dynamo on a bike

General Discussion about electric bicycles.
WALLEY   1 mW

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dynamo on a bike

Post by WALLEY » Aug 29 2019 5:57pm

I asked this very same question here about 10 years ago I got my head chopped off for not knowing thermo dynamics enough guess I still dont know
let me ask again why cant 1 48v dynamo be installed on a bike that runs with the chain when the motor is running so fast you cant help why cant a dynamo by hooked to the chan so while the motor turns I can pump the chain an spin the dynamo that charges the battery or at least power the battery enough so it doesnt drain the voltage so much
heres a dynamo for a wind turbine

https://www.alibaba.com/product-detail/ ... e506EK8HcB

this might to big but why cant I take something like this and work it out

I had a stroke and have trouble thinking this stuff out but why cant this work

cause I lave my e bike I just wish I had more amp hours
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E-HP   100 kW

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Re: dynamo on a bike

Post by E-HP » Aug 29 2019 6:53pm

WALLEY wrote:
Aug 29 2019 5:57pm
I asked this very same question here about 10 years ago I got my head chopped off for not knowing thermo dynamics enough guess I still dont know
let me ask again why cant 1 48v dynamo be installed on a bike that runs with the chain when the motor is running so fast you cant help why cant a dynamo by hooked to the chan so while the motor turns I can pump the chain an spin the dynamo that charges the battery or at least power the battery enough so it doesnt drain the voltage so much
heres a dynamo for a wind turbine

https://www.alibaba.com/product-detail/ ... e506EK8HcB

this might to big but why cant I take something like this and work it out

I had a stroke and have trouble thinking this stuff out but why cant this work

cause I lave my e bike I just wish I had more amp hours
You have efficiency and electrical losses to consider. You'd probably expend less pedaling effort and increase your range more by just turning off the motor and pedaling, then using the motor when you get tired.

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Re: dynamo on a bike

Post by John in CR » Aug 29 2019 6:56pm

If you want to better add human power get a larger chainring, since what you propose will be more lossy. In addition you would be much better off investing that money, weight and space in more battery.

If you insist on the less efficient route, then I'd suggest getting a tiny motor (a small geared hubmotor run backward so it doesn't freewheel is one possibility) along with a small controller with regen. Get everything for the same voltage as your battery pack and wire the controller so regen is always engaged. Then it's just a matter of getting the gearing right between your pedals and the motor to maximize charge output. If I ever build a velomobile, that's how I'd set up my pedals, which wouldn't be connected to the wheel at all. The purpose of my pedals would be only to add juice to the battery in an optimized cadence range for exercise and be able to add that energy to the battery travelling at any velocity, even stopped at a red light or stuck in traffic. I would in essence have an electronic chain. Someone who is more of a cyclist than I am would probably want to include the cranks in the wheel's pedal line and have a way to disengage the charging option to add power to the wheel more efficiently thru direct crank input to the wheel.

FWIW, your previous question was probably taken as connecting the electric drive to a dynamo to recharge the battery as you use it to keep the battery charged, and no that won't work and would violate the laws of thermodynamics.

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Re: dynamo on a bike

Post by dustNbone » Aug 29 2019 7:55pm

A dynamo converts mechanical energy to electrical energy, it does not create any energy on it's own.

The mechanical energy to drive the dynamo is the same mechanical energy that is being used to move the bike. If you take some of that mechanical energy away for the dynamo you have less energy moving the bike.

Some of the energy that goes to the dynamo gets converted to electricity, some is wasted as heat because there's no such thing as a perfectly efficient dynamo.

Some of that electricity will get converted back into mechanical energy by the motor, some will be wasted as heat, because there's no such thing as a perfectly efficient motor.

Every step of energy conversion involves losing a portion of that energy as heat. The more conversions, the more loss, and what you are describing involves many of those conversions. Therefore it is a very inefficient system.

The most efficient way to convert your body's energy to mechanical energy to move your bike is to pedal it. If you can't effectively pedal at the speed you typically cruise at, you need to change the gearing. Maybe a larger front sprocket.

