Bench Degree·WIND POWERchapter

Before You Start

One page. Appendix A at the back carries the full parts list, and Chapter 1 will tell you what it needs. This page is the part you should not find out later.

This subject has two hazards and neither is electrical. The voltages on this bench are a few volts. What is dangerous is a rotor, and what is lethal is a ladder.

A rotor is a flywheel with edges on it. Three card blades of 130 mm (5 in) on a cork hub sit at a tip speed near 20 m/s (45 mph) in front of a box fan. A blade that leaves the hub at that speed crosses the room before you have finished flinching. Set every pitch angle with the fan off, check the grip is tight, and stand to one side of the plane of rotation. Balance everything, every time, and fit blades only in symmetric patterns: two opposite, three at 120 degrees, or all six.

Take the load off a rotor and it speeds up. This is the most counter-intuitive fact on the bench and the reason real machines destroy themselves. The electrical load is the only brake, so disconnecting the generator of a running turbine is not stopping it. On any real small wind machine you stop it by shorting the generator’s phases together, never by opening them.

Working at height is where people in this trade actually die. Every site measurement here is taken from the ground, on a broom handle at 2 m (6.5 ft), and says in as many words not to do it on a roof. Anything on a mast can blow down, so guy it, and never raise or lower a mast in a wind you would not stand in.

Three more. Chapter 3 makes hydrogen and oxygen in the same jar, and that mixture is explosive: work in millilitres, by an open window, no flames, and never cap a collection tube. Use washing soda, not table salt, or you release chlorine. Chapter 11’s alternator is heavy and pressing bearings throws things, so eye protection, and clamp anything spun by a drill. The box fan is the most dangerous object on this bench, which is a strange sentence and a true one: fingers out of the intake, and it is a mains appliance in a room where you are pouring water.

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