| Electrics and Electronics Back to Wind Power |
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Generating power is one thing, using it is another. Various conditions need protection against, such as over charging the battery, draining it too flat and overspeed rotation of the turbine.
Here is the master plan! Hopefully Richard the friendly electronics engineer will help make this a reality...
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This is a simple voltage control test circuit I have built. Problems are it is very sensitive to the pot, the voltage is not stable when a load is applied and the MOSFET gets quite hot. |  |
 | These are the manual control boxes currently in use. The power from the tower.. comes in to the box on the right, into a 'Brake' DPDT switch which can short out the generator while isolating the battery. A 'Divert' switch allows the current to measured (between the two red sockets), and a ground (black) socket is provided for measuring voltage. A load can also be connected across one of the red sockets to the ground. A simple adjustable voltage detector lights a LED and sounds a buzzer at about 29V. The test load is two 12VDC CFL lamps in series (Thank you Salie! Now for those LED bulbs....).
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| The box on the left (which was built first) connects to the battery and load(s), and takes input from the right hand box, which in turn takes input from the generator. Both have a 'Brake' switch on the right hand side which disconnects the output amd shorts the input. The other swicthes on the left hand box from left to right are a divert switch, which can be used to measure the nett current flowing into/out of the battery. Next is a 'Battery isolate' switch which can be used to direct ly connect the generator to a load, or to allow the generator to 'freewheel' (mainly useful for frightening friends and neighbours). Then you can see a fuse holder for a 20A fuse, which I blow regularly (usually by forgetting that the multimeter is in Amps mode). Next is a switch to turn on power to two banana sockets, which I use for test loads or measuring the voltage. The main 'power out' connection is via the block connector (middle two points) on the right. | |
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The box below is a dump controller, circuit thanks to ghurd. Two LEDs indicate power on and dumping load active, and there is a divert switch and two sockets to allow easy monitoring of the current going through the dump. The circuit works by switching on a high speed low Rds power N-Fet (IRFZ44) when the voltage is above a level set by a mutiturn pot, for me at about 27.5V..
As a dump I currently use two 12V 50W bulbs in series (4 A), which is not enough for really windy times.
Either I will put two or four more in parallel, or find a different thing to use as a dump. | |
| You might ask why all the boxes are separate, and not all in one enclosure. Well... mainly because I made them over time. However, having them modular is really useful. For example, with the batteries still needing a bit of charge the dump load controller can be safely disconnected and worked on. Or the main battery connect box can be disconnected, leaving the dump controller to prevent turbine overspeed. | |
Standard bridge rectifiers have a voltage drop of about 0.6V per diode, but there are Schottky diodes with lower voltage drops. There are other factors however, such as switching speed and reverse leakage, and the actual voltage drop varies depending on the current. So the only way to be sure about what improvement is possible was to make a test circuit and do some benchtesting. This circuit has 6 Schottkys (STPS20H100CT). Each package has a pair of diodes, with the positive ends connected. Each pair is connected in parallel to double the maximum current to 20A per phase. Note how the diodes are mounted to allow attachment to a single compact block heatsink. Testing on the bench and comparing this to standard SB356 rectifiers, the Schottky method produces about 5 Watts more power (over the range of about 150 - 200rpm). Conclusion: it doesnt seem worth the bother. |
The heatsink is a chunk of aliminium I had lying around, with some holes drilled in it There are also a few holes in the box to allow hot air to escape. Any dump load can be connected via the connector block, as long as it can handle rapid swictching (so a motor is not suitable because of its inductance). 