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12 Watt Turbine | The first design aimed at trickle-charging a car battery |
200 Watt Turbine | A beefed-up turbine based on the 12 Watt design, to generate useful power. |
When starting out, you need to consider how much power the machine is likely to produce. Reading around, several hundred watts seems a common number but these are usually quite large machines so for my first machine I set myself a more modest goal:
The Goal
12V, 1 Amp (12watts).
This should provide a respectable trickle charge for a car battery. Details of this design can be found here and contains a lot of the background used in the other designs.
The goal is to make a machine that will generate power at low RPMs ( < 500) which precludes using a car alternator as they are designed to work at several thousand RPM. To generate electricity using wind, we need to somehow move magnets past coils or vica-versa. A 'standard' motor/generator uses a radial design which involves some oddly shaped coils and a difficult to make rotor. An axial design where flat disks spin past each other is more realistic to make at home. Twice the power can be generated by sandwiching coils between two spinning rotors, and with the ready availability of neodymium magnets, I reasoned it should be possible to make a small machine pretty cheaply. As it turns out, going small is not the best option as you are limited by:
All three of these factor affect the output generated - more on that later. However, I was limited by the tools at my disposal as as I had a 100mm steel holesaw, it seemed that a disk rotor diameter of 100mm was a good place to start!
I made a simple bearing housing from wood and used a length of 10mm allthread as a spindle, threading it through some mini-moto bearings bought off ebay. The disks that were to be rotors were cut from the side of an old PC case and everything mounted using nuts. I wound 6 small coils and used six magnets per rotor.
My first attempt was to say the least, somewhat disapointing. Firstly the mechanics of the machine were sadly lacking due to a poor fit of the allthread within the bearings. The steel that made the disks was too thin so tended to warp when drilled. And finally, I had wired the coils as three-phase before setting it all in resin and found I had wired it incorrectly so that the voltage generated by the coils cancelled out, resulting in me only getting tens of milliVolts even when spinning at 500 rpm. This was just prior to launching magnets at high speed around the garage.
With the leasons learned from the prototype, it was time to come up with a better design that I could make from readily available parts. Although wood had proved useful for prototyping, I could see that I needed to move to a steel mechanical structure and it dawned on me - 'there is a time in every man's life where he needs to learn to arc-weld'. Now was my time. It was also time to find some engineering works in the area to get hold of some steel and various other parts to produce a more robust structure to house the generator.
10-Jul-2007
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