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Dynamo hub to recharge e-bike motor battery--hypermiling possible?

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Dynamo hub to recharge e-bike motor battery--hypermiling possible?

Old 07-29-21, 12:16 AM
  #26  
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Originally Posted by Darth Lefty View Post
You are nibbling at the edge of the problem, but it's not just the battery. It's power. The amount of power it takes to go slightly slower downhill is the same it takes to go that amount slightly faster uphill... a hundred watts, for a bicycle? How long is that downhill, a minute? If you were in a vacuum. But you are still making drag, too, you don't get that back. Single digit watt-hours at best. If you wanted to use the motor as a generator for The Brakes, to recover that, just think how much faster you can, must, slow down than you can speed up. It would have to be a lot more powerful, several times more powerful than the forward drive, to make as much power as the friction brakes. And then it would be on the rear, in most bikes, which is not where you want brake power. It then recovers some % of your ~1wh kinetic energy.

As the vehicle gets heavier, more aero, faster, it will make more sense.
Iíll have to repeat the experiment, but my recollection was that I added around 5% of charge to the 370wh battery on my scooter during a very controlled 5 minute descent. that suggests a higher charge rate than the thing averages on the wall charger (which takes around 180 min to fully charge, not 100 min) so perhaps there are some battery level reporting shenanigans.

one minor (maybe) point for a bike is that the potential energy from the descent is not symmetric to what the motor contributed going uphill - itís symmetric to what the motor PLUS the rider contributed, minus drag and friction of course. if I ride up a 10 minute climb at 10mph by putting out 240w with my legs and 60w from the motor, and then descended at 10mph for 10 minutes the potential energy available is far more than the 10wH that the battery contribute to the climb, itís some significant fraction of the full 50wH expended, again, minus drag and friction and waste heat and noise and all that. this is actually the way I ride my turbo creo, with the assist in the 50-75w (1/4 of my 200-300w) range, and completely turned off otherwiseÖ but of course I get nothing back riding the brakes on a long fast descent.
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Old 07-29-21, 01:01 AM
  #27  
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mschwett
True, but I kinda doubt there's much market for a design that relies on the rider providing 80% of the climbing power and descending at 10 mph.
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Old 04-26-22, 07:09 AM
  #28  
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Battery & motor in rear hub.. regen braking:
https://electrek.co/2022/04/26/mini-...ative-braking/
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Old 04-26-22, 09:33 AM
  #29  
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Originally Posted by cat0020 View Post
Battery & motor in rear hub.. regen braking:
https://electrek.co/2022/04/26/mini-...ative-braking/
Too bad it'll be a snail, unless it's tweaked for non-European markets,...
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Old 04-26-22, 10:11 AM
  #30  
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Good looking bikes, but the concept doesn't appeal to me. Electricity is inexpensive and if/when I need a more intense workout, riding a bike with a heavy direct drive hub motor will suffice.
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Old 07-24-22, 01:31 PM
  #31  
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More recent take on regen:
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Old 07-24-22, 02:59 PM
  #32  
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Dynamo hub is rated for small non moving / rotating devices like led lights, your best bet is to get an ebike with regen option, using the motor itself as a dynamo while braking but even with that you get less than 10% energy back to the battery.
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Old 07-24-22, 03:11 PM
  #33  
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Good and thoughtful talk, with actual experience and not encumbered with a lot of "should"

A brake handle with a pot in it to vary the regen duty cycle would be pretty trivial to invent. I can think of a number of other things too that you could sense with solid state circuits and non-moving parts, like brake arm strain or brake fluid pressure.

I still think the amount of energy you are carrying is not much to recover for most users most of the time. If you are making the case that the point of this is to save brake pads, the generator power you would need to make it a good percentage of braking would be much larger than the forward power of the drive motor.
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Old 07-26-22, 04:02 PM
  #34  
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Originally Posted by Leisesturm View Post
Typical dynamo hub output = ~3W. Typical hub motor output = 500W. Typical bike battery capacity = 500wh to 1000wh. A properly designed hubmotor will stop making power above a certain speed to avoid burning out components, so more speed does not get you more than the rated power (3W remember?). So, NO, no one has even experimented with using a dynamo hub to keep an e-bike battery charged because the idea is a complete non-starter.
Now running a headlight or charging a cell phone or GPS, that's another story. You can buy gear to make that happen. But charging an e-bike battery from a hub dynamo, no way.
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Old 07-26-22, 05:46 PM
  #35  
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Originally Posted by Darth Lefty View Post
I bet you donít. Little energy, wrong wheel, and not made of bike parts
Copenhagen wheel had this feature years ago.
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Old 07-26-22, 07:11 PM
  #36  
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Originally Posted by Atlas Shrugged View Post
Copenhagen wheel had this feature years ago.
They did indeed. Why couldn't they have sold the idea to Giant, or Trek instead of taking their ball and going home ...
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Old 07-26-22, 07:30 PM
  #37  
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It's not new at all. Also you can't get away from the effort to pedal and charge the battery. All the energy from regenerative braking was put there by the battery in the first place when it is powering the bike. A good lightweight bike is the best way to go.
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Old 07-27-22, 11:58 AM
  #38  
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My 2017 BionX direct drive hub (company now defunct) has four levels of re-gen selected manually from the console, or one pre-set high level applied automatically with a brake lever switch. That said, the re-gen is minimal unless you live in a mountainous community like I do. I might get one bar of re-gen after a two mile descent. Just slowing down for a stop sign? ... re-gen is insignificant. The braking feature is kinda cool. Like downshifting in your car.


Last edited by BobG; 07-30-22 at 05:25 AM.
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