The most efficient way to convert the electrical energy in your battery to mechanical energy to move your bike is your motor.

There are no other sources of energy involved here, there's no free energy to be harnessed, it can only be converted from other forms of energy, and never without losing some of it to heat.
Last edited by dustNbone on Aug 29 2019 7:58pm, edited 2 times in total.

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Re: dynamo on a bike

Post by flat tire » Aug 29 2019 7:57pm

Pedaling to charge while actually on the bike is a universally bad idea because you'll get more range investing your pedal strokes into direct mechanical energy to the road. If you do get it working you will only end up riding slowly and charging very slowly while working very hard. I don't get why people keep thinking this is worthwhile.

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Re: dynamo on a bike

Post by amberwolf » Aug 30 2019 12:46am

.nm.
Last edited by amberwolf on Aug 30 2019 10:45pm, edited 1 time in total.

Ford Prefect   1 W

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Re: dynamo on a bike

Post by Ford Prefect » Aug 30 2019 2:01am

Not understanding or not being able to understand is not a crime. It doesn't make you less acceptable as a human being. There are a lot of things I am unable to comprehend. How can there be people who learn more than one foreign language? How can stainless steel not be magnetic when it is mainly iron?

But please, accept the truth. There are physical principles usually called fundamental laws or axioms or something like that which cannot be changed or tricked. If we could change them it would be a really, really bad idea. Anything we do, from digestion to space travel, actually works because these laws (and a few constants) are just the way they are.

If something won't work out because of these laws, it will not work out. Ever. There is no way it possibly could.
The fundamental laws of thermodynamics will place fixed limits on technological innovation and human advancement.

How would you react if I said that I'm not from Guildford after all, but from a small planet somewhere in the vicinity of Betelgeuse?

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Re: dynamo on a bike

Post by Drunkskunk » Aug 30 2019 5:02am

I understand what you are saying: When the motor is moving the bike so fast, that you can't pedal fast enough for the chain to keep up with the motor, meaning NO effort from your pedaling is reaching the wheel. In that very specific case, you could add some power to the bike through a dynamo.
Yes, your thinking is clear on that.

However, the amount of power you could add with a dynamo in that specific case is only about half the power you could add if you simply changed out your gearing so that your pedaling could add direct power to the wheel. If you could not add a crank sprocket big enough, you could add a jack shaft with a 2:1 ratio (or whatever was needed) that would be more efficient and less complex than adding a dynamo/generator.
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WALLEY   1 mW

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Re: dynamo on a bike

Post by WALLEY » Aug 30 2019 6:56am

SO THERES no way of getting the power enough to power a motor simple by peddling a generator or dynamo.

seems I remember a guy out of Germany who had a bike that could 50 miles a hour by peddling I haven't found that vid in a while now I guess 7 years but he had a nice concept he was trying get a patent for it. he probably sold it . now its buried

guess getting a bigger battery is the only way
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Re: dynamo on a bike

Post by docw009 » Aug 30 2019 10:13am

Think about it, Walley. If you can get more power out of the dynamo than what it takes to turn it, you have refuted hundreds of year of study from physicists and scientists.

Yet, people still want to believe.
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E-HP   100 kW

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Re: dynamo on a bike

Post by E-HP » Aug 30 2019 10:26am

docw009 wrote:Think about it, Walley. If you can get more power out of the dynamo than what it takes to turn it, you have refuted hundreds of year of study from physicists and scientists.
Ya, but pedal assist without a battery, that would make for super light builds. And if we could get the ratio up, say pedal 100 watts in and generate 5000 watts out; of course you might need to pedal 200 watts to climb 20% at 50 mph...


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MadRhino   100 GW

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Re: dynamo on a bike

Post by MadRhino » Aug 30 2019 12:13pm

Fitting a dynamo on an ebike, does result in a loss of power. Any restriction whilst the motor is powered does.

