Earth Notes: VAWT Experiment 3: Big Box on Real PM Gen

Learn how my first home-grown VAWT with real generator was more "lawn art" statue than power-house turbine...
turbine wind small VAWT big box

This experiment was my attempt to upgrade from the fairly-free-spinning cereal-box "yard art" toy VAWT, to a larger box on a real generator. The actual power output was a secondary consideration to getting something physically stable and safe, that would turn at all and/or in light winds, and that can put out any power at all.

cereal-box VAWT

(This was all part of my urban wind-power pilot project.)

For this design/implementation I visited various local DIY/tool shops, and acquired nearly a grown-up haul of G-clamps, mallets, roofing bolts, etc, since I needed some extra tools (eg hand-drill and modelling knife) and some newer widgets to make a supporting structure for the generator, which is large (7kg, 17cm/7in diameter) and had its three power wires emerging from the centre of the spindle.

FuturEnergy

scanner-box VAWT

The generator is from FuturEnergy. Handily I encountered them with their PM gen and HAWT turbine at their booth at a trade show a few days after the generator arrived (and had puzzled me). I could see that they were letting the generator's internal bearings take all the load in their turbine design, thus I can do the same.

The first thing I did was to make a support for my PM gen to allow me to build the rotor on top for a VAWT configuration. Cunning use of a plank of wood, two G-clamps, and two angle brackets to grasp the flat on the PM gen shaft, take the weight on the end of the spindle, and prevent rotation of the the spindle and its emerging wres, allowing the body to spin above it on the generator's internal bearings, with the rotor to be bolted on to and abive the generator body. It may not last but it is reasonably sturdy for experimental purposes...

This also for the first time allowed me to test when I might get cut-in to charge a 12V battery, using my analogue multimeter on 'AC Volts' across one pair of the delta-wired outputs while I turned the spindle by hand. My estimate is that bridge-rectified output will pass ~13V--14V at ~120rpm, which is probably just about reasonable for a drag-based VAWT design.

Electric Brake

PM gen support

Shorting any two of the output wires makes the spindle very hard to turn, indicating that the generator is extracting the mechanical energy efficiently.

Then I attached my biggest-available box (from my scanner) to the PM gen, and cut the vertical slots as for my smaller cereal-box rotor.

Unfortunately the cogging and torque required to start up rotation was too high for conditions on the day, and a larger/flatter box is probably necessary for this to turn in low wind speeds. Maybe 1msq minimum swept area and possibly at least a metre for enough torque.

Footnote: I gave the generator away 2015/01 when I realised that I would never get anything useful out of it with my conditions. Thanks for taking it off my hands Ben M!

Sources/Links

  • FuturEnergy sells the permanent-magnet generator (PM gen) that it uses in its own turbines: good on them!
  • ForceField/OtherPower discussion thread on this turbine.
  • Size matters: "the concept of small windmills is fundamentally flawed. The turbines that score best, are simply the largest ones [at ~5m rotor diameter]. Windmills with a rotor diameter of 4 or 5 meters do not fit on most roofs, and are not easy to integrate in a built-up environment."
  • Interesting combo VAWT from HiEnergy of Taiwan, with Darrieus (for efficiency) and Savionius (to self-start) and MPPT to extract as much useful energy as possible.