Ebikes and regenerative braking

One of the most common questions I get from people first encountering an electric-assist bike is “Does it charge while you pedal?” or “Does it have regenerative braking?”. This question shows me what a great marketing campaign Toyota and others have with respect to their hybrid cars. We hear “electric vehicle” and think “regenerative braking”. Or more unconsciouly, “free energy”. Well, unfortunately, you can’t get something for nothing in the energy world (at least not YET).

Today’s video addresses this most common question and what I tell people who ask it.

Two links to detailed analysis of Regenerative Braking (equations and calculations included – don’t say I didn’t warn you!)

http://www.ecospeed.com/regenbraking.pdf

http://www.ativsolutions.com/cblog/index.php?/archives/24-Regenerative-Braking.html

(below is a brief summary of the video)

Regenerative braking captures energy from momentum when you slow down. Momentum is a function of the speed you are going and the amount of mass(wieght) of the object. This is easy to relate to – a small ball thrown at you slowly is not going to hurt your hand when you catch it. Nether is a large, lightweight beach ball. But a large heavy ball or a ball moving fast at you might cause you to step out of the way.

In the vehicle world, a car is heavy and generally moves fast, so looses a lot of energy when is slows down. A bike is lightweight and generally moving much slower, so there is not as much energy to be lost (or gained).

In addition, bicyclists are very good at using their momentum when they ride. When you come to a stop sign, you probably slow down, but only as much as necessary to make sure it’s safe to cross. When you cruise down a hill, you get up speed that helps take you up the next hill. If you are spending this momentum energy to charge your battery, well then you’re not using it to get going again on the other side of the intersection or up the hill. Given that any form of energy transfer has some associated losses, it’s probably better to maintain your momentum for that uphill.

The other common question I get is “does the battery charge as you pedal?” While this seems like a great idea, what that means is that your leg power is now being used to charge a battery rather than make your bike go faster in the forward direction. i.e. it feels like pedaling with the brakes on. Now most people want biking to be easier, not harder. So they’d rather plug the battery in and use the 3-5 cents of energy to charge it up.

——

So there you go! Please comment below. And remember to join or Facebook page or sign up (on the upper right) for our email list to stay in touch!

-Elise

Go By Bike is a daily video series that talks about how to be green by riding more and using your car less, including electric bikes, electric kits, cargo bikes, bike safety, and getting motivated to bike

If you like this video, please  digg it, stumble upon it, tweet about it or post it to delicious or facebook using one of the links below