let’s say that you normally get 30 miles per charge on a ride, 5% of that is 1.5 miles! You have to question, is it really worth the additional weight and the resistance of pedaling a Direct Drive Motor to gain just a mile and a half?

The next problem with regenerative braking is that it causes significant heat when charging. When you are actually cruising downhill and pushing current back into the battery there is a lot of heat generated within the battery itself. Heat is not good for lithium batteries, it breaks down the overall lifecycle of the battery and it’s generally not good for it.

Finally, there are a lot of forces produced with Direct Drive Motors. Most electric bikes frames are made out of aluminum which can fatigue over time, especially the dropouts which are the places that the axle engages the frame.

Regenerative braking, even though it sounds great on paper and you think you could ride forever with it, the reality is it’s just not that practical.

I hope I’ve given you a good look at how regenerative breaking works and why it’s not practical for electric bikes!

5 responses to “Why Don’t More Bikes Use Regenerative Braking?

  1. Dear Bill,

    thank you for your article confirming what I am experiencing on my recently bought DirectPower Heinzmann ebike. It is actually very frustrating that you can’t really ride the bike w/o resistance w/o power or above 25 km/h, even if you disconnect the motor power leads! Do you know what exactly creates this resistance even when the motor is disconnected?

    Best regards,

    Stephan

    1. Hi Stephen,

      The motor has some level of resistance simply due to the magnetic field. If you had some other motor available, you could experiment and experience this yourself….One item many folks have is an electric drill…if you have one, unplug it, or remove the battery (for safety, and also to create a similar situation to when you pull the power leads off your bike.) Try to spin it by hand. If it moves at all, even a very aggressive turn will only yield about 1/2 of a rotation. Basically, motors don’t want to turn unless current is applied.

      I hope this helps explain a bit more!

      1. Thank you for your reply. I guess what could be the next generation of DirectDrive motors is a mechanism that retracts the coils from the spinning permanent magnets or include additional switching semiconductors that disconnect the coils when no power is applied. On any dynamo there is a minimal resistance due to eddy current braking, but not to the extent I am experiencing! I wrote several emails to the manufacturer but never received a response, I guess it’s to no interest to them!

  2. Hey – this is the kind of arguments that makes poor marketing. Moreover, the example given above is really not suitable. Do you know the electric drill’s cheap motor has carbons pushing against the collector that produces friction and thus dissipate energy?
    There must be a way, even if it requires redesigning the motor/gen from first principles to have decent efficiency from the generator/motor combo while regenerating. The argument of the battery charge cycle is a myth. Battery technology today assimilates fast charging without problems. Look at the charging pace of a Tesla or “lowly” Anker PowerCore+ packs.
    I am sorry, Evelo – you have to do better.

  3. If anything said above was correct, Prius and Tesla would not be selling cars. And take your drill apart, the gears will self explain why you can’t spin it by hand…
    Maybe the manufactures need to put the horse in front of the cart.

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