Extremely simple wind charging DD ebike

[veloman]

At 8mph, my 9c hub with regen on charges about 50-70watts. That's a nice low current charge rate that would add up nicely after a couple hours.

My idea is to get a bike trainer (stand that securely holds rear wheel off ground), and secure it to a wind generator, and use a simple wheel-on-wheel friction transmission. No wires, no gears, no controller, nothing but a wind turbine driving my rear wheel at 6-12mph.

Some problems - what size turbine will I need to generate the required ~120watts at the turbine shaft to spin the ebike wheel at the needed speed? Maybe it will require turbine blades that would put the shaft too high above the ground/rear tire. A solution could be a vertical turbine and laying the bike horizontal.

Tire wear? Perhaps over time. But at these low power levels, there won't be much friction needed to maintain contact. Again, I'm aiming for around 60watts regen on my CA. I find 'used' tires for cheap anyway, so not a big deal.

Controller wear? I would think it wouldn't add up compared to normal ebiking power draws.

Strong points: never will overcharge my battery since regen doesn't work above 55v on my setting. Simple, low cost. Uses what I already have (DD wheel, controller).

Thoughts?

 

[spinningmagnets]

A Savonius turbine made from a couple plastic 55-gallon drums is easy to make. They are fairly low-RPM, but they have good torque. You could use a salvage cars pulleys/timing-belt to make a 1:2 gear-up to increase the output RPMs, and a 90-degree gearbox to attach it to the rollers. They are not useful for generating significant electricity because of the lower RPMs. the problem is that they have a high solidity, so after the wind has increased up to a certain point, any additional wind just goes around it, instead of through it.

As far as how much to overlap the drum halves, 20% is good for low winds, and sliding up to 50% for high winds.

Since you are only looking for 50W, I think it might work. either way, it is a cheap experiment.

 

[Dauntless]

http://www.macarthurmusic.com/johnkwilson/MakingasimpleSavoniuswindturbine.htm

http://www.re-energy.ca/t-i_windbuild-1.shtml
http://www.re-energy.ca/t-i_windbuild-2.shtml

But if you could see this thing over the fence in my neighborhood, there'd be people trying to get the City down there to take it.

[youtube]M-aZWt6iFyc[/youtube]

 

[veloman]

Yes, this is the design I am looking at. Thanks for the links. Lightweight will be key so that it doesn't need a big wind to startup.

 

[Harold in CR]

In that video, you can see the air being batted away, and blowing the clothes of those guys standing close.

From experience, you need 3 tiers of panels, to get the optimum force and self starting features.

 

[Jeremy Harris]

Some problems - what size turbine will I need to generate the required ~120watts at the turbine shaft to spin the ebike wheel at the needed speed?

This depends very much on the mean wind speed in your area, but here goes:

The power in the wind is proportional to the cross section of it that you intercept with the turbine (usually called the swept area) and the wind speed. The formula is pretty straightforward, power (watts) = 0.5 x rho x area (m²) x wind speed (m/S), where rho is the air density at your location (about 1.225 kg/m³ at sea level, less at altitude and in hot climates). You cannot extract all the energy from the wind, as there is a limit, the Betz LImit, that restricts practical turbines to about 59% maximum efficiency. In reality few turbines get close to this, around 45% efficiency is typical.

If we assume you can make a 45% efficient wind turbine (so it needs to be 2.22 times bigger to get the power needed from the wind), and that you need 120 W out at a wind speed of 10 mph (4.5 m/S) and that you're at sea level with an average air temperature of around 15 deg C, then the swept area of your turbine needs to be:

Swept area (m²) = (power (W) / (0.5 x rho x V²(m/S))) x 2.22

= 120 / (0.5 x 1.225 x 4.5²) x 2.22

= 4.36 m² or about 47 ft²

This is equivalent to a diameter of about 8ft for an axial turbine, pretty big but doable if the wind speeds where you are are this high. If your mean wind speed is 5mph, rather than 10mph, then the turbine needs to be four times bigger in area to get the same power. If the wind speed is 20mph you only need 1/4 of the area to get the same power.

 

[veloman]

Thanks for the numbers. Typical daytime winds are 8-10mph, conservatively. 47 sq feet would be about 7'x7', so not something small.

 

[Jeremy Harris]

Thanks for the numbers. Typical daytime winds are 8-10mph, conservatively. 47 sq feet would be about 7'x7', so not something small.

That's really the problem with wind generation; power drops a heck of a lot as you scale the size of turbines down. Big wind turbines can generate a lot of power, but small ones need a high wind speed to be useful.

 

[Samd]

Perfect wattage for a lenz vawt. It's a combination of drag/bucket type, and lift/airfoil type. And nicely suited to those wind speeds.
http://www.windstuffnow.com/main/vawt.htm

 

[Chalo]

My idea is to get a bike trainer (stand that securely holds rear wheel off ground), and secure it to a wind generator, and use a simple wheel-on-wheel friction transmission. No wires, no gears, no controller, nothing but a wind turbine driving my rear wheel at 6-12mph.

That's clever.

If you use a vertical axis turbine, you'll need a right angle gearbox, which adds cost and friction. Or else you'll need a chain run long enough to rotate 90 degrees, which also adds some friction and implies a large apparatus.

Mechanically, a horizontal axis turbine is easier to implement, and it can use a transmission made of simple cheap bicycle components. The turbine itself may be more expensive or harder to make, but that's outside my expertise.

 

[REdiculous]

I've got a trailer axle from an old tow-behind cement mixer I'm planning on using for a similar project. I'll cut the axle in half so I have one wheel left. I'll weld brackets to the wheel so I can mount the vertical (Lenz-style) blades, and I'll keep the tire on. My bike's tire will press against the trailer tire, underneath the turbine, creating a right-angle gear...simple. I'll need some kind of bike-clamp-thing welded to the pole but this would be easier than a bike-clamp-thing that has to rotate around the pole, as would be needed for a horizontal.

If you go horizontal, look into furling and add a brake for when you don't want it spinning. A vertical shouldn't be allowed to free-spin either, but it should be a lot safer if it does get going with no load, or an insufficient load.

 

[veloman]

Find one of these cheap on craigslist. They are sturdy since they are to hold you and a bike pedaling hard.

 

[REdiculous]

Good idea veloman, but I've got a pocket bike so I'll need to make something custom anyway.

I'm thinking my hitch-system will work to keep the bike in the air. I just need to add a 2.5 inch long bearing-tube to the tower/pole in the proper location. If the pivot is in the right place and the bike weighs enough to keep good wheel-wheel contact, that's it. Otherwise I might need some kind of tensioner thing...maybe just a bungee.

Mechanically, a horizontal axis turbine is easier to implement, and it can use a transmission made of simple cheap bicycle components. The turbine itself may be more expensive or harder to make, but that's outside my expertise.

Normally a horizontal would be the easier build, but not when you're talking about using a heavy bike as the alternator. Also, windmills and cheap bike components do not mix well. :wink: