Toorbough ULL-Zeveigh said:
justin_le said:
What that means is that if you ran the hub motor so that it draws just enough power to overcome its internal drag so that it perfectly simulates a freewheeling setup, you would still end up with a significant net gain over a having no motor or regen at all, putting a net amount of energy into the battery pack and no extra drag on the bicycle
http://endless-sphere.com/forums/viewtopic.php?f=2&t=7891
Thanks for the informative correction.
My direct experience has only been with the kind of e-braking that engages whenever the throttle demand is less than the vehicle's road speed, and that kind is for the birds. No thanks. A bike that brakes whenever it's not being powered is just terrible, and that experience colored my impression of regen braking.
There are however situations where regen braking of any kind can't fulfill its promise (apart even from poor conversion efficiency, or problems with broken axles and damaged dropouts). For instance, when I lived in Seattle, my commute to work involved a 70 foot climb in the first quarter mile, then a 400 foot descent over the next mile and three quarters, through central city areas with lots of traffic lights. After that, there was a flat three mile stretch where pure freewheeling would have been a welcome feature. The stop-and-go descent would have been a great place to recover some significant juice for the battery, but without some sort of active battery protection it would have been very easy to stuff lots of coulombs into a battery that had already reached a fully charged state. In practice, relatively little of the descent would have been recoverable as battery charge, and there was not very much downhill to exploit on the return trip.
The e-bike I used most on that route had only the sort of passive regen braking that engaged progressively on fast downhills when the motor's back EMF exceeded the battery voltage. The amount of juice I recovered that way was never enough to cause an overcharge, as far as I could tell. It may have resulted in momentary charge rates greater than my batteries were designed for, though.
If I'd had smarter regen braking on that bike, it might only have cost me the difference between a regen-enabled controller and a basic controller, plus a braking switch. But it would not have yielded a significant increase in range or much reduction in depth of discharge on my usual route. It would only have spared me some wear and tear on the mechanical brakes, and that only when the battery's state of charge allowed me to use it. I'd have been happier with a freewheeled motor, all else equal.
I live in Austin now, down close to the river. On-demand regen braking would work much better for me here, because I have to climb to most places, and the recharge could be fully realized on the return leg.
