How to build low rpm electric generators

Written by david mcguffin
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How to build low rpm electric generators
If your wind turbine plans call for a permanent magnet generator, you can build one from scratch. (Jupiterimages/Comstock/Getty Images)

Home renewable energy systems, such as windmills-generators or mini-hydro turbines, vary in design. One such design for either system calls for low revolutions per minute due to a relatively small amount of power coming into the system, whether it is via the movement of wind or water. Designing and building a permanent magnet generator will allow for a higher yield of electricity produced at lower rpm compared to common field-wound alternator components, which would also require routine maintenance.

Skill level:

Things you need

  • Vice
  • Mallet
  • Sprocket adaptor
  • Rotor
  • Welder
  • 5/8-inch shaft
  • Power drill
  • Stator
  • File
  • Bolt couplers
  • 3/16-inch screws
  • 1/8-inch angle iron; 1-by-1 inch
  • 3/16-inch thick steel plate; 8-by-12 inches
  • Tape measure
  • Marker
  • Hardwood mounting blocks
  • 3/16-inch lag screws
  • Pillow bearings for 5/8-inch shaft

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  1. 1

    Enclose the rotor in a vice and gently use a mallet to tap the sprocket adaptor into the middle of the spline hole. Weld the sprocket so that it is permanently joined with the rotor's spline hole. Allow the welding to cool off and test it by spinning the rotor around on the 5/8-inch shaft; look for any wobbling or distortion in its rotation.

  2. 2

    Drill four, 3/16-inch holes into the rim of the stator and smooth out any rough edges or filings with a file or grinder tool. Screw bolt couplers and 3/16-inch screws into the newly drilled holes on the stator, using a socket wrench to tighten the screws and couplers.

  3. 3

    Construct the base of the permanent magnet generator. Weld the end of a 6-inch piece of angle iron to a 12-inch piece of angle iron. Weld another 6-inch and 12-inch piece together. Join the two pieces into a rectangle. Weld the iron frame to the steel base plate.

  4. 4

    Slide the rotor and stator together so that they line up as closely as possible. Insert the shaft through the stator and rotor assembly.

  5. 5

    Use a tape measure to measure the dimensions of the stator and rotor, which will be the core of the generator once it is assembled. Use a marker to trace the dimensions of the generator onto the middle of the steel plate from Step 3. Measure and mark an additional inch from the width of the generator.

  6. 6

    Place the two wooden mounting blocks on the outside of the 1-inch marks and trace the outline of the blocks onto the steel plate. Remove the blocks and use a tape measure to mark four holes spaced evenly apart down the centre line of the blocks.

  7. 7

    Use a tap and die set to drill threaded bolt holes through each of the four marked holes on the base plate where the mounting blocks are outlined. Install two lag screws from the bottom of the base plate into the mounting blocks. The lag screws should be placed on the holes on either end of the blocks.

  8. 8

    Screw in bolts for the pillow bearing mounts on top of the mounting blocks through the two centre holes of the mounting blocks. Insert the generator's shaft into the bearing mounts so that it spins freely.

  9. 9

    Weld two 5-inch angle iron uprights on the stator's side of the base plate. The uprights should be positioned so that they can nearly touch the stator. Mark holes into the uprights at the place where they are closest to the stator. Use a tap and die set to drill holes into the angle iron. Use screws and a socket wrench to connect the stator to the uprights.

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