Hey again,

I would like to charge a battery inside a tire of a bycicle.
First, I thought about using piezo sensors that produce little current by vibration. I even found a small device that makes it all useable:
https://www.mouser.de/new/Mide-Technology/mide-ehexxx/

Unfortunately, this one seems to be off the market already, couldn't find where to buy it. Anyway.

My second thought is that capacitive acceleration sensors might even work better - since a bycicle wheel is rather in a constant movement than a vibration. Calculation a wheel at 10km/h (2,78m/s) produces round about 1,3g (centrifugal I guess). Shouldn't that be enough to get some juice?
Putting multiple sensors in a row would increase the current ... any ideas?

Best regards
Dieter

 

But that 1.3g (centripetal, strictly) is a constant value. If it was that easy you could use the normal 1g to generate electricity.

 

(http://9.jokk.itaotao.de/basw/bicycle-anatomy-expert-diagram.html)
https://www.dutchbikebits.com/traditional-bicycle-wheel-rims
wheel rim cross section : \--₀__₀--/ apply magnetic conductor epoxy** to holes(-set) at ₀ magnets to the fork ....

** -- note. : that is viscous/plastic over the outdoor temperature range and won't crack from strike ((?a hi-tech substance (glue) )) /// quick alternative ? heat glue added with sanded ferrite core dust///

or how about optical (laser)(light battery)

 

Thank you ci139, but both are not an option. Inside the tire only.

 

Put magnets on the forks and coils inside the tyre.

 

Put magnets on the forks and coils inside the tyre.

No. Inside. Only.

 

A battery?

 

But that 1.3g (centripetal, strictly) is a constant value. If it was that easy you could use the normal 1g to generate electricity.

The acceleration is not constant, the direction is changing. Not saying this could provide energy for harvesting, but to say it is constant is not true.

Bob

 

If the wheel is unbalanced, it would wobble and energy could be harvessted from that movement. Again, not saying it is practical, just that it is theoretically possible.

Bob

 

But if the wheel runs smoothly at a certain speed, the force (centripetal or fugal or whatever) is constant at a certain g-level, isn't it?
The force gets higher the faster the wheel spins. So a sensor will signal this force by "generating" a certain amount of current, right? Constant as long as the wheel spins.

 

The acceleration is not constant, the direction is changing. Not saying this could provide energy for harvesting, but to say it is constant is not true.

Bob

Imagine yourself being stuck to the inside of a tyre which is roatating. You would feel pressed against the outside of the tyre and that pressure would be constant - it wouldn't come and go depending on the position of the wheel.

I don't know how well this would work but imagine something like a very small model car sitting in the tyre. As the wheel rotates the car might (?) sit at the bottom of the tyre with its wheels rotating and the wheels could then drive a generator within the car.

 

I don't know how well this would work but imagine something like a very small model car sitting in the tyre. As the wheel rotates the car might (?) sit at the bottom of the tyre with its wheels rotating and the wheels could then drive a generator within the car.

I don't think this will work ... only at low speed the car we stay at a certain position inside the tire (because of the earth). When it gets faster, the car will move around as well. I have a "glass donut" with some water in it before my eyes ...

 

But if the wheel runs smoothly at a certain speed, the force (centripetal or fugal or whatever) is constant at a certain g-level, isn't it?
The force gets higher the faster the wheel spins. So a sensor will signal this force by "generating" a certain amount of current, right? Constant as long as the wheel spins.

Generate whenever the speed changes but generate nothing while the speed is constant.

 

Imagine yourself being stuck to the inside of a tyre which is roatating. You would feel pressed against the outside of the tyre and that pressure would be constant - it wouldn't come and go depending on the position of the wheel.

That is true as long as there is no gravity in play.

Have you ever been on a carnival ride that spins on a horizontal axis? Did the acceleration feel constant to you? The combined centripetal acceleration plus gravitational acceleration will vary dramatically. At the bottom of the ride the two accelerations add making you feel heavier, at the top they subtract and you feel lighter. You can even notice this on a slow moving Ferris wheel. If it is spinning at exactly the right speed, you will be weightless at the top and feel 2G at the bottom.

Bob

 

There's some variation in force as the tire goes around and even more when the bicycle hits a bump, but, without trying to figure out how to calculate it, I don't think there's enough energy to harvest there. For sure not enough to charge a battery.

If you're fixed on generating electric inside a tire, I would suggest placing a small coil inside the tire and a magnet on the bicycle frame. Each time the coil passes the magnet it would generate a pulse which you could then store in your battery. You could even add multiple coils to increase the energy generated.

 

You could even add multiple coils to increase the energy generated.

Any thing and especially the coil and magnet is also going to increase the effort to move the bicycle too. There is no such thing as "free energy". Then with something in the tire you will also need a slip ring and brush to transfer the energy, another type of resistance to movement.

That said, if wanting to generate electricity on a bike. there are lighting generators the have been around since before I could ride a bike, and I'm 71.

 

My second thought is that capacitive acceleration sensors might even work better - since a bycicle wheel is rather in a constant movement than a vibration. Calculation a wheel at 10km/h (2,78m/s) produces round about 1,3g (centrifugal I guess).

I'm not sure what you mean by "capacitive acceleration sensors" but the only ones I can think of are piezoelectric accelerometers. In other words, they're the same thing.

In any case, an accelerometer mounted inside a bicycle tire rotating at constant speed will experience forces that can be considered in three parts: first, there is a small amount of high-frequency vibration caused by the tire rolling across an uneven road surface. Second, there is a constant, or near constant, acceleration due to the centrifugal force of the wheel rotation. And third, there is a ±1 g changing acceleration component at the wheel rotation frequency due to forward movement-- i.e., when the accelerometer inside the wheel is on the bottom (nearest the road surface) it will experience +1 g, and when it is at the top of the wheel rotation cycle it experiences -1 g).

The first component will contribute a small amount of energy that can be harvested, but unless the bicycle is traveling over an extremely rough surface it's unlikely to be significant.

The second component will contribute nothing, since it is constant (piezo accelerometers output a current only during a change in acceleration).

And the third component will contribute some, but it won't be much since the wheel is rotating only a few times a second at most.

Shouldn't that be enough to get some juice?

Yes, provided your definition of "some juice" is no more than a few microwatts.

Energy harvesting from vibration works best when it's done in conjunction with high-speed rotating machinery such as a motor-driven device running at, e.g., 3600 RPM. It's most effective when the vibration is at a constant frequency and can be enhanced by mounting the piezo sensor on some structure which is resonant at that frequency.

Bottom line: I don't think you're going to get any significant power from your scheme. I'm not sure how much you're expecting, but my best guess is that you'll fall short by between two and five orders of magnitude.

 

Put magnets on the forks and coils inside the tyre.

Wouldnt it be better to put the magnets inside the tire, and coils on the fork?
And while at it, power it with a 12V battery and you have an ebike!

 

Wouldnt it be better to put the magnets inside the tire, and coils on the fork?

Not if you want the electricity inside the tyre as TS does.

 

Could you use a pressure differential somehow? If it were possible to have a tiny chamber with constant pressure on one side of a diaphragm and the tyre pressure on the other, you could theoretically drive a small magnet backwards and forwards inside a wire coil. Not sure how you'd make it that small though.

Tyre pressure monitors pretty much all use batteries, is this not an option for you? How much juice are you looking for, or what are you trying to do with it?