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

Old 07-24-21, 05:44 PM
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Dynamo hub to recharge e-bike motor battery--hypermiling possible?

Has this been tried?
Say, a dynamo hub (front or rear) ... and the power from it recharges battery for eBike (the drive motor is front, rear or mid). Probably for experiment only .... say downhill ... then typical e-assist on level ground ... than back uphill to starting location. The ultimate hypermiling experiment!
An alternative (experiment) to the long-awaited regenerative braking eBike motor.
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Old 07-24-21, 09:49 PM
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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.
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Old 07-24-21, 10:27 PM
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Old 07-25-21, 05:43 AM
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Recently I purchased a shift-drive e-bike with regen braking & dynamo regen.
400w motor, 54.6v, 1100wh battery with max 60A.
14" wheels, chain-less, shaft-driventrain, comes with a cellphone cradle & USB charging port.
30km/h throttle cutoff for electric motor, PAS you can go faster but with single speed, you will be spinning your legs at high rpm.
Advertised 70-300km operating range, depending on usage & rider weight.
I had to change out the 170mm crankarms to 152mm to accommodate my wife (4'11", short legs), also makes it easier pedal at high rpm, with smaller pedaling circle.
Yesterday we took it out for a spin little over 12 miles, wife was charging her cell phone all along the ride, so I don't know if the regen contributed much to the main battery.
The dynamo regen adds significant more resistance to propel the bike, without PAS, the bike feels like you're climbing a decent hill all the time on the flat.


I figure the tiny e-bike may be good for city dwellers with limited space and no need for higher speeds (15 mph or below).
It has good load capacity, motor can handle my wife & myself as a passenger, totaling near 340 lb. and still cruise at 12 mph on the flat with throttle only operation; it would surely carry a good amount of groceries.
If your terrain involves lots of long, downhill sections, maybe the dynamo can regen enough juice to add 6 to 10 mile to the total range of the large battery capacity of this tiny e-bike.
I don't expect the regen to generate much beyond charging your cellphone while you pedal.
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Old 07-25-21, 09:43 AM
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Interesting full suspension design, but looks like a low end "shock". How does it ride?
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Old 07-25-21, 01:39 PM
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For its designated speed, it rides nice; anything faster or larger terrain variance, the small 14" wheels are not really designed for rough stuff.
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Old 07-25-21, 02:20 PM
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I predict we see braking regeneration built into e-bike motors soon. Extending the range without increased weight is a marketing big win.
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Old 07-25-21, 03:04 PM
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One of the early developers of regenerative braking, justin Le of Grin Technologies, has said one can get up to 10% recovery in hilly regions. Nice if you live there and have to use brakes to control your downhill descents. Where I live, I might get 20 mph coasting down a hill for 10 seconds, and the hill is over. And I have to have a direct drive motor too.

Meanwhile, battery improvements have been pretty good in the six years I have been ebiking.. I just bought an 18AH battery for less than what I paid for a 10 AH battery in 2015. That's like 80% more range. I've got more battery than I need for a ride these days,

As Cat0200 points out, having a bike dynamo capable of charging a phone is like riding uphill 24/7. Why would I want that penalty on my biking.
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Old 07-25-21, 06:24 PM
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Originally Posted by tyrion View Post
I predict we see braking regeneration built into e-bike motors soon.
I bet you don’t. Little energy, wrong wheel, and not made of bike parts
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Old 07-25-21, 06:39 PM
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I have never heard of 'dynamo regen'. It sounds like an answer to a question no one asked. Most e-batteries have taps for 5V power to charge cell phones, or the display unit has USB jacks, but either way you get the power for your electronics right from the main battery. Using energy from the battery to run the motor as a generator ... I don't even think it's possible. A motor can either be using power and providing motive force OR it is converting motive force back into power (at greatly reduced efficiency) it cannot be charging a battery or running electronics while simultaneously providing motive force. No. Just no. Unless there is a second dynamo on board, the only time power can be recovered is during coastdowns. It is only e-bike customers that want regen, because they think it is magic. Perpetual energy. Free energy. There is no free lunch.

