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Comment by Saris | Hacker News Reader

>I'm a bit surprised at the "pedaling charges the batteries" bullet point. That's extremely rare in the e-bike world.

For the most part it doesn't make much sense for most e-bike users that have power easily available, the time required to charge a battery is a lot (average person puts out about 100-150W) and the average e-bike battery is 500Wh or so, 4+ hours to charge it by pedaling.

A normal mid-drive has clutches specifically to prevent this from happening so you don't get drag from the motor while pedaling without the motor running.

In countries where power is not as readily available it makes a lot more sense.

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I would be more interested in a bike where braking charges the battery.

For commuting, every traffic light is wasted energy, and cycling on the flat doesn't need much once you're at speed. A commuter with regenerative braking could probably have a much smaller battery, making it lighter too.

Regen braking is a thing for ebikes. I can't speak to OEM ebikes, but check out grin at ebikes.ca. They offer all the parts.

There are some cool features too like setting a speed limit after which Regen activates, so coasting down a hill will recharge you and add resistance to keep you at a safe speed.

The caveat is it doesn't make sense on mid drives because they freewheel when coasting

A hub motor ebike can do this with the right controller, assuming the hub motor has no clutch in it.

But you don't gain much, there's not a lot of weight to slow down with an ebike so regen gives you very little back.

You do lose the ability to efficiently climb steep hills with a hub motor, and they add a ton of unsprung weight if you have rear suspension which ruins its performance, so if that's your kind of terrain they're a bad choice.

Would save on brake pads though.

> But you don't gain much, there's not a lot of weight to slow down with an ebike so regen gives you very little back.

But by the same token there's not a lot of weight to accelerate either, right? So while a moving bike has much less potential energy to recoup than a car, it needs much less to get back going again also.

So IMHO regen on a bike should be as useful as it is on a car, no?

>But by the same token there's not a lot of weight to accelerate either, right?

Right, most of the energy is used pushing air out of the way, which you don't get back from regen. Say you ride half a mile before stopping, the time to accelerate to 20mph is pretty small compared to the time you spend cruising at 20mph pushing all that air out of the way.

> Right, most of the energy is used pushing air out of the way

That's certainly the case once you're at speed (above 20km/hr is about the point where more energy is spent overcoming wind resistenace iirc). But I'm taking about taking off from the lights. Even to get you to 10 km/hr for free (or cheap) would be a bit boost for a commuter.

A friend of mine has an e-bike with regenerative braking using a rear hub motor.

It seems to have a recovery efficiency of about one third.

We once went up about 1200m in altitude difference, where it was completely empty. After having gone down again, it had recharged enough to work normally for the remaining 20km of our trip, driving in flat terrain.

> cycling on the flat doesn't need much once you're at speed

You need around 200 watt to hold 25kmph on a flat road without wind with a standard bicycle like the one in the video.

With moderate wind, it is between 350 and 400 watt.

> You need around 200 watt to hold 25kmph on a flat road

Most non-lycra cyclists I've observed seem to cruise at around 20km/hr; my personal experience is that 20km/hr is pretty easy once you're moving; 25 is a noticable bit more work. Also, for commuting where there are traffic lights involved (based on my own experience), you rarely have a chance to do more than 20, and if you do, any time advantage is killed by the next red light.

You might be interested in this: https://www.youtube.com/watch?v=bLu6H-K4L2Y

The video is long and the innovation is subtle, but once you understand it it's like a lightbulb moment - IMHO a really brilliant example of elegant engineering, and designed by someone who had never ridden an ebike.

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