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New Wind Generator
I'm in the process of building a new generator tailored to the Elliptical Blade turbine and I'm hoping to be able to reasonably predict generator performance based on theory as opposed to just experimental means. One assumption being made here are that the changes in the magnetic field can be approximated with a sine function. The magnetic field strength comes from an online calculator and assumed to be uniform in strength over an area equal to that of the magnet face. Please note, the web site with the online calculator is unclear about the definition of "x." In the page that shows all the available calculators, "x" is defined as a point midway between the two magnet faces. On the calculator page itself, "x" is defined as the distance between the two magnets. For the results shown below, I used the first definition and got good agreement between the theoretical and experimental values. The distance between the magnets is 0.625" but the value I entered was 0.3125". For the time being, I'm just assuming that the theory was applied correctly and the "fix" was not just the application of a fudge factor.
Magnetic Field Strength Calculator CheckA hall effect sensor is used to measure the magnetic field between two magnets at various separation distances. The results of the measurements are compared with the results from an online calculator. Based on this test, I think the value "x" in the calculator should be half the distance between the magnet faces.


Theorectical results
There are sixteen 1" x 0.75" x 0.25" thick N42 neodymium magnets mounted on each of two steel plates. The magnet faces are separated by 0.625". The magnetic field strength (B) is calculated to be 5139 Gauss ( 0.5139Tesla ). The area of the magnet face is 4.839x10^4 m^2.
Taking this information, the expression for Vpp and dividing by an expression for RPM (RPM = 60/(8*p)) the theoretical slope for a Vpp/RPM curve is 0.0542 V/RPM based on a 130 turn coil.
Taking this information, the expression for Vpp and dividing by an expression for RPM (RPM = 60/(8*p)) the theoretical slope for a Vpp/RPM curve is 0.0542 V/RPM based on a 130 turn coil.
Results from the test coil
The results shown here are the actual measurements taken with the oscilloscope sampled at various generator speeds with a line fit to the data. It is quite linear and passes through zero. I have a good deal of confidence in these measurements. The theoretical value is 1.5% lower than the experimental value.
Serpentine Coil
The 130 turn coil was nearly 3/8" thick which got me thinking that if the coil could be made thinner, the magnets could be closer together. That would increase the field strength which would mean fewer turns, lower resistance and higher efficiency. So for this generator, I'd like to try a serpentine coil similar to the test coil in the photo.
Test Coil Output
The test coil voltage output voltage turned out to be quite linear with RPM as expected. This information can be used to estimate the number of turns required in the stator assembly. Please note that the data shown here is for four turns of wire.
vppvsrpm.xlsx  
File Size:  79 kb 
File Type:  xlsx 
Serpentine Stator Construction and Testing
A serpentine coil stator was constructed with 48 turns per leg. Details of the construction process are presented here along with test results.
Serpentine Coil Construction  Part 1Construction of the preform which holds the coils in position


Serpentine Coil Construction  Part 2Construction of the stator


Serpentine Coil TestingTesting procedure and results.


Test Results
Peak to peak voltage scaled very well as more turns were added. The slope of the completed stator with 48 turns is 12 times the slope of the 4 turn test coil within 1%.
Testing a Closer Magnet SpacingSpacers between the magnet plates were exchanged with some shorter ones to bring the magnet faces closer together. The results were compared to the ones shown previously.


Closer Magnet Spacing Test Results
A comparison between the generator output with the original spacers and the output with the shorter spacers. The voltage output with the shorter spacers was about 1617% greater.
Please Note: Information displayed on this web site in text and/or video form is for documentation purposes only. Nothing presented here should be considered professional advice or instruction. The visitor should follow safe procedures in their own projects and check all information for accuracy. Caleb Engineering, LLC is not responsible for any losses that may result from errors, misprints or display of improper procedure.