I don't have exact numbers, but think of regen kind of like this: if it takes 100W of energy to go up a hill, going down that same hill with regen on will get you 10W back into your battery. So you never recover all the energy you used. Not even a decent fraction, just 10%. Maybe enough to keep your electronics on but nothing usable to extend range. So few manufacturers offer it. Ebikes.ca offer it with the proviso that it works in some situations. The rest are playing on the need for most people to think they are getting away with something. If you want to get away with something: COAST every chance you get. The world record range champions use power in bursts and coast in between. Staying off the brakes as much as possible is what extends range. You can't do that in town (not safely) and regen can keep you from using up brake pads as fast but I can't really remember the last time I put new brake pads on and I don't have regen. So ... more than you needed to know but that's how I roll. No regen holding back the flow of information ... FWIW ...
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Old 07-25-21, 08:14 PM
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Originally Posted by Darth Lefty View Post
I bet you don’t. Little energy, wrong wheel, and not made of bike parts
Yeah you're right. The energy payback in bicycles isn't nearly the same as it is in cars.
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Old 07-25-21, 10:00 PM
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With today's technology, it's not doable, but give it time
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Old 07-25-21, 11:26 PM
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Originally Posted by Leisesturm View Post
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.
The dynamo could be intelligently integrated into the braking system somehow ... say every time you squeezed brakes, or were coasting downhill. The "braking" load, experienced with a typical hub dynamo, from powering a phone or lights, could be used to recharge the drive-motor battery. Effectively: DIY regenerative braking ... until the all-in-one units (found in cars and locomotives) are a cost-effective option for eBikes. That's something Tesla should look into ... instead of wasting $$ with hyperloops and launching cars into orbit.
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Old 07-25-21, 11:33 PM
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I thought I wrote a response, but the hub motors should be easy enough to reverse from power to recharging. 1000W power or 1000W regen.

How is the accelerator?

I'd put in a 2-way twist grip. So, twist forward for power. Snap back to neutral, and twist back for braking.

Also brake calipers routed into regen.... hopefully without throwing a person over the bars.

Of course, regen needs to be limited to not over-charge. Probably not a big problem unless one lives on the top of a hill, and recharges at home, then hits regen right out the door.
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Old 07-26-21, 05:41 AM
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From my Chinese Utility E-bike thread:

Article is 8 y-o, but still good info: https://www.electricbike.com/regenerative-brakes/

Video is also few years old:

Also:

Regen is worthwhile if your e-bike has a large capacity battery, 3% to 5% regen for a large battery can be up to 6 or 10 miles of travel for a larger battery.
If your e-bike has small capacity battery and short range to begin with, regen braking is likely not worthwhile.

Video below:
Regenerative Braking on the Electrom LEV
An in-depth explanantion of how regenerative braking works on the Electrom LEV
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Old 07-26-21, 06:55 AM
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I have never experienced it, but owners of the RadCity ebike, which is a direct drive rear hub motor capable of regeneration, report than when they have it set up for full regen, they have to pedal to go downhill and keep up with non regen ebikes. How cool is that?

I suppose most owners won't set it up like that. You can choose regen to happen when brakes are applied. Then it makes for a very strong braking force. However, you still have the tradeoff of a small direct drive motor, which cannot climb as well on hills.

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Old 07-26-21, 07:35 AM
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I rode a BionX 500w-equipped bike that had variable regen and the braking force was massive when tested on a steep hill. However, for me, not desirable since the affect on the dropouts (even with a good torque arm) of the motor shifting from propelling to stopping overwhelms the small gains, and don't mind changing brake pads occasionally.
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Old 07-26-21, 10:14 AM
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Originally Posted by elcyc View Post
The dynamo could be intelligently integrated into the braking system somehow ... say every time you squeezed brakes, or were coasting downhill. The "braking" load, experienced with a typical hub dynamo, from powering a phone or lights, could be used to recharge the drive-motor battery. Effectively: DIY regenerative braking ... until the all-in-one units (found in cars and locomotives) are a cost-effective option for eBikes. That's something Tesla should look into ... instead of wasting $$ with hyperloops and launching cars into orbit.
This is exactly how regen systems work now. In the brakes are switches that sense when they are touched. Not hard enough to actually apply the brakes but to switch on the regen system. But there is never any 'free lunch'. It is about a 10:1 loss at present levels of the technology. You get 10% of the energy it took to climb a hill when you regen back down. You will NEVER break even. Overnight charging of the big battery mounted on the downtube will be the go to charging paradigm for a long time to come.