The only power increase that can be achieved with a restriction is from assisted braking system, where energy from the restriction during braking is stored and returned at the next acceleration. Generally, supercapacitors are used for such systems, but many solutions are possible for this purpose.
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Drunkskunk   100 GW

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Re: dynamo on a bike

Post by Drunkskunk » Aug 30 2019 12:21pm

WALLEY wrote:
Aug 30 2019 6:56am
SO THERES no way of getting the power enough to power a motor simple by peddling a generator or dynamo.

seems I remember a guy out of Germany who had a bike that could 50 miles a hour by peddling I haven't found that vid in a while now I guess 7 years but he had a nice concept he was trying get a patent for it. he probably sold it . now its buried

guess getting a bigger battery is the only way
Nope. Never. it takes 3500 watts or so to go 50mph. The output of the dynamo is going to be the same as it's input minus it's efficiency rating. If you pretend it's 100% efficient, it still takes 100 watts of mechanical leg power to make 100 watts of electricity. Power out equals Power in. For the same reason you can't pour a can of coke into a bathtub and have it totally fill the bathtub.
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Hephy   1 mW

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Re: dynamo on a bike

Post by Hephy » Aug 30 2019 12:52pm

Connect the Dynamo directly to a motor. Spin the wheel.

It'll always stop - because every mm of wire, every connection and every rotation of the motor and dyno creates losses.

Perpetual motion can't happen, the power has to come from somewhere. The increased drag from the Dynamo being there - takes away more than it will ever give back.

Now separated... Independently controlled and applied (so it's only added when you're coasting/braking). With some long Regen downhills you might get something back from it. On level ground - it's always a net loss. But even then it's added weight reduces your range.

Want better range - add battery or make efficiency changes to your existing system. Better bearings better lubrication in the bearings, tires with lower rolling resistance, more efficient motor, reduce the weight...

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Re: dynamo on a bike

Post by dustNbone » Aug 30 2019 3:18pm

WALLEY wrote:
Aug 30 2019 6:56am

seems I remember a guy out of Germany who had a bike that could 50 miles a hour by peddling I haven't found that vid in a while now I guess 7 years but he had a nice concept he was trying get a patent for it. he probably sold it . now its buried
There are extremely streamlined designs with very high pressure tires that have achieved speeds close to 90mph under pedal power.

Image

These are world class athletes, and the bike is basically assembled around them in preparation for the run.

Based on that though, I'd say with the right streamlining and a very fit rider, under the right conditions, 50mph is quite possible with pedal power. But the bike would be very much impractical for regular usage; susceptible to side winds, poor visibility and maneuverability, and probably not very durable.

The ticket is aerodynamics, wind drag is the enemy of speed on a bike. An upright rider sucks a ton of wind, a recumbent rider far less, and one behind a properly designed aerodynamic body shell far less than that. That's why velomobiles are faster than bicycles despite weighing several times more.

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Re: dynamo on a bike

Post by wturber » Aug 30 2019 4:10pm

Nothing new here, but maybe saying it differently will help.

1) You could add power to the motor and/or battery by pedaling a dynamo. That will work and be marginally helpful. But it is more efficient to just have your pedaling drive the bike directly. So you'd have to have some good reasons for putting up with loss in efficiency and the added weight of the dynamo.

2) Anything you attach to the motor's output will draw more energy than it could ever put back into the battery. There are always frictional or electrical losses of some kind. It is not possible to avoid this. You can observe some of this loss in the form of heat.

So if we imagine a really efficient dynamo that is 90% efficient, running it to charge the batteries will lose 10% of the power that is supplied to it. In practice, the loss is actually more since batteries don't charge at 100% efficiency either.
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E-HP   100 kW

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Re: dynamo on a bike

Post by E-HP » Aug 30 2019 5:06pm

Well since we probably won’t be able to change the laws of physics within our lifetime, we may need to turn to conventional methods to solve this ebike range issue.

Go nuclear! We should replace our batteries with small nuclear reactors*. 1 gram of plutonium can produce 18 megatons of energy. That’s enough for cross country round trips for a few lifetimes.

*We could replace both the battery and motor, but then we’d need a nuclear bike forum.

