Finishing details for my electrostatic turbine (EST) described in a previous tutorial are provided here. The EST is a motor that uses a high voltage DC power supply, such as a Van de Graaff generator, high potential transformer or electronic air purifier, to spin a plastic rotor.
I. Prepping & Painting
I disassembled the EST and laid out the parts for easier reassembly before painting. The electrode surfaces were prepped with 180 grit sandpaper. I used two coats of acrylic hobby paint (blue for ground & red for hot). BTW, the upturned project base was a useful stand for drying the electrodes. When the paint dried, I sanded the leading edges with extra-fine paper to remove any paint residue.
All cardboard surfaces were prepped with Ceramcoat, a water based sealant, before brushing on two coats of acrylic.
Important: Pop nylon bearings from the housing end caps before prepping and painting; otherwise, axle may bind in the bearings b/c of debris. The sky blue color of the two housing end caps was accidental; I didn't rinse the brush thoroughly w/thinner after using the blue paint. After brush painting the bearing retainer caps and then coloring the rotor caps w/a black Sharpie, the painting was done.
II. Last Minute Upgrades
Before bolting everything together, I rolled the rotor on a desktop to remove some troublesome air pockets under the plastic tape. These pockets would catch the electrode edges causing the turbine to stall. Reassembly took less than 5 minutes. An upcycled, wood jewelry box replaced the black plastic project base.
III. Test Run
I had to crank the input voltage to 10 kV before the turbine came to life. (A few drops of high grade compressor oil should help reduce the starting voltage -- thanks for that tip, Petercd!). At 17 kV with a draw of 1 mA, the corona discharge glow was bright enough for thse pictures that were taken with no other lighting source!
IV. Performance Evals
I used black thread to perform a vertical lift of a 1 oz container of Phili Cream Cheese (0.028 Kg, ignoring the plastic container weight) 21.5 inches (0.54 m) from the floor in 2.50 sec. Beyond that height, the rotor stalled b/c of internal sparking. This was enough data to calculate the following specs for the turbine.
Using some high school physics, the downward force exerted on a mass by acceleration due to gravity was: (0.028 Kg) X (9.8 meter/sec/sec) = 0.27 Newton. Power output of the turbine was: (0.27 Nt) X (0.54 m)/2.5 sec = 0.058 Watts. Consequently, turbine efficiency as defined by mechanical power output/electrical power input was: 0.058 W/(17,000 volts x 0.001 Amp) X 100% = 0.34%. Not very impressive, but the project still looks cool sitting on my bookshelf :>D.