This circuit is a combined full wave rectifier and voltage doubler. I discovered this circuit while experimenting with florescent tube drive circuits, it is probably is an old idea but it works well. The circuit will reduce turbine cut in speed by about 50% providing a small current at low speed but charging at normal speeds is not reduced but actually improved over the standard bridge rectifier arrangement. In consistent light wind conditions a significant amount of extra energy could be collected per day.
 
At low speed the circuit comprising D1, D2 and CI, C2 functions as a voltage doubler to gain enough voltage for charging, at speeds above the normal turbine cut in speed diodes D3, D4 switch in and with D 1, D2 function as a full wave rectifier. In full charging mode the capacitors still assist current production by allowing a larger portion of the turbine produced sine wave to be utilized. This circuit can also be useful as a battery charger booster but take care not to overheat the charger by exceeding its current ratings. The value of capacitance to use is a matter of experimentation for each application but 1000 uF is a easy starting point, the caps must have a large voltage safety margin and operate within ripple current specs or they may overheat and fail. Many wind generators have 3 phase windings , in this case 3 identical rectifier units will be required and the windings will need to be separately connected to each rectifier unit. The switch for each rectifier unit is optional and only included so you can check the difference.
 
Randal L.

JULY TECHNICAL GROUP MEETING  

The meeting began at 8.10pm with Robert beginning proceedings by welcoming everyone along. Eventually 26 people were in attendance which was quite a good number considering the weather.

Ken gave the first demonstration of the night using a microwave oven transformer that had the E and I laminations separated with the help of an angle grinder. He said that he has used this as a variac, varying the voltage by adjusting the amount the I laminations cover the E laminations. Ken gave a demonstration, with the aid of Peter, of how little power is needed to create a significant magnetic field by connecting a AAA battery (1.5 volts or less) across the winding of the transformer. Peter could not separate the two sets of laminations, in fact he  lifted  the transformer off the table by holding onto the I laminations. Ken mentioned that you should always use a diode across the coil to kill any back EMF when the battery is disconnected before it kills you! 

Ken also brought along a car alternator that he has modified by removing the voltage regulator and bringing out the wiring for each phase as well as the field windings. A power supply was connected to the field windings and a 12 volt lamp connected to the output. On turning the alternator by hand, the lamp would light quite brightly, demonstrating that a car alternator can generate power at low speeds if connected up correctly. Ken also demonstrated that it was harder to turn under load which depended on how much voltage was fed to the field coils, thus if being used on a wind generator for example, the output load can be adjusted externally by varying this voltage. This could automatically be done using a PIC controller to get maximum output under any wind conditions.  

We were then treated to a talk on electrochemical etching and pulse jet motors, both of which are subjects that Ken has an interest in. Ken etches petal valves made from steel for pulse jet engines, the basic process being, take a clean steel sheet, paint both sides with enamel paint, scribe the shape required removing the paint, then place in a bath of saline solution. (1 tablespoon salt / 1 litre of water) Finally an electric current is applied (20 volts @ 2amps) with the positive connected to the item to be etched and the negative connected to a stainless steel scourer pad laying in the bottom of the saline bath. This is left for 10 minutes up to an hour until the etching is complete. 

I brought along a batteryless torch that I have constructed. Shaking the torch causes a rare earth magnet to pass through two coils which charges a super capacitor. A switch then allows the capacitor to discharge into a high brightness LED. On average about 30 seconds of shaking gives about 15 minutes of bright light. I have discharged it once to a level of light that was really dim and this took about 2 hours. I hope to write an article for the next newsletter with the technical details for anyone who wants to build one along with suggested improvements to get more light for less shaking. I also talked briefly on the new Hope Valley hydroelectricity generator being installed by SA Water, recovering energy from water already flowing in pipelines from Ansteys Hill. 

While the next speaker was getting prepared, Ken mentioned that Jim was coming back to Adelaide and was interested in doing more experimenting while he was here. A conversation also ensued about adding metho to petrol (max 15:1 ratio) which apparently gives a cleaner exhaust. Andrew then demonstrated an experimental "Life Energy Meter", available from the US for US$299 which he said that while testing water he found that the energy level had reduced by half.  

George then spoke about welding spatter and a device that is spun by the welding gas  and creates an oil mist which stops the spatter from sticking to the job. A vortex spin atomises the oil so George suggested that this same process could maybe be used for petrol.  

Ron was next and as usual came up with some interesting things, beginning with glasses with blue LEDs fitted to them. He made these after hearing that exposure to blue light for two hours per day helps you sleep. He also mentioned that he has converted all the audio tapes onto MP3 format - thanks to Ron for all the hours he has spent doing this. Finally, Ron displayed a solar collector that he had recently bought. It has a very large surface area, with a hole at one end and an 85 watt  fan at the other so that the air which passes through the unit can be blown into a room via ducting to heat it. George added that this type of solar heating can be incorporated into the structure of a house and used to heat a low temperature phase change material which is then used as thermal storage. 

Dino was next and continued talking on the subject of solar room heating. He explained how he had designed a system of heating similar to those described above which also became the roof structure. Rather than heating air, the heat collector contained pipes for heating water which was then pumped to a tank underneath the floor of the house. The heat from the water in the tank would then radiate through the floor into the room. Dino had been also been shopping and brought along his new does everything tiny digital camera. He also demonstrated Vic's ghost receiver being used as a sensitive radio receiver, listening for electromagnetic fields being emitted from powerlines, new cars, railway lines and mobile phones. 

A couple of surprise visitors were the next speakers, Peter and David, who brought along their electric assisted bicycles. I think everyone was impressed by the ingenuity and workmanship in both cycles along with the stories of their construction and use. Peter also demonstrated a 5 watt LED that he uses for the headlamp on his bike which cost $76, has a life of 100,000 hours and is not affected by vibration. David has built his own electric motor (controlled by a PIC) for his bike and brought another motor for display. This motor was 500 watts and is approximately 85% efficient.

Robert demonstrated his gravity wheel experiment and like others we have seen it "almost" works.

Finally Randal gave a demonstration of his voltage doubler circuit along with a good description of how it works. He suggested that this circuit could be used to boost the output of a wind generator  so that useful power could be obtained at lower wind speeds.
 
The meeting ended at 11.05pm followed by lots of talking, drinking and eating as usual.........Bruce

The information on solar water heating is from. 

http://www.thermo-dynamics.com/solar_boiler.htm