The only consideration may be that nuclear is marginally more dangerous than lipos, so you should refuel in your neighbor’s backyard to be safe.


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Re: dynamo on a bike

Post by MadRhino » Aug 30 2019 6:04pm

Well, this doesn’t account for the fact that, to hold the nuclear reaction of one gram of plutonium and transform it into electricity, would probably require 100 tons of material and equipment around it.
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E-HP   100 kW

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Re: dynamo on a bike

Post by E-HP » Aug 30 2019 6:09pm

MadRhino wrote:
Aug 30 2019 6:04pm
Well, this doesn’t account for the fact that, to hold the nuclear reaction of one gram of plutonium and transform it into electricity, would probably require 100 tons of material and equipment around it.
Minor detail compared to changing the laws of the universe.

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Re: dynamo on a bike

Post by Ford Prefect » Aug 30 2019 6:19pm

You are both thinking of a nuclear reactor. There is actually something called a nuclear battery, where you catch the beta-rays and use them. I think they did it on the Voyagers?

You definitely should not brake the laws of the universe. The Imperator and his Apprentice will not be happy about this…
The fundamental laws of thermodynamics will place fixed limits on technological innovation and human advancement.

How would you react if I said that I'm not from Guildford after all, but from a small planet somewhere in the vicinity of Betelgeuse?

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Re: dynamo on a bike

Post by wturber » Aug 30 2019 9:10pm

E-HP wrote:
Aug 30 2019 5:06pm
Well since we probably won’t be able to change the laws of physics within our lifetime, we may need to turn to conventional methods to solve this ebike range issue.
We need batteries with double or triple the energy density is all . . . well . . . for now at least.
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Re: dynamo on a bike

Post by kdog » Aug 31 2019 5:54am

When I was young, I (for the fun of it) built a chainless bike. I bought a perm mag alt and built it into the front triangle. I welded a 2nd bb in to the down tube and ran a 50:12 to 50:12 step up. The pma directly powered a crappy little 200w rear Currie style motor.
Now even then i knew it would be lossy... it was mostly about learning to weld. At the time I was a competitive track cyclist racing club A grade, and going flat out on this contraption I managed about 15kph on the flat only... Ha! Rode it once :pancake:
I could have optimised some stuff but it was so hopeless I didn't bother. People were generally confused and amazed by it though.
I feel like there might be an application for this, say if your chain line is long and terrible and youre in a recumbent trike and your electrical system is powerful enough to not need your input. Maybe then if you have a nice light efficient pedal powered unit, it might be worth it.
But That's a lot of preconditions!

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Re: dynamo on a bike

Post by docw009 » Aug 31 2019 3:02pm

The Mando Footloose is a bike that has no chain, Your pedals power a generator to charge the battery. I am surprised something like this actually made it out of the concept stage. I believe you have to pedal far harder on a geneartor to put the same energy in the battery to go as far as a simple push on a conventional bike will go.

https://www.cnet.com/reviews/mando-footloose-im-review/

Then you had these Vello guys claiming their bike never needs charging. A great looking bike, if marketed as a standard ebike with batteries in the hub motor, but I sure wouldn't want to ride it w/o access to a charger.

https://www.kickstarter.com/projects/ve ... lding-bike

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Re: dynamo on a bike

Post by WALLEY » Aug 31 2019 4:26pm

wow that mando footloose looks promising though
wish I wasnt recovering from this stroke I can barely afford my electricity to ride now
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Re: dynamo on a bike

Post by gogo » Aug 31 2019 9:02pm

WALLEY wrote:
Aug 30 2019 6:56am

seems I remember a guy out of Germany who had a bike that could 50 miles a hour by peddling I haven't found that vid in a while now I guess 7 years but he had a nice concept he was trying get a patent for it. he probably sold it . now its buried

guess getting a bigger battery is the only way
You are probably thinking of this: https://www.erockit.de/en/home-2/

I could be wrong, but I think the acceleration/speed is controlled by the pressure on the pedals or the cadence. There isn't much pedal-power making it go forward, if any.
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