But, wait, it gets better ... if you continually charge your battery to 100% overnight and run it right down the next day, your battery will need replacement in as short as two years. If you never charge it more than 80% and never run it down below 20%, the same battery could last 5 years. So, buy the biggest battery you can afford and never use more than 60% of it's potential.
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Old 07-26-21, 01:44 PM
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The onemotor.co has regerative braking but thus far I have not been able to see any measurable change in the charge level displayed on the optional wireless controller. If I disconnect the battery when the roller is pressed against the tire, the LEDs on the motor housing light up if I start pedaling so I do know it is generating some power. Using the regerative braking doesn’t always slow me down as fast as I would like, so I often need to use my handbrakes as well.

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Old 07-28-21, 12:27 AM
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with the appropriate “brakes” (in addition to the regular brakes) and the right battery configuration (something very parallel, since batteries charge so much slower than they discharge) this ought to be viable for hilly rides in which wind resistance is not the primary consumer of energy and the rider is willing to descend much more slowly than usual.

I have an electric scooter which can be braked almost entirely with electric/regenerative braking, and riding it up a hill and then at moderate speed down the same hill results in a very significant amount of recaptured energy. way more than 10%. if the hill is too steep and you go down too fast, even with a lot of braking, the energy is presumably generated faster than the battery can actually charge. similarly just rolling at high speed until the end and then slamming on the brakes does nearly nothing, dumping all the energy in just a few seconds.
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Old 07-28-21, 04:05 AM
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It would be extremely inefficient to try to recharge an e-bike battery using the puny output of a generator hub — likely to the point that installing one would give a net loss of energy, as they cause extra drag even when they're turned off.
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Old 07-28-21, 06:52 AM
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It already exists. Part of the problem is that it only exists in direct-drive hub motors. Geared motors, which are lighter and have other design benefits, freewheel when coasting, this negates any potential for regen. Mid drives are almost all of the geared motor variety, there is also the point that using regen on a mid-drive would send chain tension the other way, most bicycles are not set up for that.

So, while it exists, it is not too common and direct-drive systems seem to be losing market share in the mid to high-end bike market. With that said, I don't expect to see much of it, some, but not much.
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Old 07-28-21, 08:18 AM
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Originally Posted by hydrocarbon View Post
It would be extremely inefficient to try to recharge an e-bike battery using the puny output of a generator hub — likely to the point that installing one would give a net loss of energy, as they cause extra drag even when they're turned off.
yes, regen/charging would have to be done with the primary motor, as is currently done in direct drive ebikes and scooters. it could still be disengaged to avoid parasitic drag when off and not “charging.”
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Old 07-28-21, 08:35 AM
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Originally Posted by mschwett View Post
if the hill is too steep and you go down too fast, even with a lot of braking, the energy is presumably generated faster than the battery can actually charge. similarly just rolling at high speed until the end and then slamming on the brakes does nearly nothing, dumping all the energy in just a few seconds.
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.
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Old 07-28-21, 10:08 AM
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Originally Posted by Robert C View Post
It already exists. Part of the problem is that it only exists in direct-drive hub motors. Geared motors, which are lighter and have other design benefits, freewheel when coasting, this negates any potential for regen. Mid drives are almost all of the geared motor variety, there is also the point that using regen on a mid-drive would send chain tension the other way, most bicycles are not set up for that.

So, while it exists, it is not too common and direct-drive systems seem to be losing market share in the mid to high-end bike market. With that said, I don't expect to see much of it, some, but not much.
You could overcome the problem with a singlespeed chain or belt drive combined some kind of switchable hydraulic-brake-disengage/drive-lock/reverse-freewheel mechanism to transfer power during motor-braking/downhilling I guess, but you'd still have the fundamental issue that the miniscule amount of energy recovery possible probably wouldn't make the extra complexity worth it.

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